Gait deviations and muscle strength deficits in subjects with patellar instability

Background: Abnormal tracking of the patella is a hallmark sign of patellar instability (PI). Gait deviations and strength deficits may exacerbate abnormal tracking. The identification of modifiable gait deviations and strength deficits can aid in developing more effective management strategies for individuals with PI. The purpose of this study was to identify modifiable gait and strength deficits in subjects with PI. Methods: 32 subjects (16 PI, 16 controls, 3 males/13 females in each group, 21.1 years old, 23.5 BMI), performed an instrumented gait analysis while walking at 1.5 m per second. Subjects' peak hip adduction angles, external rotation angles, hip abduction moments, knee flexion angles, knee adduction angles, and knee extensor moments were measured during walking. Hip abduction, hip external rotation, and knee extension strength were assessed with a handheld dynamometer. Results: Individuals with PI displayed significantly lower peak knee adduction angles (1.8 ± 2.8° PI, 5.5 ± 4.5° control, p <.01) and peak hip abduction moments (0.2 ± 0.1 Nm/kg*m PI, 0.4 ± 0.1 Nm/kg*m control, p <.01). Subjects with PI were weaker in knee extension strength (14.5 ± 4.1 kg/m PI, 23.8 ± 7.2 kg/m control, p <.01), hip abduction strength (12.1 ± 2.0 kg/m PI, 17.8 ± 4.0 kg/m control, p <.01), and hip external rotation strength (5.5 ± 1.9 kg/m PI, 7.1 ± 1.3 kg/m control, p =.01). Conclusion: Subjects with patellar instability have smaller joint moments and a more valgus knee position while walking. Coupled with deficits in muscle strength, this likely contributes to subjective reports of chronic patellar instability. Level of Evidence.