Influence of Frequent Corticosteroid Local Injections on the Expression of Genes and Proteins Related to Fatty Infiltration, Muscle Atrophy, Inflammation, and Fibrosis in Patients With Chronic Rotator Cuff Tears: A Pilot Study.

Background:The effect of local corticosteroid (CS) injections on rotator cuff muscles remains poorly defined, despite the significance of muscle quality as a crucial prognostic factor for patients with rotator cuff tears (RCTs). Purpose:To compare alterations in gene and protein expression patterns in the rotator cuff muscles of patients with RCTs who received frequent joint CS injections with alterations in those without a history of CS injections. Study Design:Controlled laboratory study. Methods:A total of 24 rotator cuff muscle samples with medium-sized tears from 12 patients with a frequent joint CS injection history (steroid group; 7 men and 5 women who had received ≥5 injections with at least 1 within the previous 3 months; mean age, 63.0 ± 7.2 years) and 12 age- and sex-matched control patients without a history of CS injections (no-steroid group) were acquired. Alterations in the expression of genes and proteins associated with adipogenesis, myogenesis, inflammation, and muscle fibrosis were compared between the groups using quantitative reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemistry. Statistical analysis included comparison of group means using the Mann-Whitney U test, chi-square test, or Fisher exact test and logistic regression for multivariate analysis. Results:In the steroid group, the mRNA expression levels of adipogenic CCAAT/enhancer-binding protein alpha (C/EBPα; P = .008) and muscle atrophy-related genes (atrogin; P = .019) were significantly higher, and those of myogenic differentiation 1 (MyoD; P = .035), inflammatory interleukin 6 (IL-6; P = .035), and high mobility group box 1 (P = .003) were significantly lower compared with the no-steroid group. In addition, MyoD (P = .041) and IL-6 (P = .026) expression were decreased in the steroid versus no-steroid group. Immunohistochemistry revealed increased expression of C/EBPα and atrogin and decreased expression of MyoD and IL-6 in the steroid versus no-steroid group. Conclusion:Patients with RCTs and a history of frequent CS injections exhibited an upregulation of adipogenic and muscle atrophy-related genes and proteins within the rotator cuff muscles and a downregulation in the expression of myogenic and inflammatory genes and proteins in the same muscles. Clinical Relevance:These altered gene and protein expressions by frequent local CS injections may cause poor outcomes in patients with RCTs.