Relationships Between Capsular Stiffness and Clinical Features in Adhesive Capsulitis of the Shoulder

Background: Tightening and contracture of the joint capsule are hallmarks of adhesive capsulitis of the shoulder (ACS). However, quantification of capsular stiffness and its relation to clinical features have not been investigated thoroughly. Objectives: To quantify capsular stiffness during intra-articular hydraulic distension (IHD) and to investigate its relationships with pain severity, symptom duration, range of motion (ROM), gender, and diabetes status. Design: Case series. Setting: University outpatient clinic of physical medicine and rehabilitation. Participants: A total of 107 consecutive patients with ACS who underwent IHD. Methods: Pressure-volume monitoring data during IHD, pain severity, symptom duration, shoulder ROM, and diabetes status were obtained by retrospective chart review. Capsular stiffness (K-cap) was measured by calculating the slope of the elastic phase in pressure-volume curves. ROM was evaluated in 3 directions (flexion, abduction, and external rotation) with a goniometer, and the sum of the 3 ROMs was calculated. Main Outcome Measurements: Pearson correlation coefficients and comparisons of averages were used to analyze the relationships between Kcap and clinical features. Results: The mean Kcap of the total group of participants was 26.0 +/- 14.2 mmHg/mL. Shoulder pain in motion or rest did not correlate with Kcap. Patients with stiffer capsules had smaller sums of ROMs (r = -.298, P = .002), with distinct limitations in external rotation and abduction (r = -.278, P = .004 and r = -.313, P = .001, respectively). Women had significantly stiffer capsules than men (29.5 +/- 14.3 versus 20.2 +/- 12.1 mmHg/mL, P = .001). Diabetes status had no significant effect on capsular stiffness. Conclusions: Capsular stiffness of the glenohumeral joint significantly correlated with limitation in shoulder ROM, especially in the abduction and external rotation directions, whereas there were no meaningful relationships with shoulder pain during motion or rest. This is the first study to reveal the relationships between in vivo quantified capsular stiffness and shoulder ROM limitations.