Differential mRNA Expression of COX-2 and Proinflammatory Mediators in Patients with Rotator Cuff Tears and Osteoarthritis of the Hip

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Purpose: Bursal inflammation is thought to be a major cause of pain in degenerative rotator cuff tears (RCTs). While the expression of proinflammatory mediators, such as COX-2, TNF-α, IL-1β, and IL-6, is crucial for the pathophysiology of osteoarthritis (OA), their role in degenerative RCTs remains unknown. The aim of this study was to determine the expression of COX-2 and proinflammatory mediators in the development of RCT-induced pain by comparing their levels in patients with hip OA or RCTs. Methods: We included samples obtained from 31 shoulders of 31 patients with RCTs and samples from 30 hips of 27 patients with hip OA. The mRNA levels of COX-2, TNF-α, IL-1β, and IL-6 were determined using RT-PCR, and were compared between the subacromial bursa and hip joints. We also analyzed IL-1β-induced COX-2 expression in the subacromial bursa and synovial blast of the hip. Results: COX-2, IL-1β, and IL-6 expression levels were significantly lower in the subacromial bursa of RCTs than in hip OA samples, while no significant difference was observed for TNF-α. No significant difference in the fold increase was observed between subacromial bursa and hip OA samples, even though IL-1β-induced COX-2 expression increased in both samples. Conclusion: Our findings suggest that the main mechanism underlying pain development differs between patients with RCTs and those with hip OA.