No relationship between critical shoulder angle and glenoid erosion after shoulder hemiarthroplasty: a comparative radiographic study

Introduction: Symptomatic glenoid erosion is one of the most common causes of functional impairment after shoulder hemiarthroplasty. A decrease in the critical shoulder angle (CSA) has been associated with the development of shoulder arthritis. The inter-observer reliability of the CSA and the relationship between CSA and symptomatic glenoid erosion after shoulder hemiarthroplasty were investigated. Materials and methods: Twenty-eight patients with symptomatic glenoid erosion after anatomic hemiarthroplasty were compared to a control group of 30 patients with no signs of symptomatic glenoid erosion. The CSA was measured by two blinded shoulder surgeons at a mean follow-up of 105.2 and 54.7 months, respectively. The inter-observer reliability was calculated. Results: The mean CSA in the control group in neutral, internal, and external rotations was 34°, 33°, and 33°, respectively. The corresponding values in the study group were 33°, 33°, and 33° (<0.01). The interclass correlation coefficient between the two examiners was 0.917 (P < 0.01), 0.924 (P < 0.01), and 0.948 (P < 0.01), respectively. The Mann–Whitney test between the control group and the study group were, respectively, 0.907, 0.932, and 0.602. Conclusion: There were no significant differences of CSA values between the two groups. Good inter-observer reliability was found for the CSA method.