title: Patellofemoral kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella: a preliminary study.
abstract: METHODS
  Single-group, repeated-measures design.
  
  
  OBJECTIVE
  To compare patellofemoral joint kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella.
  
  
  BACKGROUND
  The only previous study to quantify differences in patellofemoral joint kinematics during weight-bearing and non-weight-bearing tasks was limited in that static loading conditions were utilized. Differences in patellofemoral joint kinematics between weight-bearing and non-weight-bearing conditions have not been quantified during dynamic movement.
  
  
  METHODS
  Six females with a diagnosis of patellofemoral pain and lateral subluxation of the patella participated. Using kinematic magnetic resonance imaging, axial images of the patellofemoral joint were obtained as subjects extended their knee from 45 degrees to 0 degrees during non-weight-bearing (5% body weight resistance) and weight-bearing (unilateral squat) conditions. Measurements of patellofemoral joint relationships (medial/lateral patellar displacement and patellar tilt), as well as femur and patella rotations relative to an external reference system (ie, the image field of view), were obtained at 3 degrees increments during knee extension.
  
  
  RESULTS
  During non-weight-bearing knee extension, lateral patellar displacement was more pronounced than during the weight-bearing condition between 30 degrees and 12 degrees of knee extension, with statistical significance being reached at 27 degrees, 24 degrees, and 21 degrees. No differences in lateral patellar tilt were observed between conditions (P = .065). During the weight-bearing condition, internal femoral rotation was significantly greater than during the non-weight-bearing condition as the knee extended from 18 degrees to 0 degrees. During the non-weight-bearing condition, the amount of lateral patellar rotation was significantly greater than during the weight-bearing condition throughout the range of motion tested.
  
  
  CONCLUSIONS
  The results of this study demonstrated that lateral patellar displacement was more pronounced during non-weight-bearing knee extension compared to weight-bearing knee extension in persons with lateral patellar subluxation. In addition, the results of this investigation suggest that the patellofemoral joint kinematics during non-weight-bearing could be characterized as the patella rotating on the femur, while the patellofemoral joint kinematics during the weight-bearing condition could be characterized as the femur rotating underneath the patella.
authors.affiliation: Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapy, University of Southem California, Los Angles, CA, USA. powers@usc.edu
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Powers
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Ward
authors.forename: Michael
authors.initials: M
authors.lastname: Fredericson
authors.forename: Marc
authors.initials: M
authors.lastname: Guillet
authors.forename: Frank G
authors.initials: FG
authors.lastname: Shellock
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000503:physiopathology; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D007592:Joint Diseases / Q000503:physiopathology*; D007717:Knee / Q000033:anatomy & histology / Q000502:physiology; D007719:Knee Joint / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D010329:Patella / Q000033:anatomy & histology / Q000502:physiology; D011795:Surveys and Questionnaires; D016474:Weight-Bearing / Q000502:physiology*