Increased supraspinatus thickness with reduced acromohumeral distance in people with mild and moderate rotator cuff tendinopathy: A reliability and comparative study.

Background Subacromial impingement syndrome has historically been ascribed to extrinsic compression of the supraspinatus tendon (SsT) due to altered acromial morphology. More recently intrinsic tendon pathology has been proposed as an important mechanism, leading to degenerative changes in the tendon, superior translation of the humeral head occurs due to rotator cuff (RC) failure and subsequent narrowing of the subacromial space, measured as the acromiohumeral distance (AHD). The continuum model of RC pathology proposes that people in the reactive or disrepair stage may have a swollen SsT, which further compromises the subacromial space (Lewis 2010). Objectives The aims of this study were to (i) examine the intra and inter-rater reliability of ultrasound measurements of AHD and SsT thickness in healthy controls, and people with RC tendinopathy (RCT) of varying degrees. (ii) to compare AHD and SsT thickness between shoulders in controls and in people with unilateral RCT Methods A total of 25 healthy controls (mean age=50), 21 swimmers with mild unilateral RCT (mean age=53) and 21 patients with moderate-severe unilateral RCT (mean age=61) were recruited. Repeated ultrasound measurements of AHD and SsT thickness were obtained in a single session, with the shoulder in a neutral position, by one experienced rater in the controls and mild RCT group, and by two raters in the third group. Results Intra-rater reliability for AHD and SsT thickness measurement was excellent, with all intra-class correlation (ICC) values >0.9, and small standard error of measurement (SEM) values (0.1-0.4mm). Inter-rater reliability for AHD and SsT thickness measurement was also excellent for the mod-severe RCT group, with ICC values >0.9, and small SEM values (0.3-0.5mm). There was no difference between shoulders for AHD or SST thickness measures for the control group (p>0.05). There was a significantly smaller AHD in the painful shoulder for both the mild (p=0.014), and mod-severe RCT groups (p=0.009). There was also a significantly larger SsT thickness in both the mild (p=0.001), and mod-severe RCT groups in the painful shoulder (p=0.009). Conclusions The results support the reliability of ultrasound for the measurement of AHD and SsT thickness in RCT. People with RCT in this study had significantly smaller AHD and larger SsT thickness in their painful shoulder compared to non-painful side. While the finding of reduced AHD in people with RCT supports the work of other studies, the concurrent increase in SsT thickness in the painful shoulders is an important additional finding which may further compromise the subacromial space. The results of this study provide support for the continuum model of rotator cuff tendon pathology.