title: Calcium phosphate particulates increase friction in the rat knee joint.
abstract: OBJECTIVE
  Basic calcium phosphate (BCP) particulates are commonly found in cartilage and synovial fluid of osteoarthritis (OA) joints with the amount of BCP correlating with knee OA severity. How cartilage mineralization affects joint degeneration has yet to be determined. The objective of this study was to determine whether BCP in the synovial fluid affects the rat knee joint coefficient of friction (COF).
  
  
  METHODS
  The COFs of knees from both hind limbs of four mature male rats were measured post mortem using a pendulum apparatus with an infrared tracking system. The three conditions evaluated were (1) the naïve state, (2) after the injection of 100 μL of phosphate buffered saline (PBS) (sham) and (3) after the injection of 100 μL of a 1 mg/mL BCP suspension. The decrease in the pendulum amplitude (decay) was fit using two friction models: (1) a one parameter Stanton linear decay model and (2) a two parameters combination Stanton linear decay and viscous damping exponential decay model.
  
  
  RESULTS
  The COF increased 17.6% after injection of BCP compared to the naïve (P = 0.0012) and 16.0% compared to the saline injected (P = 0.0018) joints as derived from the one parameter model. The COF did not differ between naïve and saline injected joints. Results from the two parameters model showed a similar increase in COF after injection of BCP while the viscous damping was not significantly different between conditions.
  
  
  CONCLUSIONS
  The increased joint friction with BCP particulates suggests BCPs may play a role in articular surface degradation and OA development.
authors.affiliation: McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, VT 05405, USA. Electronic address: Maria.Roemhildt@med.uvm.edu.
authors.forename: M L
authors.initials: ML
authors.lastname: Roemhildt
authors.affiliation: McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, VT 05405, USA. Electronic address: Mack.Gardner-Morse@uvm.edu.
authors.forename: M G
authors.initials: MG
authors.lastname: Gardner-Morse
authors.affiliation: McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, VT 05405, USA.
authors.forename: C F
authors.initials: CF
authors.lastname: Morgan
authors.affiliation: McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, VT 05405, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Beynnon
authors.affiliation: Department of Medical Biostatistics, University of Vermont, Burlington, VT 05405, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Badger
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000139:chemically induced; D002114:Calcinosis / Q000150:complications / Q000503:physiopathology*; D002130:Calcium Phosphates / Q000494:pharmacology*; D002805:Chondrocalcinosis / Q000503:physiopathology; D017276:Friction / Q000187:drug effects; D007596:Joints / Q000187:drug effects* / Q000503:physiopathology; D008297:Male; D010003:Osteoarthritis / Q000139:chemically induced; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013582:Synovial Fluid / Q000737:chemistry
chemical_list: D002130:Calcium Phosphates; C020243:calcium phosphate
keywords: Articular cartilage; Calcification; Calcium phosphate; Cartilage mineralization; Chondrocalcinosis; Joint friction