Physical Address

304 North Cardinal St.
Dorchester Center, MA 02124

Knee and leg


The knee is the largest synovial joint in the body. It consists of three functional compartments that collectively form a dynamic, specialized hinge joint. During gait, the knee is able to withstand impressive weight-bearing loads while conducting precision movements, providing a stable yet fluid mechanism for relatively efficient bipedal locomotion. The complex arrangement of intra- and extracapsular ligaments that helps to counter the considerable biomechanical demands that are imposed on the joint can also be involved in disease (i.e. tri-compartment disease). The leg consists of two bones, with an interosseous membrane between them: the larger tibia, which transmits most of the stress of walking, and the smaller fibula, which provides secondary support and ankle stability. Muscles of the three compartments of the leg primarily permit movement of the ankle, foot and toes.

Skin and Soft Tissues

Skin

Vascular supply and lymphatic drainage

Knee

The arterial supply of the skin covering the knee is derived from genicular branches of the popliteal artery, the descending genicular branch of the femoral artery and the anterior recurrent branch of the anterior tibial artery, with small contributions from muscular branches to vastus medialis and the posterior thigh muscles ( Fig. 78.1 ). For further details, consult .

Fig. 78.1, A , The arterial anastomoses around the left knee joint, anterior aspect. B , Frontal digital subtraction angiogram of the left distal femoral artery to the trifurcation.

Cutaneous veins are tributaries of vessels that correspond to the named arteries. Cutaneous lymphatic drainage is initially to the superficial inguinal nodes, possibly also to the popliteal nodes, and then to the deep inguinal nodes.

Leg

The cutaneous arterial supply of the leg is derived from branches of the popliteal, anterior and posterior tibial and fibular vessels (see Fig. 76.5 ). Multiple fasciocutaneous perforating branches from each vessel pass along intermuscular septa to reach the skin; musculocutaneous perforators traverse muscles before reaching the skin. In some areas there is an additional, direct cutaneous supply from vessels that accompany cutaneous nerves, e.g. the descending genicular artery (saphenous artery) and superficial sural arteries. Fasciocutaneous and direct cutaneous arterial branches are oriented longitudinally in the skin, whereas the musculocutaneous branches are more radially oriented. For further details, consult .

Cutaneous veins are tributaries of vessels that correspond to the named arteries. Cutaneous lymphatic vessels running on the medial side of the leg accompany the long saphenous vein and drain to the superficial inguinal nodes, and those from the lateral and posterior sides of the leg accompany the short saphenous vein and pierce the deep fascia to drain into the popliteal nodes.

Innervation

Leg

The skin of the leg is supplied by branches of the saphenous, posterior femoral cutaneous, common fibular and tibial nerves (see p. 1391 and Figs 76.11 – 76.12 , 76.20 – 76.21 ).

Infrapatellar branch of the saphenous nerve

The infrapatellar branch of the saphenous nerve reaches the anterior aspect of the knee from the medial side. It is invariably divided in medial surgical approaches to the knee, which accounts for the numbness that inevitably occurs following such procedures. A painful neuroma may form if the nerve is partially sectioned, e.g. by the incision for an arthroscopy portal or a small medial arthrotomy. The position of the nerve relative to the line of the joint is variable. In most cases, it crosses just below the joint line, passing over the patellar ligament at its insertion on to the tibia. For further details, see .

Peripatellar plexus

Proximal to the knee, the infrapatellar branch of the saphenous nerve connects with branches of the medial and intermediate femoral cutaneous nerves, and lateral femoral cutaneous nerve. Distal to the knee, it connects with other branches of the saphenous nerve. This fine, subcutaneous network of communicating nerve fibres over and around the patella is termed the peripatellar plexus.

Soft tissues

Popliteal fossa

The popliteal fossa ( Figs 78.2 – 78.3 ) is a diamond-shaped region posterior to the knee, bordered by muscles in the posterior compartment of the thigh and leg. The boundaries are biceps femoris proximolaterally; semimembranosus and the overlying semitendinosus proximomedially; the lateral head of gastrocnemius with the underlying plantaris distolaterally; and the medial head of gastrocnemius distomedially. The anterior boundary (or floor) of the fossa is formed, in proximodistal sequence, by the popliteal surface of the femur, the oblique popliteal ligament (overlying the posterior surface of the capsule of the knee joint), and the posterior aspect of the proximal tibia covered by popliteus and its fascia. The deep fascia (fascia musculorum) acts as the roof of the fossa and is continuous with the fascia lata proximally and with the deep fascia of the leg distally. It is a dense layer that is strongly reinforced by transverse fibres and is often perforated by the short saphenous vein and medial and lateral sural cutaneous nerves; these structures are useful landmarks in the direct posterior approach to the knee joint.

Fig. 78.2, The left popliteal fossa.

Fig. 78.3, Muscles of the calf, superficial view including the boundaries of the popliteal fossa.

The popliteal fossa is approximately 2.5 cm wide. Distally, its contents are protected and hidden by the heads of gastrocnemius, which contact each other. The fossa contains the popliteal vessels (see Fig. 78.2 ; Fig. 78.4 ), tibial and common fibular nerves, short saphenous vein, medial and lateral sural cutaneous nerves, posterior femoral cutaneous nerve, articular branch of the obturator nerve, lymph nodes, fat and a variable number of bursae. The tibial nerve descends centrally immediately anterior to the deep fascia, crossing the vessels posteriorly from lateral to medial. The common fibular nerve descends laterally immediately medial to the tendon of biceps femoris. When the popliteal vessels enter the proximal region of the popliteal fossa, they maintain a side-by-side relationship, which shifts to an over–under relationship as they descend through the fossa and are held together by dense areolar tissue within the fossa. This may potentially compromise the popliteal artery in distal femoral fractures. The popliteal vein is generally located posterior to the artery. Proximally, the vein lies lateral to the artery, crossing to its medial side distally. At times, the popliteal vein may be duplicated, so that the artery lies between the veins, which are usually bridged by connecting channels. An articular branch from the obturator nerve descends along the artery to the knee. Six or seven popliteal nodes are embedded in the fat, one under the deep fascia near the termination of the short saphenous vein, one between the popliteal artery and knee joint, and the others intimate with the popliteal vessels.

Fig. 78.4, The left popliteal, posterior tibial and fibular arteries, posterior aspect.

Deep fascia

The deep fascia of the leg is continuous with the fascia lata and is attached around the knee to the patellar margin, the patellar ligament, the tuberosity and condyles of the tibia, and the head of the fibula. Posteriorly, it covers the popliteal fossa as the popliteal fascia. It receives lateral expansions from the tendon of biceps femoris and multiple medial expansions from the tendons of sartorius, gracilis, semitendinosus and semimembranosus. The deep fascia blends with the periosteum on the subcutaneous surface of the tibia and the subcutaneous surfaces of the fibular head and lateral malleolus, and is continuous below with the extensor and flexor retinacula. It is thick and dense in the proximal and anterior part of the leg, where fibres of tibialis anterior and extensor digitorum longus are attached to its deep surface, and is thinner posteriorly, where it covers gastrocnemius and soleus. On the lateral side, it is continuous with the anterior and posterior intermuscular septa of the leg, which are attached to the anterior and posterior borders of the fibula, respectively.

Transverse intermuscular septum

The transverse intermuscular septum of the leg is a fibrous stratum between the superficial and deep muscles of the calf. It extends transversely from the medial margin of the tibia to the posterior border of the fibula. Proximally, where it is thick and dense, it is attached to the soleal ridge of the tibia and to the fibula, inferomedial to the fibular attachment of soleus. Between these bony attachments, it is continuous with the fascia covering popliteus, which is, in effect, an expansion from the tendon of semimembranosus. At intermediate levels it is thin but distally, where it covers the tendons behind the malleoli, it is thick and continuous with the flexor and superior fibular retinacula.

Interosseous membrane

The interosseous membrane connects the interosseous borders of the tibia and fibula ( Fig. 78.5 ). It is interposed between the anterior and posterior groups of crural muscles; some members of each group are attached to the corresponding surface of the interosseous membrane. The anterior tibial artery passes forwards through a large oval opening near the proximal end of the membrane, and the perforating branch of the fibular artery pierces it distally. An associated ligament (ligament of Barkow), in the same plane as the interosseous membrane, may be found uniting the proximal tibiofibular joint; when present, it forms the upper half of this oval opening (see Fig. 78.5 ) ( ). Its fibres are predominantly oblique and most descend laterally; those that descend medially include a bundle at the proximal border of the proximal opening. The thickness of the interosseous membrane differs between its thin centre and thick tibial and fibular borders. The membrane is continuous distally with the interosseous ligament of the distal tibiofibular joint.

Fig. 78.5, The posterior aspect of the interosseous membrane. Note the contrasting direction of the fibre bundles around the vascular openings.

Retinacula

The retinacula at the ankle joint are described in Chapter 79 .

Compartments of the leg

The compartments of the leg are particularly well defined and are the most common sites at which osteofascial compartment syndromes occur. The three main compartments are anterior (extensor), lateral (fibular) and posterior (flexor) ( Fig. 78.6 ). The posterior compartment is divided into deep and superficial parts by the transverse intermuscular septum. These compartments are enclosed by the unyielding deep fascia and separated from each other by the bones of the leg and interosseous membrane, and by the anterior and posterior intermuscular septa that pass from the deep fascia to the fibula. The anterior compartment, the least expansile of the three, is bounded by the deep fascia, the interosseous surfaces of the tibia and fibula, the interosseous membrane and the anterior intermuscular septum. The lateral compartment lies between the anterior and posterior intermuscular septa, and is bordered laterally by the deep fascia and medially by the lateral surface of the fibula. The posterior compartment is bounded by the deep fascia, the posterior intermuscular septum, the fibula and tibia, and the interosseous membrane. Its relatively expansile superficial component is separated from the compacted deep component by the transverse intermuscular septum, reinforced by the deep aponeurosis of soleus. Knowledge of the compartmental anatomy of the leg is important in planning the treatment of compartment syndromes and for soft tissue tumour resections of the leg.

The nerve supply of the muscles in the compartments follows the ‘one compartment – one nerve’ principle: the deep fibular nerve supplies the anterior compartment, the superficial fibular nerve supplies the lateral compartment and the tibial nerve supplies the posterior compartment. Magnetic resonance imaging (MRI) is the best imaging modality for evaluating the soft tissues of the leg. Most of the muscle in the anterior compartment is supplied by the anterior tibial artery, with an additional contribution from the fibular artery to extensor hallucis longus. The muscles of the posterior compartment are supplied by the popliteal, posterior tibial and fibular arteries. The muscles of the lateral compartment are supplied by the anterior tibial and fibular arteries, and to a lesser extent proximally, by a branch from the popliteal artery.

