title: Achilles tendinosis is associated with sprouting of substance P positive nerve fibres.
abstract: OBJECTIVE
  To identify and characterise nerve fibres and inflammatory alterations in painful Achilles tendinosis and thus gain evidence about the origin of pain in Achilles tendinosis.
  
  
  METHODS
  The composition of 10 tendon samples from patients with a prior history of painful Achilles tendinosis and 10 samples from patients with spontaneously ruptured tendons but no previous pain was compared by immunohistochemistry and conventional histology.
  
  
  RESULTS
  The presence of granulation tissue was shown in 8/10 cases of Achilles tendinosis. Nociceptive substance P (SP) positive nerve fibres were significantly increased, and an inflammatory infiltration comprising B and T lymphocytes was found. Additionally, small foci with iron positive haemosiderophages, indicating prior microtraumatic events, were found in 6/10 samples. None of the spontaneously ruptured tendons contained granulation tissue or haemosiderophages. Inflammatory infiltration in these patients consisted almost exclusively of granulocytes and SP positive nerve fibres were decreased. The density of sympathetic nerve fibres did not differ in the two conditions.
  
  
  CONCLUSIONS
  Achilles tendinosis is associated with the presence of granulation tissue, haemosiderophages, and SP positive nerve fibres, which may transmit the clinically pertinent pain. Achilles tendinosis may be caused by repeated microtraumata with ensuing organisation that is accompanied by sprouting of nociceptive SP positive nerve fibres.
authors.affiliation: Department of Pathology, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany. thomas.schubert@klinik.uni-regensburg.de
authors.forename: T E O
authors.initials: TE
authors.lastname: Schubert
authors.forename: C
authors.initials: C
authors.lastname: Weidler
authors.forename: K
authors.initials: K
authors.lastname: Lerch
authors.forename: F
authors.initials: F
authors.lastname: Hofstädter
authors.forename: R H
authors.initials: RH
authors.lastname: Straub
mesh_terms: D000125:Achilles Tendon / Q000737:chemistry / Q000293:injuries / Q000294:innervation*; D016022:Case-Control Studies; D005260:Female; D006097:Granulation Tissue; D006486:Hemosiderosis / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000737:chemistry / Q000473:pathology*; D009437:Neuralgia / Q000209:etiology / Q000473:pathology*; D009475:Neurons, Afferent / Q000737:chemistry / Q000473:pathology*; D012422:Rupture, Spontaneous; D013373:Substance P / Q000032:analysis*; D052256:Tendinopathy / Q000150:complications / Q000473:pathology*
chemical_list: D013373:Substance P