Impaired dynamic balance and its association with shoulder external rotation in patients with frozen shoulder: a cross-sectional study

Frozen shoulder (FS) causes shoulder pain and limited range of motion, leading to functional deficits such as impaired balance, but the factors associated with balance in FS and differences from healthy individuals remain unclear. This study aimed to compare balance performance between FS patients and healthy controls and identify variables associated with balance using regression analysis. This cross-sectional study included 154 individuals aged 40–65, with 78 patients diagnosed with FS and 76 healthy controls. The static and dynamic balance of all participants was assessed using the Biodex Balance System. In the FS group, scapular dysfunction was assessed using the Lateral Scapular Slide Test, trunk control was evaluated using the Functional Reach Test, pain intensity was measured using the Visual Analogue Scale, pain duration and shoulder range of motion were also recorded. Independent Samples T-Tests were conducted to compare the groups, while Pearson Correlation and Simple Linear Regression Analyses were performed to identify factors associated with balance performance. Dynamic balance was significantly impaired in individuals with FS compared to healthy controls (Dynamic Overall Stability Index [DOSI]: 3.44 ± 1.42 vs. 1.54 ± 1.08, MD 1.90 [95% CI: 1.51–2.30]; Dynamic Antero-Posterior Stability Index [DAPSI]: 3.29 ± 1.28 vs. 1.60 ± 1.10, MD 1.69 [95% CI: 1.30–2.07]; Dynamic Medio-Lateral Stability Index [DMLSI]: 3.18 ± 1.07 vs. 1.61 ± 1.03, MD 1.57 [95% CI: 1.23–1.90]; all p < 0.001). Regression analysis showed that external rotation angle (ERA) was a significant predictor negatively associated with DOSI (B= -0.046, 95% CI: − 0.081 to − 0.011, β= -0.290, p = 0.010), accounting for 8.4% of the variance observed. Dynamic balance is impaired in patients with FS compared to healthy controls, and shoulder ERA is a significant variable associated with DOSI.