Predominance of the critical shoulder angle in the pathogenesis of degenerative diseases of the shoulder

HYPOTHESIS: The critical shoulder angle (CSA) could be responsible for cuff tears and concentric osteoarthritis. We aimed to assess this association when potential confounding factors were excluded and to test the hypothesis that more extreme CSAs are associated with larger tears and more severe osteoarthritis. METHODS: The study cohort was composed of 200 patients with primary concentric osteoarthritis (40 patients), isolated supraspinatus tears (40 patients), cuff tears involving at least the supraspinatus and infraspinatus (40 patients), and no history of shoulder problems (control group, 80 patients). Data pertaining to CSA, age, gender, dominant arm, smoking, hypertension, body mass index, and type of work were collected. RESULTS: The average CSA angle was 34° ± 3° in the control group, 36° ± 3° with supraspinatus tears, 40° ± 3.5° with supraspinatus and infraspinatus tears, and 28° ± 2° with concentric osteoarthritis. Patients with large cuff tears had a significantly greater CSA compared with those with isolated supraspinatus tears (P = .03). The CSA (odds, 1.7; confidence interval [CI], 1.4-2.0) was the most relevant risk factor for cuff tears. The Spearman coefficient between CSA and grade of eccentric osteoarthritis was 0.4 (P = .01). The 2 significant risk factors for concentric osteoarthritis were the CSA (odds, 0.5; CI 0.4-0.6) and age (odds, 1.1; CI, 1.0-1.2). CONCLUSION: Larger CSAs are associated with increased risk of symptomatic cuff tears, larger cuff tears, and the severity of eccentric osteoarthritis. Smaller angles increased the risk and severity of concentric symptomatic osteoarthritis. These associations remained significant even after removal of some of the potentially confounding variables.