title: Differentiation of osteophyte types in osteoarthritis - proposal of a histological classification.
abstract: OBJECTIVE
  Osteoarthritis is not only characterized by cartilage degradation but also involves subchondral bone remodeling and osteophyte formation. Osteophytes are fibrocartilage-capped bony outgrowths originating from the periosteum. The pathophysiology of osteophyte formation is not completely understood. Yet, different research approaches are under way. Therefore, a histological osteophyte classification to achieve comparable results in osteophyte research was established for application to basic science research questions.
  
  
  METHODS
  The osteophytes were collected from knee joints of osteoarthritis patients (n=10, 94 osteophytes in total) after joint replacement surgery. Their size and origin in the respective joint were photo-documented. To develop an osteophyte classification, serial tissue sections were evaluated using histological (hematoxylin and eosin, Masson's trichrome, toluidine blue) and immunohistochemical staining (collagen type II).
  
  
  RESULTS
  Based on the histological and immunohistochemical evaluation, osteophytes were categorized into four different types depending on the degree of ossification and the percentage of mesenchymal connective tissue. Size and localization of osteophytes were independent from the histological stages.
  
  
  CONCLUSIONS
  This histological classification system of osteoarthritis osteophytes provides a helpful tool for analyzing and monitoring osteophyte development and for characterizing osteophyte types within a single human joint and may therefore contribute to achieve comparable results when analyzing histological findings in osteophytes.
authors.affiliation: Department of Internal Medicine and Rheumatology, Justus-Liebig-University Giessen, Kerckhoff-Klinik Benekestraße 2-8, 61231 Bad Nauheim, Germany.
authors.forename: Susann
authors.initials: S
authors.lastname: Junker
authors.affiliation: Department of Internal Medicine and Rheumatology, Justus-Liebig-University Giessen, Kerckhoff-Klinik Benekestraße 2-8, 61231 Bad Nauheim, Germany.
authors.forename: Grit
authors.initials: G
authors.lastname: Krumbholz
authors.affiliation: Department of Internal Medicine and Rheumatology, Justus-Liebig-University Giessen, Kerckhoff-Klinik Benekestraße 2-8, 61231 Bad Nauheim, Germany.
authors.forename: Klaus W
authors.initials: KW
authors.lastname: Frommer
authors.affiliation: Department of Orthopaedics and Orthopaedic Surgery, Markus Hospital, 60431 Frankfurt am Main, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rehart
authors.affiliation: Department of Orthopedics, Justus-Liebig-University of Giessen, 35390 Giessen, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Steinmeyer
authors.affiliation: Department of Orthopedics and Orthopedic Surgery, Justus-Liebig-University of Giessen, 35390 Giessen, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Rickert
authors.affiliation: Department of Internal Medicine 3, University of Erlangen-Nuremberg, 91054 Erlangen, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Schett
authors.affiliation: Department of Internal Medicine and Rheumatology, Justus-Liebig-University Giessen, Kerckhoff-Klinik Benekestraße 2-8, 61231 Bad Nauheim, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Müller-Ladner
authors.affiliation: Department of Internal Medicine and Rheumatology, Justus-Liebig-University Giessen, Kerckhoff-Klinik Benekestraße 2-8, 61231 Bad Nauheim, Germany. Electronic address: e.neumann@kerckhoff-klinik.de.
authors.forename: Elena
authors.initials: E
authors.lastname: Neumann
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007719:Knee Joint / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology* / Q000601:surgery; D054850:Osteophyte / Q000473:pathology*
keywords: Basic science; Histological classification; Osteoarthritis; Osteophytes