title: Patellar maltracking correlates with vastus medialis activation delay in patellofemoral pain patients.
abstract: BACKGROUND
  Delayed onset of vastus medialis (VM) activity compared with vastus lateralis activity is a reported cause for patellofemoral pain. The delayed onset of VM activity in patellofemoral pain patients likely causes an imbalance in muscle forces and lateral maltracking of the patella; however, evidence relating VM activation delay to patellar maltracking is sparse. The aim of this study was to investigate the relationship between VM activation delay and patellar maltracking measures in pain-free controls and patellofemoral pain patients.
  
  
  OBJECTIVE
  Patellar tilt and bisect offset, measures of patellar tracking, correlate with VM activation delay in patellofemoral pain patients classified as maltrackers.
  
  
  METHODS
  Case control study; Level of evidence, 3.
  
  
  METHODS
  Vasti muscle activations were recorded in pain-free (n = 15) and patellofemoral pain (n = 40) participants during walking and jogging. All participants were scanned in an open-configuration magnetic resonance scanner in an upright weightbearing position to acquire the position of the patella with respect to the femur. Patellar tilt and bisect offset were measured, and patellofemoral pain participants were classified into normal tracking and maltracking groups.
  
  
  RESULTS
  Correlations between VM activation delay and patellar maltracking measures were statistically significant in only the patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset (R(2) = .89, P < .001, with patellar tilt during walking; R(2) = .75, P = .012, with bisect offset during jogging). There were no differences between the means of activation delays in pain-free and all patellofemoral pain participants during walking (P = .516) or jogging (P = .731).
  
  
  CONCLUSIONS
  There was a relationship between VM activation delay and patellar maltracking in the subgroup of patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset.
  
  
  CONCLUSIONS
  A clinical intervention such as VM retraining may be effective in only a subset of patellofemoral pain participants-namely, those with excessive tilt and excessive bisect offset measures. The results highlight the importance of appropriate classification of patellofemoral pain patients before selection of a clinical intervention.
authors.affiliation: Department of Bioengineering, Stanford University, James H. Clark Center, 318 Campus Drive, Stanford, CA 94305-5450, USA. spal5@stanford.edu
authors.forename: Saikat
authors.initials: S
authors.lastname: Pal
authors.forename: Christine E
authors.initials: CE
authors.lastname: Draper
authors.forename: Michael
authors.initials: M
authors.lastname: Fredericson
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
authors.forename: Gary S
authors.initials: GS
authors.lastname: Beaupre
authors.forename: Thor F
authors.initials: TF
authors.lastname: Besier
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007590:Jogging / Q000502:physiology; D008297:Male; D010329:Patella / Q000503:physiopathology*; D046788:Patellofemoral Pain Syndrome / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000503:physiopathology*; D016138:Walking / Q000502:physiology