Magnitude and Location of Isolated Thumb Forces in Control and LRTI Surgery Participants: Mapping Force to Three-Dimensional Kinematics.

The thumb carpometacarpal (CMC) joint is highly susceptible to osteoarthritis (OA), often leading to weakness. As the most functionally important finger, it is vital to monitor thumb force, both the magnitude and location, to track disease progression and evaluate treatments and surgeries for CMC OA. However, current tools fail to measure isolated thumb force or capture varied thumb postures. This work developed a device that measured thumb force independently of the other fingers in 24 thumb postures in participants without CMC OA, and participants with CMC OA before, 3-months, and 6-months after a trapeziectomy with ligament reconstruction and tendon interposition (LRTI) surgery. Thumb postures were combinations of force direction (pull, push), force region (close, far, comfortable), and wrist rotation (0 deg, 30 deg, 60 deg, 90 deg). In control participants, three-dimensional force locations were investigated and mapped into the thumb kinematic space to create a "normalized force volume." Fifty-two (26 male and 26 female) control and 13 female surgical participants were tested and statistically analyzed. Three male surgical participants were tested and reported, but not statistically analyzed. In controls, force direction, region, and wrist rotation significantly affected isolated thumb force magnitudes. In surgical participants, only force direction was significant. Force did not significantly change across surgical timepoints, even after rehabilitation. Force application locations in controls were similar across sexes and ages and were consistent with daily tasks. This novel's work enables comprehensive evaluation of thumb force, supporting improved assessment methods and the potential for tailored rehabilitation routines for patients.