Pelvic girdle and lower limb: Overview and surface anatomy

Arterial perforators of the lower limb and surgical flaps

Achieving adequate and aesthetically satisfactory skin and soft tissue cover for large, superficial tissue defects is a perennial challenge in the field of plastic and reconstructive surgery, and accounts for a substantial part of a plastic surgeon’s workload. Generally, split-thickness and full-thickness skin grafts are suitable only for very superficial defects. To achieve tissue coverage for deeper and larger tissue defects, one of a variety of autologous tissue flaps may be used. A fasciocutaneous flap is composed of skin, fat and deep fascia (fascia musculorum); a lower-extremity fasciocutaneous flap ( ) is very useful in the repair of soft tissue defects of the leg.

The viability of a flap transplanted from one part of the body to another is crucially dependent on the blood supply of the flap. An appreciation of the angiosome concept ( Chapter 6, Chapter 7 ), coupled with technological advances in reconstructive microsurgery, has stimulated the development and use of perforator (or perforator-based) flaps. These are flaps of skin or subcutaneous tissue supplied by one or more fascial ‘perforators’, i.e. arteries that reach the suprafascial plexus either directly from a source vessel, or indirectly from some other neighbouring tissue ( ) ( Fig. 76.6 ). Perforator-based flaps are typically harvested with sparing of underlying muscle tissue and minimal trauma; their use is said to reduce postoperative pain, donor site morbidity and functional loss.

The lower limb is the largest donor site in the body for perforator-based flaps. Commonly used flaps include anterolateral thigh flaps, which provide a large amount of skin; superior and inferior gluteal artery perforator flaps used in breast reconstruction; vascularized fibular flaps for reconstruction of deficient bone; vascularized tensor fasciae latae flaps for tendon reconstruction; vascularized sural nerve flaps for nerve reconstruction; and the gracilis muscle flap, used in, for example, reanimation of paralysed muscle.

In the context of perforator flap surgery, the lower limb may be considered in terms of four anatomic regions: gluteal; anterior hip and thigh; knee and leg; ankle and foot. Each lower limb accounts for approximately 23% of the total body surface area (thigh 10.5%, leg 6.5%, buttock 2.5% and foot 3.5%) and contains an average of 90 arterial perforators ( Fig. 76.7 ). FLOAT NOT FOUND

Venous (muscle) pumps

While standing, venous return from the lower limb depends largely on muscular activity, especially contraction of the calf and foot muscles, known as the ‘muscle pump’, aided by the tight sleeve of deep fascia ( ). ‘Perforating’ veins connect the long saphenous vein with the deep veins, particularly near the ankle, distal calf and knee. Their valves are arranged so as to prevent flow of blood from the deep to the superficial veins. At rest, pressure in a superficial vein is equal to the height of the column of blood extending from that vein to the heart. When the posterior leg muscles contract, blood is pumped proximally into the deep veins and is normally prevented from flowing into the superficial veins by the valves in the perforating veins. During muscular relaxation, blood is drawn into the deep veins from the superficial veins. If the valves in the perforating veins become incompetent, these veins become sites of ‘high-pressure leaks’ during muscular contraction, and the superficial veins become dilated and varicose. There are similar perforating connections in the anterolateral region, where varicosities may also occur. Incompetence of the valves in the connecting veins between the long saphenous vein and femoral vein in the adductor canal may predispose to superficial varicosities along the medial aspect of the thigh ( ). Venous plexuses, which may be intramuscular (soleus) or intermuscular (in the foot and gluteal region), communicate with the axially running deep veins and are components of the ‘muscle pump’ mechanism.

Superficial tissues

The superficial lymph vessels begin in subcutaneous plexuses. Collecting vessels leave the foot either medially with the long saphenous vein, or laterally with the short saphenous vein. Medial vessels are larger and more numerous. They start on the medial side of the dorsum of the foot, ascend anterior or posterior to the medial malleolus, accompany the long saphenous vein and drain to the distal superficial inguinal nodes. Lateral vessels begin on the fibular side of the dorsum of the foot. Some cross anteromedially in the leg to join the medial vessels and so pass to the distal superficial inguinal lymph nodes, while others accompany the short saphenous vein and drain to the popliteal nodes. Superficial lymph vessels from the gluteal region run anteriorly to the proximal superficial inguinal nodes.

Deeper tissues

The deep lymph vessels accompany the anterior and posterior tibial, fibular, popliteal and femoral vessels. Popliteal nodes interrupt the deep vessels from the foot and leg; deep vessels from the thigh pass to the deep inguinal nodes. The deep lymphatic vessels of the gluteal region follow their corresponding blood vessels. Those accompanying the superior gluteal vessels end in a node near the intrapelvic part of the superior gluteal artery, adjacent to the superior border of the greater sciatic foramen, while those that follow the inferior gluteal vessels traverse one or two of the small nodes inferior to piriformis and then pass to the internal iliac nodes.

