RASL Procedure

Abstract

Scapholunate instability, caused by injury to the scapholunate interosseous ligament, typically occurs after a fall onto an extended wrist. The combination of axial load, wrist extension, intercarpal supination, and ulnar deviation leads to supraphysiologic loads across the SLIL. Motions of the scaphoid and lunate are linked, such that both bones flex with wrist flexion and radial deviation and extend with wrist extension and ulnar deviation. When disruption of the SLIL occurs, this relative motion between the scaphoid and lunate is no longer linked, causing the scaphoid to flex while the lunate extends. This can lead to pain, weakness, limitation of wrist motion, and progressive arthritis. Static DISI prior to the onset of osteoarthritis at the capitolunate joint can be corrected with the motion-sparing reduction and association of the scaphoid and lunate (RASL) procedure. Common indications include chronic static DISI deformity, without osteoarthritic involvement of the capitolunate joint. Radiographic evaluation is a useful tool in detecting the presence of SLIL injury. Physical examinations typically reveal tenderness dorsally, localizing to the scapholunate ligament. The RASL procedure is an effective approach to correct for static scapholunate instability without midcarpal arthritis and has been supported by long-term follow-up clinical studies.