gms | German Medical Science

Objectives/Interrogation: The purpose of this study was to understand the biomechanical consequence of endoscopic carpal tunnel release (ECTR) on the interactions between the thenar muscles and transverse carpal ligament (TCL) in cadaveric hands. We hypothesized that ECTR would lead to greater changes in carpal arch height (CAH), width (CAW), and area (CAA) under thenar muscle loading compared to the intact condition.

Methods: Three female specimens (aged 60±1 years) without musculoskeletal pathology were dissected to expose the flexor pollicis brevis (FPB), the opponens pollicis (OPP), and the abductor pollicis brevis (APB) for loading. Magnitude for loading was set as 15% of each muscle's maximum physiological force production. Loading directions were determined by the muscle's anatomical orientation with the thumb placed in an abducted and pronated position. Loads on the individual and combined thenar muscles were applied in a randomized order with 30 sec ultrasound videos recording morphological changes at the distal TCL. After initial testing, each specimen underwent ECTR, and the same testing procedures were repeated. Custom LabVIEW programs were used to track carpal arch morphological changes.

Results and Conclusions: The FPB failed alone in one specimen and the FPB and the OPP failed in one specimen. For pre-release hands, APB loading generated a CAH increase of 0.049±0.046 mm, a CAW decrease of 0.23±0.31 mm, and a CAA increase of 0.32±0.24 mm². After ECTR, APB loading generated a CAH decrease of 0.041±0.21mm, CAW increase of 0.35±0.25 mm, and a CAA decrease of 0.53±1.58 mm².

Overall, our preliminary results showed APB loading generated small morphological changes in carpal arch for both the intact and released TCL, suggesting that ECTR may not affect the muscle-ligament biomechanics under low muscle contraction force. The small changes may be explained by the relatively low muscle force of a single muscle. It is likely that synergistic muscle contraction by all three thenar muscles with higher force magnitude would generate more appreciable carpal arch changes, allowing for better understanding of the biomechanical implications of carpal tunnel release. This data will be completed with additional specimens by the time of presentation.