SLAC WRIST IN THE ABSENCE OF TRAUMA AND CPPD: A PROSPECTIVE BLINDED KINEMATIC COMPARATIVE ANALYSIS

Abstract

The traditionally accepted etiology of Scapholunate Advanced Collapse (SLAC) requires traumatic rupture of the scapholunate (SL) ligament which leads to abnormal wrist kinematics and thereafter severe localised degenerative arthritis of the wrist. The purpose of this prospective blinded kinematic analysis was to demonstrate that SLAC wrist also exists in the absence of trauma, and that abnormal carpal bone kinematics (specifically, decreased lunate flexion) is the initiating factor.

Patients with SLAC and no history of upper extremity trauma were compared with an age matched control group. All patients completed a questionnaire, personal interview, and a physical examination. A specialised flexion / extension radiographic jig was designed to control for the magnitude of force and position of the wrist in all planes.

A total of thirty-five subjects (sixty-nine wrists) were retained for the study, including thirty-three non-traumatic SLAC wrists and thirty-six control wrists. The non-traumatic SLAC group had significantly different radiographic kinematic analysis compared to the control group: increased Watson Stage (2 v 0), SL gap (3.4 v 1.8mm), revised carpal height ratio (rCHR) (77 v 68), SL angle in flexion (forty-one v twenty-eight degrees), and decreased radiolunate (RL) joint flexion (nine v twenty-seven degrees). Most importantly 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). Non-traumatic or developmental SLAC does exist. SLAC can thus be classified into non-traumatic (developmental) and traumatic types.

Non-traumatic SLAC begins with abnormal wrist kinematics. Over time restricted lunate flexion and normal scaphoid flexion leads to increased SL angles and eventual attrition of the SL ligament and predisposes patients to SLAC despite having no history of trauma.