Immunoreactive neuropeptide nerves in ligamentous tissue in chronic shoulder pain

Coracoacromial ligament and periligamentous fatty and loose connective tissue obtained during Neer's acromioplasty in patients with chronic painful rotator cuff tendinitis/impingement syndrome was studied for possible signs of inflammatory involvement and for the presence of neuropeptide-containing nerves, using routine histology and immunoperoxidase staining. No accumulations of inflammatory cells were found in the tissues studied. The dense ligamentous tissue proper was practically aneural, as was seen in staining for the generalized neuronal markers protein gene product 9.5 and synaptophysin. In contrast, the periligamentous fatty and loose connective tissue was innervated. Almost all nerves in such tissue contained C-flanking peptide of neuropeptide Y, whereas substance P, calcitonin gene-related peptide, and vasoactive intestinal peptide-containing nerves were not found at all or were extremely rare. This suggests that the coracoacromial ligament is not a target of irritative inflammation. In the periligamentary sheath, nerves containing markers for the C-type nociceptive pain fibers were practically absent and all local nerves were postganglionic sympathetic vaso-regulatory nerves.