Soft Tissue Injury to the Ankle : Tendon Injuries

Etiology

Ankle tendon injuries most commonly occur as a result of chronic microtearing due to overuse from athletic activity and/or primary degeneration. Systemic diseases such as rheumatoid arthritis, seronegative spondyloarthropathies, gout, hyperparathyroidism, and diabetes can also lead to tendon infiltration or degeneration. Discrete tears of the ankle tendons occur as a result of specific biomechanical forces applied to the tendon that are frequently superimposed on a background of tendinosis. Penetrating injuries are another less common cause of ankle tendon rupture. Other tendon injuries include tenosynovitis and paratenonitis, entrapment, and dislocation.

Prevalence and Epidemiology

Prevalence of ankle tendon pathology is closely related to the underlying clinical scenarios. The Achilles tendon is commonly injured in athletes and “weekend warriors.” Tibialis posterior tendinopathy is common in obese patients, middle-aged women, and patients with underlying diabetes; because of its high incidence and function as a dynamic stabilizer of the arch, injury to this tendon is the most common source of painful acquired flatfoot in adults. Pathology of the peroneal tendons is common and associated with previous ankle sprains. Injuries of the tibialis anterior and flexor hallucis longus tendons are uncommon.

Clinical Presentation

Tendinosis may be asymptomatic or manifest as chronic dull pain in the region of the affected tendon worsened by activity. Acute and chronic tendinopathies are defined by the duration of symptoms, corresponding to either less than or greater than 3 months, respectively.

Acute tendon rupture is often superimposed on a background of tendinosis and typically occurs during forceful eccentric contraction of the associated muscle. Patients with tendon rupture present with pain and tendon dysfunction.

Paratenonitis and tenosynovitis present as local swelling, tenderness, and weakness. The Achilles, tibialis posterior, and peroneal tendons are most commonly injured and are discussed in more detail later.

Pathophysiology

Anatomy

All tendons are enclosed in a connective tissue covering known as the epitenon , containing blood vessels, nerves, and lymphatics. Another connective tissue layer surrounds the epitenon, termed the paratenon , and is frequently lined by synovium. The paratenon and epitenon are collectively referred to as the peritendon .

Posterior Ankle Tendons (Achilles, Plantaris)

Achilles Tendon

The Achilles tendon is the largest tendon in the body, derived from the fibers of the gastrocnemius and soleus muscles in the superficial posterior compartment in the calf. Collectively, the three muscle heads of the gastrocnemius and soleus are referred to as the triceps-surae . Proximally, the tendon begins at midcalf level where the muscle fibers coalesce, extending distally to insert on the midposterior aspect of the calcaneal tuberosity. The normal tendon measures a maximum of 3.5 to 6.8 mm in anteroposterior diameter. In 90% of patients it demonstrates a flat or concave configuration of its deep surface; a convex configuration is seen in 10% of patients. In contrast to other tendons, the Achilles paratenon does not include a tenosynovial sheath. The tendon is encased by visceral and parietal connective tissue layers with an intervening mesotendon. An area of relative hypovascularity is present in the tendon distally, located 4 to 6 cm proximal to the calcaneal insertion. Two small bursae, the retro-Achilles (also termed superficial ) and retrocalcaneal bursae , are located adjacent to the superficial and deep surfaces of the tendon, respectively.

The retrocalcaneal bursa is a horseshoe-shaped structure that communicates with the anterior Achilles paratenon, providing lubrication for the tendon and protection from wear against the adjacent calcaneal tuberosity.

The normal bursae measure less than 2 mm in anteroposterior diameter. The Kager fat pad (also termed the pre-Achilles fat pad ) is a triangular area of fatty tissue situated anterior to the retrocalcaneal bursa.

Achilles Tendon Variants

An accessory soleus muscle is present when the soleus muscle tissue extends more distal than is typically present, with a separate insertion on the calcaneus. The accessory muscle can produce a masslike abnormality in the posterior ankle. The level at which the soleus myotendinous junction appears is quite variable and may be close to the calcaneus itself.

