Hip External Rotation Decreases Ischiofemoral Distance: A Positive Correlation Between Cadaveric and Fluoroscopic Studies

Purpose

To determine the effect of hip external rotation or extension/adduction on minimizing the ischiofemoral distance (IFD) and assess the correlation between cadaveric and fluoroscopic IFD measurements in different hip positions.

Methods

This cadaveric study involved 33 hip joints from 17 embalmed cadavers. IFD, the distance between the lesser trochanter and lateral ischium, was measured in different hip positions: neutral, external rotation at 30°, and external rotation at 60° with the hip in both neutral extension and adduction as well as 10° hip extension and 10° hip adduction. Differences in IFD related to positions and correlation between cadaveric and fluoroscopic measurements were analyzed.

Results

IFD measurements showed that the greatest reduction occurred at 60° of external hip rotation, with a significant difference observed only between neutral and 60° external rotation in cadaveric groups (7.60 ± 4.68 vs 5.05 ± 3.48, 95% CI, 0.14-4.96; P = .036). No substantial difference was observed between the extension and adduction positions. Positive correlations were observed between cadaveric and fluoroscopic measurements, especially in the neutral position (r = 0.492, P = .004), external rotation at 30° (r = 0.52, P = .002), external rotation at 60° (r = 0.419, P = .015), and the extension/adduction positions combined with neutral rotation (r = 0.396, P = .023).

Conclusions

The IFD significantly decreased with increasing degrees of hip external rotation, particularly at 60°. No significant reduction was observed in the extension/adduction positions. In addition, positive correlations were observed between cadaveric and fluoroscopic measurements for specific hip positions: neutral rotation, external rotation at 30° and 60°, and extension/adduction at 10° with neutral rotation.

Clinical Relevance

Surgeons can use this knowledge to improve hip impingement assessment through radiography, focusing on positions in which IFD reduction is most notable. Understanding the relationship between hip positions and IFD can enhance the diagnosis of ischiofemoral impingement syndrome and benefit patient care and outcomes.