Three-Dimensional Analysis of the First Metacarpal Axes in Healthy Individuals and Early-Stage Thumb Carpometacarpal Osteoarthritis Patients-Potential Implication on First Metacarpal Corrective Osteotomy.

Numerous anatomical features of the first carpometacarpal (CMC I) joint have been investigated as potential predispositions for CMC I osteoarthritis (OA). Even though load transmission through the CMC I joint-and, therefore, the development of osteoarthritis-is believed to be influenced by the geometry of the first metacarpal (MC I) bone, there is no common definition of the MC I axes. CT scans of twenty healthy volunteers and pre- and postoperative CT scans of six patients with CMC I OA undergoing Wilson osteotomy were analyzed. We proposed a calculation method based on anatomical landmarks for the proximal joint surface axis (PA) angle and the definition of an anatomical (AA) and a mechanical (MA) longitudinal axis. We hypothesized that for an MC I extension osteotomy to be effective, the AA and MA need to be aligned surgically. : To align AA and MA, an average correction angle of 22.60° (SD 2.53°) at 1 cm and 26.73° (SD 2.55°) at 1.5 cm distal to the CMC I joint line is required. The hereby proposed method for patient-specific calculation of the correction can be used to improve the surgical technique.