Intra-articular betamethasone plus medical-grade chitosan for primary adhesive capsulitis: a retrospective real-world pilot cohort with repeated measures

Background Primary adhesive capsulitis causes persistent shoulder pain, stiffness, and functional limitation. Intra-articular corticosteroid injections provide short-term benefit, but durability varies. Medical-grade chitosan is a bioresorbable viscoelastic biomaterial with anti-inflammatory and lubricating properties; its clinical role in adhesive capsulitis remains unclear. Methods We conducted a single-center retrospective observational cohort including adults with primary adhesive capsulitis treated between February 2023 and March 2025 with a three-session, course-based, landmark-guided intra-articular anterior injection regimen of betamethasone plus medical-grade chitosan, combined with usual-care rehabilitation instructed by therapists. The Constant–Murley score (CMS; 0–100) was recorded at baseline and follow-ups (Week 2, 4, 6; and ~ 1, ~3, and ~ 6 months). The primary endpoint was the within-patient change at ~ 6 months; the key secondary endpoint was the change at Week 6. Paired mean changes were summarized with effect sizes (Cohen’s dz) and 95% confidence intervals; responder proportions used 95% Wilson confidence intervals. Linear mixed-effects models (LMM) were used as supportive analyses under a missing-at-random assumption. Results Twenty-one patients were included (mean age 60.9 ± 10.2 years; range 47–82; 71.4% female). Mean CMS improvement was 39.2 points at Week 6 (n = 16; 95% CI 31.2–46.3) and 49.1 points at ~ 6 months (n = 7; 95% CI 42.9–55.3). LMM estimates versus baseline remained substantial (Week 6: 38.3; 95% CI 33.1–43.5; ~6 months: 43.5; 95% CI 36.4–50.5; all p < 0.001). Using a prespecified ≥ 10-point responder threshold, responder rates were 93.8% at Week 6 and 100% at ~ 6 months among paired observations. No injection-related adverse events were recorded in available documentation. Conclusions In this exploratory real-world cohort, a course-based intra-articular regimen combining betamethasone with medical-grade chitosan was associated with large improvements in CMS from early time points, with sustained gains observed among patients with available long-term follow-up. Given the retrospective single-arm design and attrition, findings should be interpreted cautiously and warrant prospective controlled validation.