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Pilot Study: Changes in Metacarpophalangeal Joint Loading After First Metacarpal Osteotomy for Thumb Carpometacarpal
Shigeki Ishibashi1, Akira Kodama1, Yuichi Sumida1
1From the Department of Orthopaedic Surgery, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.
Background:
First metacarpal osteotomy is a joint-preserving option for thumb carpometacarpal osteoarthritis, but its effect on the adjacent metacarpophalangeal (MCP) joint remains unclear. We evaluated postoperative changes in MCP kinematics and subchondral stress distribution.
Methods:
We retrospectively analyzed 21 thumbs in 19 patients who underwent first metacarpal extension-abduction osteotomy. Assessments before surgery and at follow-up included pain and function, dynamic radiography of MCP motion, and computed tomography-based Hounsfield unit (HU) measurements as an index of subchondral bone density at 9 regions on the metacarpal head and proximal phalanx. Preoperative and postoperative data were compared with Wilcoxon signed-rank tests; regional HU distributions were assessed with Friedman tests and Dunn post hoc tests.
Results:
Median clinical follow-up was 1.5 years. Median MCP hyperextension improved from 16 (interquartile range [IQR], 5-28 degrees) to 0 degrees (IQR, 0-10 degrees; P < 0.01), whereas flexion did not change. Ulnar deviation at maximal palmar adduction increased from 8 (IQR, 5-10.5 degrees) to 12 degrees (IQR, 7-15 degrees; P = 0.011). One-year computed tomography showed significant postoperative HU decreases in dorsal regions of the metacarpal head, whereas the proximal phalanx showed no significant regional change. No radiographic progression of MCP osteoarthritis was observed.
Conclusions:
First metacarpal extension-abduction osteotomy improved MCP alignment and altered subchondral loading at the metacarpal head. These findings suggest that the procedure favorably affects thumb-ray biomechanics beyond the carpometacarpal joint.
