Background:Frozen shoulder is a common, painful, and movement-restricting condition. Although primary frozen shoulder is idiopathic, secondary frozen shoulder can occur after trauma or surgery. Prophylactic and therapeutic options are often unsatisfactory. Vitamin C (ascorbic acid) is a potent physiological antioxidant and likely inhibits the activation of nuclear factor κB, which plays a decisive role in inflammatory reactions.Hypothesis:Because of its anti-inflammatory effects, vitamin C may be valuable in the prevention of secondary frozen shoulder.Study Design:Controlled laboratory study.Methods:An in vivo shoulder contracture model was conducted by fixation of the right proximal limb of Sprague-Dawley rats. A treatment group (n = 8) receiving vitamin C orally was compared with a control group (n = 9) without vitamin C. The primary outcome was capsular thickness at the shoulder joint measured on magnetic resonance imaging (MRI) examination. Further histological examination was performed but was not statistically analyzed because of variability of the cutting plane through the glenoid.Results:Vitamin C treatment resulted in less thickening of the axillary fold of the operated shoulder at 2 of the 3 locations measured on MRI compared with untreated controls (insertion to the glenoid,P= .074; insertion to the humerus,P= .006; middle of the axillary recess,P= .008). The observed structural changes in histological examination corroborated the significant changes obtained from the MRI measurements.Conclusion:Prophylactic vitamin C seemed to reduce the thickening of the axillary recess in secondary frozen shoulder in this preclinical study.Clinical Relevance:Vitamin C may be helpful as a noninvasive therapeutic measure to prevent secondary frozen shoulder (eg, within the context of surgery in the shoulder region or immobilization) or to treat primary frozen shoulder at an early stage. Further studies are required to evaluate the effect of this treatment in humans and the necessary dosage in humans.