CHAPTER 1 Gross Anatomy of the Ankle Joint
The first attempts of arthroscopic interventions were made in the beginning of the 20th century.1 Originally, the knee joint was the focus of attention because of its more accessible anatomy than other joints, such as the ankle, shoulder, and smaller joints. Technical difficulties and the lack of appropriate equipment contributed to the late emergence of ankle arthroscopy compared with other joints.
In the late 1970s, Watanabe and subsequently some of his followers reported on the first attempts of ankle arthroscopy.2 Later, Ferkel, Guhl, and others reported series of ankle arthroscopies, outlining the indications, the type of pathology that could be treated, and long-term outcomes.3–5 They also reported a methodology to evaluate and address the ankle joint from an arthroscopic approach.
The ankle joint has a well-described and easily identifiable topographic anatomy, which decreases the chances of arthroscopic complications. Most of the vital structures are readily visualized, making ankle arthroscopy a technically reasonable and reliable operation for which the results are easily reproduced. A review of the topographic anatomy and the expected location of vital structures is essential to better understand the ankle joint and guide the operator safely through ankle arthroscopy.
The ankle joint is formed by the distal tibia, fibula, and the talus. Because it is a highly congruent joint with complex, curved articular surfaces tightly bound by ligaments, access to the entirety of the joint from a single portal is not possible. To simplify the description of the ankle joint, it is divided into the anterior and posterior compartments.
Anterior Ankle Topographic Anatomy
The anteromedial aspect of the ankle joint presents the most superficial portion of the distal tibia and the medial malleolus, whose tip is approximately 1 cm distal to the joint line. Slightly anterior to the medial malleolus are the saphenous nerve and the saphenous vein, both of which are located medial to the anterior tibialis tendon. The saphenous vein is at risk for being punctured during the creation of the anteromedial portal (Fig. 1-1).3
FIGURE 1-1 Anteromedial aspect of the ankle joint. AT, anterior tibialis tendon; EHL, extensor hallucis longus tendon; MM, medial malleolus; SaN, saphenus nerve; 1, soft spot of the ankle joint.
The anterior tibialis tendon represents the lateral margin of the so-called soft spot of the ankle joint. The soft spot is delineated by the anterior tibialis tendon laterally, the most distal portion of the tibial plafond superiorly, and the lateral margin of the medial malleolus medially. This soft spot is the site of choice for placement of the anteromedial portal and for performing intra-articular injections of the ankle joint. The distal medial aspect of the tibia demonstrates a superiorly oriented notch of variable height known as the notch of Harty. This notch often affords easier initial placement of the arthroscopic cannula into the joint. In both applications, penetration of the ankle joint through the soft spot should be as lateral as possible and close to the anterior tibialis tendon to avoid damage to the saphenous vein and possibly to the more medially located saphenous nerve. Portal placement immediately adjacent to the medial border of the tibialis anterior tendon and as far away from the medial malleolus as possible facilitates manipulation of the arthroscope and instruments, avoiding mechanical impingement of the cannula on the medial malleolus.
The extensor hallucis longus (EHL) tendon is located lateral to the anterior tibialis tendon. The EHL tendon is easily palpated and identified by passive range of motion of the great toe. This tendon represents a safe landmark to avoid any damage to the anterior neurovascular bundle, which includes the anterior tibialis artery and veins and the deep peroneal nerve. The anterior neurovascular bundle is located immediately lateral to the EHL tendon. Use of the anterior central portal was advocated in the early arthroscopic ankle literature to allow complete joint access. The combination of noninvasive methods of ankle joint distraction and improved optics that allow excellent picture clarity with 2.7-mm diameter arthroscopes has made this portal, which places the anterior neurovascular bundle at risk for injury, unnecessary.
The extensor digitorum longus (EDL) tendon is located lateral to the anterior neurovascular bundle. Lateral to it, the dorsal cutaneous branch of the superficial peroneal nerve is found, which can be visualized or palpated in most patients by placing the foot in forced maximum plantar flexion and adding maximal plantar flexion of fourth metatarsophalangeal (MTP) joint.6 At the level of the ankle joint line, the course of the dorsal cutaneous branch of the superficial peroneal nerve ranges from the anterior margin of the lateral malleolus to the lateral aspect of the extensor digitorum longus tendon (Fig. 1-2).7
FIGURE 1-2 Anterolateral aspect of the ankle joint. AT, Achilles tendon; C, calcaneus; DCSPN, dorsal cutaneous branch of the superficial peroneal nerve; Fi, fibula; JL, joint line; PT, peroneal tendons; SuN, sural nerve.
Creation of the anterolateral portal should take the location of the dorsal cutaneous branch of the superficial peroneal nerve into consideration to avoid damage to the nerve. The dorsal cutaneous branch of the superficial peroneal nerve is the neurologic structure at highest risk for complication during ankle arthroscopy.4 It is important to avoid injury to the superficial peroneal nerve by using proper portal creation technique, known as the nick and spread technique. First, only the skin is incised. The knife blade is not allowed to penetrate into the subcutaneous tissues. Second, the subcutaneous tissues are bluntly dissected using a small mosquito forceps. Third, the portal is created using a blunt trocar. The joint capsule is quite thin, and avoiding sharp trocars helps to minimize the likelihood of nerve injury.
The lateral malleolus is the most lateral structure of the ankle joint. It is located slightly posterior to the medial malleolus, which allows a larger exposure of the lateral wall of the talus along the lateral gutter as compared with the medial aspect of the ankle joint. The tip of the lateral malleolus is approximately 2 cm distal to the joint line and 1 cm posterior to the medial malleolus. The peroneal tendons are immediately posterior to the lateral malleolus. The peroneus brevis tendon is the closest one to the posterior margin of the fibula. Posterior to it, the peroneus longus tendon is found.
Posterior Ankle Topographic Anatomy
The sural nerve is located between the peroneal tendons and the Achilles tendon, approximately 1 to 1.5 cm distal to the tip of the fibula and 1.5 to 2 cm posterior to it.5 The location of the sural nerve has some variability within the posterolateral aspect of the ankle joint. It is always located close to the lesser saphenous vein.8 These two structures are the only ones at risk in the posterolateral aspect of the ankle joint (Fig. 1-3).
FIGURE 1-3 Posterior aspect of the ankle joint. AT, Achilles tendon; C, calcaneus; PNVB, posterior neurovascular bundle; SuN, sural nerve.
The Achilles tendon has an average width of 1 to 1.5 cm immediately above the superior margin of the calcaneus tuberosity. The deep flexor tendons are located medial to the Achilles tendon, and the flexor hallucis longus (FHL) tendon is the most lateral of the deep flexor tendons. Identification of this tendon is key to avoiding damage to the posterior neurovascular structures. The posterior neurovascular bundle is located immediately adjacent and medial to the FHL, and it includes the posterior tibial artery, veins, and tibial nerve. The flexor digitorum longus (FDL) tendon is located medial to the posterior neurovascular bundle. The posterior tibialis tendon is anterior and medial to the FDL. The posterior tibialis tendon is located on the medial malleolus at the level of the joint line (Fig. 1-4).
FIGURE 1-4 Posteromedial aspect of the ankle joint. AT, anterior tibialis tendon; C, calcaneus; MM, medial malleolus; PNVB, posterior neurovascular bundle; PT, posterior tibialis tendon; SaN, saphenus nerve.
Before performing ankle arthroscopy, the topographic anatomy of the ankle joint should be clearly marked and delineated with a sterile surgical marker to avoid damage to critical structures. This step is of key importance to appreciate the location of the structures at risk during the intervention.