Differences in Hip Joint Biomechanics and Muscle Activation in Individuals With Femoroacetabular Impingement Compared With Healthy, Asymptomatic Individuals: Is Level-Ground Gait Analysis Enough?

BACKGROUND: Femoroacetabular impingement (FAI) is a recognized cause of hip and groin pain and a significant factor in hip joint function during sport. Objective tests for understanding hip function are lacking in this population. PURPOSE: To determine whether biomechanical and electromyographic features of hip function during level-ground walking differ between a group diagnosed with FAI and those with no symptoms of FAI. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 20 asymptomatic individuals and 20 individuals with FAI walked on a dual-belt instrumented treadmill at self-selected walking velocities. Sagittal and frontal plane joint motions, moments, and muscle activation for the gluteus medius, gluteus maximus, rectus femoris, and medial and lateral hamstrings were analyzed. Discrete measures were extracted from each biomechanical waveform, and principal component analysis was used to determine hip joint muscle activation and hip adduction moment patterns. Statistical significance was determined by use of Student t tests with Bonferroni adjustments for multiple comparisons (α = .05). RESULTS: Individuals with FAI walked more slowly (P = .015) and had lower self-reported function (P < .001). No differences in muscle strength were found between the symptomatic and contralateral legs in the FAI group (P > .017), but those with FAI had lower strength in the knee extensors and flexors and the hip extensors, flexors, and adductors compared with the asymptomatic group (P < .017). Individuals with unilateral symptomatic FAI walked with similar biomechanical and hip muscle electromyographic results bilaterally. The only differences found were a greater amplitude of gluteus maximus activation in the FAI symptomatic leg compared with the asymptomatic group and greater medial hamstring activation than lateral hamstring activation in the FAI group in both limbs compared with the asymptomatic group. CONCLUSION: Individuals with FAI were generally deconditioned and reported significantly more functional limitations. No biomechanical differences existed between groups during level walking, yet hamstring and gluteus maximus activation differed when the symptomatic group was compared with the asymptomatic group. CLINICAL RELEVANCE: The field lacks objective testing of hip joint function to understand implications of FAI for dynamic movements, particularly with applications to biomechanics and electromyography. Level walking was of limited value for understanding FAI hip function, and the development of a more challenging gait assessment is warranted.