Experimentally induced ulno-carpal instability. A study on 13 cadaver wrists.

This experimental work studies the role of ligamentous structures in suspending the carpal bones from the radius and ulna. Thirteen human cadaver wrists underwent a distal radio-ulnar arthrodesis in a neutral position and an arthrodesis between the three bones of the first carpal row. Progressive postero-anterior forces in a palmar direction were applied to the fused carpal bones. Displacement was measured by two dial gauges before and after sequential section of the different fibrous structures. The largest absolute average displacement (both, dorso-palmar and induced rotational displacement) was observed after section of the ulnar styloid process. No significant differences were observed after section of the extensor retinaculum, extensor carpi ulnaris sheath, posterior ulno-carpal and posterior radio-carpal ligaments. This work suggests that the carpus is suspended not only from the radius, but also from the distal ulna and particularly at the ulnar styloid and the structures which insert onto it.