title: Effects of knee injection on skeletal muscle metabolism and contractile force in rats.
abstract: OBJECTIVE
  We tested the hypothesis that intrusion of the knee joint capsule alters quadriceps muscle metabolism and function independently from the damage induced to knee cartilage.
  
  
  METHODS
  Adult rats were separated into four groups: intraarticular injections of saline (SAL; n=9); intraarticular injections of papain, a model for osteoarthritis (PIA; n=7); sham injections (SHAM; n=8); and controls (CTL; n=5). 31P magnetic resonance spectroscopy (31P-MRS) was performed after 2 weeks. Spectra were obtained from the left quadriceps: two at baseline, eight during electrical stimulation with simultaneous measurement of contractile force, and 15 during recovery. 31P-MRS data were presented as the ratio of inorganic phosphate (Pi) to phosphocreatine (PCr), concentrations of PCr [PCr], intramuscular pH, and the rates and time constants of PCr breakdown during stimulation and PCr recovery. Intramuscular cytokine concentrations were measured within the quadriceps. Histologic slides of the knees were scored for severity of cartilage damage.
  
  
  RESULTS
  The interventional groups produced values of Pi/PCr ratio, [PCr], contractile force and pH that were significantly different from CTL. These changes in muscle function were accompanied by higher concentrations of interleukin-1 observed with PIA and SAL. We did not observe any effect of cartilage damage on muscle function or metabolism.
  
  
  CONCLUSIONS
  Knee joint intrusion alters quadriceps muscle metabolism with accelerated depletion of energy stores and fatigue during stimulation. This study demonstrates that needle intrusion into the knee joint results in muscle dysfunction, independently from the extent of cartilage damage.
authors.affiliation: Drug Delivery and Kinetics Resource, Division of Bioengineering and Physical Science, Office of Research Services, National Institutes of Health, Bethesda, MD 20892-5766, USA. gallbanc@ors.od.nih.gov
authors.forename: C J
authors.initials: CJ
authors.lastname: Galbán
authors.forename: S M
authors.initials: SM
authors.lastname: Ling
authors.forename: C J
authors.initials: CJ
authors.lastname: Galbán
authors.forename: D D
authors.initials: DD
authors.lastname: Taub
authors.forename: I
authors.initials: I
authors.lastname: Gurkan
authors.forename: K W
authors.initials: KW
authors.lastname: Fishbein
authors.forename: R G
authors.initials: RG
authors.lastname: Spencer
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects; D016207:Cytokines / Q000032:analysis; D005260:Female; D007270:Injections, Intra-Articular / Q000009:adverse effects; D009682:Magnetic Resonance Spectroscopy; D023421:Models, Animal; D009119:Muscle Contraction / Q000502:physiology*; D010003:Osteoarthritis / Q000139:chemically induced; D010206:Papain / Q000494:pharmacology; D010725:Phosphocreatine / Q000032:analysis; D010758:Phosphorus; D052097:Quadriceps Muscle / Q000378:metabolism / Q000502:physiology; D051381:Rats; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D016207:Cytokines; D010725:Phosphocreatine; D010758:Phosphorus; D012965:Sodium Chloride; D010206:Papain