Background: Intra-articular corticosteroid or hyaluronic acid (HA) is commonly prescribed for frozen shoulder. However, few studies have investigated histological and molecular changes after injection.
Purpose: To compare the effectiveness of intra-articular injections of triamcinolone and HA in a frozen shoulder rat model and verify a greater effect of triamcinolone in passive shoulder abduction compared with HA.
Study design: Controlled laboratory study.
Methods: Twenty male Sprague-Dawley rats were randomly allocated into 4 groups (n = 5 in each): control group, which did not receive cast immobilization or injection, and 3 experimental groups, which received 3 weeks of unilateral shoulder immobilization followed by intra-articular injections (normal saline, triamcinolone, or HA) at the immobilized shoulder. Passive shoulder abduction angle, histological and immunohistochemical staining, and Western blotting results were assessed 2 weeks after injection. The intensity and extent of staining were converted to semiquantitative scores for further analysis.
Results: Shoulder abduction angles before sacrifice were 153.0°± 2.7° (control group), 107.0°± 5.7° (saline group), 139.0°± 9.6° (triamcinoline group), and 110.0°± 10.6° (HA group), showing significant differences between control and saline groups, control and HA groups, saline and triamcinoline groups, and triamcinoline and HA groups (P < .001) but not between control and triamcinoline groups (P = .053). Histologic evaluation revealed an increase in synovial folds and thickening of the capsular membrane in the saline and HA groups; this change was not evident in the triamcinolone group. A comparison of semiquantitative scores revealed greater expression levels of proteins involved in fibrosis and angiogenesis in the saline and HA groups compared with the control and triamcinolone groups. In Western blotting, the expression of inflammatory cytokines and the receptor for advanced glycation end products was significantly lower in the triamcinolone and HA groups than in the saline group.
Conclusion: Triamcinolone injection was more effective than normal saline or HA injection in improving range of motion and reversing fibrotic and angiogenic features of frozen shoulder. Both triamcinolone and HA injections elicited anti-inflammatory effects.
Clinical relevance: The antifibrotic and antiangiogenic properties of triamcinolone and the anti-inflammatory properties of both triamcinolone and HA should be considered when performing injections in clinical settings.
Keywords: frozen shoulder; hyaluronic acid; intra-articular injection; triamcinolone.