Association between functional scores, radiological parameters, and muscle strength in shoulders with asymptomatic or...

Differences in function and morphology between shoulders with symptomatic and asymptomatic rotator cuff tears are poorly understood. This study aimed to compare functional scores, radiological parameters, muscle strength and their association in shoulders with rotator cuff disorders and healthy shoulders. We hypothesized that symptomatic shoulders would have lowest functional scores, muscle strength, and subacromial space and highest critical shoulder angles and fat fraction.

Twenty-five older patients with unilateral symptomatic rotator cuff tears (45-85 years), 25 older control subjects (45-85 years), and 25 younger control subjects (20-30 years) were enrolled. Functional scores, critical shoulder angle, subacromial space, muscle volume, and fat fraction of the rotator cuff muscles, as well as isometric muscle strength measurements were assessed for both shoulders of all participants. Differences in these parameters between groups defined by magnetic resonance imaging diagnosis were analyzed using univariate analysis of variance with post-hoc tests (Bonferroni). Pearson's cross-correlations between these parameters were performed.

The final analyses included 43 healthy shoulders, 24 shoulders with rotator cuff tendinopathy, 38 shoulders with asymptomatic rotator cuff tears, and 25 shoulders with symptomatic rotator cuff tears. Twenty shoulders were excluded because of magnetic resonance imaging findings not related to the rotator cuff. Lowest functional scores were found in symptomatic rotator cuff tears (P < .001). No significant differences in the critical shoulder angle or the subacromial space (P > .05) were observed between shoulder types. Symptomatic rotator cuff tears had 2%-8% higher fat fractions than healthy shoulders in all rotator cuff muscles (P ≤ .021), and 3% higher fat fractions than asymptomatic rotator cuff tears in the supraspinatus muscle (P = .018). Muscle strength of symptomatic rotator cuff tears was half that of healthy shoulders (P < .001). Asymptomatic rotator cuff tears were 38% stronger in external rotation than symptomatic rotator cuff tears (P = .011) and between 18% and 30% weaker in abduction and external and internal rotation than healthy shoulders (P ≤ .014). Functional scores moderately correlated with muscle strength (0.21 ≤ R ≤ 0.68) and fat fraction (-0.69 ≤ R ≤ -0.21), and muscle strength correlated with fat fraction (-0.66 ≤ R ≤ -0.51). Only very few and low correlations were found between functional scores and anatomical parameters (-0.20 ≤ R ≤ 0.37).

Functional scores appeared to reflect muscle morphology and strength but not anatomical variations. Fat fraction of the supraspinatus muscle may be able to discriminate symptomatic from asymptomatic shoulders. Considering quantitative 3-dimensional fat fraction and dynamometric muscle strength measurements in abduction and rotation in the clinical evaluation of rotator cuff disorders may benefit treatment decisions.