Exploring the impact of systemic n-acetyl cysteine administration on capsular fibrosis and locomotor activity in a rat model of frozen shoulder induced by immobilization

Objective: This study aims to observe the prophylactic antifibrotic effects of N-acetylcysteine (NAC) by comparing joint range of motion (ROM) and upper extremity activities between subjects administered NAC and those not administered NAC during immobilization in a rat frozen shoulder model. Methods: Shoulder immobilization was performed under general anesthesia using internal scapulohumeral fixation on 28 twelve-week-old Sprague-Dawley rats. Subjects were randomized into two groups: Group1(n=14) received 1200mg/kg/day of NAC orally during the 8-week immobilization period, and Group2(n=14) did not. After 8 weeks, remobilization was performed. Upper extremity activity and shoulder abduction/flexion ROM were measured before immobilization and after remobilization. Activity was evaluated using Montoya's staircase test. ROM was determined by calculating the difference in scapulohumeral angles in radiographic imaging conducted in the anterior-posterior/lateral plane without and with applied standard force. Results: Before immobilization, there was no significant difference in sagittal/coronal plane ROM and activity measurements between the two groups(p>0.05). Post-remobilization measurements showed a significant decrease in abduction/flexion ROM and upper extremity activity compared to pre-immobilization in both groups(p<0.05). Post-remobilization flexion ROM showed a significant difference between the groups(p<0.05), while abduction ROM did not(p>0.05,p=0.051). There was no significant difference in the upper extremity activity test between the groups post-remobilization(p>0.05). The losses in upper extremity activity and abduction/flexion ROM due to immobilization did not show significant differences between the groups(p>0.05). Conclusion: The group receiving NAC prophylaxis was affected less. NAC is beneficial in preventing frozen shoulder due to its antifibrotic effects, indicating a potential role for oxidant-antioxidant mechanisms in frozen shoulder.