Why Do Tendons Hurt? Lessons from the Study of Calcific Tendinitis: Commentary on an article by Lisa Hackett, AMS, et al.: "Are the Symptoms of Calcific Tendinitis Due to Neoinnervation and/or Neovascularization?".

Abstract

Calcific tendinitis is an interesting clinical condition in the shoulder, as it can be clinically silent and can be found incidentally in an asymptomatic patient, or it can also present with severe and acute pain. The underlying pathophysiology is not well understood. In addition, due to our lack of understanding of what initiates formation of the calcific deposit in the tendon, we also do not know what factors trigger the pain that can acutely develop in patients with a calcific deposit. The study by Hackett et al. demonstrates that there is an accumulation of inflammatory cells, neovascularization, and nerve fiber ingrowth in and around calcific deposits in symptomatic patients. This is consistent with the clinical presentation in patients with calcific tendinitis, as they can present with acute pain. The immunohistochemistry findings are consistent with the basic pathophysiology of inflammation, as it is known that inflammation is associated with neovascularization. Furthermore, neoinnervation is associated with new capillary formation. Similar findings of new capillary formation and expression of nociceptive mediators have been reported in analyses of angiofibroblastic hyperplasia lesions seen in rotator cuff tendinosis1. The presence of nociceptive chemicals and mediators in the rotator cuff, as found by Hackett et al., is consistent with the severe pain in these patients. A distinct limitation in this study is the inability to study biopsy specimens in asymptomatic patients with calcific deposits. This leads to consideration of one of the primary outstanding questions related to calcific tendinitis: …