Relationship of Serum Relaxin to Generalized and Trapezial-Metacarpal Joint Laxity

Purpose The reproductive hormone relaxin acts to loosen pelvic ligaments in preparation for childbirth and is thought to be a mediator of joint laxity. The purpose of this study was to evaluate the correlation of serum relaxin with radiographic laxity at the trapezial-metacarpal joint and with generalized joint laxity. Methods We enrolled 289 healthy subjects prospectively. Participants completed a demographic questionnaire and were examined for generalized joint hypermobility using the Beighton-Horan scale. Stress radiographs of the trapezial-metacarpal joint were obtained in 163 subjects (56%). Blood samples were collected, and serum relaxin was measured for 287 subjects using enzyme-linked immunosorbent assay for human relaxin-2. Results The mean serum relaxin level among all subjects was 1.84 pg/mL (range, 0-45.25 pg/mL). Relaxin was not detectable in 166 of 287 samples, whereas the mean serum relaxin level among the 121 subjects with a detectable relaxin level (of 287 total relaxin samples) was 4.37 pg/mL (range, 0.46-45.25 pg/mL). Mean trapezial-metacarpal subluxation ratio scores were higher among those with a detectable relaxin level compared to those without a detectable relaxin level (0.34 vs 0.30 pg/mL). The average Beighton-Horan laxity score was 1.8 (range, 0-9). There was no correlation between generalized joint laxity measures and serum relaxin levels. Conclusions In a large volunteer population, we demonstrated a relationship between circulating relaxin and trapezial-metacarpal joint laxity. However, we were unable to show a direct link between serum relaxin and generalized joint laxity. (J Hand Surg 2013,38A:721-728. Published by Elsevier Inc. on behalf of the American Society for Surgery of the Hand.)