Instrumented measurement of glenohumeral joint laxity reliability and normative data

This study assessed shoulder laxity using an instrumented arthrometer. We c ompared anterior and posterior translations at various force levels to dete rmine the reliability of our measurement technique and to provide normative data in healthy shoulders. Fifty shoulders were assessed for glenohumeral joint laxity in two directions (anterior and posterior) and at four force l evels (67, 89, 111, and 134 N). The dependent measure was joint displacemen t. Laxity values were widely, yet normally, distributed in our group of hea lthy shoulders. Intraclass correlation coefficients revealed excellent betw een-trial reliability (0.92) and fair between-session (0.73) and between-ex aminer (0.74) reliability. The average standard error of measurement betwee n trials (0.56 mm), sessions (1.5 mm), and examiners (1.7 mm) demonstrated an unprecedentedly high degree of precision for quantifying glenohumeral jo int laxity. Paired t tests revealed no significant laxity differences betwe en sides (P>0.05), indicating bilateral symmetry. A 2(direction) x 4 (force ) analysis of variance revealed significant differences in laxity between d irections (P<0.0001) and force levels (P<0.0001). Our results show that our instrumented technique for quantifying glenohumeral joint laxity is precis e and reproducible. Posterior translation was significantly greater than an terior, and a significant increase in translation was observed between incr easing levels of force.