Index Metacarpal Fracture Risk in Suture Button Suspensionplasty and the Effects of Drill Hole Position: A Cadaveric Study.

PURPOSE: Suture button suspensionplasty (SBS) has gained popularity for the treatment of thumb carpometacarpal joint osteoarthritis; however, fractures of the index metacarpal (MC) at the site of fixation have been reported. The biomechanical effect of SBS on index MC integrity and the influence of K-wire drill hole trajectory remain incompletely understood. This cadaveric study evaluates the mechanical strength of the index MC following SBS using three commonly employed K-wire trajectories compared with native controls.

METHODS: Forty-three fresh-frozen cadaveric hands were randomized into four groups with differing K-wire hole trajectories: native control (n = 10); single central bicortical pass (BC; n = 11); dorsal unicortical followed by bicortical pass (DUC; n = 11); and volar unicortical followed by bicortical pass (VUC; n = 11). SBS was performed using a Mini TightRope. Index MCs were subjected to a custom cantilever bend test using a servo-hydraulic testing system until failure. Maximum load to failure and peak stress were calculated. Group comparisons were performed using heteroscedastic analysis of variance with post hoc testing, Welch t tests, and Bayesian analyses.

RESULTS: All index MCs failed via fracture at the K-wire hole fixation site. While a notable overall difference in maximum load among groups was observed, post hoc testing did not identify a single drill trajectory that conferred a statistically significant biomechanical advantage. When aggregated, SBS specimens demonstrated a 33% reduction in force-to-failure compared with native controls, with a large effect size and moderate to strong Bayesian evidence supporting reduced index MC strength after SBS. No statistically significant differences in peak stress were identified. Bayesian analysis of peak stress demonstrated weak evidence favoring VUC.

CONCLUSIONS: Suture button suspensionplasty considerably reduces the load-bearing capacity of the index metacarpal, independent of drill hole trajectory. The VUC construct demonstrated more favorable stress characteristics than DUC. These findings provide biomechanical context for reported index metacarpal fractures following SBS and may inform surgical technique and patient counseling.

TYPE OF STUDY/LEVEL OF EVIDENCE: Bench Research V.