RESUMO
INTRODUCTION: Non-dissociative carpal instability (CIND) may lead to severe functional impairment. Destabilisation of the scapho-trapezial-trapezoidal (STT) ligament complex seems to result in a CIND. MATERIALS AND METHODS: In one group with eight cadaver arms, distal scaphoid pole was resected with the adjacent ligaments. In the other eight cadavers, hemitrapeziectomy was performed followed by total trapeziectomy. CT scans were performed in different wrist positions, and the changed positions of the scaphoid, lunate and capitate were measured in comparison to non-operated wrists. RESULTS: Mainly in clenched fist position, dissociation between proximal and distal row can be determined after total trapeziectomy and resection of distal scaphoid pole. Capitate rotates dorsally up to 24°, the scaphoid up to 17° and the lunate up to 7° compared to the non-operated wrists. Resection of the distal scaphoid pole results in dorsal rotation of capitate and scaphoid of about 14° and the lunate 8°. Relative scapholunate and capitolunate angle increased significantly after total trapeziectomy, especially in clenched fist position. After scaphoid pole resection, significant SL and CL angles changes could be seen in almost every wrist position. CONCLUSION: Destabilisation of the STT ligament complex by total trapeziectomy or distal scaphoid pole resection results in dissociation of the proximal and distal carpal row without instability within the proximal or distal row, corresponding to a CIND. LEVEL OF EVIDENCE: III.