Applied Surgical Anatomy of the Approaches to the Ankle

Applied Surgical Anatomy of the ‌

Approaches to the Ankle

Overview

The key structures that cross the ankle joint fall into specific groups.

Tendons

Three sets of tendons cross the ankle joint in addition to the Achilles and plantaris tendons, which lie posteriorly in the midline.

The flexor tendons—the tibialis posterior, flexor digitorum longus, and flexor hallucis longus (which are supplied by the tibial nerve)—pass behind the medial malleolus.
The extensor tendons—the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius (which are supplied by the deep peroneal nerve)—pass in front of the ankle joint.
The evertor tendons—the peroneus longus and peroneus brevis (which are supplied by the superficial peroneal nerve)—pass behind the lateral malleolus.

The tendons are all prevented from bowstringing around the ankle by thickened areas in the deep fascia of the leg, called retinacula.

The different nerve supplies of the groups offer three potential internervous planes through which the ankle can be approached: Medially, between flexors (tibialis posterior) and extensors (tibialis anterior); posterolaterally, between flexors (flexor hallucis longus) and evertors (peroneus brevis); and laterally, between extensors (peroneus tertius) and evertors (peroneus brevis).

Neurovascular Bundles

Two major neurovascular bundles cross the ankle joint and supply the foot. They present the major surgical concerns for all approaches around the ankle.

The anterior neurovascular bundle crosses the front of the ankle roughly halfway between the malleoli. It lies between the tibialis anterior and extensor hallucis longus muscles proximal to the joint (see Fig. 12-59) and between the tendons of the extensor hallucis longus and extensor digitorum longus muscles distal to the joint. The tendon of the

extensor hallucis longus crosses the bundle in a lateral to medial direction at the level of the ankle joint (see Fig. 12-58).

The anterior tibial artery, which crosses the front of the ankle joint before becoming the dorsalis pedis artery, is palpable on the dorsum of the foot. It also communicates with the medial plantar artery through the first metatarsal space. Fractures through the base of the metatarsal bones and dislocations at the tarsometatarsal joint (Lisfranc fracture/dislocation∗) can damage both elements of this anastomosis and cause ischemia to the medial side of the distal portion of the foot.

The deep peroneal nerve accompanies the anterior tibial artery. It supplies two small muscles on the dorsum of the foot: The extensor digitorum brevis and the extensor hallucis brevis. It also supplies a sensory branch to the first web space. Anesthesia in this web space is one of the first clinical signs of anterior compartment compression.

Ischemia of the deep peroneal nerve occurs before ischemic muscle damage (see Figs. 12-58 and 12-59).
The posterior neurovascular bundle runs behind the medial malleolus, between the tendons of the flexor digitorum longus and flexor hallucis longus muscles (Figs. 12-54 and 12-55).

The posterior tibial artery passes behind the flexor digitorum longus before entering the sole of the foot, where it divides into medial and lateral plantar arteries (see Fig. 12-55).

The tibial nerve passes behind the medial malleolus with the posterior tibial artery. It gives off a calcaneal branch to the skin of the heel. After entering the sole of the foot, it divides into the medial and lateral plantar nerves, which supply motor power to the small muscles of the foot and sensation to the sole (see Fig. 12-55).

Figure 12-54 The superficial structures of the medial aspect of the foot and ankle. Fibers of the flexor retinaculum cross the neurovascular bundle, binding it to the medial side of the foot.

Superficial Sensory Nerves

Three major sensory nerves cross the ankle joint superficially, all supplying the dorsum of the foot. Knowledge of their course is vital in planning skin incisions. The sensory supply to the sole and heel comes from the lateral and medial plantar nerves, which are branches of the tibial nerve that lies deep at the level of the ankle.

The saphenous nerve is the terminal branch of the femoral nerve. It runs with the long saphenous vein in front of the medial malleolus, where it usually divides into two branches that lie on either side of the vein and bind closely to it. It supplies the medial, non–weight-bearing side of the middle part and the hindpart of the foot (see Fig. 12-54).
The superficial peroneal nerve is a terminal branch of the common peroneal nerve. It crosses the ankle joint roughly along the anterior midline, where it usually divides into several branches. It supplies non–weight-bearing skin on the dorsum of the foot. The nerve is quite superficial at the level of the ankle joint; great care must be taken with

skin incision in its area (Fig. 12-58; see Fig. 12-82).
The sural nerve, a terminal branch of the tibial nerve, runs with the short saphenous vein just behind the lateral malleolus. Similar to the saphenous nerve, the sural nerve binds very closely to its vein; preserving the vein is the key to preserving the nerve during surgery. The sural nerve supplies an area of non–weight-bearing skin on the lateral side of the foot (see Fig. 12-61).

Landmarks

Bony Structures of the Ankle

The dome of the talus and the inferior articular surface of the tibia form the articulation that bears weight in the ankle. The joint itself is stabilized by the medial and lateral malleoli, the bony landmarks of the area. The medial malleolus is both shorter and more anterior. It remains in contact with the medial side of the talus throughout the range of motion (see Fig. 12-57).

The configuration of the malleoli causes the ankle mortise to point 15 degrees laterally. During dorsiflexion, the widest portion of the talus (the anterior portion) is the ankle mortise, forcing the mortise itself to widen. The mortise narrows to accommodate the narrower part of the talus during plantar flexion. Hence, if an ankle must be immobilized, it must be put in the functional position, that is, dorsiflexion (Fig. 12-63; see Figs. 12-57, 12-60, and 12-66). Note also that, if a screw is inserted between the fibula and the tibia (as in the reconstruction of a diastasis), then that screw should be inserted with the ankle placed in maximal dorsiflexion.

