Abstract
IMPORTANCE: Understanding how tendon structure relates to disability improvement during exercise interventions in rotator cuff tendinopathy is essential for optimizing individualized treatment strategies. OBJECTIVE: The objectives of this study were to characterize changes in supraspinatus tendon thickness and internal architecture over an 8-week resistive exercise intervention and evaluate the relationship between these changes and patient-reported shoulder disability. DESIGN: This was a prospective longitudinal observational study. SETTING: The settings were a university-based research laboratory and virtual supervision in participants' homes. PARTICIPANTS: Forty-seven adults with unilateral rotator cuff tendinopathy were the study participants. INTERVENTION: The intervention was an 8-week progressive resistive exercise program, supervised twice weekly by a physical therapist. MAIN OUTCOMES AND MEASURES: Primary outcomes were the Pennsylvania Shoulder Score, supraspinatus tendon thickness, and internal tendon architecture assessed using the peak spatial frequency radius via ultrasound. Measurements were taken at baseline and at 2, 4, and 8 weeks. Linear mixed-effects models were used to assess changes and associations. RESULTS: Significant improvements from baseline were observed for the Pennsylvania Shoulder Score at 2, 4, and 8 weeks. Tendon thickness decreased significantly; changes in internal tendon architecture were not significant. A decrease in tendon thickness was associated with an improved Pennsylvania Shoulder Score at 2 weeks but not at 4 and 8 weeks. CONCLUSIONS: Reductions in tendon thickness were associated with improved shoulder outcomes within the first 2 weeks of the intervention. Internal tendon architecture remained unchanged over the intervention. These findings suggest that tendon variables included in this study may be relevant only early in the intervention and that other factors should be investigated across different times of the intervention.