Lesions of the lumbar and sacral plexuses

The deep and protected situation of the plexuses means that lesions are not common. The lumbar plexus may be involved in retroperitoneal pathology and the sacral plexus may be invaded by pelvic malignancies and both may be involved in the reticuloses, affected by plexiformneuromas, or damaged in fractures of the lumbar spine and pelvis or in other conditions that cause severe retroperitoneal and pelvic haemorrhage. Temporary lesions may occur after pregnancy and childbirth, e.g. after difficult forceps delivery of a large baby. Pain, which may be diffuse, is the most common feature. Iatrogenic injury can occur during surgical approaches to the abdomen and pelvis, particularly when operating within the retroperitoneal space and also during the lateral approach to spine.

Sciatica is pain in the lower back and hip region, radiating inferiorly along the posterior thigh to the leg. It is often caused by a herniated intervertebral disc, compressing the L5 or S1 ventral rami. The so-called piriformis syndrome, which may result from a variant or anomalous relationship between piriformis and the sciatic nerve, may also produce hip pain that radiates inferiorly along the course of the sciatic nerve. Diagnosis of specific nerve injuries relies on the distribution and characteristics of clinical findings in combination with supportive electrophysiological studies and/or MRI and CT scans. The clinical presentation of lesions can vary as a result of anatomical variation and overlapping innervation patterns. Generally, loss of hip flexion and knee extension indicates a lumbar lesion; loss of hip abduction, knee flexion, and plantarflexion and dorsiflexion are symptoms of sacral lesions ( ).

Femoral nerve (L2–L4)

The femoral nerve is the nerve of the anterior compartment of the thigh. It arises from the posterior divisions of the second to fourth lumbar ventral rami, descends through psoas major and emerges on its lateral border to pass between it and iliacus. It enters the thigh behind the inguinal ligament and lateral to the femoral sheath. Its terminal branches form in the femoral triangle about 2 cm distal to the inguinal ligament. In the abdomen, the nerve supplies small branches to iliacus and a branch to the proximal part of the femoral artery. It subsequently supplies a large cutaneous area on the anterior and medial thigh, medial leg and foot, and gives articular branches to the hip, knee and ankle. The femoral nerve is described in detail on pages 1391–1392 .

The femoral nerve is susceptible to compression, resulting in isolated motor or sensory deficits, either within psoas major or as it passes under the inguinal ligament. Partial or complete nerve injury can occur during surgery directed to the hip, pelvis or spine; with femoral artery catheterization; from trauma; or as a result of a retroperitoneal haematoma or mass. Consequences include paralysis of the hip flexors and quadriceps (with loss of the patellar reflex) and sensory deficits in the medial and anterior thigh and medial side of the leg (saphenous branch).

Obturator nerve (L2–L4)

The obturator nerve is the nerve of the medial compartment of the thigh. It arises from the anterior divisions of the second to fourth lumbar ventral rami, descends through psoas major and emerges from its medial border at the pelvic brim. It crosses the sacroiliac joint behind the common iliac artery and lateral to the internal iliac vessels, runs along the lateral pelvic wall medial to obturator internus, and enters the thigh through the upper part of the obturator foramen. Near the foramen, it divides into anterior and posterior branches that are initially separated by part of obturator externus and more distally by adductor brevis. It provides articular branches to the hip and knee, and can supply the skin of the medial thigh and leg. An accessory obturator nerve may also be present and leaves the pelvis anterior to the pubis. The obturator nerve is described in detail on page 1392 .

Isolated lesions of the obturator nerve are rare, and usually occur in combination with injury to other nerves of the lumbosacral plexus. They can result from an acetabular fracture, pelvic tumour, obturator hernia, prolonged labour or direct trauma, and can be produced iatrogenically following manipulation, transection or retraction during pelvic surgery. The obturator nerve can become entrapped within the fascia overlying adductor brevis. Resulting symptoms include radiating pain and numbness on the medial side of the thigh and adductor muscle paralysis. Pain or loss of sensation in the groin with weakness of adduction and medial rotation of the thigh may be noted.

Sciatic nerve (L4, L5, S1–S3)

The sciatic nerve is typically 2 cm wide at its origin and is the thickest nerve in the body. It travels in the posterior compartment of the thigh and supplies the leg and foot. It is formed in the pelvis from the ventral rami of the fourth lumbar to third sacral spinal nerves, enters the lower limb via the greater sciatic foramen inferior to piriformis and descends between the greater trochanter and ischial tuberosity. In its descent along the posterior thigh it is crossed by the long head of biceps femoris. The sciatic nerve ‘divides’ into the tibial and common fibular (peroneal) nerves proximal to the knee. The tibial nerve is derived from the anterior divisions of the sacral plexus and the common fibular nerve is derived from the posterior divisions of the plexus: the two large nerves are only loosely held together as the sciatic nerve and the level of their separation in the thigh is variable.

