Factors affecting outcomes of arthroscopic ankle fusion: pre-existing triple fusion and the risk to non-union

A. Woods, S. Henari, A. Kendal, M. Rogers, R. Brown, R. Sharp, C.L. Loizou

Background: Open or arthroscopic ankle fusion (AAF) is a successful operative treatment for end-stage ankle arthritis. Evidence suggest that AAFs have better outcomes. In addition to the operative technique other patient-factors can influence outcomes. The most significant complication of ankle fusion is a non-union. To better understand the risk factors related to this we undertook a retrospective investigation of primary AAFs.

Methods: We reviewed all AAFs conducted at our institution over a 10-year period. Patients excluded if they had simultaneous fusion of neighbouring joints or were lost to follow-up. The primary outcome variable was radiographic union. Other operative complications were analysed as secondary outcomes. Two hundred and eighty-four eligible AAFs in 271 patients were performed over the study period.

Results: The overall non-union rate was 7.7 %. Univariate logistic regression analysis found that smoking (6.2% non-union in non-smokers vs 24% in smokers) and prior triple fusion (5.5% non-union in the absence of prior triple fusion vs 70% in the presence of a prior triple fusion) were independent risk factors for non-union. Multivariate analysis showed that only prior triple fusion was predictive (OR 40.0 [9.4,170.3], p<0.0001). Increasing age, obesity (BMI>30), surgical grade (trainee vs consultant), diabetes or the degree of weightbearing status post-operatively were not significant risk factors of non-union. The leading cause of reoperation was the removal of metal (18%). There were 5 superficial (1.8%) and 4 deep (1.4%) infections. Kaplan-Meier survival analysis showed a 75% ‘survivorship’ of the subtalar joint at 10 years following an arthroscopic ankle fusion.

Conclusion: This is the largest case series of AAFs in the literature and the first to demonstrate that patients who had an AAF performed after a previous triple fusion have unacceptably high non-union rates and may benefit from other surgical options. This study data could also useful for patient consenting purposes.