title: The layered structure of the articular surface.
abstract: OBJECTIVE
  Articular cartilage is roughly separated into three areas: the tangential, middle, and deep zones. The structure and molecular components of an additional important zone, the most superficial zone (MSZ), which directly faces the joint cavity, have yet to be conclusively elucidated. The purpose of the present study was to use multiple methods to study the MSZ in order to determine its structure.
  
  
  METHODS
  Knees from 16 pigs (age, 6 months) were used. Full-thickness cartilage specimens were harvested from the femoral groove. The MSZ was observed using light microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) in combination with histochemical and immunohistochemical methods.
  
  
  RESULTS
  The combined findings from the three different observational methods indicate that the MSZ is subdivided into three layers. Among these three layers, collagen subtypes I, II, and III are present in the innermost (third) layer of the MSZ. Beneath the third layer, type II collagen is the predominant type, with small amounts of type III collagen. This layer beneath the third layer is considered to be the tangential layer.
  
  
  CONCLUSIONS
  Our observations indicate that the MSZ is subdivided into three layers. Further analysis of the molecular components in each layer may improve our understanding of the structure of the articular surface.
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. fujioka.rune.34w@st.kyoto-u.ac.jp
authors.forename: R
authors.initials: R
authors.lastname: Fujioka
authors.forename: T
authors.initials: T
authors.lastname: Aoyama
authors.forename: T
authors.initials: T
authors.lastname: Takakuwa
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000737:chemistry / Q000648:ultrastructure*; D003094:Collagen / Q000032:analysis / Q000648:ultrastructure; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D016253:Microscopy, Immunoelectron; D034421:Sus scrofa
chemical_list: D003094:Collagen
keywords: Articular surface; Collagen subtypes; Lamina splendens; Scanning electron microscopy; Transmission electron microscopy