Divergent vs Parallel Screw Configurations for Subtalar Arthrodesis: Comparing Clinical Outcomes

CATEGORY: Ankle Arthritis; Hindfoot INTRODUCTION/PURPOSE: Subtalar arthrodesis is a frequently performed surgery used to treat several hindfoot pathologies. Rigid fixation is essential for successful fusion and percutaneous screws are most commonly used. Controversy still exists regarding the most optimal screw configuration. While cadaveric biomechanical studies have shown diverging screw configuration to be superior to parallel screws, this has never been proven in the clinical setting. The aim of this study was to compare fusion rates and clinical outcomes between patients treated with divergent versus parallel screw constructs for subtalar arthrodesis. METHODS: We conducted a retrospective review of 58 patients that underwent subtalar arthrodesis during a four-year period at our institutions. Patients were divided into two groups based on screw construct; diverging versus parallel. Outcomes measured were radiographic and clinical evidence of fusion at 3 months, American Orthopaedic Foot & Ankle (AOFAS) ankle-hindfoot and Visual Analog Scale (VAS) scores at final follow up and post-operative complications. RESULTS: Thirty patients underwent subtalar fusion with a divergent screw construct and twenty-four with parallel screws. The mean age was 58.5+-13.9 years and mean follow up period was 44.5+-20.8 months. The overall fusion rate at 3 months was 94.8%. The fusion rate for the divergent screw group was 93.3% versus 96.4% for the parallel screw group, showing no statistical significance (p=0.60). Overall, the mean AOFAS and VAS scores improved post-operatively by 28.1+-5.49 and 4.27+-1.45 points respectively (p<.0001). In the divergent group, mean improvement in AOFAS and VAS scores was 28.5+- 4.99 and 4.39+-1.42 versus 27.7+-6.05 and 4.14+-1.48 in the parallel screw group, showing no statistical significance (p=0.59 and p=0.44). The overall complication rate was 5.2% with no statistically significant difference between the two groups (6.7% versus 3.6%, p=0.60). CONCLUSION: When used for fixation during subtalar arthrodesis, divergent and parallel screw constructs have similar radiological union rates and clinical outcomes when it comes to fusion rates at 3 months, post-operative improvement in AOFAS scores and complication rates. Screw configuration should be determined by surgeon experience and comfort level.