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Purpose: We aimed to evaluate the stability of the thumb carpometacarpal joint following either complete removal of the trapezium(TR) or partial removal of the trapezium and of the base of the first metacarpal (PTR). We utilized local capsular tissue for interposition graft in both cases. Methods: Right and left fresh frozen cadaveric hands from the same donor were randomized so that TR or PTR repair was performed randomly on the right or left hand of each pair. In the TR group we removed the entire trapezium. In the PTR group we removed 2mm of distal trapezium and 2mm of thumb metacarpal base. For both repairs, we interposed a capsular tissue graft. The cadaveric hands were stabilized in a jig designed to apply load across six thumb tendons. We measured gap closure distances prior to and following surgery and examined the joints by radiograph. Distances were measured using the Hough Transform model for measurement of abstract shapes. In order to detect a difference in gap distances between groups of 2mm with an alpha error of 0.05 and a beta error of 0.20, 18 hands were required. Results: The designated surgery was successfully performed on all hands. At baseline, mean gap differences did not vary between groups under load, while after surgery the TR group had greater mean gap closure when compared to the PTR group (4.44mm±1.70 vs 2.42mm±1.92, P<.001). No bone on bone contact was noted in any of the operated joints. Discussion: We found that PTR of the thumb basal joint leads to less gap closure of the joint when placed under simulated physiological load when compared to the complete removal of the trapezium. Clinical Relevance: Decreased gap closure under load may lead to preservation of thumb length and stability. Key words: Arthroplasty; thumb; carpometacarpal joints; trapezium; bone osteoarthritis

Purpose: We aimed to evaluate the stability of the thumb carpometacarpal joint following either complete removal of the trapezium(TR) or partial removal of the trapezium and of the base of the first metacarpal (PTR). We utilized local capsular tissue for interposition graft in both cases. Methods: Right and left fresh frozen cadaveric hands from the same donor were randomized so that TR or PTR repair was performed randomly on the right or left hand of each pair. In the TR group we removed the entire trapezium. In the PTR group we removed 2mm of distal trapezium and 2mm of thumb metacarpal base. For both repairs, we interposed a capsular tissue graft. The cadaveric hands were stabilized in a jig designed to apply load across six thumb tendons. We measured gap closure distances prior to and following surgery and examined the joints by radiograph. Distances were measured using the Hough Transform model for measurement of abstract shapes. In order to detect a difference in gap distances between groups of 2mm with an alpha error of 0.05 and a beta error of 0.20, 18 hands were required. Results: The designated surgery was successfully performed on all hands. At baseline, mean gap differences did not vary between groups under load, while after surgery the TR group had greater mean gap closure when compared to the PTR group (4.44mm±1.70 vs 2.42mm±1.92, P<.001). No bone on bone contact was noted in any of the operated joints. Discussion: We found that PTR of the thumb basal joint leads to less gap closure of the joint when placed under simulated physiological load when compared to the complete removal of the trapezium. Clinical Relevance: Decreased gap closure under load may lead to preservation of thumb length and stability. Key words: Arthroplasty; thumb; carpometacarpal joints; trapezium; bone osteoarthritis