Outcomes of Subtalar Arthrodesis in the Setting of Isolated vs Following Ankle Arthrodesis

Category: Ankle Arthritis; Ankle Introduction/Purpose: Subtalar arthrodesis is commonly used to treat both primary subtalar arthritis and subtalar arthritis that develops secondary to the altered biomechanics present after ankle arthrodesis. Biomechanical studies have shown that ankle fusion increases the motion in the subtalar joint which may cause arthritis and increased difficulty healing after subtalar arthrodesis. A recent clinical study of subtalar fusion after ipsilateral ankle fusion2 found a higher non-union rate in the post-arthrodesis group, but the certainty of their conclusion was limited by the relatively small size of the of ankle arthrodesis group (n=13) compared to the non-arthrodesis group (n=138). This study aims to contribute to the expanding body of evidence that subtalar arthrodesis in the setting of prior ankle fusion, yields inferior outcomes compared to isolated subtalar arthrodesis. Methods: We conducted a single-center retrospective chart review of a consecutive series of 26 adult patients who underwent subtalar fusion with (n=12) compared to without (n=14) prior ankle arthrodesis. The average age was 57 years, comprising 10 males and 16 females. Minimum follow-up of 2 years. Demographic data, surgical techniques, risk factors, laterality, comorbidities, and pre- and post-orthopedic surgical interventions were extracted through chart review. Clinical outcomes included: (1) delayed union when there was less than 25% bony fusion of the posterior facet on CT scan obtained 3 -months after surgery, (2) Non-union when there was absence radiographic fusion on radiographs taken at 6 months with persistent symptoms, and (3) union rate was determined through XR and CT scans, monitoring the progression from wearing a boot to weight-bearing activities. Results: Delayed union occurred in 8 out of 14 patients (57.14%) with previous ankle arthrodesis, compared to 4 out of 12 patients (33.3%) without previous arthrodesis. Nonunion occurred in 7 out of 14 patients (50%) with prior ankle fusion compared to 3 out of 12 patients (25%) without prior fusion. Smoking history, diabetes, and gender did not significantly impact the rate of fusion. Following subtalar fusion, patients commonly underwent surgeries such as ankle arthroscopy, wound infection debridement, hardware removal, subtalar arthrodesis revision, and midfoot arthrodesis. Among the 12 patients with delayed healing, 9 required subsequent surgery, averaging 2.7 additional procedures. Conclusion: In this retrospective study of subtalar fusion outcomes in patients with and without prior ankle arthrodesis we found that the previous arthrodesis group had higher rates of delayed union (57.14%) and nonunion (50%) compared to the isolated subtalar group (33.3% and 25%, respectively). This study adds to the growing body of literature that demonstrates inferior outcomes for subtalar fusion after ankle fusion. Moreover, it supports the growing popularity of total ankle arthroplasty as an alternative to ankle fusion in the setting of preexisting subtalar arthritis.