OP4.4 Kinematics of the Ischiofemoral Space and Evaluation of Hip Morphologic Characteristics

Background: Ischiofemoral impingement (IFI) is an extra-articular form of posterior hip pain caused by narrowing of the space between the ischial tuberosity and lesser trochanter. The ischiofemoral space (IFS) can vary with differences in hip and pelvic morphology, as well as dynamically change throughout hip range of motion.

Purpose: To evaluate morphologic characteristics of the hip and pelvis in relation to the IFS during standing, gait, and standing pivot (hip extension/adduction/external rotation).

Methods: Twenty-four asymptomatic participants (11 men, 13 women; mean age 22 ± 2 years) were enrolled in this study. Synchronized biplane radiographs were collected during standing, gait, and standing pivot. Subject-specific models were created by segmenting computed tomography (CT) scans of each participant’s femur and pelvis. Bone motion was determined by a validated volumetric model-based tracking technique that matched digitally reconstructed radiographs to biplane radiographs. Anatomic coordinate systems were established in each femur and hemi-pelvis and regions of interest including the lateral cortex of the ischial tuberosity and medial aspect of the lesser trochanter were digitally marked to dynamically measure the IFS. Morphologic measurements of the hip and pelvis were performed and correlated with the minimum distance of the IFS using the Pearson coefficient.

Results: Across all hips, the average minimum IFS during standing, gait, and standing pivot were 24.9 ±7.0 mm, 14.5 ±6.5 mm, and 13.3 ±6.8 mm, respectively. Significant differences were present between average minimum IFS during standing as compared to gait (r=0.864, p<0.001) and standing pivot (r=0.824, p<0.001). Intertuberous distance had a negative correlation with IFS during standing (r=0.336, p=0.030) and gait (r=0.359, p=0.013). Femoral version was inversely correlated with IFS during standing pivot (r=0.336, p=0.026). There was a negative correlation between acetabular version and IFS during standing (r=0.350, p=0.025), gait (r=0.394, p=0.007), and standing pivot (r=0.405, p=0.007). The McKibbin index was negatively correlated with IFS during gait (r=0.351, p=0.017) and standing pivot (r=0.431, p=0.004).

Conclusion: The IFS varies with hip position, with motion involving hip extension generally resulting in a smaller IFS. Hip morphology including increased intertuberous distance, femoral version, acetabular version, and hip McKibbin index appear to be associated with a smaller IFS.