title: Factors associated with arthrogenous muscle inhibition in patellofemoral osteoarthritis.
abstract: OBJECTIVE
  Arthrogenous muscle inhibition (AMI) is thought to contribute to quadriceps weakness in knee osteoarthritis (OA), but its relationship with structural changes of bone marrow lesions (BMLs), capsular distension and pain is unclear. This study's objective was to investigate the factors associated with AMI in subjects with symptomatic patellofemoral joint OA (PFJOA).
  
  
  METHODS
  126 Subjects with predominant PFJOA were assessed for pain by the visual analogue scale (VAS) for a nominated aggravating activity. Their more symptomatic knee underwent a magnetic resonance imaging (MRI) scan which was used to assess BMLs and synovitis which were scored using the Whole Organ MRI score (WORMS). Quadriceps AMI was measured by calculating the activation deficit and quadriceps strength assessed by isometric maximum voluntary contraction. Multiple linear regressions were used to assess factors associated with AMI.
  
  
  RESULTS
  We studied 124 subjects [mean age 55.5 (SD 7.5); 57.14% female]. In regression analyses, higher levels of AMI were significantly associated with more severe knee pain and with lower BML score.
  
  
  CONCLUSIONS
  Quadriceps AMI in knee OA is associated with severity of knee pain and surprisingly with lower BML scores.
authors.affiliation: Arthritis Research UK Centre for Epidemiology, Centre for Musculoskeletal Research, University of Manchester, Oxford Road, Manchester, UK. Electronic address: michael.callaghan@manchester.ac.uk.
authors.forename: M J
authors.initials: MJ
authors.lastname: Callaghan
authors.affiliation: Arthritis Research UK Centre for Epidemiology, Centre for Musculoskeletal Research, University of Manchester, Oxford Road, Manchester, UK. Electronic address: matthew.parkes@manchester.ac.uk.
authors.forename: M J
authors.initials: MJ
authors.lastname: Parkes
authors.affiliation: Warwick Medical School, The University of Warwick, Coventry, UK. Electronic address: c.e.hutchinson@warwick.ac.uk.
authors.forename: C E
authors.initials: CE
authors.lastname: Hutchinson
authors.affiliation: Arthritis Research UK Centre for Epidemiology, Centre for Musculoskeletal Research, University of Manchester, Oxford Road, Manchester, UK; NIHR Manchester Musculoskeletal Biomedical Research Unit, Manchester Academic Health Sciences Centre, Manchester, UK; Clinical Epidemiology Unit, Boston University School of Medicine, Boston, MA, USA. Electronic address: david.felson@manchester.ac.uk.
authors.forename: D T
authors.initials: DT
authors.lastname: Felson
mesh_terms: D000328:Adult; D000368:Aged; D001853:Bone Marrow / Q000473:pathology* / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D018908:Muscle Weakness / Q000473:pathology* / Q000503:physiopathology; D020370:Osteoarthritis, Knee / Q000175:diagnosis; D010147:Pain Measurement; D057071:Patellofemoral Joint / Q000473:pathology* / Q000503:physiopathology; D011379:Prognosis; D052097:Quadriceps Muscle / Q000473:pathology* / Q000503:physiopathology; D016059:Range of Motion, Articular / Q000502:physiology; D012189:Retrospective Studies; D012307:Risk Factors; D012720:Severity of Illness Index
keywords: Arthrogenous muscle inhibition; Bone marrow lesions; Knee; MRI; Osteoarthritis; Quadriceps