Fifth Metacarpus Instability and the Effect on Hamatometacarpal Arthritis Patterns – a Cadaveric Study

Objective: Arthritis of the little finger hamatometacarpal joint is an uncommon complaint with most cases occurring post-traumatically. The aim of this study was to determine the contribution of the different joint stabilizers on joint stability and biomechanics. In addition, we stratified the arthritis patterns affecting the hamatometacarpal joint and assessed their correlation to joint instability.

Methods: A cadaver study on ten embalmed cadavers was performed. The fifth hamatometacarpal joint was biomechanically evaluated through extensor carpi ulnaris traction and sequential dissection of the joint stabilizers. Gross macroscopic evaluation for degenerative changes of the joint articular surface was conducted and graded on a scale of 0–3 (with 0 representing normal cartilage with no visible lesions).

Results: Biomechanical data was available from 18 specimens (ten right; eight left) and arthritic patterns were available from all 20 specimens (ten right; ten left). Biomechanical measurements showed major contribution by the proximal and distal intermetacarpal ligaments. Minor stability was conferred by the volar stabilizer and minimal stability by the dorsal stabilizer. Arthritis was present in 16/20 specimens (80%) with the average arthritic grade being 1.6 on the right hands and 1.0 on left hands. The most common site of arthritis was the dorso-ulnar quadrant.

Conclusions: Our study found that both the proximal and distal intermetacarpal ligaments are key in stabilizing the hamatometacarpal joint. This may have an impact on both the treatment of this relatively rare injury and its diagnosis. Further studies may reveal if partial injury to these stabilizers has a role in causing arthritis at this key load transferring joint.