Fig. 78.6, A , A transverse (axial) section through the left leg, approximately 10 cm distal to the knee joint. B, A colour-coded axial magnetic resonance image (MRI) of the leg. Key: anterior (blue), lateral (red) and posterior (deep part yellow and superficial part green) compartments of the leg. C , An axial T2-weighted MRI of the upper leg.

Trauma and soft tissues of the leg

The relative paucity of soft tissue in the shin region and the subcutaneous position of the medial surface of the tibia means that even trivial soft tissue injury may lead to serious problems such as ulceration and osteomyelitis. In the elderly these soft tissues are often especially thin and unhealthy, reflecting the effects of ageing and venous stasis (see p. 1427 ). Tibial fractures are common in the young and, partly as a result of poor soft tissue coverage, they are often open injuries. Diminished blood supply to the bone, caused by traumatic stripping of attached soft tissues, and the risk of contamination add greatly to the risk of non-union and infection of the fracture. Healing of fractures at the junction of the middle and lower thirds of the tibia is compromised by the relatively poor blood supply to this region. Injury to the leg may result in elevated pressures of one or more compartments (so-called compartment syndrome); this clinical scenario is manifested by the ‘six Ps’: pain, paraesthesiae, pallor, paralysis, pulselessness and poikilothermia (differing temperatures in the affected and unaffected limbs).

Bones

The relevant bones are the femur (described in Chapter 77 ), tibia, fibula and patella.

Tibia

The tibia lies medial to the fibula and is exceeded in length only by the femur ( Figs 78.7 – 78.8 ). The tibial shaft is triangular in section and has expanded ends; a strong medial malleolus projects distally from the smaller distal end. The anterior border of the shaft is sharp and curves medially towards the medial malleolus. Together with the medial and lateral borders, it defines the three surfaces of the bone. The exact shape and orientation of these surfaces show individual and racial variations. In children, the mean tibial length is greater in males than in females ( ).

Fig. 78.7, A , The left tibia and fibula showing sites of muscular and capsular attachment and epiphysial lines, anterior aspect. Key: 1, medial condyle; 2, tibial tuberosity; 3, anterior border of tibia; 4, interosseous border of tibia; 5, medial surface; 6, medial malleolus; 7, Gerdy’s tubercle; 8, lateral condyle; 9, head of fibula; 10, interosseous border of fibula; 11, anterior border of fibula; 12, medial crest; 13, anterior surface; 14, subcutaneous area; 15, lateral malleolus. B , Muscle attachments. Key: 1, semimembranosus; 2, medial patellar retinaculum; 3, epiphysial line (growth plate); 4, tibial collateral ligament; 5, gracilis; 6, sartorius; 7, semitendinosus; 8, tibialis anterior; 9, attachment site of ankle joint capsule; 10, iliotibial tract; 11, attachment site of knee joint capsule; 12, fibular collateral ligament; 13, biceps femoris; 14, patellar ligament; 15, epiphysial line (growth plate); 16, fibularis longus; 17, extensor digitorum longus; 18, tibialis posterior; 19, fibularis brevis; 20, extensor hallucis longus; 21, fibularis tertius; 22, epiphysial line (growth plate); 23, epiphysial line (growth plate).

Fig. 78.8, A , The left tibia and fibula showing sites of muscular and capsular attachment and epiphysial lines, posterior aspect. Key: 1, groove for tendon of popliteus; 2, apex of head of fibula; 3, head of fibula; 4, neck of fibula; 5, medial crest; 6, interosseous border of tibia; 7, posterior border; 8, groove for fibular tendons; 9, lateral malleolus; 10, intercondylar eminence; 11, groove for semimembranosus attachment; 12, soleal line; 13, nutrient foramen; 14, vertical line; 15, medial border of tibia; 16, medial malleolus; 17, groove for tibialis posterior tendon. B , Muscle attachments. Key: 1, gap in capsule for popliteus tendon; 2, soleus; 3, flexor hallucis longus; 4, fibularis brevis; 5, epiphysial line (growth plate); 6, attachment site of knee joint capsule; 7, semimembranosus; 8, epiphysial lines (growth plates); 9, popliteus; 10, soleus; 11, tibialis posterior; 12, flexor digitorum longus; 13, epiphysial line (growth plate); 14, attachment site of ankle joint capsule.

Proximal end

The expanded proximal end bears the weight transmitted through the femur. It consists of medial and lateral condyles, an intercondylar area and the tibial tuberosity.

Condyles

The tibial condyles overhang the proximal part of the posterior surface of the shaft. Both condyles have articular facets on their superior surfaces, separated by an irregular, non-articular intercondylar area. The condyles are visible and palpable at the sides of the patellar ligament, the lateral being more prominent. In the passively flexed knee, the anterior margins of the condyles are palpable in depressions that flank the patellar ligament.

The fibular articular facet on the posteroinferior aspect of the lateral condyle faces distally and posterolaterally. The angle of inclination of the superior tibiofibular joint varies between individuals, and may be horizontal or oblique. Superomedial to it, the condyle is grooved on its posterolateral aspect by the tendon of popliteus; a synovial recess intervenes between the tendon and bone. The anterolateral aspect of the condyle is separated from the lateral surface of the shaft by a sharp margin for the attachment of deep fascia. The distal attachment of the iliotibial tract makes a flat and usually definite marking (Gerdy’s tubercle) on its anterior aspect. This tubercle, which is triangular and facet-like, is usually palpable through the skin.

The anterior condylar surfaces are continuous with a large triangular area whose apex is distal and formed by the tibial tuberosity. The lateral edge is a sharp ridge between the lateral condyle and lateral surface of the shaft.

Tibial tuberosity

The tibial tuberosity is the truncated apex of a triangular area where the anterior condylar surfaces merge. It projects only a little, and is divided into distal rough and proximal smooth regions. The distal region is palpable and is separated from skin by the subcutaneous infrapatellar bursa. A line across the tibial tuberosity marks the distal limit of the proximal tibial growth plate (see Fig. 78.7 ). The patellar ligament is attached to the smooth bone proximal to this, its superficial fibres reaching a rough area distal to the line. The deep infrapatellar bursa and fibroadipose tissue intervene between the bone and tendon proximal to its site of attachment. The latter may be marked distally by a somewhat oblique ridge, on to which the lateral fibres of the patellar ligament are inserted more distally than the medial fibres. This knowledge is necessary for avoiding damage to this structure when performing an osteotomy just above the tibial tuberosity in a lateral to medial direction. In habitual squatters, a vertical groove on the anterior surface of the lateral condyle is occupied by the lateral edge of the patellar ligament in full flexion of the knee.

Shaft

The shaft is triangular in section and has (antero)medial, lateral and posterior surfaces separated by anterior, lateral (interosseous) and medial borders. It is narrowest at the junction of the middle and distal thirds, and expands gradually towards both ends. The anterior border descends from the tuberosity to the anterior margin of the medial malleolus and is subcutaneous throughout. Except in its distal quarter, where it is indistinct, it is a sharp crest. It is slightly sinuous, and turns medially in the distal quarter. The interosseous border begins distal and anterior to the fibular articular facet and descends to the anterior border of the fibular notch; it is indistinct proximally. The interosseous membrane is attached to most of its length, connecting the tibia to the fibula. The medial border descends from the anterior end of the groove on the medial condyle to the posterior margin of the medial malleolus. Its proximal and distal quarters are ill defined but its central region is sharp and distinct.

The anteromedial surface, between the anterior and medial borders, is broad, smooth and almost entirely subcutaneous. The lateral surface, between the anterior and interosseous borders, is also broad and smooth. It faces laterally in its proximal three-quarters and is transversely concave. Its distal quarter bends to face anterolaterally, on account of the medial deviation of the anterior and distal interosseous borders. This part of the surface is somewhat convex. The posterior surface, between the interosseous and medial borders, is widest above, where it is crossed distally and medially by an oblique, rough soleal line. A faint vertical line descends from the centre of the soleal line for a short distance before becoming indistinct. A large vascular groove adjoins the end of the line and descends distally into a nutrient foramen. Deep fascia and, proximal to the medial malleolus, the medial end of the superior extensor retinaculum are attached to the anterior border. Posterior fibres of the tibial collateral ligament and slips of semimembranosus and the popliteal fascia are attached to the medial border proximal to the soleal line, and some fibres of soleus and the fascia covering the deep calf muscles are attached distal to the line. The distal medial border runs into the medial lip of a groove for the tendon of tibialis posterior. The interosseous membrane is attached to the lateral border, except at either end of this border. It is indistinct proximally where a large gap in the membrane transmits the anterior tibial vessels. Distally, the border is continuous with the anterior margin of the fibular notch, to which the anterior tibiofibular ligament is attached.

The anterior part of the tibial collateral ligament is attached to an area approximately 5 cm long and 1 cm wide near the medial border of the proximal medial surface. The remaining medial surface is subcutaneous and crossed obliquely by the long saphenous vein. Tibialis anterior is attached to the proximal two-thirds of the lateral surface. The distal third, devoid of attachments, is crossed in mediolateral order by the tendons of tibialis anterior (lying just lateral to the anterior border), extensor hallucis longus, the anterior tibial vessels and deep fibular nerve, extensor digitorum longus and fibularis tertius.

On the posterior surface, popliteus is attached to a triangular area proximal to the soleal line, except near the fibular articular facet. The popliteal aponeurosis, soleus and its fascia, and the transverse intermuscular septum are all attached to the soleal line; the proximal end of the line does not reach the interosseous border, and is marked by a tubercle for the medial end of the tendinous arch of soleus. Lateral to the tubercle, the posterior tibial vessels and tibial nerve descend on tibialis posterior. Distal to the soleal line, a vertical line separates the attachments of flexor digitorum longus and tibialis posterior. Nothing is attached to the distal quarter of this surface, but the area is crossed medially by the tendon of tibialis posterior travelling to a groove on the posterior aspect of the medial malleolus. Flexor digitorum longus crosses obliquely behind tibialis posterior; the posterior tibial vessels and nerve and flexor hallucis longus contact only the lateral part of the distal posterior surface.

Distal end

The slightly expanded distal end of the tibia has anterior, medial, posterior, lateral and distal surfaces. It projects inferomedially as the medial malleolus. The distal end of the tibia, when compared to the proximal end, is laterally rotated (tibial torsion). The torsion begins to develop in utero and progresses throughout childhood, mainly during the first four years of life ( ), until skeletal maturity is attained. Some of the femoral neck anteversion seen in the newborn may persist in adult females: this causes the femoral shaft and knee to be medially rotated, which may lead the tibia to develop a compensatory external torsion to counteract the tendency of the feet to turn inwards. Tibial torsion is approximately 30° in Caucasian and Asian populations, but is significantly greater in Africans ( ).

