Arthroscopic gap distance can predict the degree of scapholunate ligament tears: a cadaver study

Midcarpal joint arthroscopy is essential for diagnosing scapholunate (SL) instability, but a discrepancy may exist between the grade of arthroscopic evaluation and the extent of SL ligament tears. This study aimed to investigate whether the magnitude of arthroscopic SL gap distance could predict the extent of ligamentous disruptions in a simulated SL dissociation model. Eight upper extremities of fresh cadavers were analyzed. Static and dynamic SL gap distances were measured with using custom-made probes via midcarpal arthroscopy in intact wrists following sequential sectioning of the SL stabilizing ligaments. Comparisons of static and dynamic SL gaps between stages were conducted using analysis of variance followed by the Games-Howell test. Receiver operating characteristic (ROC) curves were constructed to assess the diagnostic performance of the SL gap distance in identifying simulated ligament tears. There were no significant differences between stages in the static SL gap distance. Dynamic SL gap distance increased significantly following SL interosseous ligament (SLIL) sectioning. According to the ROC curve for dynamic SL gap distance, the area under the curve was 0.94 for the assessment of the diagnostic performances in identifying complete SLIL sectioning. A cut-off value of 1.4 mm for the dynamic SL gap showed the highest diagnostic accuracy rate (91%). The dynamic SL gap distance showed a high diagnostic performance in the detection of dorsal intercarpal ligament (DICL) sectioning. The highest accuracy rate (85%) was noted when the threshold value was set at 2.8 mm. The SLIL is the primary stabilizer of the SL joint in the viewpoint of arthroscopic measurement. Dynamic SL joint widening of more than 1.4 mm showed the best predictive ability for complete SLIL tears, while 2.8 mm widening made it possible to predict both DICL and SLIL tears.