Association of Preexisting Triple Fusion and Arthroscopic Ankle Arthrodesis nonunion

Background: Arthroscopic ankle arthrodesis (AAA) is a successful treatment for end-stage ankle arthritis. A significant early complication of AAA is symptomatic nonunion. Published nonunion rates range from 8% to 13%. Longer term, there is concern that it predisposes to subtalar joint (STJ) fusion. To better understand these risks, we undertook a retrospective investigation of primary AAA. Methods: All adult AAA cases conducted at our institution over a 10-year period were reviewed. A total of 284 eligible AAA cases in 271 patients were analyzed. The primary outcome measure was radiographic union. Secondary outcome measures included reoperative rate, postoperative complications and subsequent STJ fusion. Univariate and multivariate logistic regression analysis was performed to identify nonunion risk factors. Results: The overall nonunion rate was 7.7%. Smoking (odds ratio [OR] 4.76 [1.67, 13.6], P = .004) and previous triple fusion (OR 40.29 [9.46, 171.62], P < .001) were independent risk factors on univariate analysis. Only prior triple fusion persisted as a major risk factor associated with nonunion on multivariate analysis (OR 18.3 [3.4, 99.7], P < .001). Seventy percent of patients with a previous triple fusion went on to develop nonunion compared to 5.5% of those without. Increasing age, obesity, surgical grade, diabetes, postoperative weightbearing plan, steroid use, and inflammatory arthropathy were not significant risk factors. The leading cause of reoperation was hardware removal (18%). There were 5 superficial (1.8%) and 4 deep (1.4%) infections. Eleven (4.2%) required subsequent STJ fusion. The "survivorship" of STJ post AAA was 98%, 85%, and 74% at 2, 5, and 9 years, respectively. Conclusion: As the largest study of AAA in the literature, our findings suggest prior triple fusion is a major independent risk factor for AAA nonunion. These patients should be counseled of this high risk and may benefit from alternative surgical options.