Is the Superficial Peritendinous Tissue an Additional Pain Driver in Patellar Tendinopathy?-Studies on Morphology and Innervation in a Case Series.

Background and Objectives: Ultrasound (US) and Doppler (DP) guided arthroscopic shaving targeting the area with neovessels and nerves on the dorsal side of the tendon has shown good clinical results. Recently, we observed that in a sub-group of patients there is also local tenderness on the superficial side of the proximal patellar tendon; Material and Methods: The aim was to examine morphology and innervation patterns of the superficial peritendinous tissue from patients (four men and two women; mean age 23 years, range 17-31 years) that on US+DP examination showed a locally thickened paratenon including high blood flow. Tissue sections were stained for morphology (hematoxylin and eosin, H&E) and immunohistochemically for nerve markers (ß-tubulin; tyrosine hydroxylase, TH; calcitonin related gene peptide, CRGP); Results: All tissue specimens contained high levels of blood vessels and nerves (fascicles, sprouting nerve fibers, perivascular innervation) as evidenced by evaluation for H&E and ß-tubulin reactions. Nerve fascicles mainly contained sensory but also sympathetic axons. Nerves related to blood vessels were sympathetic fibers; Conclusions: There was a marked innervation in the superficial peritendinous tissue in a sub-group of patients with patellar tendinopathy and severe tenderness in the proximal patellar tendon. The results indicate that this tissue might be an additional pain driver in some patients and should be considered in further studies.