Do therapeutic exercises impact supraspinatus tendon thickness? Secondary analyses of the combined dataset from two randomised controlled trials in patients with rotator cuff-related shoulder pain

Background The mechanistic response of rotator cuff tendons to exercises within the context of rotator cuff-related shoulder pain (RCRSP) remains a significant gap in current research. A greater understanding of this response can shed light on why individuals exhibit varying responses to exercise interventions. It can also provide information on the influence of certain types of exercise on tendons. The primary aim of this article is to explore if changes in supraspinatus tendon thickness (SSTT) ratio differ between exercise interventions (high load vs. low load). The secondary aims are to explore if changes in SSTT ratio differ between ultrasonographic tendinopathy subgroups (reactive vs. degenerative) and if there are associations between tendinopathy subgroups, changes in tendon thickness ratio, and clinical outcomes (disability). Methods This study comprises secondary analyses of the combined dataset from two randomized controlled trials that compared high and low-load exercises in patients with RCRSP. In those trials, different exercise interventions were compared: 1) progressive high-load strengthening exercises, and 2) low-load strengthening with or without motor control exercises. In one trial, there was also a third group that was not allocated to exercises (education only). Ultrasound-assessed SSTT ratio, derived from comparing symptomatic and asymptomatic sides, served as the primary measure in categorizing participants into tendinopathy subgroups (reactive, normal and degenerative) at baseline. Results Data from 159 participants were analyzed. Two-way repeated measures ANOVAs revealed significant Group (p<0.001) and Group X Time interaction (p<0.001) effects for the SSTT ratio in different tendinopathy subgroups, but no Time effect (p=0.63). Following the interventions, SSTT ratio increased in the "Degenerative" subgroup (0.14 [95% CI: 0.09 to 0.19]), decreased in the "Reactive" subgroup (-0.11 [95% CI: -0.16 to -0.06]), and remained unchanged in the "Normal" subgroup (-0.01 [95% CI: -0.04 to 0.02]). There was no Time (p=0.21), Group (p=0.61), or Group X Time interaction (p=0.66) effect for the SSTT ratio based on intervention allocation. Results of the linear regression did not highlight any significant association between the tendinopathy subgroup (p=0.25) or change in SSTT ratio (p=0.40) and change in disability score. Conclusion Findings from this study suggest that, over time, SSTT in individuals with RCRSP tends to normalize, compared to the contralateral side, regardless of the exercise intervention. Different subgroups of symptomatic tendons behave differently, emphasizing the need to potentially consider tendinopathy subtypes in RCRSP research. Future adequately powered studies should investigate how those different tendinopathy subgroups may predict long-term clinical outcomes.