The Relationship Between Quadriceps Strength And Gait Mechanics In Individuals With Patellar Instability

PURPOSE: Patellar instability is a common athletic injury leading to increased risk for early development of patellofemoral osteoarthritis. After injury, these individuals often demonstrate altered gait patterns to offload and “protect” the knee joint; however, factors that may contribute to these gait patterns, such as quadriceps strength, have not been investigated in this population. Therefore, the purpose of this study was to explore the effect of quadriceps strength on gait mechanics in individuals with patellar instability. METHODS: 16 individuals with patellar instability (8 F, age: 21 +/- 7 years) were recruited to participate. Isometric knee extension strength testing was completed using an isokinetic dynamometer at 90° of knee flexion. Peak torque was determined as the average of 4 maximum effort kicks and compared between limbs. A three-dimensional gait analysis was performed as participants walked at 1.2 m/s on an instrumented treadmill. Knee angle at initial contact and knee flexion excursion during stance were collected and compared between the injured (INJ) and noninjured (NON) limbs. Relationships between peak torque, knee angle at initial contact, and knee flexion excursion were explored with Pearson’s correlations and linear regressions. Significance was set at p < 0.05. RESULTS: Significant between limb differences were present for peak torque (INJ: 2.0, NON: 2.6 Nm/kg, p < 0.01), knee flexion excursion (INJ: 13.9°, NON: 17.4°; p < 0.01), and knee angle at initial contact (INJ: 5.5°, NON: 2.5°; p = 0.03). A significant positive correlation was present between peak torque and knee flexion excursion (R2 = 0.35, p = 0.02), but not between peak torque and knee angle at initial contact (R2 = 0.12, p = 0.19). CONCLUSIONS: After patellar dislocation, individuals have reduced quadriceps strength and display traits of a quadriceps avoidant gait pattern, including greater knee flexion at initial contact and reduced knee flexion excursion throughout stance. However, these compensatory gait patterns were partially mitigated by greater quadriceps strength. Emphasis on restoring quadriceps strength after injury should be considered to help normalize gait mechanics in individuals with patellar instability, especially since altered gait mechanics have been shown to affect patellofemoral joint stress. Supported by: Department of Defense Grant No. CDMRP- PR191214