Validation of the spontaneous lateral laxity sign for radial collateral ligament sprain of the metacarpophalangeal joint of the fingers: Anatomical study.

Severe collateral ligament sprain of the metacarpophalangeal joint (MCP) of the fingers is rare. Clinical examination is mandatory to diagnose severity. The purpose of our study was to validate a clinical sign for MCP joint laxity: the spontaneous lateral laxity sign (SLLS), recently described by Meyer et al. to diagnose severe MCP radial collateral ligament (RCL) sprain, with a comparison with the already validated rotational laxity test (RLT). SLLS and RLT were assessed before RCL transection, after RCL transection and after RCL repair on 40 long fingers in 10 fresh thawed cadavers. SLLS was performed with the elbow on the table, wrist in 70° flexion, in neutral pronation-supination, hands drooping passively with the dorsal side toward the examiner and the ulnar side toward the table. The MCP joints were at rest, in passive slight extension. Positive results were defined as an overlap of the damaged finger on the next, or as an increased abduction of the little finger. Correlation between the two tests was calculated. SLLS was positive in 0% of cases before RCL transection, 100% after transection and 0% after repair. Mean arcs of pronation and supination on RLT were 16 and 19.5 mm before section, 24 and 33 mm after section (52% and 69% increase compared to preoperative data), and 17 and 21 mm after repair (7% and 8% increase). Correlation between the two tests was 100%. The spontaneous lateral laxity sign is a simple and reliable clinical sign for diagnosing complete long-finger MCP RCL tears requiring surgery. LEVEL OF EVIDENCE: : III, case-control study.