Subtalar Arthrodesis

Simon Lee, MD

Stephen K. Jacobsen, MD

Dr. Lee or an immediate family member serves as a board member, owner, officer, or committee member of the American Orthopaedic Foot & Ankle Society. Neither Dr. Jacobsen nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

This chapter is adapted from Carr JB: Subtalar arthrodesis, in Flatow E, Colvin AC, eds: Atlas of Essential Orthopaedic Procedures. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2013, pp 515-518.

PATIENT SELECTION

Indications

The primary indication for subtalar arthrodesis is painful arthritis.¹ Common causes of arthritis include osteoarthritis, posttraumatic arthritis, and arthritis from inflammatory diseases.² Subtalar arthrodesis has also been described for the primary treatment of comminuted calcaneus fractures.³ These etiologies may cause alterations in the normal foot alignment, which must be identified and accounted for in preoperative planning. For example, a severe valgus alignment associated with posterior tibial tendon insufficiency must be corrected in addition to the goal of obtaining an arthrodesis. Surgical treatment is considered after nonsurgical treatments, such as cortisone injections, medications, orthotics, and rocker-bottom shoes, have failed.

Contraindications

There are no absolute contraindications to subtalar arthrodesis, but certain situations make a satisfactory result less likely.⁴ Charcot arthropathy places the limb at much higher risk of failure with either infection or nonunion. Smoking and prior hindfoot surgery also increase the chance of poor healing and delayed/nonunion. Active infection should be controlled before the definitive arthrodesis and may require alternative techniques such as external fixation. It can be difficult to localize the source of posttraumatic pain, and an injection of local anesthetic into the subtalar joint using fluoroscopic guidance or ultrasonography may be useful for diagnostic purposes in such situations. The midfoot and forefoot should be carefully checked for alignment, stability, and arthritis. If midfoot and forefoot pathology are identified, these conditions may require additional procedures in addition to a subtalar arthrodesis. Poor vascularity or soft-tissue compromise can contraindicate surgery on the hindfoot.

PREOPERATIVE (DIAGNOSTIC) IMAGING

The initial diagnostic workup should include AP, lateral, and axial views of the hindfoot (Figure 1). The hindfoot alignment view should include the distal tibia to delineate calcaneal-tibial alignment (Figure 2). Brodén views may be used to better evaluate the subtalar joint but are most useful intraoperatively to judge implant placement.

The definitive imaging modality for defining the bony anatomy is a CT scan. This will accurately define the presence/severity of arthritis, image adjacent joints, and provide useful information about the alignment of the hindfoot (Figure 3). In complex cases, a three-dimensional image can be obtained and provide a readily understandable method to visualize the anatomy of the situation. The surgeon can also plan the length and direction of implants if desired. The status of healing is also better determined with CT scanning.⁵ Recently, the availability of weight-bearing CT scans has provided additional ability to evaluate deformity in a more dynamic fashion.

MRI is also useful in imaging the subtalar joint preoperatively. For example, in cases of subtalar arthritic symptoms without obvious pathology on other modalities, MRI may identify areas of bone marrow edema adjacent to the articular surfaces that correlate with symptomatic regions within the joint (Figure 4). MRI is also the best tool for assessing vascularity of the talus in cases of osteonecrosis (eg, after talus fracture).

PROCEDURE

Room Setup/Patient Positioning

The patient is typically positioned in a supine position, with a “bump” under the ipsilateral hip and a tourniquet on the surgical leg. There should be a plan to gain access to the posterior aspect of the heel to place screws into the posterior tuberosity of the calcaneus. Methods include the figure-of-4 position, flexion of the knee to place the point of the heel off the side of the bed, positioning that
leaves the point of the heel off the foot of the bed, or having an assistant elevate the leg. Intraoperative imaging is provided by either a large C-arm brought in from the opposite side of the bed or a smaller C-arm positioned by the surgeon. In cases of distraction arthrodesis of the subtalar joint, consideration for a prone position and a posterior approach to the subtalar joint can be used.

FIGURE 1 Preoperative lateral radiograph showing advanced subtalar arthritis and preserved tibiotalar joint space.

FIGURE 2 Long axial radiograph of the tibia, talus, and calcaneus demonstrates the weight-bearing line falling medial to the calcaneus. The calcaneus is in excessive valgus and thus would require correction if subtalar arthrodesis were performed.

Special Instruments/Equipment/Implants

Large cannulated screws, such as 6.5 mm or larger, provide the ability to use guide wires to maintain joint reduction and establish screw trajectories prior to placement. Screws can be partially threaded or threaded with a variable pitch to compress across the subtalar joint. Partially threaded screws allow the threads to be kept out of the joint and optimize compression. In smaller patients or patients with limited bone stock, arthrodesis can be performed using a single screw, although two screws improve compression and provide rotational stability at the fusion site (Figure 5).

Surgical Technique

In Situ Arthrodesis

Under tourniquet control, a 4- to 6-cm incision is made starting just distal to the tip of the fibula and overlying the anterior process of the calcaneus to the base of the fourth tarsometatarsal joint (Figure 6). The dissection may encounter the peroneal tendons but should leave them undisturbed in their sheath. The sural nerve should lie plantar to the incision. The extensor digitorum brevis muscle belly is encountered and can be reflected distally or splint in line with its fibers. Deep dissection is carried sharply over the anterior process of the calcaneus. The tissues from the floor of the sinus tarsi are elevated. This will lead to the posterior facet of the subtalar joint. Exposure is improved if the talocalcaneal interosseous ligament is released. This allows for better separation of the joint surfaces for exposure. It also exposes the middle and anterior facets. In addition to the sinus tarsi approach, medial approach to the subtalar joint and arthroscopic techniques have been described.⁶^,⁷

Occasionally, large osteophytes will have to be removed from the lateral process of the talus to improve exposure. A small lamina spreader can be introduced between the talus and calcaneus to distract the two surfaces. Alternatively, a Hintermann-type distractor with pins placed into the talus and calcaneus can be used to gain access to the joint. An osteotome may be used initially to elevate as much of the remaining articular cartilage as possible from the subchondral bone. Remaining cartilage is removed with curets or by careful use of a burr, to completely expose the subchondral bone. Care must be given to the deep, curvilinear shape of the posterior facet, which may be difficult to thoroughly prepare. The anterior and middle facets should also be prepared to bleeding bone. Not only will this assist in healing, but it will also prevent the two facets from keeping the prepared surfaces of the posterior facet separated.

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