Ischiofemoral impingement: the evolutionary cost of pelvic obstetric adaptation

Abstract

The risk for ischiofemoral impingement has been mainly related to a reduced ischiofemoral distance and morphological variance of the femur. From an evolutionary perspective, however, there are strong arguments that the condition may also be related to sexual dimorphism of the pelvis. We, therefore, investigated the impact of gender-specific differences in anatomy of the ischiofemoral space on the ischiofemoral clearance, during static and dynamic conditions. A random sampling Monte-Carlo experiment was performed to investigate ischiofemoral clearance during stance and gait in a large (n = 40 000) virtual study population, while using gender-specific kinematics. Subsequently, a validated gender-specific geometric morphometric analysis of the hip was performed and correlations between overall hip morphology (statistical shape analysis) and standard discrete measures (conventional metric approach) with the ischiofemoral distance were evaluated. The available ischiofemoral space is indeed highly sexually dimorphic and related primarily to differences in the pelvic anatomy. The mean ischiofemoral distance was 22.2 ± 4.3 mm in the females and 29.1 ± 4.1 mm in the males and this difference was statistically significant (P < 0.001). Additionally, the ischiofemoral distance was observed to be a dynamic measure, and smallest during femoral extension, and this in turn explains the clinical sign of pain in extension during long stride walking. In conclusion, the presence of a reduced ischiofemroal distance and related risk to develop a clinical syndrome of ischiofemoral impingement is strongly dominated by evolutionary effects in sexual dimorphism of the pelvis. This should be considered when female patients present with posterior thigh/buttock pain, particularly if worsened by extension. Controlled laboratory study.

Fig. 1.

Secundary ischiofemoral impingement in a 20-year-old gymnast following apophysiolysis of the left tuber ischiadiucum (asterisk).

Fig. 2.

Radiographic assessment in a patient suspected with ischiofemoral impingement, demonstrating a narrow ischiofemoral distance on MRI (A) and 3D reconstructions (B) in combination with edema of the quadratus femoris muscle (A).

Fig. 3.

Anatomical descriptors used to evaluate the impact of ischiofemoral distance on gender-specific gait and shape. (A and B) The femoral anatomic measures of femoral anteversion, lesser trochanter retroversion, femoral offset, femoral neck–shaft angle and head radius for the femur. (C and D) pelvic anatomic measures of pelvic width and interspinous distance shown in the frontal plane.

Fig. 4.

Pelvifemoral anatomic differences between sexes in the virtual population.

Fig. 5.

Ischiofemoral distance determined as a function of hip flexion angle on each of 40 000 virtual population models. Minimum ischiofemoral distance was observed during terminal stance to pre-swing phase of the gait cycle.

Fig. 6.

Gender-specific shape regressions for ±3 standard deviations of ischiofemoral distance calculated from the virtual population. The impact of hemipelvic version is shown by red arrows.