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

Area of Science:

• Orthopedic biomechanics
• Hand anatomy and pathology

Background:

• Osteoarthritis (OA) of the fifth carpometacarpal joint is uncommon, often linked to trauma.
• Ligamentous supports, particularly volar and intermetacarpal ligaments, are primary stabilizers.
• Deforming forces include the extensor carpi ulnaris (ECU) and flexor carpi ulnaris.

Purpose of the Study:

• To quantify the contribution of different stabilizers to fifth carpometacarpal joint stability.
• To biomechanically analyze the joint under stress.
• To characterize the patterns of osteoarthritis in this joint.

Main Methods:

• Biomechanical testing on embalmed cadavers involving ECU traction and sequential ligament transection.
• Macroscopic evaluation and grading of articular cartilage degeneration (0-3 scale).
• Analysis of data from 18 specimens for biomechanics and 20 for arthritis patterns.

Main Results:

• Proximal and distal intermetacarpal ligaments significantly contribute to joint stability.
• The volar stabilizer offers minor stability, while the dorsal stabilizer provides minimal stability.
• 80% of specimens showed OA, most commonly in the dorso-ulnar quadrant, with average grades of 1.6 (right) and 1.0 (left).

Conclusions:

• Intermetacarpal ligaments are critical for fifth carpometacarpal joint stability.
• Understanding these biomechanical contributions is vital for managing OA in this joint.
• Specific OA patterns and locations were identified, aiding in diagnosis and treatment strategies.