Kinematics of the ischiofemoral space and evaluation of hip morphologic characteristics

Abstract Ischiofemoral impingement is an extra-articular form of hip pain caused by narrowing of the space between the ischial tuberosity and lesser trochanter. The ischiofemoral space (IFS) can vary with hip morphology, as well as dynamically change throughout hip range of motion. The objectives of this study were to evaluate the impact of movement (gait, standing pivot, and neutral standing) and sex on IFS, as well as determine what morphological characteristics correlate with IFS. Synchronized biplane radiographs were collected from 24 participants during treadmill walking, standing pivot, and neutral standing. Subject-specific bone models, created from CT images, were used to create digitally reconstructed radiographs that were registered to the biplane radiographs using a validated matching technique. The ischial tuberosity and lesser trochanter were digitally marked to dynamically measure the IFS. Morphologic measurements were correlated with the IFS, and the effects of sex and movement on IFS were calculated. During the gait cycle, IFS was narrowest at contralateral heel strike (47%–53% of the gait cycle) and greatest during mid-swing (~85% of the gait cycle). Across all movements, IFS was greatest during standing (P < .001). There was a moderate negative correlation between acetabular version (AV) and IFS during gait (P = .002) and standing pivot (P = .007). McKibbin index was moderately negatively correlated with IFS during standing pivot (P = .001). The IFS varies with hip position, with motion involving hip extension, such as walking and pivot activities, resulting in a smaller IFS. Greater central AV and McKibbin index are associated with a smaller IFS.