title: In vivo and noninvasive load sharing among the vasti in patellar malalignment.
abstract: OBJECTIVE
  It is not clear how the knee extension torque is distributed quantitatively among the lateral and medial vasti in patellofemoral pain (PFP) patients with patellar malalignment, which was investigated in vivo and noninvasively in ten PFP patients and eleven controls. We hypothesized that the vastus medialis oblique (VMO) and vastus medialis longus (VML) of PFP patients contribute less to knee extension than that in controls.
  
  
  METHODS
  Electrical stimulation was used to activate each vastus component selectively. The relationship between the knee extension torque generated by each individual vastus component and the corresponding compound muscle action potential (M-wave) was established over different contraction levels, which was used to calibrate the corresponding voluntary EMG signal and determine torque ratios of VMO/VL (vastus lateralis), VMO/VML, VML/VL and (VMO+VML)NL during voluntary isometric knee extension.
  
  
  RESULTS
  The VMO and VML of PFP patients contributed significantly less to knee extension than their counterparts in controls. The combination of VMO and VML generated comparable amount of extension torque as the VL in the controls, while it produced significantly lower extension torque than that of the VL in the PFP patients. In addition, the VMO/VL was lower than VMO/VML and VML/VL in both PFP and control groups.
  
  
  CONCLUSIONS
  Compared to controls, the VMO and VML in the PFP patients contributed significantly less to the knee extension torque. The approach can be used to investigate load sharing among quadriceps muscles in vivo and noninvasively, in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Illinois 60611, USA.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Makhsous
authors.forename: Fang
authors.initials: F
authors.lastname: Lin
authors.forename: Jason L
authors.initials: JL
authors.lastname: Koh
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Nuber
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Zhang
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000503:physiopathology*; D016022:Case-Control Studies; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010329:Patella / Q000503:physiopathology*; D019415:Torque