Left and Non-Dominant Shoulders Were More Frequently Affected in Patients with Frozen Shoulder: A Systematic Review and Meta-Analysis

Abstract

Background: If trauma has a considerable impact on frozen shoulder, the right or dominant shoulder is more frequently affected than the left or non-dominant shoulder. Herein it is examined whether the right or dominant shoulder was more frequently affected in patients with frozen shoulder using PubMed. Materials and methods: PubMed was searched to retrieve relevant studies. The search term used was frozen shoulder. The studies obtained were published between 1966 and 2007, and included 10 or more patients with only one affected side. Patients with bilateral shoulder involvement were excluded. Results: The right shoulder was affected in 718 patients (46.3%), while the left shoulder was affected in 833 (53.7%). The dominant shoulder was affected in 298 patients (41.1%), while the non-dominant shoulder was affected in 427 (58.9%). The left shoulder was affected significantly more than the right shoulder (p<0.01). The non-dominant shoulder was affected significantly more than the dominant shoulder (p<0.01). Conclusion: Trauma including repeated minor trauma is less likely to cause frozen shoulder, or the influence of brain abnormalities is stronger than that of trauma. The left shoulder may have been more frequently affected because of the side-to-side asymmetry of the brain for various reasons. If this hypothesis is correct, brain abnormalities may be one cause of frozen shoulder, suggesting that central neuropathic pain or braingenic pain contributes to the pain associated with frozen shoulder. The right and dominant shoulders were less frequently affected in patients with frozen shoulder.