Plantaris Tendon

The plantaris muscle and tendon are located in the posterior superficial compartment of the calf. The muscle originates from the posterior superior aspect of the lateral femoral condyle, running obliquely from the lateral to the medial aspect of the proximal calf, then forming a long tendon that passes between the medial gastrocnemius and soleus muscles. In the distal calf, the tendon is situated adjacent to the deep medial aspect of the Achilles tendon and often inserts into the medial aspect of the distal Achilles tendon or occasionally onto the medial aspect of the calcaneal tuberosity. It is called the “fool's nerve” because this long and slender tendon can be readily mistaken for a nerve by individuals unfamiliar with anatomy. The plantaris tendon is congenitally absent in up to 6% of patients either unilaterally or bilaterally. The plantaris tendon has a minor functional role contributing to flexion of the knee and plantarflexion of the foot. The Achilles-plantaris tendons are termed the triceps-surae complex . This vestigial tendon is often harvested for tendon reconstruction by surgeons.

Medial Ankle Tendons (Tibialis Posterior, Flexor Hallucis Longus, and Flexor Digitorum Longus)

Tibialis Posterior

The tibialis posterior muscle arises from the proximal posterior tibia, fibula, and interosseous membrane, located in the deep posterior compartment of the calf. The tendon forms in the lower third of the calf and travels from the calf into the foot and ankle with the other medial ankle tendons (flexor hallucis longus and flexor digitorum longus) and tibial neurovascular bundle. The arrangement of the ankle flexor tendons is easily remembered by the mnemonic “Tom, Dick, And Very Nervous Harry” reflecting the location of the tibialis posterior and flexor digitorum longus tendons, posterior tibial artery and vein, tibial nerve, and flexor hallucis longus tendon situated from anterior to posterior behind the medial malleolus, respectively. The tendons pass posteroinferior to the medial malleolus and adjacent to the calcaneal body, where they are covered by the flexor retinaculum in a fibro-osseous compartment termed the tarsal tunnel . Distal to the tarsal tunnel, the tibialis posterior tendon divides into several fascicles to insert primarily on the navicular tuberosity with other tendon slips attaching to all three cuneiforms; second, third, and fourth metatarsal bases; and the cuboid. The tibialis posterior tendon diameter is normally twice the size of its companion flexor digitorum longus tendon. A congenital variant composed of an unfused accessory navicular ossicle can be present and is considered to reflect incomplete fusion of the navicular tuberosity, which may be symptomatic (see Manifestations of the Disease—Tibialis Posterior ).

The accessory navicular ossicle may be small, round, and completely separate from the navicular tuberosity (type 1) or can be large and joined to the navicular bone by a synchondrosis or syndesmosis (type 2 [see Fig. 33-6 ]). In the presence of a type 2 accessory navicular bone, abnormal stress may be placed on the tibialis posterior tendon owing to its direct insertion on the accessory ossicle, and a pathologic process can occur at the junction of the ossicle and navicular bone. A type 1 accessory navicular bone, also termed an os tibiale externum , is not associated with tendon dysfunction.

Flexor Hallucis Longus

The flexor hallucis longus tendon arises from the posterior fibula and interosseous membrane distal to the soleal line in the deep posterior compartment of the calf. At the level of the posterior talus, the tendon passes through a fibro-osseous tunnel between the medial and lateral tubercles of the posterior process of the talus. It then courses posterior to the medial malleolus with the other flexor tendons and beyond this medial to the posterior calcaneal body, located within the tarsal tunnel (see earlier). This tendon passes below the sustentaculum tali and then crosses the flexor digitorum longus tendon at the knot of Henry, where one or more small bridging tendon slips may be shared between the two adjacent tendons. The relatively fixed and rigid anatomy predisposes the flexor hallucis longus tendon to tendinosis, partial and complete tears, and tenosynovitis. The tendon inserts into the base of the distal phalanx of the great toe.

Flexor Digitorum Longus

The flexor digitorum longus muscle makes up part of the deep posterior compartment of the calf, arising from the proximal posterior tibia. The tendon passes posterior to the medial malleolus positioned between the tibialis posterior and flexor hallucis longus tendons. The flexor digitorum longus tendon bears a close anatomic relation to the flexor hallucis longus tendon where the two tendons cross at the knot of Henry (see earlier). The tendon then divides into four slips on the plantar aspect of the foot, inserting into the bases of the second through fifth distal phalanges.

