Anatomy, Evaluation, and Operative Setup for Posterior Ankle Arthroscopy

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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

Flexor Hallucis Longus Tenosynovitis

FHL tenosynovitis has long been described in ballet dancers and in athletes with rapid start and stop (toe-off) running, such as soccer players. The repeated stress causes as tenosynovitis, which becomes painful with repetitive use. Rest and omission of painful activities typically alleviate symptoms.

Symptoms can develop in the midfoot at the knot of Henry, in the tarsal tunnel, and more proximally. Differentiating pain in these three areas is necessary to predict the potential surgical avenues available for treatment.

Long-standing symptoms may lead to the formation of a nodular thickening of the FHL in the area of the tarsal tunnel. If the thickening becomes ensnared on the flexor retinaculum, a triggering or catching sensation may be reported by the patient. The patient may report long periods of the great toe being stuck in a flexed position.

Nonoperative treatment is curative in most patients. The mainstay of therapy, as with os trigonum syndrome, is immobilization and anti-inflammatory medications. Some physicians advocate the use of corticosteroid injections into the triggering nodule, as is commonly used in the hand. For recurrent or recalcitrant symptoms, tenosynovectomy with surgical release of the FHL slip or posterior edge of the FHL sheath can be curative.

From the posterior arthroscopic portals, the FHL and the stout edge of the FHL sheath can easily be identified and released. Débridement of the stenosing tenosynovitis can be carried out on the tendon.

Michelson and coworkers reported a 67% success rate with nonoperative treatment. All of their patients who failed nonoperative treatments had successful outcomes after an open approach to the FHL at the proximal portion of the fibro-osseus tunnel.¹⁰

DIAGNOSTIC IMAGING

Plain Radiographs

Weight-bearing radiographs of the affected foot and ankle are mandatory. Other helpful images include the contralateral foot and ankle views, axial and lateral heel views, long leg alignment films, and specialized views of the subtalar joint. The radiographs are evaluated for alignment, stress reaction, acute bony pathology, and chronic disease.

Views of the ankle are evaluated for obvious fractures, including an osteochondral fracture of the talus. The tibiotalar joint is assessed for symmetry of the joint space and for degenerative changes, including anterior and posterior osteophytic disease. An os trigonum or fracture of a prominent lateral tubercle of the posterior process of the talus can be seen on the lateral view. Axial and lateral heel views are used to evaluate the calcaneus posterosuperior process, and they typically provide a good view of the posterior facet of the subtalar joint (Fig. 7-2).

FIGURE 7-2 The lateral radiograph shows an os trigonum and a prominent posterosuperior process of the calcaneus.

Computed Tomography

Computed tomography (CT) provides valuable information for evaluating subchondral bone in the setting of an osteochondral lesion of the talus (OLT). Subchondral cysts in the talus are seen on CT. The size and surrounding bone structure of these lesions is evaluated better than with magnetic resonance imaging (MRI).

CT can show the bony detail of the os trigonum. The os can be an unfused ossification center with a fibrous connection, or it can be a symptomatic, fully fused, large tubercle of the posterior process of the talus. A fracture of the os shows obvious cortical discontinuity on CT (Fig. 7-3).

FIGURE 7-3 Coronal computed tomography shows a posteromedial osteochondral lesion of the talus.

Magnetic Resonance Imaging

MRI provides the greatest amount of information about involved soft tissues. The tendon can be evaluated on standard sequences, but the fluid-sensitive, fat-suppressed images delineate most pathologies better. In these sequences, tendons are typically very dark and homogeneous. Tendons may be torn, split, or surrounded by fluid, which is indicative of tenosynovitis. Attention is focused on the FHL tendon and the anatomy of the posterior neurovascular bundle for operative planning.

The fat-saturated and fluid-sensitive, fat-suppressed MR images are useful for evaluation of bone. In the fat-saturated images, the bone marrow has high signal intensity, and subchondral and cortical bone tissues are dark.

