Single-screw fixation for subtalar joint fusion does not increase nonunion rate

A philosophical shift toward more joint-sparing procedures has led to increased use of isolated subtalar joint (STJ) versus triple arthrodesis. Union rates for STJ fusion range from 47% to 100%, leading to controversy regarding the optimal type, orientation, and amount of internal fixation. The purpose of this study was to determine if single-screw fixation is a predisposing factor to nonunion. Single-screw fixation is parallel to the STJ axis and may result in motion. It is hypothesized that higher nonunion rates will be observed in single-screw versus 2-screw fusions. Isolated STJ arthrodeses performed in 113 patients were retrospectively reviewed. Single screws were used in 89 (78.8%) fusions; 2 screws were used in 24 (21.2%) fusions. The mean follow-up was 11 months (range, 9-17 months). Nonunion occurred in 13 (14.6%) single-screw and 6 (25.0%) 2-screw fusions. Twenty (22.5%) single-screw and 3 (12.5%) 2-screw fusions required hardware removal. Revision surgery was performed in 6 (6.7%) single-screw and 3 (12.5%) 2-screw fusions. No significant differences in demographics were calculated between single and 2-screw fusions. Furthermore, no significant differences were observed in nonunion rate, postoperative complication incidence, or subsequent surgeries. The results from this study do not support the contention that single-screw fixation predisposes STJ fusions to nonunion. Comparable nonunion and complication incidences were observed between single and 2-screw fusions. These data suggest that the motion occurring from single-screw fixation may not be significant enough to directly affect the rate of union.