Lateral Tendons (Peroneus Brevis and Peroneus Longus)

The peroneus longus and peroneus brevis muscles predominantly originate from the proximal lateral third and distal lateral two thirds of the fibula, respectively. Both tendons pass posterior to the lateral malleolus through the common peroneal tunnel in a small sulcus located 1 cm proximal to the fibular tip, termed the retromalleolar groove (also known as the fibular groove ). The retromalleolar groove is present in approximately 80% of the population and may be deepened by the presence of a fibrocartilaginous ridge extending from the posterior margin of the lateral malleolus. At the level of the groove, both tendons are contained within a common synovial sheath, with the peroneus brevis tendon located anteromedial to the peroneus longus tendon. The superior peroneal retinaculum covers the tendons in the fibular groove, serving as an important stabilizer to prevent subluxation. The calcaneofibular ligament shares the calcaneal attachment of the superior peroneal retinaculum. Injury to the calcaneofibular ligament may be associated with disruption of the superior peroneal retinaculum. Slightly distal to the ankle, the tendons pass adjacent to the calcaneus, where they are frequently separated by a small bony prominence termed the peroneal tubercle (see later). Immediately proximal to the peroneal tubercle, the common synovial sheath shared by both peroneal tendons divides to envelop each tendon separately. In the region of the peroneal tubercle, the peroneal tendons pass through a second fibro-osseous tunnel, covered by the inferior peroneal retinaculum . The peroneus brevis inserts on the tuberosity of the fifth metatarsal base. The peroneus longus makes a sharp turn in the region of the calcaneocuboid joint deep to the long plantar ligament. The peroneus longus tendon then moves to the plantar aspect of the foot and inserts on the base of the first metatarsal and medial cuneiform. Both peroneal tendons serve to evert the hindfoot, maintain heel alignment, and preserve the medial longitudinal arch of the foot.

Anatomic Variants of the Peroneal Tendons

Absence of the retromalleolar groove occurs in 20% of the population, replaced by a flat or convex shape of the posterodistal fibula. This configuration predisposes the tendons to subluxation and other injuries.

Two osseous prominences are often present arising from the lateral cortex of the calcaneal body, termed the peroneal tubercle anteriorly and retrotrochlear eminence posteriorly. The peroneal tubercle occurs in 40% of the population and separates the peroneus brevis anteriorly from the peroneus longus posteriorly. An enlarged peroneal tubercle predisposes the peroneus longus tendon to injury and the tendon sheath to inflammation due to impingement and mechanical irritation. The retrotrochlear eminence occurs in 98% of the population, is located posterior to the peroneal tubercle, and can serve as the site of insertion for an accessory peroneus quartus muscle (see below).

The os peroneum is a fibrocartilaginous sesamoid bone located in the cuboid tunnel that is always present but ossified in only 20% of patients. Abnormalities of the ossicle can be associated with peroneal tendon injuries (see below).

Several accessory peroneal muscles have been described, with inconsistent nomenclature in the literature. Because of the confusing terminology and variable anatomy, many authors commonly term any variant of the lateral compartment muscles as the peroneus quartus muscle . The peroneus quartus muscle occurs in up to 20% of the population and typically arises from the distal lateral fibula and lower peroneus brevis muscle. It has a variable insertion on the retrotrochlear eminence, fifth metatarsal and phalanx, cuboid, peroneal tendons, and lateral retinaculum. This anomalous muscle and tendon can result in mass effect within the peroneal groove and stretching of the overlying peroneal retinaculum, predisposing the peroneal tendons to sublux. The accessory peroneus quartus tendon can also mimic a longitudinal split tear of the peroneus brevis tendon.

Anterior Ankle Tendons (Tibialis Anterior, Extensor Digitorum Longus, Peroneus Tertius, and Extensor Hallucis Longus)

Tibialis Anterior

The tibialis anterior muscle arises from the anterolateral proximal tibia, interosseous membrane, and intermuscular septum in the deep anterior compartment of the calf. Just above the level of the ankle, the tendon courses under the superior extensor retinaculum and may be contained within a separate tunnel of its own. At the level of the ankle, the position of the extensor tendons can be remembered by the pneumonic “Tom, Harry, and Not Dick,” corresponding to the tibialis anterior and extensor hallucis longus tendons, dorsalis pedis neurovascular bundle, and extensor digitorum longus tendon. Below the level of the ankle, the tibialis anterior tendon passes under the inferior extensor retinaculum, inserting on the medial cuneiform and first metatarsal base.

