Abstract
BACKGROUND: Frozen shoulder after COVID-19 vaccination is sparsely discussed in the medical literature. We aimed to evaluate: (1) the differences in the baseline clinical features and functional outcomes of conservatively treated frozen shoulder following COVID-19 vaccination compared to idiopathic frozen shoulder (2) the improvements in pain scores, functional outcomes, and range of motion (ROM) at 6-10 months and at 1 year of follow-up in patients with frozen shoulder after COVID-19 vaccination treated by conservative therapy. METHODS: Between June 2021 and December 2021, 12 patients (13 shoulders) that were diagnosed with frozen shoulder after COVID-19 vaccination (vaccine related frozen shoulder [VRF] group) (final follow-up of 12.4 months ± 0.8 months) were compared with 20 patients that were diagnosed as idiopathic frozen shoulder unrelated to vaccination (unvaccinated frozen shoulder [UFS] group) (average follow-up of 13.4 ± 3.1 months). All patients were treated with home-based stretching exercises. Four (33%) patients in the VRF group and 15 (75%) patients in the UFS group underwent steroid injection in the suprascapular notch by an experienced radiologist. RESULTS: The left side was affected more frequently in the VRF group [n = 10 (83.3%)] than in the UFS group [n = 8 (40%), P = .03]. The VRF and the UFS groups were similar in the rest of the baseline clinical features, such as the age distribution, men/women ratio, baseline Oxford Shoulder Scores (OSS), ROM deficit, and pain visual analogue scale (VAS) scores. The OSS, VAS pain scores, and the ROM deficit significantly improved in the VRF group at the 6-10-month follow-up and then at the final (12.4 ± 0.8 months) follow-up compared to the baseline values. At the final follow-up, there were no significant differences in the average external rotation, external rotation deficit, elevation, elevation deficit, internal rotation, pain VAS scores, and OSS between the VRF and the UFS group. CONCLUSION: To conclude, frozen shoulder following COVID-19 vaccination may present with clinical features similar to those of the idiopathic frozen shoulder. Furthermore, the patients with frozen shoulder following COVID-19 vaccination may continue to improve over one year with conservative treatment; the final improvements in function and ROM are similar to those with idiopathic frozen shoulder.