[Anatomical and biomechanical study on scaphoid ring sign of advanced Kienbock's disease]

To demonstrate the anatomical and biomechanical basis of scaphoid ring sign in advanced Kienbock's disease.

The study consisted of two sections. The ligaments stabilizing the proximal pole of the scaphoid were observed in 5 specimens. Under 12 kg dead weight load through the tendons of the flexion carpal radial, the flexion carpal ulnar, the extension carpal radial, and the extension carpal ulnar for 5 minutes, the stresses of the scaphoid fossa and lunate fossa were measured in the case of neutral, flexion, extension, radial deviation and ulnar deviation of the wrist joint under normal and rupture conditions respectively by FUJI prescale film and FPD-305E,306E.

Based on anatomical study, the ligaments stabilizing the proximal pole of the scaphoid consisted of the radioscaphocapitate ligament, long radiolunate ligament and scapholunate interosseous ligament; and the latter two ligaments restricted dorsal subluxation of the proximal pole of the scaphoid. When compared rupture condition with normal condition, the scaphoid fassa stress of radial subregion was not significantly different (0.90 +/- 0. 43 vs 0.85 +/- 0.15), and the ones of palmar, ulnar and dorsal subregions decreased (0.59 +/- 0.20, 0.52 +/- 0.05 and 0.58 +/- 0. 23 vs 0.77 +/- 0.13, 0.75 +/- 0.08 and 0.68 +/- 0.09) in the case of extension; the scaphoid fassa stresses of all subregions increased or had no difference in the case of neural, flexion, radial deviation and ulnar deviation. The lunate fossa stresses of all subregions increased in the case of neural, and the ones of all subregions decreased or had no difference in the case of flexion, extension, radial deviation and ulnar deviation.

Rotary scaphoid subluxation should be treated operatively at III B stage of Kienbock's disease to avoid traumatic arthritis of the radioscaphoid joint.