Wrist Kinetics Post-Scapholunate Dissociation: Experimental and Computational Analysis of Scapholunate Interosseous Ligament Injury.

Purpose: The scapholunate ligament, linking the scaphoid and lunate bones, is crucial for wrist stability and motion. An injury to this ligament disrupts wrist biomechanics, leading to compromised functionality and a higher risk of osteoarthritis. Methods: Eight wrist specimens were used on a custom rig to study the effects of scapholunate ligament injury. The rig stabilized the hand while allowing controlled finger flexion. Sensors measured contact pressure, and motion sensors tracked scaphoid and lunate movements. Forces simulated finger flexion, and a finite element analysis model replicated wrist kinematics and pressure distribution. Results: Scaphoid and lunate movement significantly varied with ligament condition, showing increased scapholunate distance in distal-proximal directions and decreased in medial-lateral directions for full tears. Lunate angles shifted from flexion to extension with fully torn ligaments, whereas the scaphoid shifted from extension to flexion. Proximal movement was noted for all groups, with significant differences in the partial tear group. A significant lateral deviation of the scaphoid and lunate was found when the ligament was damaged.An increase in radioscaphoid contact area was noted in the presence of a ligament tear; however, statistical significance was not established. Conversely, only finger pressure exhibited a statistically significant decrease in the presence of an scapholunate ligament tear.The findings, confirmed by finite element analysis and experiments, accurately replicated scaphoid and lunate movements, with peak radiocarpal pressure significantly differing between intact and fully torn ligaments. Conclusions: Scapholunate ligament damage alters wrist stability, affecting bone movement and angles, leading to radial deviation and proximal displacement of the scaphoid and lunate bones. Clinical relevance: Chronic untreated conditions may lead to early arthritis. Experimental results, validated through finite element analysis, suggest potential utility in clinical decision-making and treatment selection.