The influence of tibiofemoral kinematics and kinetics on patella cartilage stress: a comparison of recreational runners with and without patellofemoral pain

A commonly cited hypothesis to the cause of patellofemoral pain (PFP) is elevated patellofemoral joint stress. Previous studies have reported that persons with PFP exhibit elevated patellofemoral joint stress during walking and squatting. It also has been suggested that the location and magnitude of patellofemoral stress may be dependent on tibiofemoral kinematics and kinetics in the frontal, transverse, and/or sagittal planes. To date, it is not known which kinematic and/or kinetic variables are most predictive of the magnitude or location of peak patellofemoral joint stress. The purpose of this dissertation was to quantify the interrelationship among tibiofemoral kinematics/kinetics and patella cartilage stress in recreational runners with and without PFP. To accomplish this objective, 3 studies were undertaken. ❧ The purpose of Chapter III was to determine the influence of femur and tibia rotations in the frontal and transverse planes on average patella cartilage stress. Patella cartilage stress profiles of 6 healthy females were obtained during a squatting task using subject-specific finite element (FE) models of the patellofemoral joint (45° of knee flexion). Input parameters for the FE model included joint geometry, quadriceps muscle forces, and weight-bearing patellofemoral joint kinematics. The femur and tibia of each model were then rotated 10° (in 2° increments) along their respective axes beyond that of the natural degree of rotation. The process was repeated for the transverse plane (internal and external rotation) and frontal plane (adduction and abduction). Quasi-static loading simulations were performed to quantify average patella cartilage stress. In the transverse plane, incremental femur internal rotation beyond that of the natural rotation resulted in progressively higher average patella cartilage stress (41-77%), whereas incremental tibia internal rotation resulted in a decrease in average patella cartilage stress (7-10%). Femur and tibia external rotation resulted in a mild increase in average patella cartilage stress, but only at 10° (9%). In the frontal plane, incremental femur adduction resulted in an increase in average patella cartilage stress, but only at 10° (43%). Femur abduction and frontal plane tibia rotation in either direction had no influence on average patella cartilage stress. ❧ The purpose of Chapter IV was to determine whether recreational runners with PFP exhibit greater peak patella cartilage stress compared to pain-free runners. A secondary purpose was to determine the kinematic and/or kinetic predictors of peak patella cartilage stress during running. Twenty-two female recreational runners participated (12 with PFP and 10 pain-free controls). Patella cartilage stress profiles were quantified using subject-specific FE models simulating the maximum knee flexion angle during stance phase of running. Input parameters to the FE model included subject-specific patellofemoral joint geometry, quadriceps muscle forces, and lower extremity kinematics in the frontal and transverse planes. Tibiofemoral kinematics and kinetics were quantified to determine the best predictor of elevated peak patella cartilage stress using stepwise regression analysis. Compared to the pain-free runners, those with PFP exhibited greater peak patella cartilage hydrostatic pressure (mean ± SD, 21.2 ± 5.6 MPa vs. 16.5 ± 4.6 MPa, p<0.05) and maximum shear stress (11.3 ± 4.6 MPa vs. 8.7 ± 2.3 MPa, p<0.05). Transverse plane knee external rotation was the best predictor of peak hydrostatic pressure and peak maximum shear stress (38% of variance, r=0.62 and 25% of variance, r=0.50, respectively) followed by the knee extensor moment (21% of variance, r=0.36 and 25% of variance, r=0.49, respectively). ❧ The purpose of Chapter V was to determine whether the location and magnitude of peak patella cartilage stress varies among runners with and without PFP. A secondary purpose was to determine whether tibiofemoral kinematics in the frontal and transverse planes predict peak lateral and medial patella cartilage stress. Twelve runners with PFP and 10 pain-free controls participated. Peak patella cartilage stress (hydrostatic pressure) was quantified using subject-specific FE models simulating maximum knee flexion angle during stance phase of running. Chi-square analysis was used to determine whether the location of peak patella cartilage stress (medial or lateral facet) varied between runners with and without PFP. Independent t-tests were used to determine whether the magnitude of peak cartilage stress on the medial and lateral patella facets varied between groups. In addition, stepwise regression analysis was performed to determine if tibiofemoral kinematics in the frontal and transverse planes were predictive of peak medial and lateral cartilage stress for both groups combined. Among all subjects, 64% exhibited peak cartilage stress on the lateral patella facet. The proportion of runners who exhibited peak cartilage stress on the medial and lateral patella facets was statistically similar between groups. No group differences were found for the magnitude of peak cartilage stress on the medial or lateral facets. Tibiofemoral rotation in the transverse plane was positively correlated with peak lateral stress and was the best predictor (45% of the variance, r=0.67). Tibiofemoral rotation in the transverse plane was negatively correlated with peak medial stress (44% of the variance, r=-0.67) and was the best predictor, followed by tibiofemoral rotation in the frontal plane (26% of the variance, r=0.57). ❧ Taken together, the results of the dissertation suggest that tibiofemoral kinematics and kinetics are associated with the location and magnitude of patella cartilage stress. Our study provides justification for the hypothesis that excessive rotations of the femur and tibia in the transverse and frontal planes contribute to mechanical overloading of the patellofemoral joint, and therefore, may play a role in the development of PFP. These findings emphasize the need for clinicians to identify and correct altered tibiofemoral kinematics in the transverse and frontal planes (if present), in runners with PFP.