Association between shoulder pain and nerve growth factor expression in the synovial tissues of patients with rotator cuff tears

Rotator cuff tears (RCTs) are often associated with severe shoulder pain. Non-steroidal anti-inflammatory drugs, which are not recommended for long-term use, do not effectively manage RCT-induced pain and can reduce the quality of life. To improve management, a better understanding of the fundamental properties of RCT pain is needed. Here, we aimed to compare the expression levels of nerve growth factor (NGF) and cyclooxygenase-2 (COX-2) mRNA in the synovial tissues of patients with RCT-induced pain and patients with non-painful recurrent shoulder dislocation (RSD). The study included 32 patients with RCT who underwent arthroscopic rotator cuff repair and 28 patients with non-painful RSD who underwent arthroscopic Bankart repair. Synovial tissue samples were harvested from the subacromial bursa and rotator interval of RCT patients and the rotator interval of RSD patients. Samples were analyzed quantitatively for the expression levels of NGF and COX-2 mRNA and NGF protein. NGF mRNA and protein levels were significantly higher in the rotator interval of RCT patients than in that of RSD patients (p=0.0017 and p=0.012, respectively), while COX-2 mRNA levels did not differ significantly between the groups. The expression of NGF mRNA in the synovium of the rotator interval was significantly correlated with the numeric rating scale for pain (ρ=0.38, p=0.004). NGF mRNA and protein levels were elevated in patients with painful RCT compared with those in patients with non-painful RSD, whereas COX-2 levels were comparable between the groups. These findings provide insights into novel potential strategies for the clinical management of RCTs.