BACKGROUND

Patients with frog-leg squatting have restricted internal rotation and adduction of the affected hips during sitting or squatting. In the surgical literature, the cause generally has been presumed to arise from and be pathognomonic for gluteal muscle contracture. However, we have encountered patients with frog-leg squatting but without gluteal muscle contracture.

QUESTIONS/PURPOSES: We therefore raised the following questions: What are the imaging features of patients with frog-leg squatting? Do conditions other than gluteal muscle contracture manifest frog-leg squatting?

PATIENTS AND METHODS

We retrospectively reviewed the MR images of 67 patients presenting with frog-leg squatting from April 1998 to July 2010. There were four females and 63 males; their mean age was 22.2 years (range, 4-50 years). During MRI readout, we observed aberrant axes of some femoral necks and obtained additional CT to measure femoral torsion angles in 59 of the 67 patients.

RESULTS

MR images of 27 (40%) patients had signs of gluteal muscle contracture. Twenty-two (33%) patients (40 femora) had aberrant femoral torsion, including diminished anteversion (range, 6°-0°; average, 3.9°) in 11 femora of eight patients and femoral retroversion (range, < 0° to -31°, average, -7.5°) in 29 femora of 17 patients. The remaining 18 (27%) patients did not have gluteal muscle contracture or aberrant femoral torsion. The observation of aberrant femoral torsion was not anticipated before imaging studies.

CONCLUSIONS

In addition to gluteal muscle contracture, aberrant femoral torsion can be a cause of frog-leg squatting.

LEVEL OF EVIDENCE

Level II, diagnostic study. See the guidelines for Authors for a complete description of levels of evidence.