title: In vivo and noninvasive three-dimensional patellar tracking induced by individual heads of quadriceps.
abstract: OBJECTIVE
  Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components.
  
  
  METHODS
  Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements.
  
  
  RESULTS
  Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella.
  
  
  CONCLUSIONS
  The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Lin
authors.forename: Guangzhi
authors.initials: G
authors.lastname: Wang
authors.forename: Jason L
authors.initials: JL
authors.lastname: Koh
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Hendrix
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Zhang
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000295:instrumentation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D010329:Patella / Q000000981:diagnostic imaging / Q000502:physiology*; D011859:Radiography