The smooth anterior surface projects beyond the distal surface, from which it is separated by a narrow groove. The capsule of the ankle joint is attached to an anterior groove near the articular surface. The medial surface is smooth and continuous above and below with the medial surfaces of the shaft and medial malleolus, respectively; it is subcutaneous and visible. The posterior surface is smooth except where it is crossed near its medial end by a nearly vertical but slightly oblique groove, which is usually conspicuous and extends to the posterior surface of the malleolus. The groove is adapted to the tendon of tibialis posterior, which usually separates the tendon of flexor digitorum longus from the bone. More laterally, the posterior tibial vessels, tibial nerve and flexor hallucis longus contact this surface. The lateral surface is the triangular fibular notch; its anterior and posterior edges project and converge proximally to the interosseous border. The floor of the notch is roughened proximally by a substantial interosseous ligament but is smooth distally and is sometimes covered by articular cartilage. The anterior and posterior tibiofibular ligaments are attached to the corresponding edges of the notch. The distal surface articulates with the talus and is wider in front, concave sagittally and slightly convex transversely, i.e. saddle-shaped. Medially, it continues into the malleolar articular surface, which may extend into the groove that separates it from the anterior surface of the shaft. Such extensions, medial or lateral or both, are squatting facets, and they articulate with reciprocal talar facets in extreme dorsiflexion. These features have been used in the field of forensic medicine to identify the race of skeletal material.

Medial malleolus

The short, thick medial malleolus has a smooth lateral surface with a crescentic facet that articulates with the medial surface of the talus. Its anterior aspect is rough and its posterior aspect features the continuation of the groove from the posterior surface of the tibial shaft for the tendon of tibialis posterior. The distal border is pointed anteriorly, posteriorly depressed and gives attachment to the deltoid ligament. The tip of the medial malleolus does not project as far distally as the tip of the lateral malleolus, the latter also being the more posteriorly located of the two malleoli. The capsule of the ankle joint is attached to the anterior surface of the medial malleolus, and the flexor retinaculum is attached to its prominent posterior border.

Muscle attachments

The patellar ligament is attached to the proximal half of the tibial tuberosity. Semimembranosus is attached to the distal edge of the groove on the posterior surface of the medial condyle; a tubercle at the lateral end of the groove is the main attachment of the tendon of this muscle. Slips from the tendon of biceps femoris are attached to the lateral tibial condyle anteroproximal to the fibular articular facet (see Fig. 78.7B ). Proximal fibres of extensor digitorum longus and (occasionally) fibularis longus are attached distal to this area. Slips of semimembranosus are attached to the medial border of the shaft posteriorly, proximal to the soleal line. Some fibres of soleus attach to the posteromedial surface distal to the line. Semimembranosus is attached to the medial surface proximally, near the medial border, behind the attachment of the anterior part of the tibial collateral ligament. Anterior to this area (in anteroposterior sequence) are the linear attachments of the tendons of sartorius, gracilis and semitendinosus; these rarely mark the bone. Tibialis anterior is attached to the proximal two-thirds of the lateral (extensor) surface. Popliteus is attached to the posterior surface in a triangular area proximal to the soleal line, except near the fibular articular facet (see Fig. 78.8B ). Soleus and its associated fascia are attached to the soleal line itself. Flexor digitorum longus and tibialis posterior are attached to the posterior surface distal to the soleal line, medial and lateral, respectively, to the vertical line (see above).

Vascular supply

The proximal end of the tibia is supplied by metaphysial arteries from the genicular anastomosis. The nutrient foramen usually lies near the soleal line and transmits a branch of the posterior tibial artery; the nutrient vessel may also arise at the level of the popliteal bifurcation or as a branch from the anterior tibial artery. On entering the bone, the nutrient artery divides into ascending and descending branches. The periosteal supply to the shaft arises from the anterior tibial artery and from muscular branches. The distal metaphysis is supplied by branches from the arterial anastomosis around the ankle.

Innervation

The proximal and distal ends of the tibia are innervated by branches from the nerves that supply the knee joint and ankle joint, respectively. The periosteum of the shaft is supplied by branches from the nerves that innervate the muscles attached to the tibia.

Ossification

The tibia ossifies from three centres: one in the shaft and one in each epiphysis. Ossification ( Fig. 78.9 ) begins in mid-shaft during stages 21–23 (50–58 days post fertilization). The proximal epiphysial centre is usually present at birth: at approximately 10 years, a thin anterior process from the centre descends to form the smooth part of the tibial tuberosity. A separate centre for the tuberosity may appear at about the twelfth year and soon fuses with the epiphysis. Distal strata of the epiphysial plate are composed of dense collagenous tissue in which the fibres are aligned with the patellar ligament. Exaggerated traction stresses may account for Osgood–Schlatter disease, in which fragmentation of the epiphysis of the tibial tuberosity occurs during adolescence and produces a painful swelling around it. Healing occurs once the growth plate fuses, leaving a bony protrusion. Prolonged periods of traction with the knee extended, both in children and adolescents, can lead to growth arrest of the anterior part of the proximal epiphysis, which results in bowing of the proximal tibia as the posterior tibia continues to grow. The proximal epiphysis fuses in the sixteenth year in females and the eighteenth in males. The distal epiphysial centre appears early in the first year and joins the shaft at about the fifteenth year in females and the seventeenth in males. The medial malleolus is an extension from the distal epiphysis and starts to ossify in the seventh year; it may have its own separate ossification centre. An accessory ossification centre sometimes appears at the tip of the medial malleolus, more often in females than in males. It fuses during the eighth year in females and the ninth year in males; it should not be confused with an os subtibiale, which is a rare accessory bone found on the posterior aspect of the medial malleolus. The average growth rate of the distal tibia decreases from a plateau of about 11 years of age in boys and 10 years of age in girls ( ).

Fig. 78.9, Stages in the ossification of the tibia (not to scale).

Fibula

The fibula (see Figs 78.7 – 78.8 ) is much more slender than the tibia and is not directly involved in transmission of weight. It has a proximal head, a narrow neck, a long shaft and a distal lateral malleolus. The shaft varies in form, being variably moulded by attached muscles; these variations may be confusing.

Head

The head of the fibula is irregular in shape and projects anteriorly, posteriorly and laterally. A round facet on its proximomedial aspect articulates with a corresponding facet on the inferolateral surface of the lateral tibial condyle. It faces proximally and anteromedially, and has an inclination that may vary among individuals from almost horizontal to an angle of up to 45°. A blunt apex projects proximally from the posterolateral aspect of the head and is often palpable approximately 2 cm distal to the knee joint. The fibular collateral ligament is attached in front of the apex, embraced by the main attachment of biceps femoris. The tibiofibular joint capsule is attached to the margins of the articular facet. The common fibular nerve crosses posterolateral to the neck and can be rolled against the underlying bone at this location.

Shaft

The shaft has three borders and surfaces, each associated with a particular group of muscles. The anterior border ascends proximally from the apex of an elongated triangular area that is continuous with the lateral malleolar surface, to the anterior aspect of the fibular head. The posterior border, continuous with the medial margin of the posterior groove on the lateral malleolus, is usually distinct distally but often rounded in its proximal half. The interosseous border is medial to the anterior border and somewhat posterior. Over the proximal two-thirds of the fibular shaft the two borders approach each other, with the surface between the two being narrowed to 1 mm or less.

The lateral surface, between the anterior and posterior borders and associated with the fibular muscles, faces laterally in its proximal three-quarters. The distal quarter spirals posterolaterally to become continuous with the posterior groove of the lateral malleolus. The anteromedial (sometimes simply termed anterior, or medial) surface, between the anterior and interosseous borders, usually faces anteromedially but often directly anteriorly. It is associated with the extensor muscles. Though wide distally, it narrows in its proximal half and may become a mere ridge. The posterior surface, between the interosseous and posterior borders, is the largest and is associated with the flexor muscles. Its proximal two-thirds are divided by a longitudinal medial crest, separated from the interosseous border by a grooved surface that is directed medially. The remaining surface faces posteriorly in its proximal half; its distal half curves on to the medial aspect. Distally, this area occupies the fibular notch of the tibia, which is roughened by the attachment of the principal interosseous tibiofibular ligament. The triangular area proximal to the lateral surface of the lateral malleolus is subcutaneous; muscles cover the rest of the shaft.

The anterior border is divided distally into two ridges that enclose a triangular subcutaneous surface. The anterior intermuscular septum is attached to its proximal three-quarters. The lateral end of the superior extensor retinaculum is attached distally on the anterior border of the triangular area and the lateral end of the superior fibular retinaculum is attached distally on the posterior margin of the triangular area. The interosseous border ends at the proximal limit of the rough area for the interosseous ligament. The interosseous membrane attached to this border does not reach the fibular head, which leaves a gap through which the anterior tibial vessels pass. The posterior border is proximally indistinct, and the posterior intermuscular septum is attached to all but its distal end. The medial crest is related to the fibular artery. A layer of deep fascia separating the tendon of tibialis posterior from flexor hallucis longus and flexor digitorum longus is attached to the medial crest.

Lateral malleolus

The distal end of the fibula forms the lateral malleolus, which projects distally and posteriorly (see Figs 78.7 – 78.8 ). Its lateral aspect is subcutaneous while its posterior aspect has a broad groove with a prominent lateral border. Its anterior aspect is rough, round and continuous with the tibial inferior border. The medial surface has a triangular articular facet, vertically convex, its apex distal, which articulates with the lateral talar surface. Behind this facet is a rough malleolar fossa pitted by vascular foramina. The posterior tibiofibular ligament and, more distally, the posterior talofibular ligament, are attached in the fossa. The anterior talofibular ligament is attached to the anterior surface of the lateral malleolus; the calcaneofibular ligament is attached to the notch anterior to its apex. The tendons of fibularis brevis and longus groove its posterior aspect; the latter is superficial and covered by the superior fibular retinaculum.

Muscle attachments

The main attachments of biceps femoris embrace the fibular collateral ligament in front of the apex of the fibular head. Extensor digitorum longus is attached to the head anteriorly, fibularis longus anterolaterally, and soleus posteriorly. Extensor digitorum longus, extensor hallucis longus and fibularis tertius are attached to the anteromedial (extensor) surface. Fibularis longus is attached to the whole width of the lateral (fibular) surface in its proximal third, but in its middle third only to its posterior part, behind fibularis brevis. The latter continues its attachment almost to the distal end of the shaft.

