Anatomic and Biomechanical Study of Thumb Carpometacarpal Dislocations: A Laboratory Study

No previous study recreating an isolated thumb carpometacarpal (CMC) dislocation with or without suture augmentation has been performed in the laboratory. This investigation aimed to evaluate the mechanism and ligamentous complex of isolated thumb CMC dislocations. Biomechanical analysis was performed in 10 cadaveric specimens. A posteriorly directed force or axial loading with hyperflexion through the CMC joint was applied. Load was applied at a rate of 1 mm/s until posterior CMC dislocation was achieved. Maximum load, displacement under nominal loading, stiffness, and mode of failure were recorded. The native ligament was repaired, augmented with high-tensile suture, and testing was repeated. Posteriorly directed force produced posterior CMC dislocations, while axial loading and hyperflexion through the CMC joint caused fractures. Load-to-failure of the native CMC joint was 217.76 N (SD = 66.03). Stiffness of the ligamentous complex on average was 18.86 N/mm (SD = 8.83). Mean load-to-failure after repair with suture augmentation was 94.62 N (SD = 39.77), with average stiffness of 8.21 N/mm (SD = 3.06). The native ligament was noted to have greater stiffness ( P = .002) and greater load-to-failure ( P = .0001) than repair with suture augmentation. Maximum displacement-to-failure of the native ligament was 14.5 mm compared with repair with suture augmentation 11.9 mm ( P = .068). Isolated CMC dislocation was achieved with a posteriorly directed force rather than hyperflexion of the joint. Ultimate failure load of the repaired ligaments with suture augmentation was about half of that of the native ligaments. Further research into this technique is warranted.