Carpal boss: destabilization of the third carpometacarpal joint after a wedge excision.

In a standard carpal boss procedure, the dorsal ligament of the involved carpometacarpal joint is cut in the process of performing a wedge excision. We studied the effect of such a dorsal ligament sectioning on the joint between the capitate and middle metacarpal bone in ten fresh-frozen wrist specimens. The passive range of motion of this joint was measured with the joint loaded into flexion and extension and in the unloaded neutral position. After the dorsal ligament of the carpometacarpal joint was cut, simulating a dorsal wedge excision, the passive range of motion was measured again. Analysis indicated that this simulated wedge excision approximately doubled the passive range of motion of the carpometacarpal joint. This study shows that such a procedure disturbs the normal anatomy and creates instability of the involved joint.