Muscle attachments to the posterior surface, which is divided longitudinally by the medial crest, are complex. Between the crest and interosseous border, the posterior surface is concave. Tibialis posterior is attached throughout the proximal three-quarters of this area, and an intramuscular tendon may ridge the bone obliquely. Soleus is attached between the crest and the posterior border on the proximal quarter of the posterior surface and its tendinous arch is attached to the surface proximally (see Fig. 78.8B ). Flexor hallucis longus is attached distal to soleus on the posterior surface and almost reaches the distal end of the shaft.

Vascular supply

A little proximal to the midpoint of the posterior surface (14–19 cm from the apex), a distally directed nutrient foramen on the fibular shaft receives a branch of the fibular artery. An appreciation of the detailed anatomy of the fibular artery in relation to the fibula is fundamental to the raising of osteofasciocutaneous free flaps. Free vascularized diaphysial grafts may also be taken on a fibular arterial pedicle. The proximal and distal ends receive metaphysial vessels from the arterial anastomoses at the knee and ankle, respectively ( ).

Innervation

The proximal and distal ends of the bone are supplied by branches of nerves that innervate the knee and superior tibiofibular joint, and the ankle and inferior tibiofibular joints, respectively. The periosteum of the shaft is supplied by branches from the nerves that innervate the muscles attached to the fibula.

Ossification

The fibula ossifies from three centres: one each for the shaft and the extremities. The process begins in the shaft during stage 23 (approximately 53–58 days post fertilization); in the distal end in the first year; and in the proximal end at about the third year in females and the fourth year in males. The distal epiphysis unites with the shaft at about the fifteenth year in females and the seventeenth year in males, whereas the proximal epiphysis does not unite until about the seventeenth year in females and the nineteenth year in males. A longitudinal radiographic study of children has shown that the proximal growth plate of the fibula contributes more to growth than the proximal growth plate of the tibia, their growth contributions being 61% and 57%, respectively ( ).

An os subfibulare is an occasional and separate entity and lies posterior to the tip of the fibula, whereas the distal fibular apophysis lies anteriorly. An os retinaculi is rarely encountered; if present, it overlies the bursa of the distal fibula within the fibular retinaculum.

Fibular dimelia is characterized by duplication of the fibula, tibial aplasia and partial duplication of the foot with pre-axial mirror polydactyly, and may be associated with ulnar dimelia and calcaneal duplication. It resembles duplication of the zone of polarizing activity that defines the postaxial border, but along the preaxial limb border of the limb ( Ch. 19 ) ( , , ).

Patella

The patella is the largest sesamoid bone in the body ( Figs 78.10 – 78.11 ) and is embedded in the tendon of quadriceps femoris, lying anterior to the distal femur (femoral condyles). It is flat, distally tapered and proximally curved, and has anterior and articular surfaces, three borders and an apex, which is the distal end of the bone. Most surfaces and borders are palpable. With the knee in extension, the apex is positioned proximal to the line of the knee joint by 1–2 cm.

Fig. 78.10, The left patella, showing sites of muscular and soft tissue attachment and articular surfaces. A , Anterior aspect. Key: 1, area of attachment of rectus femoris; 2, medial border: attachment of medial retinaculum (expansion); 3, apex; 4, area of attachment of vastus intermedius; 5, markings of attachment of tendon of quadriceps femoris; 6, lateral border, for attachment of lateral retinaculum (expansion). B , Articular (posterior) surface. Key: 1, upper lateral facet: in contact with femur in flexion of the knee; 2, lower lateral facet: in contact with femur in extension of the knee; 3, area overlain by edge of circumferential fat pad; 4, upper medial facet: in contact with femur in flexion of the knee; 5, medial vertical (‘odd’) facet: in contact with femur in extreme flexion of the knee; 6, lower medial facet: in contact with femur in extension of the knee; 7, ridge; 8, area covered by infrapatellar fat pad; 9, area for attachment of patellar ligament.

Fig. 78.11, Anteroposterior ( A ) and lateral ( B ) radiographs of the knee of a boy aged 14 years. Key: 1, patella; 2, cartilaginous growth plates; 3, intercondylar eminence; 4, prolongation of proximal tibial epiphysis and growth plate forming the tibial tuberosity.

The subcutaneous, convex anterior surface is perforated by numerous nutrient vessels. It is longitudinally ridged, separated from the skin by the subcutaneous prepatellar bursa, and covered by an expansion from the tendon of quadriceps femoris, which blends distally with superficial fibres of the patellar ligament (inaccurately named because this structure is the continuation of the tendon of quadriceps femoris). The posterior surface has a proximal smooth, oval articular area, crossed by a smooth vertical ridge, which fits the intercondylar groove on the femoral patellar surface and divides the patellar articular area into medial and lateral facets; the lateral is usually larger. Each facet is divided by faint horizontal lines into approximately equal thirds. A seventh ‘odd’ facet is present as a narrow strip along the medial border of the patella; it contacts the medial femoral condyle in extreme knee flexion. Distal to the articular surface, the apex is roughened by the attachment of the patellar ligament. Proximal to this, the area between the roughened apex and the articular margin is covered by an infrapatellar fat pad. The patellar articular cartilage is the thickest in the body, reflecting the magnitude of the stresses to which it is subjected.

The thick superior border (surface) of the patella slopes anteroinferiorly. Its medial and lateral borders are thinner and converge distally; the expansions of the tendons of vasti medialis and lateralis (medial and lateral patellar retinacula, respectively) are attached to them. The lateral retinaculum receives contributions from the iliotibial tract. Ossification occasionally extends from the lateral margin of the patella into the tendon of vastus lateralis.

The shape of the patella can vary and certain configurations are associated with patellar instability. Not infrequently, a bipartite and, less commonly, a tripartite patella are seen on imaging ( ). The bone seems to be in separate parts, usually with a smaller superolateral fragment: this has long been attributed to the presence of a separate ossification centre but, in some cases, could represent failed union following either a stress fracture or a violent contraction of quadriceps femoris (e.g. landing on the feet after jumping from a substantial height) resulting in a traumatic fracture.

Structure

The patella consists of more or less uniformly dense trabecular bone, covered by a thin compact lamina. Trabeculae beneath the anterior surface are parallel to the surface; elsewhere, they radiate from the articular surface into the substance of the bone.

Muscle attachments

Quadriceps femoris is attached to the superior surface, except near its posterior margin; the attachment extends distally on to the anterior surface. The attachment for rectus femoris is anteroinferior to that for vastus intermedius. Rough markings can be traced in continuity around the periphery of the bone from the anterosuperior surface to the deep surface of the apex. Those at the lateral and medial borders represent the attachments of vasti lateralis and medialis, and those at the apex represent the attachment of the patellar ligament.

Vascular supply

The arterial supply of the patella is derived from the genicular anastomosis, particularly from the genicular branches of the popliteal artery and from the anterior tibial recurrent artery. An anatomical study in children and fetuses confirmed that this network is already well developed in these age groups ( ).

Ossification

Several centres appear during the third to sixth years and these coalesce rapidly. Accessory marginal centres appear later and fuse with the central mass.

Joints

Superior tibiofibular joint

The superior (proximal) tibiofibular joint is a synovial joint (plane variety) between the lateral tibial condyle and head of the fibula.

Articulating surfaces

The articulating surfaces vary in size, form and inclination. The joint line may be transverse or oblique (in the latter case, the joint surfaces are inclined at an angle of greater than 20°). The fibular facet is usually elliptical or circular, and almost flat or slightly grooved. The surfaces are covered with hyaline cartilage. The volume of articular cartilage peaks at Tanner stage 2; boys gain articular cartilage faster than girls. The rate of cartilaginous volume development is +233 μl/year for the patella, +350 μl/year for the medial tibial compartment and +256 μl/year for the lateral tibial compartment ( ).

Fibrous capsule

The capsule is attached to the margins of the articular surfaces of the tibia and fibula, and is thickened anteriorly and posteriorly.

Ligaments

The ligaments of the superior tibiofibular joint are not entirely separate from the capsule. The anterior ligament is made up of two or three flat bands, which pass obliquely up from the fibular head to the front of the lateral tibial condyle in close relation to the tendon of biceps femoris. The posterior ligament is a thick band that ascends obliquely between the posterior aspect of the fibular head and the lateral tibial condyle, covered by the popliteal tendon.

Synovial membrane

The synovial membrane of the superior tibiofibular joint is occasionally continuous with that of the knee joint via the subpopliteal recess.

Vascular supply and lymphatic drainage

The superior tibiofibular joint receives an arterial supply from the anterior and posterior tibial recurrent branches of the anterior tibial artery. Lymphatics follow the arteries and drain to the popliteal nodes.

Innervation

The superior tibiofibular joint is innervated by branches from the deep fibular nerve and from the nerve to popliteus.

Factors maintaining stability

Stability of the superior tibiofibular joint is maintained by the fibrous capsule and the anterior and posterior ligaments, assisted by the biceps femoris tendon and the interosseous membrane of the leg.

Movements

Very little movement other than limited gliding takes place at the superior tibiofibular joint. Some movement must occur in conjunction with movement at the inferior tibiofibular joint; however, surgical fusion (arthrodesis) of the superior tibiofibular joint seems to have no effect on movements of the ankle joint.

Relations

The common fibular nerve runs posterior to the head of the fibula, medial to the tendon of biceps femoris, which is closely associated with the anterior capsule. The anterior and posterior tibial branches of the popliteal artery, and the fibular artery are all vulnerable inferomedial to the joint.

Patellofemoral joint

The patellofemoral joint is a synovial joint and is part of the knee joint.

Articulating surfaces

The articular surface of the patella is adapted to that of the femur. The latter extends on to the anterior surfaces of both femoral condyles like an inverted U. Since the whole area is concave transversely and convex in the sagittal plane, it is an asymmetric sellar surface. The ‘odd’ facet on the articular surface of the patella contacts the anterolateral aspect of the medial femoral condyle in full flexion, when the highest lateral patellar facet contacts the anterior part of the lateral femoral condyle. As the knee extends, the middle patellar facets contact the lower half of the femoral surface; in full extension, only the lowest patellar facets are in contact with the femur. In summary, on flexion, the patellofemoral contact point moves proximally and the contact area broadens to cope with the increasing stress that accompanies progressive knee flexion.

Fibrous capsule

See page 1407 .

Ligaments

The patellar ligament is an essential component of the extensor mechanism of the knee. The key medial structures involved in patellofemoral joint stabilization are the medial patellofemoral, patellotibial and medial patellomeniscal ligaments ( Fig. 78.12 ).

Fig. 78.12, Insertions of the medial patellar ligaments on the femur, patella tibia, and medial meniscus in a left knee (compare with Fig. 78.19 ).

