The Effect of Scapholunate Interval and Angle on Radiocarpal Joint Loading

Introduction: Carpal instability related to scapholunate ligament injury can manifest as an increased scapholunate (SL) interval and/or angle. Radiocarpal arthrosis is expected with chronic carpal instability due to an imbalance of normal joint loading. This study seeks to quantify the effect of an increased SL interval and angle on joint loading properties. Methods: Radioscaphoid (RS) and radiolunate (RL) contact area and pressure were collected in 13 cadaveric specimens tested under the following conditions (#): normal SL interval and SL angle (1), increased interval only (2), increased angle only (3), and both increased interval and angle (4). Results: Compared with condition 1, RS contact area decreased by 21%, 49%, and 33% in conditions 2, 3, and 4, respectively, and RL contact area increased by 0.3%, 55%, and 36%. Compared with condition 1, RS pressure increased by 167%, 207%, and 185% in conditions 2, 3, and 4, respectively, and RL pressure decreased by 13% in condition 2 and increased by 27% and 76% in conditions 3 and 4, respectively. Conclusions: Radioscaphoid and RL joint loading properties change with an increased SL interval and angle. An increased SL angle alters radiocarpal joint loading to a greater extent than an increased SL interval. As a result, an increased SL angle likely has a more significant impact on the development of carpal arthrosis.