Correlation of Scaphotrapezoid Contact Pressures With Degree of Trapezoid Resection: Does Eliminating Contact Matter?

<h3>Purpose</h3> Scaphotrapeziotrapezoid (STT) arthritis is the third most common hand arthritis in the United States. In the setting of thumb carpometacarpal arthroplasty, varying degrees of partial excision of the proximal trapezoid have been suggested. We sought to quantify how much resection was adequate to prevent scaphotrapezoid (ST) impingement through a biomechanical cadaveric study. It was hypothesized that the commonly suggested 2 mm of trapezoid excision would be inadequate to prevent ST impingement in all planes of motion. <h3>Methods</h3> Eight fresh-frozen cadaveric upper extremities were screened for normal STT morphology for inclusion. Each extremity was prepared for testing with the forearm transfixed in neutral rotation, then mounted in a servohydraulic testing system. A motion capture system was used to evaluate the range of motion. A dorsal approach to the thumb carpometacarpal was performed with trapezium excision. A Tekscan sensor was secured within the ST joint, and the following conditions were tested: 45N in terminal flexion, 45N in terminal extension, 89N in terminal extension, and 45N in radial deviation. Flexion and extension loads were applied axially in line with the forearm, and radial deviation was applied 90° tangentially to the forearm. Tests were repeated after incremental 2-mm trapezoid resections up to 6 mm. Data normality was assessed using the Kolmogorov–Smirnov test, followed by Kruskal–Wallis and Dunn's post hoc tests for nonparametric comparisons. <h3>Results</h3> No significant ST joint contact occurred in extension at any resection depth. A statistically significant decrease in contact pressures required a 4-mm resection (<i>P</i> = .008) in flexion and a 6-mm resection (<i>P</i> = .028) in radial deviation. <h3>Conclusions</h3> Significant reduction in ST contact pressures in flexion and radial deviation requires 4–6 mm of resection. There is no significant ST impingement in wrist extension. Achieving impingement-free motion in flexion and radial deviation requires more resection than previously believed. <h3>Clinical relevance</h3> If the goal of ST arthritis management through partial trapezoid resection is impingement-free range of motion, then at least 4–6 mm of trapezoid must be resected. Our data may support investigating alternative interventions for the management of ST arthritis.