ANATOMY

The subtalar joint is composed of three articulations: the posterior, middle, and anterior joints or facets (Figs. 18-1 and 18-2). Several extra-articular ligaments stabilize the subtalar joint. The major ligaments encountered during subtalar arthroscopy are the intra-articular components, which consist of the interosseous, lateral, and anterior talocalcaneal ligaments. These components coalesce to form the division between the posterior and the middle facets of the subtalar joint. The interosseous ligament is a broad, stout structure that is approximately 2.5 cm wide from its medial to lateral side. It marks the arthroscopic boundary for posterior subtalar arthroscopy.

FIGURE 18-1 Gross dissection of the lateral posterior subtalar joint shows the talus (A), calcaneus (B), and subtalar joint (C).

FIGURE 18-2 A view of the posterior subtalar joint shows the undersurface of the talus (A), the middle facet of the talus (B), the anterior facet of the talus (C), and the superior surface of calcaneus (D).

Open subtalar arthrodesis has historically been the fusion method of choice, and results have generally been favorable. Studies reporting the results of open fusion techniques have all described similar results for fusion rate, time to union, and complications, such as nonunion or malunion, infection, and symptomatic hardware problems.⁸^–¹² Open procedures entail removal of the interosseous ligaments and their vasculature and a lateral incision that can result in nerve dysfunction. Nonunion rates of 5% to 16% have been reported.⁴^,⁶ The successful results of arthroscopic ankle fusion have stimulated the development of an arthroscopic approach for subtalar joint arthrodesis, which has the advantages of reduced perioperative morbidity and preservation of the blood supply.¹³^–¹⁵

Arthroscopic subtalar arthrodesis was designed to improve traditional methods by using a minimally invasive technique. Subtalar arthroscopy has been described by several investigators, but few reports of arthroscopic subtalar fusion have been published.¹⁶ The development of an arthroscopic technique for subtalar arthrodesis was intended to lower morbidity using techniques and principles similar to those used for arthroscopic ankle fusion. It was hypothesized that perioperative morbidity could be reduced, blood supply preserved, and proprioceptive and neurosensory input enhanced. These theoretical advantages prompted us to initiate a prospective study to document the effectiveness of the procedure and to determine the time until complete fusion, the incidence of delayed unions and nonunions, and the incidence of complications.

PATIENT EVALUATION

History and Physical Examination

Subtalar pathology is often difficult to diagnose. The patient may have a history of lateral hindfoot pain that can easily be confused with ankle pathology. A clue that helps direct the clinician toward subtalar pathology is an increase in symptoms with weight bearing or ambulating on uneven terrain. A history of calcaneal fracture should immediately alert the physician to the possibility of subtalar pathology. Clinical findings consist of pain over the sinus tarsi and the posterolateral subtalar joint. Physical examination may reproduce these symptoms with inversion and eversion of the subtalar joint with the ankle locked in dorsiflexion. Differential injections continue to be a valuable diagnostic tool to confirm and distinguish ankle pain from subtalar pain.

Diagnostic Imaging

Evaluation for subtalar pathology should include plain radiographs of the ankle and subtalar joints. The Broden view provides the best visualization of the posterior subtalar joint and may be sufficient to confirm the diagnosis of subtalar pathology (Fig.18-3). Profound degenerative radiographic changes in the joint are not needed to confirm a diagnosis, because only small alterations in the biomechanics of this joint can produce significant symptoms. Computerized tomography (CT) is best able to define the bony anatomy, and with thin sections, scanning reconstructions in the axial, coronal, and sagittal planes can be performed. Magnetic resonance imaging (MRI) can be used to confirm associated bony changes such as subchondral bone edema and may be useful in evaluating the adjacent soft tissues to rule out other causes of hindfoot pain. Bone scanning and arthrography are usually not required, and these studies have largely been replaced by MRI.

FIGURE 18-3 A Broden view of an arthritic posterior subtalar joint shows the talus (A), the calcaneus (B), and the subtalar joint (C).

TREATMENT

Indications and Contraindications

Arthroscopic subtalar arthrodesis is indicated for patients with intractable subtalar pain from a variety of conditions. Most of the earlier literature on subtalar surgery addressed the stabilization of paralytic deformities caused by poliomyelitis. However, most patients currently requiring this procedure have post-traumatic and primary arthritic conditions. A small number of patients who require subtalar arthrodesis have posterior tibial tendon dysfunction or a talocalcaneal coalition.

The contraindications to arthroscopic subtalar arthrodesis include prior failed subtalar fusions, gross malalignment requiring correction, infection, and significant bone loss. A patient with moderate malalignment may be a candidate for in situ stabiliza tion. Although significant bone loss has not frequently been encountered, moderate bone loss has not presented a serious problem in a study of arthroscopic ankle arthrodesis.¹⁵

Conservative Management

Severe subtalar joint pain should initially be treated conservatively with nonsurgical treatments. Conservative treatments include orthotics, nonsteroidal anti-inflammatory drugs, activity modification, and corticosteroid injections into the subtalar joint. Patients who have not been successfully treated with nonsurgical management may be considered for arthroscopic subtalar fusion. These individuals should also be advised that an open procedure may still be indicated if the arthroscopic approach is found to be unsafe or not technically feasible.

Arthroscopic Technique

Our preferred method begins by placing the patient in the lateral decubitus position and lying on the unaffected side. We place two pillows between the legs while the affected ankle and subtalar joint hang over a blanket roll in a natural position of plantar flexion and neutral version. The patient is prepared and draped, after which the anatomic landmarks and portal sites are identified and marked with a surgical pen. A thigh tourniquet is then inflated.

Establishing the portal sites is one of the more challenging aspects of the procedure. It is critical to predetermine the angles of the subtalar joint, because its unique geometry and limited access requires precise determination to prevent error. Fluoroscopy should be used to confirm portal location if necessary.

The anterolateral and the posterolateral portals are conventionally used. An accessory portal usually needs to be established approximately 1 cm posterior to the anterolateral portal (Fig. 18-4). This portal can be used for debridement or for outflow enhancement and may occasionally be used for visualization. The anterolateral and posterolateral portals are used in an alternating manner for viewing and for instrumentation. If significant arthrofibrosis makes entry and visualization difficult, the accessory anterolateral portal is quite useful.