Figure 12-55 The extensor retinaculum and part of the flexor retinaculum have been removed to reveal the deeper tendons and the neurovascular bundle. The abductor hallucis has been detached from its origin to reveal the knot of Henry and the medial and lateral plantar arteries and nerves.

Medial Approaches to the Ankle

Two groups of flexors lie on the medial side of the ankle:

Three plantar flexors of the ankle and foot insert into the plantar surface of the foot and are supplied by the tibial nerve. Their positions behind the medial malleolus are remembered best in the form of the mnemonic “Tom, Dick, and Harry.” The tibialis posterior is closest to the medial malleolus; the flexor digitorum longus is behind it; and the flexor hallucis longus is the most posterior and lateral of the three. A second mnemonic, “Timothy Doth Vex Nervous Housemaids,” is older; it points out that the posterior tibial vessels and tibial nerve lie between the flexor d igitorum longus and flexor hallucis longus muscles (see Figs.

12-54 and 12-55 ).
The three muscles that insert into the posterosuperior part of the os calcis (the gastrocnemius, soleus, and plantaris) do so via their common

Achilles tendon. Supplied by the tibial nerve, they are the most powerful plantar flexors of the ankle. Since they insert more to the medial side of the posterior surface of the calcaneus than to the lateral side, they also invert the heel.

The Achilles tendon inserts into the middle third of the posterior surface of the calcaneus. The collagen fibers that comprise the tendon rotate about 90 degrees around its longitudinal axis, between its origin and its insertion onto bone. Viewed from behind, the rotation is in a medial to lateral direction. Thus, fibers that begin on the medial side of the tendon lie posteriorly, and those that begin on the lateral side lie anteriorly at the level of the insertion. This anatomic fact makes it possible to lengthen the Achilles tendon by dividing its anterior two-thirds near the insertion and its medial two-thirds 5 cm more proximally. Dorsiflexion of the foot lengthens the tendon, and no suture is required. The operation can be done either as an open or as a subcutaneous procedure.5 This arrangement of the fibers can be remembered by thinking of this tendon lengthening as the “DAMP operation,” which stands for distal anterior medial proximal.

A fat pad lies between the Achilles tendon and the bone, with a bursa that may become inflamed. A second bursa exists between the insertion of the tendon into the os calcis and the skin (see Fig. 12-54).

The flexor retinaculum is a thickening of the fascia that stretches from the medial malleolus to the back of the calcaneus. It covers the three flexor tendons that pass around the back of the tibial malleolus, as well as the neurovascular bundle.

Figure 12-56 The flexor and extensor tendons have been resected to expose the deltoid ligament of the ankle joint.

Figure 12-57 Osteology of the medial side of the foot and ankle.

Figure 12-58 The anatomy of the superficial structures of the anterior portion of the ankle and the dorsum of the foot. At the level of the ankle joint, the neurovascular bundle lies immediately lateral to the extensor hallucis longus tendon.

The tibial nerve may be trapped by this retinaculum, producing pain and paresthesia in the distribution of the medial and lateral plantar nerves and their calcaneal branches. The syndrome is known as the tarsal tunnel syndrome (see Fig. 12-54).

Anterior Approach to the Ankle

Extensor Muscles

Four muscles cross the anterior aspect of the ankle joint. All are extensors of the ankle and are supplied by the deep peroneal nerve. The muscles, from medial to lateral, are the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius. The neurovascular bundle crosses the front of the ankle virtually under the tendon of the extensor hallucis longus (see Fig. 12-58).

Extensor Retinacula

The superior extensor retinaculum is a thickening of the deep fascia above the ankle. It runs between the tibia and the fibula, and is split by the tendon of the tibialis anterior muscle, which lies in a synovial sheath just above the ankle (see Fig. 12-58).

Figure 12-59 The extensor tendons have been resected to reveal the ligaments of the anterior portion of the ankle joint and the joints of the middle part of the foot.

The inferior extensor retinaculum, on the dorsum of the foot, is attached to the lateral side of the upper surface of the os calcis. The retinaculum is split medially; the upper part attaches to the medial malleolus, whereas the lower part travels across the foot, where it sometimes joins the plantar aponeurosis in the sole. The two retinacula prevent the anterior tendons from bowstringing; they should be repaired after any approach that cuts them (see Fig. 12-58).

Lateral Approaches to the Ankle

The tendons of the peroneal muscles pass behind the lateral malleolus to reach the foot. Both evert the foot and are supplied by the superficial peroneal nerve (see Fig. 12-61).

The peroneus brevis tendon, which lies immediately behind the lateral malleolus. The peroneus brevis is recognizable both by its position immediately behind the lateral malleolus and by its muscularity almost down to the level of the ankle joint.

The superior peroneal retinaculum is a thickening of the deep fascia extending from the tip of the lateral malleolus to the calcaneus (see Fig. 12-61 ).

The inferior peroneal retinaculum runs from the peroneal tubercle to the lateral side of the calcaneus (see Fig. 12-61).

The peroneal tendons are enclosed in a synovial sheath as they pass around the back of the lateral malleolus. The sheath encloses both tendons down to the peroneal tubercle. At this point, each tendon gains its own separate sheath. This also is the site of peroneal tendinitis, which commonly occurs in joggers.

Figure 12-60 Osteology of the anterior part of the ankle joint and middle part of the foot.

Figure 12-61 The superficial anatomy of the lateral and dorsolateral aspects of the foot and ankle. The peroneal tendons are held in place by their superior and inferior retinacula.

Figure 12-62 The peroneal and extensor tendons have been resected to reveal the ligaments of the lateral and anterolateral ankle joints. Note the peroneal tubercle and the resected portion of the inferior peroneal retinaculum, which forms separate fibro-osseous tunnels for the peroneal tendons. The calcaneofibular ligament is visible deep to the superior peroneal retinaculum.