CHAPTER 7 Anatomy, Evaluation, and Operative Setup for Posterior Ankle Arthroscopy

Arthroscopy of the posterior ankle was originally described as a diagnostic tool. As surgeons became more proficient with the technique, therapeutic procedures were incorporated.¹^–⁵ The posterior portion of the ankle is often poorly visualized from traditional arthroscopic portals, and certain lesions are more easily dealt with by performing a dedicated posterior arthroscopy. Although the prone position and the proximity of the tibial neurovascular bundle have led some away from the technique, recent articles demonstrate that the procedure can be undertaken safely.⁶

To undertake a posterior arthroscopy, small joint arthroscopy skills, anatomic knowledge, and understanding the limitations of the procedure are necessary. This chapter outlines the pertinent anatomy, clinical entities that are treatable, indications, techniques, and postoperative care regimens.

ANATOMY

The anatomy of the posterior ankle can be divided into pertinent surface anatomy, relationships of deep structures and abnormal, congenital, or acquired deformities of the typical anatomy.

The posterior view of the ankle’s surface anatomy includes the posterior edges of the malleoli, the Achilles tendon, and its insertion. Delineating these structures can guide marking of other structures in the superficial layers.

The sural nerve lies lateral to the Achilles tendon at a distance of approximately 1 cm form the lateral edge of the Achilles tendon at the level of the posterolateral portal. It courses obliquely away from the Achilles as it heads toward the lateral portion of the foot. Medially, the flexor hallucis longus (FHL) tendon is encountered first when moving from the margin of the Achilles tendon. Immediately adjacent to that is the tibial nerve. Further medially and anteriorly lie the posterior tibial artery and vein (Fig. 7-1).

FIGURE 7-1 In the drawing of the surface and subcutaneous anatomy, notice the course of the sural nerve.

Deep to the distal portion of the Achilles tendon lies the retrocalcaneal bursa. The posterior joint capsule is the next layer encountered. Deep to the capsule, the tibiotalar and subtalar joints are apparent, as is the posterior process of the talus with a medial and more often prominent lateral tuberosity.

In dealing with surgical conditions in the posterior hindfoot, certain pathologic anatomic variations can be encountered. Retrocalcaneal bursitis, refractory os trigonum syndrome, hindfoot impingement, FHL tenosynovitis and stenosing tenosynovitis, and posterior osteochondral lesions of the talus are pathologic entities that can be identified and treated with posterior ankle arthroscopy. Loose bodies that are unreachable from anterior portals can be removed posteriorly.

Retrocalcaneal bursitis is primarily treated nonoperatively, but refractory symptoms can be treated with bursa excision through the arthroscope. The normal bursa is encountered routinely in posterior arthroscopy, because it is often the first potential space developed.

Os trigonum syndrome is marked by pain in the posterior ankle, especially with plantar flexion weight bearing. The os trigonum is an accessory ossicle that represents an unfused lateral tuberosity of the posterior process of the talus. A painful os trigonum can be the result of acute fracture of a large tuberosity of the same structure.

Tenosynovitis of the FHL can develop as an overuse injury, often with plantar flexion weight bearing and particularly in the en point toe position in ballet dancing. This reactive synovitis from overuse can lead to pain and triggering in the posteromedial ankle.

CLINICAL EVALUATION

The diagnostic clinical encounter begins with a thorough history of the chief complaint. Important personal information from the patient includes a history of operations or injuries to the feet or ankles. A history of all symptoms and previous treatments is elicited. The relative successes of nonoperative treatments are documented. Activities at the time symptoms began are recorded, as are activities that aggravate the symptoms.

Examination of the affected and unaffected leg begins with appropriate exposure of the patient. The legs from the knees down are bare and without socks and shoes. The examination progresses from standing alignment to observation of gate to seated examination. Range of motion, strength, and sensory and vascular status are assessed before provocative maneuvers are used. Gaits are described with a focus on pain-mediated gaits (i.e., antalgic or foot flat), those indicative of joint stiffness (i.e., vaulting), and those indicative of neurologic disorders (i.e., footdrop, steppage, or circumduction).

The weight-bearing and non–weight-bearing alignment of the hindfoot are assessed. The alignment of the forefoot is recorded with the hindfoot stabilized in neutral. The range of motion of the tibiotalar and subtalar joints is examined. Strength testing of the ankle plantar flexors and dorsiflexors are compared with the unaffected side. Testing of the peroneal and posterior tibial tendons is carried out with the foot in a dorsiflexed position. Isolated strength testing of the FHL is indicated if pathology is suspected.

Some resistive strength testing maneuvers are provocative examinations. Further provocative examinations include direct palpation the posterior talus, palpation of the FHL in the tarsal tunnel, palpation of the Achilles tendon insertion, and a posterior ankle impingement test, which is performed by forcing plantar flexion in a slightly inverted foot.

Retrocalcaneal Bursitis

Retrocalcaneal bursitis is a disease of the tissue adjacent to the insertion of the Achilles tendon on the calcaneus. Some authorities think that it part of a spectrum of disease that includes calcific insertional Achilles tendinitis and that it is not as much an inflammatory phenomenon as it is a fibroproliferative disease of the Achilles insertion, akin to lateral epicondylitits.⁵ A prominent posterosuperior part of the calcaneus (i.e., Haglund’s deformity) contributes to the symptoms is some patients.²^,³^,⁷^,⁸

Symptoms typically manifest as overuse injuries with a bimodal pattern. There is pain and sometimes swelling or bony deformity at the insertion of the Achilles tendon. Pain often occurs with resisted strength testing and with forced dorsiflexion.

Radiographs can reveal a calcaneal spur or intrasubstance calcific tendinosis. The posterosuperior process of the calcaneus is evaluated by measuring the superior calcaneal angle and observing the parallel pitch lines.

Treatment mainstays are anti-inflammatory medications and immobilization. A stretching program is often used after the initial discomfort has diminished. Night splinting can be recommended during periods of provocative activity.

Surgical treatment is reserved for failure of maximal nonoperative treatment. Treatment is often directed at adjacent, secondarily inflamed structures if no obvious insertional disease is present. The retrocalcaneal bursa and fat pad are completely excised. Calcaneal exostectomy is often combined with the excision. The postoperative course is further immobilization.

Watson and colleagues ⁸ described a series of patients with retrocalcaneal bursitis with or without calcific insertional tendinitis. They found that patients without obvious insertional disease fared better than those with a spur. There was a 93% satisfaction rating, with an average time to maximal improvement of 5 months.⁸

Os Trigonum Syndrome

The os trigonum syndrome is the primary cause for the posterior ankle impingement syndrome. Typically, patients have a history of a hyper-plantar flexion or inversion injury, or they have a slow, insidious onset of symptoms in the setting of increased activities, indicating an overuse injury. The overuse injury often occurs in runners and dancers. Physical examination reveals pain with direct posterior palpation and in response to the posterior ankle impingement test.

Nonoperative treatment consists primarily of immobilization and nonsteroidal anti-inflammatory medications. Casting for a period of 4 to 6 weeks with regimented anti-inflammatory medications can relieve symptoms in most patients. For those with recurrent or recalcitrant symptoms, excision of the os trigonum can alleviate pain. Open excision has long been used successfully, but there have been complications related to infection and hematoma.⁹

Great success with arthroscopic excision has been reported.²^–⁴ Scholten and colleagues thought they were better able to address soft tissue impingement syndromes with posterior arthroscopy. They followed 55 patients for a minimum of 2 years, with none lost to follow-up. They found a significant increase in the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score (75 to 90) and no degenerative changes on repeat radiographs.²

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