Increased Expression of Pain-Related Factors in Structures Adjacent to Pathologic Biceps Long Head Tendons in Patients with Rotator Cuff Tears

Different levels of pain, with various symptoms, are present in patients with rotator cuff tears. The purpose of this study was to evaluate the expression of factors related to pain on the long head of the biceps tendon (LHBT) and structures adjacent to the LHBT in patients with supraspinatus tears and to compare the differences in order to verify whether the structures are affected by the condition of the LHBT. Forty patients who underwent arthroscopic supraspinatus repair were enrolled. Patients with an intact LHBT were allocated to group 1 and patients with pathologic LHBTs were allocated to group 2. With the acquisition of tissues from the LHBT, anterior capsule, rotator interval, and subacromial bursa, the expressions of protein gene product 9.5 (PGP9.5), growth-associated protein 43 (GAP43), calcitonin gene-related peptide (CGRP), substance P, P75, S100, and CD34 were analyzed using real-time reverse transcription polymerase chain reaction and immunohistochemistry. The gene expression levels of PGP9.5 (p = 0.02), GAP43 (p = 0.03), CGRP (p = 0.007), and CD34 (p = 0.03) from the LHBT were significantly higher in group 2. PGP9.5 (p = 0.04 and p = 0.01), GAP43 (p = 0.02 and p = 0.004), and P75 (p = 0.02 and p = 0.02) from the anterior capsule and rotator interval were also significantly higher in group 2. Immunohistochemistry revealed increased expression of pain-related factors in the anterior capsule and rotator interval of group 2. Enhanced expression of pain-related factors in the LHBT, anterior capsule, and rotator interval of patients with pathologic LHBTs suggests that a pathologic LHBT functions as a pain generator itself and adjacent structures can be influenced by the condition of the LHBT.