Fifth metacarpal instability and its effect on hamatometacarpal arthritis patterns-a cadaver study

Osteoarthritis (OA) of the fifth carpometacarpal joint is a rare diagnosis with most cases occurring post-traumatically. The joint's ligamentous supports have not been described extensively; however we know that the volar and intermetacarpal ligaments acts as the primary stabilizers. The major deforming forces on this joint are the extensor carpi ulnaris (ECU) dorsally and the flexor carpi ulnaris volarly, via the pisimetacarpal ligament. The aim of this study was to determine how the different joint stabilizers contribute to fifth carpometacarpal joint stability and biomechanics. We also sought to describe the OA patterns affecting the fifth carpometacarpal joint. A study was performed on 10 embalmed cadavers. The fifth carpometacarpal joint was evaluated biomechanically through ECU traction and sequential transection of the joint stabilizers. Gross macroscopic evaluation of degenerative changes in the articular surface was conducted and graded on a scale of 0-3 (with 0 representing normal cartilage with no visible lesions). Biomechanical data were available from 18 specimens (10 right; 8 left) and arthritic patterns were available from all 20 specimens (10 right; 10 left). Based on the biomechanical data, the proximal and distal intermetacarpal ligaments were found to be major contributors to stability. The volar stabilizer was a minor contributor to stability and the dorsal stabilizer was a minimal contributor to stability. OA was present in 16/20 specimens (80%) with an average arthritis grade of 1.6 on the right hand and 1.0 on the left hand. The most common site of OA was the dorso-ulnar quadrant.