title: The influence of weakness in the vastus medialis oblique muscle on the patellofemoral joint: an in vitro biomechanical study.
abstract: OBJECTIVE
  Investigation of the influence of weakness in the vastus medialis oblique muscle on patellar tracking.
  
  
  METHODS
  In vitro biomechanical study.
  
  
  BACKGROUND
  Currently, the influence of weakness in the vastus medialis oblique muscle on patellar tracking has not been well understood.
  
  
  METHODS
  Seven human cadaveric knees were used. The direction of loading forces in the rectus femoris/vastus intermedius, vastus medialis oblique, and the vastus lateralis muscles was decided by the muscle alignment of each cadaver knee measured at the time of dissection. The loads used were 60 N in the rectus femoris, 50 N in the vastus lateralis, and 40 N in the vastus medialis oblique, according to the ratio calculated from the cross-sectional study. The weakness of vastus medialis oblique was simulated at 30 N (75%), 20 N (50%), 10 N (25%), and 0 N (0%), and the patellar position was measured for each condition using a magnetic 3 Space Tracker System. The influence of weakness in the vastus medialis oblique muscle on patellar position was investigated with seven cadaver knees using a magnetic 3 Space Tracker System.
  
  
  RESULTS
  At 0 degrees and 15 degrees of knee flexion, 75%, 50%, 25% and 0% of the normal vastus medialis oblique muscle led to a significant difference in lateral patellar shift compared to the normal (P<0.05).
  
  
  CONCLUSIONS
  Weakness of the vastus medialis caused the patellar lateral shift at 0 degrees and 15 degrees of knee flexion.
  
  
  CONCLUSIONS
  Weakness of the vastus medialis is thought to be an important factor causing patellar subluxation and dislocation. Understanding the relationship between the vastus medialis weakness and patellar tracking will be useful in diagnosis, treatment and prevention of patellar subluxation and dislocation.
authors.affiliation: Department of Orthopaedic Surgery, Yokohama City University School of Medicine, 3-9 Fukuura, Yokohama, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Sakai
authors.forename: Z P
authors.initials: ZP
authors.lastname: Luo
authors.forename: J A
authors.initials: JA
authors.lastname: Rand
authors.forename: K N
authors.initials: KN
authors.lastname: An
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D066298:In Vitro Techniques; D007719:Knee Joint / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010329:Patella / Q000503:physiopathology*; D016059:Range of Motion, Articular