Patellar ligament sheath and patellar ligament

The patellar ligament is a continuation of the tendon of quadriceps femoris and therefore is a misnomer. It continues from the patella to the tibial tuberosity (see Figs 77.44 and 77.46 ). It is strong, flat and 6–8 cm in length. Proximally, it is attached to the apex of the patella and adjoining margins, to roughened areas on the anterior surface and to a depression on the distal posterior patellar surface. Distally, it is attached to the superior smooth area of the tibial tuberosity. This attachment is oblique, and is more distal laterally. Its superficial fibres are continuous over the patella with the tendon of quadriceps femoris, the medial and lateral parts of which descend, flanking the patella, to the sides of the tibial tuberosity, where they merge with the fibrous capsule as the medial and lateral patellar retinacula. The patellar ligament is separated from the synovial membrane by a large infrapatellar fat pad and from the tibia by a bursa, and lies within its own well-defined sheath.

In the procedure of tibial osteotomy, the tibia is cut transversely just above the insertion of the patellar ligament. Failure to appreciate the obliquity of the tibial attachment of the tendon may lead to inadvertent division of the tendon during this procedure. The middle third of the patellar ligament may be harvested for surgical repair of a cruciate ligament.

Medial patellofemoral ligament

The femoral attachment of the medial patellofemoral ligament is consistently anterior and distal to the adductor tubercle with soft tissue attachments to the tendon of adductor magnus. Its fibres course deep to vastus medialis obliquus to attach broadly to the proximal third of the superomedial aspect of the patella, with a long, thin attachment adjacent to the quadriceps tendon and superficial to the patellar articular cartilage and joint capsule.

Medial patellotibial and patellomeniscal ligaments

The medial patellotibial ligament is a thin, single-layered structure (compared to the rounded, cord-like medial patellomeniscal ligament) located superficial and intimately adherent to the medial capsule. Both ligaments insert on the inferomedial patella; a portion of the patellar attachment lies deep to the patellar ligament but superficial to the patellar articular cartilage and deeper joint capsule. From its patellar attachment site, the medial patellotibial ligament passes inferomedially to the medial tibial tubercle of the anteromedial proximal tibia. The medial patellomeniscal ligament courses more horizontally than the medial patellotibial ligament and has a distinct attachment medial to the anterior horn of the medial meniscus ( ).

Lateral patellar dislocation is a relatively frequent injury, with an overall annual incidence of approximately 23.2 per 100,000 person years; the highest incidence, of approximately 147.7 per 100,000 person years, is in adolescents aged 14–18 years ( ). The medial patellofemoral ligament is the primary medial stabilizer of the patella throughout the first 30° of flexion and is the most commonly injured ligament with a lateral patellar dislocation. The medial patellotibial and patellomeniscal ligaments have a role in restricting lateral translation, patellar tilt and patellar rotation at increased degrees of knee flexion. They also maintain normal kinematics of the patellofemoral joint, particularly at higher flexion angles. Patellar re-dislocation occurs in 15–72% of patients treated non-operatively. However, significant reductions in patellar re-dislocation rates have been reported following surgical intervention, with medial patellofemoral ligament reconstruction ( ).

All other aspects of the patellofemoral joint are described with the tibiofemoral joint.

Tibiofemoral joint

The tibiofemoral joint is a complex synovial joint and is part of the knee joint.

Articulating surfaces

The articulating surfaces of the tibiofemoral joint are the proximal tibial surface, the intercondylar area and the femoral surface.

Proximal tibial surface

The proximal tibial surface (unofficially referred to as the tibial plateau) slopes posteriorly and downwards relative to the long axis of the shaft ( Fig. 78.13 ). The tilt, which is maximal at birth, decreases with age, and is more marked in habitual squatters. The tibial plateau presents medial and lateral articular surfaces (facets) for articulation with the corresponding femoral condyles. The posterior surface, distal to the articular margin, displays a horizontal, rough groove to which the capsule and posterior part of the tibial collateral ligament are attached. The anteromedial surface of the medial tibial condyle is a rough strip, separated from the medial surface of the tibial shaft by an inconspicuous ridge. The medial patellar retinaculum is attached to the medial tibial condyle along its anterior and medial surfaces, which are marked by vascular foramina.

Fig. 78.13, The left tibial plateau, showing sites of ligamentous and meniscal attachments and articular surfaces. Key: 1, tibial tuberosity; 2, attachment of anterior horn, lateral meniscus; 3, lateral condyle; 4, attachment of posterior horn, lateral meniscus; 5, attachment of anterior horn, medial meniscus; 6, attachment of anterior cruciate ligament; 7, medial condyle; 8, intercondylar eminence; 9, attachment of posterior horn, medial meniscus; 10, attachment of posterior cruciate ligament.

The medial articular surface is oval (long axis anteroposterior) and longer than the lateral articular surface. Around its anterior, medial and posterior margins, it is related to the medial meniscus; the meniscal imprint, wider posteriorly and narrower anteromedially, is often discernible. The surface is flat in its posterior half and the anterior half slopes superiorly about 10°. The meniscus covers much of the posterior surface so that, overall, a concave surface is presented to the medial femoral condyle. Its lateral margin is raised as it reaches the intercondylar region.

The lateral tibial condyle overhangs the shaft of the tibia posterolaterally above a small circular facet for articulation with the fibula. The lateral articular surface is more circular and coapted to its meniscus. In the sagittal plane, the articular surface is fairly flat centrally, and anteriorly and posteriorly the surface slopes inferiorly. Overall, this creates a rather convex surface so that, with the lateral femoral condyle in contact, there are anterior and posterior recesses (triangular in section), which are occupied by the anterior and posterior meniscal ‘horns’. Elsewhere, the surface has a raised medial margin that spreads to the lateral intercondylar tubercle. Its articular margins are sharp, except posterolaterally, where the edge is rounded and smooth: here the tendon of popliteus is in contact with bone.

Intercondylar area

The rough-surfaced area between the condylar articular surfaces is narrowest centrally where there is an intercondylar eminence, the edges of which project slightly proximally as the lateral and medial intercondylar tubercles. The intercondylar area widens behind and in front of the eminence as the articular surfaces diverge (see Fig. 78.13 ; Fig. 78.14 ).

Fig. 78.14, A , The superior aspect of the left tibia, showing the menisci and the attachments of the cruciate ligaments. B , Compounded image of two sequential axial MRI slices (T2-weighted with fat suppression) at the left knee joint showing the menisci and related ligaments.

The anterior intercondylar area is widest anteriorly. Anteromedially, anterior to the medial articular surface, a depression marks the site of attachment of the anterior horn of the medial meniscus. Behind this, a smooth area receives the anterior cruciate ligament. The anterior horn of the lateral meniscus is attached anterior to the intercondylar eminence, lateral to the anterior cruciate ligament. The eminence, with medial and lateral tubercles, is the narrow central part of the area. The raised tubercles are thought to provide a slight stabilizing influence on the femur. It is believed that the eminence becomes prominent once walking commences and that the tibial condyles transmit the weight of the body through the tibia.

The posterior horn of the lateral meniscus is attached to the posterior slope of the intercondylar area. The posterior intercondylar area inclines down and backwards behind the posterior horn of the lateral meniscus. A depression behind the base of the medial intercondylar tubercle is for the attachment of the posterior horn of the medial meniscus. The rest of the area is smooth and provides attachment for the posterior cruciate ligament, spreading back to a ridge to which the capsule is attached.

Femoral surface

The femoral condyles, bearing articular cartilage, are almost wholly convex. There are various opinions as to the contours of their sagittal profiles. One view is that they are spiral with a curvature increasing posteriorly (‘a closing helix’), that of the lateral condyle being greater. An alternative view is that the articular surface for contact with the tibia on the medial femoral condyle describes the arcs of two circles. According to this view, the anterior arc makes contact with the tibia near extension and is part of a virtual circle of larger radius than the more posterior arc, which makes contact during flexion. The lateral femoral condyle is believed to describe a single arc and thus to possess a single radius of curvature.

Tibiofemoral congruence is improved by the menisci, which are shaped to produce concavity of the surfaces presented to the femur; the combined lateral tibiomeniscal surface is deeper. The lateral femoral condyle has a faint groove anteriorly, which rests on the peripheral edge of the lateral meniscus in full extension. A similar groove appears on the medial condyle but does not reach its lateral border, where a narrow strip contacts the medial patellar articular surface in full flexion. These grooves demarcate the femoral patellar and condylar surfaces. The differences between the shapes of the articulating surfaces correlate with the movements of the knee joint.

Menisci

The menisci (semilunar cartilages) are crescentic, intracapsular, fibrocartilaginous laminae (see Fig. 78.14 ; Fig. 78.15 ). They serve to widen, deepen and prepare the tibial articular surfaces that receive the femoral condyles. Their peripheral attached borders are thick and convex, and their free, inner borders are thin and concave. Their peripheries are vascularized by capillary loops from the fibrous capsule and synovial membrane, while their inner regions are less vascular. Tears of the menisci are common. Peripheral tears (e.g. in the vascularized zone) have the potential to heal satisfactorily, especially with surgical intervention. Tears in the less vascular or inner zones seldom heal spontaneously; if surgery is indicated, these menisci are often resected. The meniscal horns are richly innervated compared with the remainder of the meniscus. The central one-third is devoid of innervation ( ). The proximal surfaces are smooth and concave, and in contact with the articular cartilage on the femoral condyles. The distal surfaces are smooth and flat, resting on the tibial articular cartilage. Each covers approximately two-thirds of its tibial articular surface. Canal-like structures open on to the surface of the menisci in infants and young children, and may transport nutrients to deeper, less vascular areas.

Fig. 78.15, Left knee joint. A, T1-weighted coronal magnetic resonance image (MRI). Key: 1, posterior cruciate ligament; 2, tibial collateral ligament; 3, medial meniscus; 4, lateral meniscus; 5, fibular collateral ligament; 6, anterior cruciate ligament. B, Medial meniscus, proton density (PD) weighted sagittal MRI. Key: 1, suprapatellar fat pad; 2, tendon of quadriceps femoris; 3, patellar articular cartilage; 4, patella; 5, femoral articular cartilage; 6, patellar ligament; 7, infrapatellar fat pad; 8, medial meniscus.

Two structurally different regions of the menisci have been identified. The inner two-thirds of each meniscus consist of radially organized collagen bundles, and the peripheral one-third consists of larger circumferentially arranged bundles ( ). Thinner collagen bundles parallel to the surface line the articular surfaces of the inner part, while the outer portion is covered by synovium. This structural arrangement suggests specific biomechanical functions for the two regions: the inner portion of the meniscus is suited to resisting compressive forces while the periphery is capable of resisting tensional forces. With ageing and degeneration, compositional changes occur within the menisci, which reduce their ability to resist tensional forces. Outward displacement of the menisci by the femoral condyles is resisted by firm anchorage of the peripheral circumferential fibres to the intercondylar bone at the meniscal horns.

