Pain Relief Strategies after Acromioclavicular Joint Corticosteroid Injection as a Predictor of Final Functional Outcome: A Prospective Observational Study

Abstract

Background: Acromioclavicular (AC) joint pain is a prevalent source of shoulder disability, frequently managed with corticosteroid injections. Despite the widespread use of this intervention, the early post-injection pain relief trajectory as a predictive marker for long-term functional recovery has not been systematically studied. Objective: To evaluate whether the pattern and magnitude of pain relief in the first four weeks following AC joint corticosteroid injection predicts the final functional outcome at six months. Methods: A prospective observational cohort study was conducted over 24 months at a tertiary orthopaedic referral centre. Eighty-six patients with clinically and radiologically confirmed AC joint pathology receiving ultrasound-guided corticosteroid injections were enrolled. Pain was assessed using the Visual Analogue Scale (VAS) and Numerical Rating Scale (NRS) at baseline, 1 week, 2 weeks, and 4 weeks post-injection. Functional outcome was assessed at 6 months using the Disabilities of the Arm, Shoulder and Hand (DASH) score and the Constant-Murley Score (CMS). Receiver Operating Characteristic (ROC) analysis and logistic regression were used to identify predictive thresholds. Results: A clinically significant pain reduction of ≥50% NRS at 2 weeks post-injection was identified as the strongest independent predictor of favourable 6-month functional outcome (AUC = 0.84; sensitivity 78%, specificity 82%). Patients achieving this threshold demonstrated significantly superior DASH (mean 18.4 ± 6.2 vs. 41.7 ± 9.8; p < 0.001) and Constant-Murley scores (74.3 ± 8.1 vs. 51.2 ± 10.4; p < 0.001) at follow-up. Persistent pain at 4 weeks was associated with a 3.8-fold increased risk of poor outcome (OR 3.82; 95% CI 1.94–7.51). Conclusion: Early pain relief trajectory following AC joint corticosteroid injection is a reliable and clinically practical predictor of final functional outcome. A ≥50% reduction in NRS pain score at 2 weeks should be incorporated into decision-making algorithms to identify patients requiring earlier escalation of care.