Biomechanical Factors Contributing to Patellomoral Pain: The Dynamic Q Angle Division Biokinesiology & Physical Therapy Co Director, oratory University of Southern California Movement Performance Institute Los Angeles, CA Abnormal loading as a potential factor in the genesis of patellofemoral pain Dye, Sports Med Arthroscopy Rev, 2001 Pain readily reproduced with activities that require quadriceps contraction Do Persons with PFP Demonstrate Elevated PFJ Loading?
Subject specific 3D PFJ model 3D Representation of the Extensor Mechanism (MRI) Kinematics, kinetics, and EMG during functional activities 3D Vasti Muscle & Patellar Ligament Orientation Optimization Routine to Establish Vasti & Patellar Ligament Forces 3D PFJRF s Chen, Scher & Powers, J Appl Biomech, 2010 Model Validation Powers et al., J Biomech, 2006 Model Validation Powers et al., J Biomech, 2006 Total magnitude (N) 350 300 250 200 150 100 50 In-vitro measurements Computer model Total mag nitude: Compu ter model 300 250 200 150 0deg 20deg 40deg 60deg R 2 = 0.91 0 0 deg 20 deg 40 deg 60 deg Knee flexion angle 100 100 150 200 250 300 Total magnitude: In-vitro measurement
Resultant PFJRF: Running * Chen & Powers (in review) Walking 6.4 (1.8) Posterior force Superior force Lateral force PFP Control PFP Control PFP Control 8.0 (2.1) 5.1 (1.0) 6.7 (1.4) 1.8 (0.6) 1.6 (0.8) Descent 20.9 27.7 5.1 6.9 7.2 3.3 (2.3) (2.9) (1.3) (1.1) (1.5) (1.2) Ascent 28.2 (3.1) Running 41.2 (4.2) 34.5 (4.1) 51.6 (4.7) 6.5 (1.7) 15.0 (2.4) 8.9 (2.1) 18.9 (3.0) 7.8 (1.6) 8.4 (1.0) 4.1 (1.3) 6.6 (0.7) Average 24.2 30.5 7.9 10.4 6.3 3.9 Chen & Powers (in review) Lower limb alignment & lateral forces on the patella Q angle: 15 Lateral vector
Dynamic Q Angle Subject specific 3D PFJ model 3D Representation of the Extensor Mechanism (MRI) Kinematics, kinetics, and EMG during functional activities 3D Vasti Muscle & Patellar Ligament Orientation Optimization Routine to Establish Vasti & Patellar Ligament Forces 3D PFJRF s Dynamic Q-angle Chen, Scher & Powers, J Appl Biomech, 2010 Dynamic Q angle Stair descent 39.1 vs. 24.2 p = 0.01 Chen & Powers (in review)
Predictors of the Dynamic Q angle Four variables combined explained 70.3% of the variance in average dynamic Q angle 1. Kneefrontal plane motion (40.1%) 2. Knee transverse plane motion (13.8%) 3. Patella ligament orientation in the frontal plane (9.1%) 4. Vastus lateralis frontal plane orientation (7.3%) Chen & Powers (in review) Distal factors Dynamic Q Angle Pronation Tibial internal rotation Proximal factors Femoral adduction Femoral internal rotation
Distal motions that can influence the Dynamic Q angle Powers CM. J Orthop Sports Phys Ther, 2003 Foot Pronation Tibia rotation Foot pronation contributes to tibia internal rotation Common assumption: Excessive Pronation contributes to PFP
Tibia internal rotation decreases the Q Angle 15 6 PFJ contact pressure & tibial rotation Tibia internal rotation had no influence on contact area & pressure Tibial external rotation results in an increase in lateral facet pressure. Lee et al., J Rehabil Res Dev, 2001. Foot Pronation & Patellofemoral Pain Messier et al., 1991 No difference between controls and PFP runners on running rearfoot motion measures. Powers et al., 2002 No differences in peak pronation between patients with PFP and healthy controls.
Foot Pronation & Patellofemoral Pain Levinger & Gilleard, 2006 Prolonged rearfoot eversion in females with PFP. No difference in tibial rotation between PFP and control groups. Hetsroni et al., 2006 No relationship between static & dynamic rearfoot measures and the development of PFP. Proximal motions that can influence the patellofemoral joint Powers CM. J Orthop Sports Phys Ther, 2003, 2010. Hip internal rotation Contributes to dynamic knee valgus & maltracking Hip adduction Contributes to dynamic knee valgus Half of the PFJ is the Femur!!
Femoral Rotation Powers et al. JOSPT, 2003 Non weightbearing Weightbearing Powers et al. JOSPT, 2003
Hip Internal Rotation PFP vs. Control p < 0.001 Drop Jump Running Step Down Souza & Powers, JOSPT, 2009
Weight bearing MRI 25 15 PFP subject (right leg) Control subject (left leg) Souza & Powers, JOSPT, 2010 Femoral IR: Weightbearing MRI PFP vs. Control Souza & Powers, JOSPT, 2010 Femoral Adduction
Dynamic knee valgus increases the Q Angle 15 23 Dynamic Q Angle
Dynamic Q Angle Increased lateral forces Q Q How much of a change in the Q angle is relevant? Huberti & Hayes., JBJS, 1984 10 degree change in the Q angle increased peak pressures by 45%. A decrease in the Q angle decreased stress on the lateral facet and median ridge
Summary The lateral forces acting on the patella are largely influenced by abnormal motions of the lower extremity. Excessive hip rotation and adduction have the largest influence on the dynamic Q angle. Excessive Foot pronation would not be expected to alter the lateral forces acting on the patella Musculoskeletal Biomechanics Research Laboratory University of Southern California Questions?