The sciatic nerve sends articular branches to the hip joint through its posterior capsule (these can be derived directly from the sacral plexus) and to the knee joint. The medial (tibial) component innervates the posterior thigh muscles, including the ischial part of adductor magnus, but not the short head of biceps femoris, which is supplied by the lateral (common fibular) component. The common variations of the sciatic nerve have been classified into six types ( ). The sciatic nerve is described in detail on pages 1392–1393 .

Sciatic nerve injury may result from gluteal trauma, hip fracture, vasculitis, myositis piriformis syndrome or iatrogenically damaged by misplaced gluteal injections or during total hip replacement surgery. Complete sciatic nerve palsy is rare, with injury to its common fibular component more frequent, possibly because it lies posterior, lateral and superficial to the tibial nerve.

Tibial nerve (L4, L5, S1–S3)

The tibial nerve is derived from the anterior divisions of the sacral plexus. It descends through the posterior thigh and popliteal fossa to the distal border of popliteus, passes anterior to soleus with the popliteal artery and continues into the leg. In the popliteal fossa, it initially lies lateral to the popliteal vessels, then becomes superficial to them and crosses to the medial side of the artery. In the leg, it is the nerve of the posterior compartment, descending with the posterior tibial vessels to lie between the heel and the medial malleolus and ending deep to the flexor retinaculum by dividing into the medial and lateral plantar nerves. The tibial nerve supplies articular branches to the knee and ankle joints, cutaneous branches to the back of the calf, the sole, the lateral border of the foot and the medial and lateral sides of the heel, and motor branches to gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus and flexor hallucis longus. The tibial nerve is described in detail on pages 1427–1428 .

The tibial nerve is at risk of direct injury in the popliteal fossa, and can be compressed at the level of the tarsal tunnel as the nerve passes under the flexor retinaculum (tarsal tunnel syndrome). The medial plantar nerve may be compressed between abductor hallucis and the navicular bone (‘jogger’s foot’). Depending on the level of the injury, weakness of knee flexion, plantarflexion, inversion and toe flexion may result, accompanied by sensory loss in the lower lateral leg, heel and sole of the foot.

Common fibular nerve (L4, L5, S1, S2)

The common fibular nerve (common peroneal nerve) is derived from the posterior divisions of the sacral plexus and is the nerve of the anterior and lateral compartments in the leg. It descends obliquely along the lateral side of the popliteal fossa to the fibular head, lying between the tendon of biceps femoris and the lateral head of gastrocnemius, then curves lateral to the neck of the fibula, lying on the bone deep to fibularis longus, and divides into superficial and deep fibular (peroneal) nerves. The common fibular nerve supplies the anterolateral part of the knee joint capsule and the proximal tibiofibular joint and the skin on the anterior, posterior and lateral surfaces of the proximal leg. The superficial fibular (peroneal) nerve supplies fibulares longus and brevis and the skin of the lower leg before dividing into medial and intermediate dorsal cutaneous nerves. The deep fibular (peroneal) nerve supplies muscular branches to tibialis anterior, extensors hallucis longus and digitorum longus and fibularis tertius, and an articular branch to the ankle joint, before dividing into lateral and medial terminal branches. The common fibular nerve is described in detail on page 1428 .

The common fibular nerve is prone to iatrogenic or traumatic injury: patients with common fibular neuropathy present with foot drop. Injury specifically to the superficial fibular nerve will result in paralysis of eversion and sensory loss in the lower lateral aspect of the leg extending onto the dorsum of the foot. Damage to the deep fibular nerve results in paralysis of dorsiflexion and toe extension with sensory loss in the first interdigital web space.

Gluteal nerves (L4, L5, S1, S2)

The gluteal nerves arise from the posterior divisions of the sacral plexus. The superior gluteal nerve (L4, L5, S1) leaves the pelvis through the greater sciatic foramen superior to piriformis and supplies gluteus medius, gluteus minimus, tensor fasciae latae and the hip joint. The inferior gluteal nerve (L5, S1, S2) passes through the greater sciatic foramen inferior to piriformis and supplies gluteus maximus. The gluteal nerves are described in detail on page 1393 .

Focal lesions of the superior and inferior gluteal nerves usually occur concurrently with those of the sciatic nerve, posterior femoral cutaneous nerve and/or pudendal nerve. However, both gluteal nerves are vulnerable to injury during total hip replacement, and less commonly due to blunt trauma or misplaced gluteal injections. Injury to the superior gluteal nerve causing paralysis of gluteus medius and minimus can result in Trendelenburg’s sign, where the pelvis drops on the unsupported side (in the coronal plane) when standing on the affected limb. Injury to the inferior gluteal nerve results in weakness of gluteus maximus causing impaired hip extension ( ).