title: Cartilage boundary lubrication of ovine synovial fluid following anterior cruciate ligament transection: a longitudinal study.
abstract: OBJECTIVE
  To assess ovine synovial fluid (oSF) from different post-injury time points for (1) proteoglycan-4 (PRG4) and hyaluronan (HA) concentration, (2) HA molecular weight (MW) distribution, (3) cartilage boundary lubrication function, and (4) lubricant composition-function relationships. The association between cartilage boundary lubrication and gross cartilage changes after injury was also examined.
  
  
  METHODS
  oSF was collected 2, 4, 10, and 20 weeks post anterior cruciate ligament (ACL) transection in five skeletally mature sheep. PRG4 and HA concentrations were measured using sandwich enzyme-linked immunosorbent assay, and HA MW distribution by agarose gel electrophoresis. Cartilage boundary lubrication of oSF was assessed using a cartilage-cartilage friction test. Gross damage to articular cartilage was also quantified at 20 weeks using modified Drez scoring protocol.
  
  
  RESULTS
  Early (2-4 weeks) after ACL injury, PRG4 concentrations were significantly higher (P = 0.045, P = 0.037), and HA concentrations were substantially lower (P = 0.005, P = 0.005) compared to 20 weeks. The HA MW distribution also shifted towards lower ranges in the early post-injury stage. The kinetic friction coefficients were significantly higher 2-4 weeks post injury (P = 0.008 and P = 0.049) compared to 20 weeks. Poor cartilage boundary lubricating ability early after injury was associated with cartilage damage at 20 weeks.
  
  
  CONCLUSIONS
  Altered composition and diminished boundary lubrication of oSF early after ACL transection may pre-dispose the articular cartilage to degenerative changes and initiate osteoarthritis (OA). These observations also provide potential motivation for biotherapeutic interventions at earlier time points post injury.
authors.affiliation: McCaig Institute for Bone and Joint Health, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Electronic address: matarodp@ucalgary.ca.
authors.forename: M
authors.initials: M
authors.lastname: Atarod
authors.affiliation: Biomedical Engineering, University of Calgary, Calgary, Alberta, Canada. Electronic address: teludwig@ucalgary.ca.
authors.forename: T E
authors.initials: TE
authors.lastname: Ludwig
authors.affiliation: Department of Surgery, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. Electronic address: cfrank@ucalgary.ca.
authors.forename: C B
authors.initials: CB
authors.lastname: Frank
authors.affiliation: Faculty of Kinesiology, Biomedical Engineering, University of Calgary, Calgary, Alberta, Canada. Electronic address: tschmidt@ucalgary.ca.
authors.forename: T A
authors.initials: TA
authors.lastname: Schmidt
authors.affiliation: Department of Civil Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada. Electronic address: ngshrive@ucalgary.ca.
authors.forename: N G
authors.initials: NG
authors.lastname: Shrive
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D002358:Cartilage, Articular / Q000502:physiology*; D004195:Disease Models, Animal; D005260:Female; D006820:Hyaluronic Acid / Q000032:analysis / Q000737:chemistry; D008137:Longitudinal Studies; D008970:Molecular Weight; D010003:Osteoarthritis / Q000209:etiology / Q000503:physiopathology*; D011509:Proteoglycans / Q000032:analysis; D012756:Sheep; D013582:Synovial Fluid / Q000737:chemistry / Q000502:physiology*
chemical_list: D011509:Proteoglycans; D006820:Hyaluronic Acid
keywords: ACL injury; Boundary lubrication; Cartilage; Ovine; Synovial fluid