Ischiofemoral impingement: defining the lesser trochanter-ischial space.

PURPOSE: The purpose of this study was to define changes in the ischial-lesser trochanteric space associated with medial and lateral hip rotation in neutral and 10° of extension and adduction.

METHODS: Twenty-five hip joints from 14 embalmed cadavers (7 males and 7 females) were used for this study. The pelvic region of each cadaver was skeletonized, and the hip capsule released distally. With the hip joint in 0° flexion-extension/abduction-adduction, the distance between the lesser trochanter and ischium was measured in: neutral rotation, 40° medial rotation, and 60° lateral rotation. A one-way ANOVA with post hoc analysis determined the difference in the ischiofemoral space in these three positions. An additional position was then tested by laterally rotating the femur with the hip joint positioned in 10° extension and adduction.

RESULTS: The average distance between the lesser trochanter and ischium was different (p < .0005) in neutral rotation, 40° medial rotation, and 60° lateral rotation at 2.8 cm (SD 1.1), 4.3 cm (SD 1.2), and 1.4 cm (SD 0.7), respectively. With the hip joint laterally rotated from a starting position of 10° extension and adduction, 21 of 25 (84 %) hips made contact between the lesser trochanter and ischium at an average position of 29° (SD 20) of lateral rotation.

CONCLUSIONS: The lesser trochanter is closest to the ischium in lateral rotation and is furthest away in medial rotation when the hip is in neutral flexion-extension/abduction-adduction. The lesser trochanter approximates the ischium when the hip is laterally rotated in 10° extension and adduction. The information gained through this investigation helps to define the pathomechanics associated with ischiofemoral impingement and validate clinical tests to diagnose ischiofemoral impingement.