Alternatively, each meniscus can be considered as consisting of three contiguous segments, namely an anterior horn/root, a body, and a posterior horn/root. The anterior roots of both menisci have relatively simple, planar insertions into the tibial plateau, while the posterior roots reveal complex, three-dimensional insertions into the tibial plateau.

The menisci spread load by increasing the congruity of the articulation, provide stability by their physical presence and proprioceptive feedback, and may cushion the underlying bone from the considerable forces generated during extremes of flexion and extension of the knee. They play a vital role in protecting against osteochondral damage of the tibiofemoral joint with specific importance afforded to the meniscal root. The loss of attachment at the root of the meniscus impairs the ability to maintain hoop strain when loading the tibiofemoral joint. (Hoop strain refers to the circumferential nature of the stress on meniscal fibres during axial loading.) This decrease in hoop strain resistance is responsible for increased articular cartilage contact pressure, which can lead to rapid degenerative changes ( ). An avulsion of the posterior root of the medial meniscus is biomechanically equivalent to a complete meniscectomy due to abnormally high peak tibiofemoral contact pressures ( ).

Medial meniscus

The medial meniscus is broader posteriorly and is almost a semicircle in shape (see Fig. 78.14 ). The anatomical location of the anterior root attachment of the medial meniscus has been described using surgical and arthroscopic vantage points. With reference to relevant open surgical landmarks, the centre of the anterior root is proximal to the superior aspect of the medial edge of the tibial tuberosity, and proximomedial to the centre of the superior edge of the tibial tuberosity. With regard to arthroscopic landmarks, the centre of the anterior root is anterior to the apex of the medial tibial eminence, anteromedial to the centre of the anterior cruciate ligament, and anteromedial to the centre of the lateral root of the lateral meniscus. The central, prominent root fibres that attach to the tibia encompass an area of approximately 56.3 mm 2 ( ). When the transverse (anterior intermensical) ligament is present it spans between the posteromedial aspect of the anterior horn of the medial meniscus and the anterolateral aspect of the anterior root of the lateral meniscus.

The posterior root is attached posterior to the apex of the medial tibial plateau, lateral to the inflection point of the articular cartilage of the medial tibial plateau, and anteromedial to the tibial attachment of the posterior cruciate ligament. The footprint area formed by the central fibres of the posterior root at its attachment is approximately 30.4 mm 2 ( ).

The peripheral border of the meniscus is attached to the fibrous capsule and the deep surface of the tibial collateral ligament. The tibial attachment of the meniscus is known as the ‘coronary or meniscotibial ligament’. Collectively, these attachments ensure that the medial meniscus is relatively fixed and moves much less than the lateral meniscus.

Lateral meniscus

The lateral meniscus forms approximately four-fifths of a circle and covers a larger area than the medial meniscus (see Fig. 78.14 ). Its breadth, except at its short tapered horns, is more or less uniform. It is grooved posterolaterally by the tendon of popliteus, separating it from the fibular collateral ligament. The central fibres of its anterior root are attached anteromedial to the apex of the lateral tibial eminence, and anterolateral to the centre of the tibial attachment of the anterior cruciate ligament. The tibial attachment area of the anterior root is approximately 140.7 mm 2 , and there is significant overlap with the tibial footprint of the anterior cruciate ligament ( ).

The posterior root is attached posteromedial to the lateral tibial eminence apex, medial to the edge of the lateral articular cartilage, anterior to the tibial attachment of the posterior cruciate ligament, and anterolateral to the posterior root of the medial meniscus. Its footprint area is approximately 39.2 mm 2 . In addition to the main attachment a continuation of the posterior fibres pass to the posterior aspect of the lateral margin of the medial tibial eminence ( ). Near its posterior attachment, it commonly sends a posterior meniscofemoral ligament superomedially behind the posterior cruciate ligament to the medial femoral condyle. An anterior meniscofemoral ligament may also connect the posterior horn to the medial femoral condyle anterior to the posterior cruciate ligament. The meniscofemoral ligaments are often the sole attachments of the posterior horn of the lateral meniscus. More laterally, part of the tendon of popliteus is attached to the lateral meniscus, and so mobility of its posterior horn may be controlled by the meniscofemoral ligaments and by popliteus. A meniscofibular ligament occurs in most knee joints. As with the medial meniscus, there is a tibial attachment via the so-called coronary ligament, but the meniscus has no peripheral bony attachment in the region of popliteus; in the surgical literature, this gap is referred to as the popliteus hiatus.

Discoid lateral meniscus

A discoid lateral meniscus occasionally occurs, often bilaterally. The distinguishing features of a discoid lateral meniscus are its shape and posterior ligamentous attachments. The following classification of the abnormality is based on the work of . In its mildest form, the partial discoid meniscus is simply a wider form of the normal lateral meniscus. The acute, medial free edge is interposed between the femoral and tibial condyles but it does not completely cover the tibial plateau. A complete discoid meniscus appears as a biconcave disc with a rolled medial edge and covers the lateral tibial plateau. The Wrisberg type of meniscus has the same shape as a complete discoid meniscus but its only peripheral posterior attachment is by the meniscofemoral ligaments. In this case, the normal tibial attachment of the posterior horn of the lateral meniscus is lacking but the posterior meniscofemoral ligament persists. As a result, this type of meniscus is attached anteriorly to the tibia and posteriorly to the femur, which renders the posterior horn unstable. Under these circumstances, the meniscus is liable to become caught between the femur and tibia: this accounts for the classic presenting symptom of the ‘clunking knee’ in some patients. The aetiology of discoid meniscus is not clear. Most are asymptomatic and are often found by chance at arthroscopy. However, they may cause difficulty in gaining access to the lateral compartment at arthroscopy. A discoid medial meniscus is extremely rare.

Transverse ligament of the knee

The transverse ligament of the knee connects the anterior convex margin of the lateral meniscus to the anterior horn of the medial meniscus (see Figs 78.14 , 78.22 ). It varies in thickness and is often absent. Its exact role is conjectural, although one study found that the ligament was slightly taut in knee extension ( ); presumably, it helps to decrease tension generated in the longitudinal circumferential fibres of the menisci when the knee is subjected to load. A posterior meniscomeniscal ligament is sometimes present.

Meniscofemoral ligaments

Two meniscofemoral ligaments connect the posterior horn of the lateral meniscus to the inner (lateral) aspect of the medial femoral condyle ( Fig. 78.16B ). The anterior meniscofemoral ligament (ligament of Humphrey) passes anterior to the posterior cruciate ligament. The posterior meniscofemoral ligament (ligament of Wrisberg) passes behind the posterior cruciate ligament and attaches proximal to the margin of attachment of the posterior cruciate.

Fig. 78.16, A posterior dissection of the knee. A , Capsule intact. B , Capsule removed.

Anatomical cadaveric studies found that at least one meniscofemoral ligament was typically present in the knees examined; both sometimes coexisted ( ). Biomechanical studies have revealed the cross-sectional area and strength of the meniscofemoral ligaments to be comparable to those of the posterior fibre bundle of the posterior cruciate ligament.

The meniscofemoral ligaments are believed to act as secondary restraints, supporting the posterior cruciate ligament in minimizing displacement caused by posteriorly directed forces on the tibia. They are also involved in controlling the motion of the lateral meniscus in conjunction with the tendon of popliteus during knee flexion.

Soft tissues

Recent advances in imaging and surgery on knee ligaments have contributed to an improved understanding of anatomy, particularly of the medial and lateral soft tissues of the knee.

Fibrous capsule and retinacula

The joint capsule is a fibrous membrane of variable thickness. Anteriorly it is replaced by the patellar ligament and does not pass proximal to the patella or over the patellar area. Elsewhere it lies deep to expansions from vasti medialis and lateralis, separated from them by a plane of vascularized loose connective tissue. The expansions are attached to the patellar margins and patellar ligament, extending back to the corresponding collateral (tibial and fibular) ligaments and distally to the tibial condyles. They form medial and lateral patellar retinacula, the lateral being reinforced by the iliotibial tract.

Posteriorly the capsule contains vertical fibres that arise from the articular margins of the femoral condyles and intercondylar fossa, and from the proximal tibia. The fibres mainly pass downwards and somewhat medially. The oblique popliteal ligament is a well-defined thickening across the posteromedial aspect of the capsule, and is one of the major extensions from the tendon of semimembranosus.

Medial ligaments and soft tissues

The medial soft tissues are arranged in three layers from superficial to deep ( ).

Layer 1

Layer 1 is the deep fascia that invests sartorius. The saphenous nerve and its infrapatellar branch are superficial to the deep fascia of the leg. Sartorius inserts into the fascia as an expansion rather than as a distinct tendon. The fascia spreads inferiorly and anteriorly to lie superficial to the distinct and readily identifiable tendons of gracilis and semitendinosus and their insertions. These tendons are commonly harvested for surgical reconstruction of damaged cruciate ligaments. To gain access to them, the upper edge of sartorius can be identified and the sartorius (layer 1) fascia is incised to reveal the tendons. Deep to the tendons is the anserine bursa, which overlies the superficial part of the tibial collateral ligament; this bursa sometimes becomes inflamed, especially in track and field athletes. Posteriorly, layer 1 overlies the tendons of gastrocnemius and the structures of the popliteal fossa. Anteriorly, layer 1 blends with the anterior limit of layer 2 and the medial patellar retinaculum. More inferiorly, layer 1 blends with the periosteum.

A condensation of tissue passes from the medial border of the patella to the medial epicondyle of the femur (the medial patellofemoral ligament), the anterior horn of the medial meniscus (the meniscopatellar ligament) and the medial tibial condyle (the patellotibial ligament).

Layer 2

Layer 2 is the plane of the superficial part of the tibial collateral ligament (medial collateral ligament) ( Fig. 78.17 ). The tendons of gracilis and semitendinosus lie between layers 1 and 2. The superficial part of the tibial collateral ligament is the largest structure of the medial aspect of the knee, measuring approximately 10–12 cm in length ( Fig. 78.17 ; see Fig. 78.15 ). It has one femoral and two tibial (proximal and distal) attachments. The femoral attachment is to a small depression just proximal and posterior to the centre of the medial epicondyle of the femur. As the superficial part of the tibial collateral ligament passes distally, it is separated from the tibia by the inferior medial genicular artery and vein, and a corresponding branch from the tibial nerve. Its proximal tibial attachment is primarily to soft tissues (the anterior arm of the tendon of semimembranosus) rather than directly to bone. The distal tibial attachment is broad-based and located just anterior to the posteromedial crest of the tibia: the majority of the fibres are located within the anserine bursa ( ). There is a vertical split in layer 2 anterior to the superficial part of the tibial collateral ligament. The fibres anterior to the split pass superiorly to blend with the fascia over vastus medialis and layer 1 in the medial patellar retinaculum. The fibres posterior to the split pass superiorly to the medial epicondyle and continue anteriorly as the medial patellofemoral ligament (see Figs 78.12 , 78.17 ).

