title: Morphologic changes in the vastus medialis muscle in patients with osteoarthritis of the knee.
abstract: OBJECTIVE
  To investigate the frequency of structural changes in the vastus medialis muscle in patients with osteoarthritis (OA) of the knee.
  
  
  METHODS
  Specimens of vastus medialis muscle from 78 patients with end-stage OA of the knee undergoing total joint arthroplasty were examined histopathologically. Morphologic changes were assessed in relation to clinical features that might have contributed to muscle injury.
  
  
  RESULTS
  All muscle specimens exhibited atrophy of type 2 fibers. In 32% of the patients, atrophy of type 1 fibers was also noted. Fiber type grouping of type 1 fiber in 15% of the patients and type 2 fiber in 37%, indicating reinnervation, led to the diagnosis of neurogenic muscular atrophy in 32% of the patients; selective atrophy of type 2 fiber in 68% of the specimens was interpreted as possibly resulting from pain-associated disuse. Signs of muscle degeneration and regeneration were found in 65% and 96% of the samples, respectively. Soft tissue changes indicating long-term disease, such as calcification, fibrosis, and lipomatosis, were frequently observed (in 69%, 71%, and 94% of the patients, respectively). Statistical analysis of clinical and morphologic parameters revealed a significant association between degenerative muscle changes and the presence of a varus deviation of the leg axis.
  
  
  CONCLUSIONS
  Patients with OA of the knee frequently exhibit muscle changes, with probable multifactorial etiology. Selective atrophy of type 2 fibers might reflect pain-related immobilization of a limb. Changes such as neurogenic muscular atrophy, muscle fiber degeneration, and regeneration might contribute as cofactors in the development or progression of OA.
authors.affiliation: Orthopaedic Clinic Markgröningen, Markgröningen, Germany. b.fink@okm.de
authors.forename: Bernd
authors.initials: B
authors.lastname: Fink
authors.forename: Monika
authors.initials: M
authors.lastname: Egl
authors.forename: Joachim
authors.initials: J
authors.lastname: Singer
authors.forename: Martin
authors.initials: M
authors.lastname: Fuerst
authors.forename: Michael
authors.initials: M
authors.lastname: Bubenheim
authors.forename: Eva
authors.initials: E
authors.lastname: Neuen-Jacob
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D002114:Calcinosis / Q000209:etiology / Q000473:pathology; D018450:Disease Progression; D005260:Female; D005355:Fibrosis; D006801:Humans; D008068:Lipomatosis / Q000209:etiology / Q000473:pathology; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000473:pathology; D018657:Muscle Fibers, Slow-Twitch / Q000473:pathology; D009133:Muscular Atrophy / Q000150:complications* / Q000473:pathology*; D020370:Osteoarthritis, Knee / Q000209:etiology* / Q000473:pathology* / Q000601:surgery; D052097:Quadriceps Muscle / Q000473:pathology*