This comparative cohort study was designed to determine whether non-traumatic SLAC wrist exists, and is associated with abnormal carpal bone kinematics (specifically, decreased lunate flexion).
SLAC patients with no recognised history of upper extremity trauma were prospectively compared with an age-matched control group.
Thirty-five subjects (69 wrists), included 33 non-traumatic SLAC wrists and 36 control wrists. The non-traumatic SLAC group had significantly different radiographic kinematic analysis compared to the control group. Flexion of the asymptomatic non-degenerative wrist of the non-traumatic SLAC group was distributed 70% through the lunocapitate (LC) joint and only 30% through the RL joint (p < 0.05). Conversely, flexion was more evenly distributed in the control group (48% LC and 52% RL). The non-traumatic SLAC group had abnormal wrist kinematics even in the non-involved side.
This study suggests that non-traumatic SLAC does exist. We believe that non-traumatic SLAC begins with abnormal wrist kinematics and that the dorsal radiolunate ligament restricts lunate flexion but not scaphoid flexion, leading to increased SL angles and, with years, eventual attrition of the SL ligament.