22 Subtalar Joint Fusion Abstract Subtalar fusion is a successful operation for patients with symptomatic degeneration of the subtalar joint. Open and arthroscopic approaches provide good union rates, consistently above 90% and the majority of patients experience significant improvements in pain and functional outcomes. Careful surgical technique is important to minimize wound complications and maximize chances of union. Attention to patient selection, joint preparation, alignment, and adequate compression is vital. Keywords: subtalar, arthrodesis, fusion • Primary osteoarthritis isolated to the subtalar joint. • Posttraumatic arthritis. • Inflammatory arthropathy. • Subtalar tarsal coalitions in adults. • Failed nonoperative management. • Patients complain of symptoms of pain in the sinus tarsi and distal to the fibula, typically this is worse on walking on uneven surfaces. With more advanced disease, pain will be present while walking on flat ground and also at rest. • Clinical examination will reveal painful, restricted movement in the subtalar joint. Typically the tenderness is most apparent in the sinus tarsi. • It is important to evaluate the coronal plane alignment of the midfoot and the forefoot, and in particular their relationship with the hindfoot. With increasing valgus deformity, there will be supination of the foot. If this is marked or if it is not passively correctable, it will need to be addressed at the same time as the subtalar fusion. • Similarly assess for a contracture of the gastrocnemius in severe deformity. These biomechanical risk factors need to be addressed to minimize the risk of recurrence of the deformity. • Weight bearing radiographs of the ankle will usually demonstrate subtalar joint posterior facet arthritis, particularly on the lateral radiograph. Confirmation can be obtained with preoperative computed tomography (CT) scan or magnetic resonance imaging (MRI; see Figs. 22.1, 22.2). This also enables assessment of the talonavicular joints and calcaneocuboid joints. • If adjacent joints are painful or appear to be degenerate, it may be helpful to perform preoperative steroid and local anesthetic injection under ultrasound scan (USS)/CT guidance to confirm that the subtalar joint is symptomatic. Contrast is helpful as joints can frequently communicate, especially in late stages of disease (Fig. 22.3). Fig. 22.1 Subtle radiographic signs of subtalar joint osteoarthritis. Note normal appearance of talonavicular and calcaneocuboid joints. Fig. 22.2 MRI (magnetic resonance imaging) showing involvement of posterior and middle facets of subtalar joint. Fig. 22.3 Fluoroscopic guided injection of subtalar joint with local anesthetic and contrast. • UCBL (University of California at Berkeley Laboratory) inserts. • Custom rigid ankle–foot orthosis (AFO) bracing (Arizona or molded ankle–foot orthosis [MAFO]). • Intra-articular steroid injections. • Anti-inflammatory medications. • Activity modification. • Infection: if there is a history of infection inflammatory markers, white cell scan and bone biopsies may be necessary. • Forefoot supination: long-standing valgus can be associated with first ray elevation; if this is not correctable, then it may require middle column osteotomy or triple fusion instead. • Smoking should be stopped; nonunion is more common than for some other fusions. Our aim is to provide pain relief, by achieving a solid bony fusion, which we achieve in the majority of cases. • Shorter learning curve than arthroscopic approach. • Ability to correct defects or bone loss in the posterior facet with graft. • Can be quicker. • Smaller incision with less wound complications. • Full visualization of the posterior facet. • Visualization of the medial ST joint and middle facet. • Easier deformity correction. In the authors’ opinion, the arthroscopic approach is preferable, particularly in the presence of severe deformity or where the lateral skin is poor/has had previous surgery. • Remove all cartilage: use laminar spreaders to inch inward toward the medial side. You need to see the flexor hallucis longus (FHL) tendon moving to know that you have gotten to the medial extent. • Avoid undercorrection of hindfoot deformity. Even in normal alignment, it is easy to take more bone off the lateral side than the medial side. It is very important to avoid this especially when there is a preoperative valgus deformity. In that case, it is necessary to take more of the medial side than the lateral and the middle facet can be a block to reduction. • Feather the bone surfaces and achieve adequate compression with partially threaded screws, with entry point in calcaneus to try to avoid symptomatic hardware. Make sure all the threads cross the fusion site and in osteoporotic bone it may be helpful to not drill all the way in order to ensure the best hold possible in the talus. • After correction and fixation, check the first ray and midfoot for supination and the gastrocnemius for contracture. These are risk factors for recurrence of deformity. The patient is supine in a semilateral position, achieved by placing a sandbag under the ipsilateral buttock. X-ray comes in from the same side. A lateral sinus tarsi approach, from the tip of the fibula to the fourth tarsometatarsal joint (Fig. 22.4). Avoid fixed retraction of the skin with self-retainers; instead use assistant to retract intermittently with Langenbeck’s retractors. Superficially identify extensor digitorum brevis and the sinus tarsi fat pad. It is important that some of the sinus tarsi fat pad is preserved. It may be easier visualization to remove it, but if it is completely removed it may result in skin devascularization and a dead space, which may compromise wound healing. Identify and protect the superficial peroneal nerve anteriorly.
22.1 Indications and Pathology
22.1.1 Clinical Evaluation
22.1.2 Radiographic Evaluation
22.1.3 Nonoperative Options
22.1.4 Contraindications
22.2 Goals of the Surgical Procedure
22.3 Advantages of the Surgical Procedure
22.3.1 Open Procedure
22.3.2 Arthroscopic Fusion
22.4 Key Principles
22.5 Operative Technique
22.5.1 Open Fusion
Setup and Positioning
Incision
Surgical Procedure
Musculoskeletal Key
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