What is the implication of scaphoid ring sign in advanced Kienböck's disease? Is it a sign of advanced carpal collapse or rotary scaphoid subluxation?

Objective: To discuss the clinical implication of scaphoid ring sign in Lichtman's X-ray Ills stage of the lunate avascular necrosis. Methods: In a series of 17 cases of advanced Kienböck's diseases, carpal height (CH) and carpal height ratio (CHO) were measured in posteroanterior X-ray view (PA) preoperatively, which included seven cases in stage IIIA and 10 cases in stage IIIB. Radioscaphoid angles were also measured in the lateral X-ray view. All these measurements above were to study what were the differences between stages IIIA and IIIB. In addition, five fresh normal wrist specimens were dissected to observe the ligaments stabilizing the proximal pole of scaphoid. Results: The results of CH and CHR between stages IIIA and IIIB were similar, which illustrated no significant difference in carpal collapse between two substages, however, the results of RSA were significantly different between two substages, which implied the position of the proximal pole of scaphoid changed in two substages. Based on the results of anatomical observation, three ligaments were important to stabilize the proximal pole of scaphoid, namely the radioscaphocapitate (RSC) ligament, long radiolunate (LRL) ligament and scapholunate interosseous ligament (SLIL). The function of RSC ligament was to restrict palmar subluxation of the proximal pole of scaphoid; LRL and SLIL were to restrict dorsal transposition of the proximal pole of scaphoid. Conclusion: Based on the results, we suppose the scaphoid ring sign is the implication of rotary scaphoid subluxation in stage IIIB, which was caused by destructions of LRL and SLIL ligaments. All procedures aimed at stage IIIB must account for this important factor.