Maine Medical Center, Medical Education, Maine Medical Center Research Institute, Orthipedics
Rotator Cuff Injuries, Rotator Cuff, Cross-Sectional Studies, Pain
Purpose/Background: Rotator cuff weakness is a common finding in patients with shoulder pain. Weakness may be a result of aging, neuropathy, full-thickness rotator cuff tearing, decreased voluntary activation due to inhibition, or muscle atrophy. Rotator cuff atrophy is not uncommon in the presence of a rotator cuff tear but can also be seen in aging populations and overhead athletes with intact rotator cuffs. The primary aim of this study was to compare the cross-sectional area (CSA) of the supraspinatus (SS) and infraspinatus (IS) muscles and SS tendon thickness between painful and non-painful shoulders. Secondarily, we aimed to determine if there was a difference in SS and IS CSA between dominant and non-dominant shoulders. Lastly, we explored the relationship of SS and IS CSA to rotator cuff endurance and isometric strength. We hypothesized that there would be a significant difference in the CSA between dominant and non-dominant shoulders and between painful and non-painful shoulders. Furthermore, we believed that age and weight would covary with muscle CSA. We also hypothesized that there would be a significant difference in muscle CSA, strength and endurance in painful and non-painful shoulders based on chronicity of pain; however, we did not believe we would discover a difference in endurance and strength between non-painful dominant and non-dominant shoulders
Methods/Appriach: This was a cross-sectional study. Demographic information, the PENN shoulder score and the modified Constant score were collected at the time of testing. 24 subjects were recruited for this study: Twelve right hand dominant subjects with unilateral, right shoulder pain were recruited into the shoulder pain group. Subjects were excluded if they were found to have a full-thickness rotator cuff tear. Twelve healthy controls matched by gender, age, height and weight were recruited into the non-painful control group. All subjects underwent a diagnostic ultrasound evaluation of bilateral shoulders to determine the CSA of the SS and IS muscles, and tendon thickness. Additionally, shoulder endurance and isometric strength were evaluated with hand-held dynamometry and the posterior shoulder endurance test (PSET).
Results: Independent sample t-tests found no significant differences in age, height or weight between groups (p<0.05). 2x2 mixed-model analyses of variance (ANOVA) found no significant differences in SS and IS CSA and SS tendon thickness between painful and non-painful shoulders, and between dominant and non-dominant shoulders in all subjects (p>0.05). However, there were significant differences shoulder strength and endurance between painful shoulders and non-painful shoulders in the painful group and the painful shoulder in the shoulder pain group and the dominant and non-dominant shoulders in the control group (p<0.05).
Conclusions: This study showed that there is no significant difference in SS and IS CSA and SS tendon thickness between subjects with moderate shoulder pain and disability and non-painful shoulders. Additionally, differences between dominant and non-dominant shoulders were not found. The results of this study suggest that rotator cuff weakness in subjects with moderate shoulder pain and intact rotator cuffs is not due to decreased rotator cuff CSA.
Kokmeyer, Dirk; Thein-Brody, Lori; Koppenhaver, Shane; and Thigpen, Charles, "The Influence of Pain on Rotator Cuff CrossSectional Area" (2020). Costas T. Lambrew Research Retreat 2020. 84.