Volumetric definition of shoulder range of motion and its correlation with clinical signs of shoulder hyperlaxity. A motion capture study.

Background: Shoulder hyperlaxity (SHL) is assessed with clinical signs. Quantification of SHL remains difficult, however, because no quantitative definition has yet been described. With use of a motion capture system (MCS), the aim of this study was to categorize SHL through a volumetric MCS-based definition and to compare this volume with clinical signs used for SHL diagnosis.

Method: Twenty-three subjects were examined with passive and active measurement of their shoulder range of motion (SROM) and then with an MCS protocol, allowing computation of the shoulder configuration space volume (SCSV). Clinical data of SHL were assessed by the sulcus sign, external rotation with the arm at the side (ER1) >85° in a standing position, external rotation >90° in a lying position, and Beighton score for general joint laxity. Active and passive ER1, EIR2 (sum of external and internal rotation at 90° of abduction), flexion-extension, and abduction were also measured and correlated to SCSV.

Results: Except for the sulcus sign, SCSV was significantly correlated with all clinical signs used for SHL. Passive examination of the different SROMs was better correlated to SCSV than active examination. In passive examination, the worst SROM was ER1 (R = 0.36; P = .09), whereas EIR2, flexion, and abduction were highly correlated to SCSV (P < .01).

Conclusion: SCSV appears to be an appealing tool for evaluation of SHL regarding its correlation with clinical signs used for SHL diagnosis. The sulcus sign and ER1 >85° in a standing position appear less discriminating and should be replaced by EIR2 measurement for SHL diagnosis.