In the region of the OLT, the fat-sensitive sequence can show decreased signal intensity in subchondral bone, indicative of edema. Decreased signal intensity can be seen in the cartilage overlying the defect, possibly indicating calcified fibrocartilage in the defect. On the fluid-sensitive sequence, undermining of an unstable cartilage flap can be seen. Fluid-filled cysts are identified. High intensity signal in the bone marrow beneath the OLT indicates inflammation and continued injury (Fig. 7-4).

FIGURE 7-4 A sagittal magnetic resonance imaging shows the same osteochondral lesion of the talus (seen in Figure 7-3. Notice the large area of signal change.

The same signal characteristics hold true for the MRI evaluation of the os trigonum. Edema in the ossicle or in the adjacent posterior talus indicates ongoing injury, supporting its role as the pain generator (Fig. 7-5).

FIGURE 7-5 A fluid-sensitive, fat-suppressed sagittal image of a patient shows a symptomatic os trigonum (arrow) and posterior ankle impingement.

Fluid about the FHL tendon can be seen clearly on fluid-sensitive sequences, and it is an indicator of ongoing inflammation and edema in the tendon. Tendon nodules, hypertrophy, and tears are also identified (Fig. 7-6).

FIGURE 7-6 In a fluid-sensitive, fat-suppressed image of a patient with flexor hallucis longus tendonitis, notice the fluid signal around the tendon (arrow).

An inflamed retrocalcaneal bursa is bright on fluid-sensitive images, and Achilles tendon pathology is identified as fusiform swelling of the tendon, intrasubstance fluid near the insertion, or the low-intensity signal of calcified material in the tendon substance.

Bone Scan

A three-phase bone scan can be useful in the diagnosis of overuse injuries, particularly a stress fracture that may be causing symp toms similar to those of the discussed pathology. Active OLT and symptomatic os trigonum syndrome should have increased uptake on the bone scan.

TREATMENT

Surgical Technique

The patient is placed in the prone position. All bony prominences are well padded, and the operative leg is supported on a pad to allow the foot to lie in a neutral position and to provide space to manipulate the foot during the procedure. A thigh tourniquet is placed, and the lower extremity is prepared to the knee (Fig. 7-7).

FIGURE 7-7 An operating room photograph shows positioning and setup. Notice that the foot is free to allow manipulation. Arthroscopy fluid is being injected where the lateral portal will be established.

The Achilles tendon, medial malleolus, and lateral malleolus are palpated and marked. The approximate course of the sural nerve and the posteromedial neurovascular bundle are drawn on the skin. The level of the tibiotalar joint is estimated by palpating the tips of the malleoli and the anterior and posterior joint while moving the foot (Fig. 7-8).

FIGURE 7-8 A clinical photograph of the posterior ankle shows the surface anatomy and portal sites drawn with a skin marker.

The posterolateral portal is established 5 mm distal to the estimated level of the tibiotalar joint and adjacent to the Achilles tendon. Using an 18-guage needle, 20 mL of arthroscopy fluid is injected into the joint to expand the capsule (see Fig. 7-7). A nick is created in the skin only, and a small hemostat is used to bluntly dissect toward the lateral aspect of the joint. A small joint arthroscopy canula for a 2.7- or 3.0-mm, 30-degree arthroscope with two stopcock valves is placed in this portal. Inflow fluid is placed on one valve, and suction or gravity drainage is attached to the other. By alternating opening the valves, blood can be cleared from the joint and visibility obtained.

The medial portal is established with direct arthroscopic guidance. The entry location in the skin is at the same level as the lateral portal and is adjacent to the Achilles tendon. An 18-guage spinal needle is used to ensure the pathway of the medial portal enters lateral to the FHL. By staying lateral to the FHL the medial neurovascular structures are protected from damage by the arthroscopic instruments (Fig. 7-9).