Layer 3

Layer 3 is formed by the joint capsule, including the deep part of the tibial collateral ligament (mid-third capsular ligament) and can be separated from layer 2 everywhere except anteriorly close to the patella, where it blends with the more superficial layers. The deep part of the tibial collateral ligament is a distinct thickening of the anterior aspect of the medial joint capsule. It is deep to, and roughly parallels, the anterior aspect of the superficial part of the tibial collateral ligament. The deep part of the tibial collateral ligament consists of two components: the meniscotibial and meniscofemoral ligaments. The meniscotibial component is attached just distal to the tibial joint line. It is shorter and thicker than the meniscofemoral component, which is attached proximal to the femoral joint line ( ). Anteriorly the separation of the superficial and deep parts of the tibial collateral ligament is distinct, whereas posteriorly layers 2 and 3 blend to form a conjoined posteromedial capsule.

Factors maintaining medial stability

The tibial collateral ligament is important for stabilization of the medial knee, and is the most commonly injured ligament of the knee. The superficial and deep parts of the tibial collateral ligament are the primary and secondary static stabilizers, respectively, to valgus motion. The primary stabilizer for lateral (external) rotation is the distal attachment of the superficial part of the tibial collateral ligament; the proximal attachment of the superficial part of the tibial collateral ligament and the deep part of the tibial collateral ligament have secondary roles. The posterior oblique ligament also plays a significant role in resisting posteromedial rotatory instability of the knee ( ).

Lateral ligaments and soft tissues

The arrangement of the lateral soft tissues of the knee is controversial. Three distinct layers are recognized ( ), but views as to their contents vary. The first layer may be divided into superficial (oblique fibres of the iliotibial tract ending on the patella) and deep (lateral patellofemoral ligament, the transverse retinaculum and the patellotibial band) parts. These two parts are joined posteriorly by the iliotibial tract. The second layer contains the fibular collateral ligament, patellofemoral ligament, fabellofibular ligament and arcuate ligament, and the third layer is the joint capsule. An alternative view is that the first layer consists only of the oblique iliotibial tract fibres; the second layer contains the lateral patellofemoral ligament, the transverse retinaculum and the patellotibial band; and the third layer consists of superficial and deep portions, where the superficial part contains the fibular collateral ligament, patellofemoral ligament, fabellofibular ligament and the arcuate ligament and the deep part contains the joint capsule ( ). The recently described anterolateral ligament ( ) of the knee may be a component of the superficial layer ( ).

The lateral patellar retinaculum consists of superficial oblique and deep transverse portions. The former runs from the iliotibial tract to the patella. The latter is thicker and subdivided into three parts: the lateral patellofemoral ligament, running from the lateral patellar border to the lateral epicondyle of the femur; the transverse retinaculum, running from the iliotibial tract to the mid-patella; and the patellotibial band, running from the patella to the lateral tibial condyle.

The fascia lata and the iliotibial tract lie posterior to the lateral retinaculum. They come together distally to insert on to the tibia at a tubercle (Gerdy’s tubercle) on the anterolateral proximal tibia; some fibres continue to insert on the tibial tuberosity. Proximally, the fascia lata merges with the lateral intermuscular septum. Posteriorly, it blends with the fascia over biceps femoris. Here, as it emerges from behind the biceps femoris tendon, the common fibular nerve lies in a thin layer of fat bound by the fascia.

Posterolateral corner of the knee

The posterolateral corner of the knee contains several important structures that maintain varus and rotational stability throughout all ranges of motion; the three primary stabilizers are the fibular collateral ligament, popliteus tendon and popliteofibular ligament ( , ) ( Fig. 78.17 ).

Fig. 78.17, The major components of the medial aspect of the knee.

The fibular collateral ligament has a mean length of 7 cm and arises from a depression located just proximal and posterior to the lateral epicondyle, posterior to the insertion of popliteus. It passes underneath the superficial layer of the iliotibial tract and is inserted approximately 2.8 cm distal to the tip of the fibular head, with the majority of fibres extending to encompass the distal one-third of the lateral aspect of the fibular head. The fibular collateral ligament is separated from the capsule by a thin layer of fat and the inferior lateral genicular vessels. It is the primary restraint to varus stress on the knee and assists in limiting lateral rotation when the knee is slightly flexed.

The femoral insertion of the popliteus tendon constitutes the most anterior femoral insertion site of the posterolateral corner (see p. 1416 ).

The single most important stabilizer of the posterolateral knee is the popliteofibular (short external lateral) ligament that spans between the musculotendinous junction of popliteus and the posteromedial aspect of the fibular head. This ligament has a smaller anterior and a larger posterior division that embrace the musculotendinous junction of popliteus. The distolateral attachment of the anterior division is positioned on the anterior downslope of the medial aspect of the fibular styloid process. In a similar fashion, the posterior division is attached to the tip and posteromedial aspect of the fibular styloid process. The popliteofibular ligament contributes to the external rotatory stability of the knee ( ). Its connection to the tendon of popliteus also allows ‘dynamic’ tensioning.

The fabellofibular ligament is a condensation of fibres that runs either from the fabella (a sesamoid bone sometimes found within the tendon of the lateral head of gastrocnemius) or from the lateral head of gastrocnemius (if the fabella is absent), to the apex of the head of the fibula. The arcuate ligament is a condensation of fibres that runs from the apex of the head of the fibula, posteromedially over the emerging tendon of popliteus below the level of the tibial joint surface, to the tibial intercondylar area. The lateral joint capsule is thin and blends posteriorly with the arcuate ligament. Anteriorly, it forms the weak, lax coronary or meniscotibial ligament, which attaches the inferior border of the meniscus to the lateral tibia.

Intra-articular ligaments

Cruciate ligaments

The cruciate ligaments, so named because they cross each other, are very strong, richly innervated intracapsular structures. The point of crossing is located a little posterior to the articular centre. They are named anterior and posterior with reference to their tibial attachments ( Figs 78.19 – 78.22 ; see Fig. 78.25 ). A synovial membrane almost surrounds the ligaments but is reflected posteriorly from the posterior cruciate ligament to adjoining parts of the capsule; the intercondylar part of the posterior region of the fibrous capsule therefore has no synovial covering.

Fig. 78.18, The three major components of the posterolateral corner: lateral collateral ligament, tendon of popliteus and popliteofibular ligament.

Fig. 78.19, A , MRI of the anterior cruciate ligament. A , Proton density (PD)-weighted sagittal view. Key: 1, suprapatellar bursa; 2, patella; 3, infrapatellar fat pad; 4, femoral articular cartilage; 5, patellar ligament; 6, anterior cruciate ligament. B , T2-weighted sagittal image. Key: 1, femoral articular cartilage; 2, infrapatellar fat pad; 3, patellar ligament; 4, anterior cruciate ligament.

Fig. 78.20, Posterior cruciate ligament, PD-weighted sagittal MRI. Key: 1, epiphyseal line; 2, femoral articular cartilage; 3, patellar ligament; 4, popliteus; 5, posterior cruciate ligament; 6, gastrocnemius.

Fig. 78.21, The left knee joint. A , Anterior aspect in full flexion. B , Posterior aspect in extension.

Fig. 78.22, Arthroscopic view of the anterior and posterior cruciate ligaments of the left knee.

Anterior cruciate ligament

The anterior cruciate ligament is attached to the anterior intercondylar area of the tibia, just anterior and slightly lateral to the medial intercondylar tubercle, partly blending with the anterior horn of the lateral meniscus (see Fig. 78.14 ). It ascends posterolaterally, twisting on itself and fanning out to attach high on the posteromedial aspect of the lateral femoral condyle ( ). The average length and width of an adult anterior cruciate ligament are 38 mm and 11 mm, respectively. It is formed of two, or possibly three, functional bundles that are not apparent to the naked eye but can be demonstrated by microdissection techniques. The bundles are named anteromedial, intermediate and posterolateral, according to their tibial attachments ( , ).

Posterior cruciate ligament

The posterior cruciate ligament is thicker and stronger than the anterior cruciate ligament (see Fig. 78.14 ), the average length and width of an adult posterior cruciate ligament being 38 mm and 13 mm, respectively. It is attached to the lateral surface of the medial femoral condyle and extends up on to the anterior part of the roof of the intercondylar fossa, where its attachment is extensive in the anteroposterior direction. Its fibres are adjacent to the articular surface. They pass distally and posteriorly to a fairly compact attachment posteriorly in the intercondylar region and in a depression on the adjacent posterior tibia. This gives a fan-like structure in which fibre orientation is variable. Anterolateral and posteromedial bundles have been defined; they are named (against convention) according to their femoral attachments. The anterolateral bundle tightens in flexion while the posteromedial bundle is tight in extension of the knee. Each bundle slackens as the other tightens. Unlike the anterior cruciate ligament, it is not isometric during knee motion, i.e. the distance between attachments varies with knee position. The posterior cruciate ligament ruptures less commonly than the anterior cruciate ligament and rupture is usually better tolerated by patients than rupture of the anterior cruciate ligament.

Synovial membrane, plicae and fat pads

The synovial membrane of the knee is the most extensive and complex in the body. It forms a large suprapatellar bursa between quadriceps femoris and the lower femoral shaft proximal to the superior patellar border ( Figs 78.23 – 78.24 ). The bursa is an extension of the joint cavity. The attachment of articularis genus to its proximal aspect prevents the bursa from collapsing into the joint. Alongside the patella, the membrane extends beneath the aponeuroses of the vasti, especially under vastus medialis. It extends proximally a hand’s breadth above the superior pole of the patella. Distal to the patella, the synovial membrane is separated from the patellar ligament by an infrapatellar fat pad. Where it lies beneath the fat pad, the membrane projects into the joint as two fringes, alar folds, which bear villi. The folds converge posteriorly to form a single infrapatellar fold or plica (ligamentum mucosum), which curves posteriorly to its attachment in the femoral intercondylar fossa ( Fig. 78.25 ). This fold may be a vestige of the inferior boundary of an originally separate femoropatellar joint. The extent of the infrapatellar plica ranges from a thin cord to a complete sheet that can obstruct the passage of instruments during knee arthroscopy. When substantial, it has been mistaken for the anterior cruciate ligament, which is directly posterior to it. The medial plica extends in the midline anteriorly from the medial alar fold medially to the suprapatellar bursa. Occasionally, it can be thickened and inflamed, usually following acute or chronic trauma.

Fig. 78.23, The left knee joint, lateral aspect. The synovial cavity is distended and the synovial membrane appears grey.