Extensor Digitorum Longus and Peroneus Tertius

The extensor digitorum longus muscle arises from the proximal lateral tibia, proximal fibula, and interosseous membrane, situated in the deep anterior compartment. The tendon courses distally, located lateral to the extensor hallucis longus tendon, traveling under both the superior and inferior extensor retinacula to insert on the dorsal aspects of the middle and distal second through fifth phalanges. The peroneus tertius muscle is a small separate part of the extensor digitorum longus muscle arising from the distal medial fibula and interosseous membrane. The tendon passes lateral to and within the same sheath as the extensor digitorum longus tendon, inserting on the base of the fifth metatarsal. Peroneus tertius is absent in up to 17% of the population.

Extensor Hallucis Longus

The extensor hallucis longus muscle takes its origin from the proximal fibula and interosseous membrane. Its tendon travels between the tibialis anterior and extensor digitorum longus tendons, passing deep to the superior and inferior extensor retinacula and inserting on the dorsal aspect of the base of the first distal phalanx.

Pathology

The spectrum of acute tendon injuries ranges from microtearing to discrete areas of fiber disruption that may be partial or complete. Tendinopathy is considered to be the result of chronic repetitive microtrauma and degeneration and may progress to discrete partial tears and eventually complete rupture. Pathologically, tendinosis is manifested by disorganization of and reduction in the number and size of tendon collagen fibers, decreased vascularity, and, in more advanced disease, areas of necrosis and calcification. The terms tendinopathy and tendinosis are frequently used interchangeably. In tendon degeneration no inflammatory response is present histologically and, therefore, the term tendinitis is an inaccurate term and generally should be avoided.

Tenosynovitis may be acute or chronic, demonstrating increased tenosynovial fluid and/or tenosynovial thickening. The Achilles tendon is the only ankle tendon that does not have a tenosynovial covering, and therefore the terms paratenonitis and peritendinitis are used to refer to inflammation of the surrounding paratenon, consisting of acute inflammatory cells, capillary proliferation, and neovascularity.

The terms partial tear and tendinosis are frequently used interchangeably, but the term partial tear can be confusing to clinicians, who may interpret this term as reflecting an area of distinct tendon fiber discontinuity potentially necessitating surgery. The terms partial tear and rupture (either partial or complete) ideally should be applied when discrete tendon fiber disruption is present to avoid confusion.

Biomechanics

Achilles Tendon

The major function of the Achilles tendon is plantarflexion of the ankle with a minor contribution to heel inversion. It is the largest tendon in the body, and its tensile strength is approximately 70% that of bone. The insertion of the Achilles tendon fibers is somewhat eccentric on the posterior calcaneus because the gastrocnemius and soleus fibers form a 90-degree spiral in the distal tendon, predisposing to injury due to an imbalance of forces during running and jumping.

Medial Tendons

The flexor hallucis longus tendon primarily serves to plantarflex the hallux distal interphalangeal joint and also contributes to plantarflexion of the ankle and hallux metatarsophalangeal joint.

The tibialis posterior is the strongest invertor of the foot and maintains the longitudinal arch of the foot. It also aids in plantarflexion of the ankle and forefoot adduction and stabilizes the hindfoot against valgus deformity. Injury of the tibialis posterior typically occurs at the level of the medial malleolus, owing to the frictional forces created as it curves around the medial malleolus, constrained by the flexor retinaculum. The tibialis posterior is a dynamic stabilizer of the arch; increasing significance is being attributed to the spring ligament, which is composed of three bundles deep to the tibialis posterior and which acts as a static stabilizer of the arch.

The flexor digitorum longus flexes the second through fifth metatarsals and phalanges and contributes to plantarflexion of the ankle and inversion of the foot.

Lateral Tendons

The peroneus brevis tendon everts and dorsiflexes the ankle. The peroneus longus tendon plantarflexes the ankle. The peroneal tendons also augment the lateral ankle ligaments, contributing to lateral stability of the ankle.

The peroneal tendons are most susceptible to injury where they experience the greatest mechanical stress. The peroneus brevis tendon is usually injured at the level of the distal fibula where the tendon is forcibly compressed against the posterior fibular cortex during an inversion injury. Peroneus longus injury often occurs distally adjacent to the peroneal tubercle in the midlateral calcaneal body or distally under the cuboid where the tendon changes direction from vertical to horizontal.

Anterior Tendons

The tibialis anterior serves as the main dorsiflexor of the ankle. The extensor hallucis longus and extensor digitorum longus and peroneus tertius tendons provide dorsiflexion to the interphalangeal and metatarsophalangeal joints and assist with eversion of the foot.

Imaging Techniques

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