Fig. 78.24, A , A sagittal section through the left knee joint, lateral aspect. B , Sagittal mean intensity projection of the knee from a CT arthrogram.

Fig. 78.25, The left knee joint in full flexion. The tendon of quadriceps femoris has been sectioned and the patella retracted distally. Compare with Fig. 78.14A .

The suprapatellar plicae are remnants of an embryonic septum that completely separates the suprapatellar bursa from the knee joint. Occasionally, a septum persists, either in its entirety or perforated by a small peripheral opening.

The infrapatellar fat pad is the largest part of a circumferential extrasynovial fatty ring that extends around the patellar margins ( ).

At the sides of the joint, the synovial membrane descends from the femur and lines the capsule as far as the menisci, whose surfaces have no synovial covering. Posterior to the lateral meniscus, the membrane forms a subpopliteal recess between a groove on the meniscal surface and the tendon of popliteus, which may connect with the superior tibiofibular joint. The relationship of the synovial membrane to the cruciate ligaments is described above.

Bursae

Numerous bursae are associated with the knee. Anteriorly, there is a large subcutaneous prepatellar bursa between the lower half of the patella and skin; a small, deep infrapatellar bursa between the tibia and patellar ligament; a subcutaneous infrapatellar bursa between the distal part of the tibial tuberosity and skin; and a large suprapatellar bursa, which is the superior extension of the knee joint cavity (see Fig. 78.24 ). Posterolaterally, there are bursae between the lateral head of gastrocnemius (lateral subtendinous bursa of gastrocnemius) and the joint capsule (this bursa is sometimes continuous with the joint cavity); the fibular collateral ligament and the tendon of biceps femoris; the fibular collateral ligament and the tendon of popliteus; and the tendon of popliteus and the lateral femoral condyle, which is usually an extension of the synovial cavity of the joint. The last two bursae may communicate with each other.

Medially, the arrangement of the bursae is complex. The bursa between the medial head of gastrocnemius and the fibrous capsule is prolonged between the medial tendon of gastrocnemius and the tendon of semimembranosus (the semimembranosus bursa), and usually communicates with the joint. The bursa between the tendon of semimembranosus and the medial tibial condyle and the medial head of gastrocnemius may communicate with this bursa. The anserine bursa is located between the tibial collateral ligament and the tendons of sartorius, gracilis and semitendinosus. Bursae that vary in both number and position lie deep to the tibial collateral ligament between the joint capsule, femur, medial meniscus, tibia or tendon of semimembranosus. Occasionally, there may be a bursa between the tendons of semimembranosus and semitendinosus. Posteriorly, bursae associated with the knee are variable.

The clinically important bursae are the anterior group, the anserine bursa and the semimembranosus bursa. Inflammation of the subcutaneous prepatellar bursa and infrapatellar bursa are referred to colloquially as ‘housemaid’s knee’ and ‘clergyman’s knee’, respectively. The anserine bursa can become inflamed, especially in athletes. In adults, bursal inflammation producing a popliteal fossa swelling commonly occurs secondary to degeneration within the knee joint; regardless of its size and position, it almost always arises from the plane between semimembranosus and the tendon of the medial head of gastrocnemius.

Relations and ‘at risk’ structures

The tendon of quadriceps femoris (which encloses and is attached to the non-articular surfaces of the patella), the patellar ligament, tendinous expansions from vasti medialis and lateralis (which extend over the anteromedial and anterolateral aspects of the capsule, respectively), and the patellar retinacula all lie anterior to the knee joint. Posteromedially are sartorius and the tendon of gracilis (which lies along its posterior border); both descend across the joint. Posterolaterally the tendon of biceps femoris and the common fibular nerve (which lies medial to the tendon) are in contact with the capsule, and thereby separated from the tendon of popliteus. Posteriorly the popliteal artery and associated lymph nodes lie posterior to the oblique popliteal ligament; the popliteal vein is posteromedial or medial, and the tibial nerve is posterior to both. The nerve and vessels are overlapped by both heads of gastrocnemius and laterally by plantaris. Gastrocnemius contacts the capsules on either side of the vessels. Semimembranosus lies between the capsule and semitendinosus, medial to the medial head of gastrocnemius.

Biomechanics of the Knee

The knee joint is a complex synovial joint consisting of the tibiofemoral and patellofemoral articulations. It functions to control the centre of body mass and posture in the activities of daily living. This necessitates a large range of movement in three dimensions coupled with the ability to withstand high forces. These conflicting parameters of mobility and stability are only achieved by the interactions between the articular surfaces, the passive stabilizers and the muscles that cross the joint.

The relatively incongruent nature of the joint surfaces makes the knee joint inherently mobile. In addition, because it acts as a pivot between the longest bones in the body, and is subjected to considerable loads in locomotion, the joint is also potentially at risk of injury if any of the multiple factors providing joint stability are compromised. The long bones may act as levers, increasing the stresses on the stabilizing ligaments.

Movements

Movements at the knee are customarily described as flexion, extension, medial (internal) and lateral (external) rotation. Flexion and extension differ from true hingeing, in that the articular surface profiles of the femoral and tibial articular surfaces produce a variably placed axis of rotation during the flexion arc, and when the foot is fixed, flexion entails corresponding conjunct (coupled) lateral rotation. These conjunct rotations are a product of the complex geometry of the articular surfaces and, to an extent, the disposition of the associated ligaments. There is differential motion in the medial and lateral tibiofemoral compartments. Laterally, there is considerable displacement of the femur on the tibia, with rolling as well as sliding at the joint surface. In contrast, medially, for most of the flexion arc there is minimal relative motion of the femur and tibia, and the motion almost exclusively involves one joint surface sliding on the other. In full flexion, the lateral femoral condyle is close to posterior subluxation off the lateral tibial articular surface. Medially, significant posterior femoral displacement only occurs when flexion exceeds 120°. The menisci move with the femoral condyles, the anterior horns more than the posterior, and the lateral meniscus considerably more than the medial.

The axial rotations have a smaller range than the arc of flexion and extension. These rotations are conjunct, and integral with flexion and extension, i.e. they are obligatory. They can also be adjunct and independent, i.e. voluntary, and are best demonstrated with the knee semi-flexed. The degree of axial rotation therefore varies with flexion and extension.

The range of extension is 5–10° beyond the ‘straight position’. Active flexion is approximately 120° with the hip extended, 140° when it is flexed, and 160° when aided by a passive element, e.g. sitting on the heels. Voluntary rotation is 60–70° but conjunct rotation only 20°.

Conjunct medial rotation of the femur on the tibia in the later stages of extension is part of a ‘locking’ mechanism, the so-called ‘screw-home movement’, which is an asset when the fully extended knees are subjected to strain. Full extension results in the close-packed position, with maximal spiralization and tightening of the ligaments. The roles of the articular surfaces, musculature and ligaments in generating conjunct rotations remain controversial ( , ) but the following points can be made. The lateral combined meniscotibial ‘receiving surface’ is smaller, more circular and more deeply concave. Since the articular surface is virtually convex in sagittal section, the depth of the receiving surface is largely due to the presence of the lateral meniscus. The lateral femoral articular surface is also smaller. Consequently, the lateral femoral condyle approaches full congruence with the opposed surface some 30° before full extension (well before the medial condyle). Simple extension cannot continue, but medial rotation of the femur occurs on a vertical axis through its head and medial condyle; the medial femoral condyle moves very little in the sagittal plane and is stabilized by the ‘upslope’ of the anterior half of the medial tibia, while rotation of the lateral femoral condyle and meniscus brings the anterior horn of the latter on to the anterior ‘downslope’ of the lateral tibial condyle. Rotation and extension follow simultaneously and smoothly until final close packing of both condyles is accomplished. At the beginning of flexion from full extension (with the foot fixed), lateral femoral rotation occurs, which ‘unlocks’ the joint. While joint surfaces and many ligaments are involved, electromyographic evidence reveals that contraction of popliteus is important, and that it pulls down and backwards on the lateral femoral condyle, lateral to the axis of femoral rotation. It also retracts the posterior horn during lateral rotation and continuing flexion, via its attachment to the lateral meniscus, and so prevents traumatic compression.

Any position of extension adopted is a balance between forces (torque) extending the joint and passive mechanisms resisting them. The range near to close packing is functionally important. In symmetrical standing, the line of the body’s weight is anterior to the transverse axes of the knee joints, but the passive mechanisms noted above preserve posture with minimal muscular effort ( ). Active contraction of quadriceps femoris and a close-packed position only occurs in asymmetrical postures, e.g. in leaning forward, during heavy loading, or when powerful thrust is needed.

In knee extension, parts of the cruciate ligaments, the tibial and fibular collateral ligaments, the posterior capsular region, the oblique popliteal ligament, skin and fasciae are all taut. Passive and sometimes active tension exists in the posterior thigh muscles and gastrocnemius, and the anterior part of the medial meniscus is compressed between the femoral and tibial condyles. During extension, the patellar ligament is tightened by quadriceps femoris but is relaxed in the erect attitude. When the knee flexes, the fibular collateral ligament and the posterior part of the tibial collateral ligament relax but the cruciate ligaments and the anterior part of the tibial collateral ligament remain taut; the posterior parts of the menisci are compressed between the femoral and tibial condyles. Flexion is checked by quadriceps femoris, anterior parts of the knee joint capsule, posterior cruciate ligament and compression of soft tissues behind the knee. In extreme passive flexion, contact of the calf with the thigh may be the limiting factor and parts of both cruciate ligaments are also taut. In addition to conjunct rotation with terminal extension or initial flexion, relaxed collateral ligaments also allow independent medial and lateral rotation (adjunct rotation) when the joint is flexed.

Accessory movements

Wider rotation can be obtained by passive movements when the knee is semi-flexed. To a limited extent, the tibia can also be translated backwards and forwards on the femur. Abduction and adduction are prevented in full extension by the collateral ligaments and secondary restraints such as the cruciate ligaments. With the knee slightly flexed, limited adduction and abduction are possible, both passive and active. Slight separation of the femur and tibia can be achieved by strong traction on the leg with countertraction applied to the thigh.

Physiological knee joint laxity may occur during puberty. Increased knee joint flexibility is seen more frequently in adolescent girls than boys. There is an inverse relationship between Tanner stage and the degree of laxity with a progressive decrease of sagittal laxity at the onset of Tanner stage 2 ( ).

Muscles producing movements

Flexion

Flexion is produced by biceps femoris, semitendinosus and semimembranosus, assisted by gracilis, sartorius and popliteus. With the foot stationary, gastrocnemius and plantaris also assist (see Fig. 78.3 ).

Extension

Extension is produced by quadriceps femoris, assisted by tensor fasciae latae.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

Related Posts