MRI Effective in Assessing Abnormal Femoral Antetorsion, or In-Toeing

MRI is effective in measuring abnormal femoral antetorsion, or in-toeing, with good reproducibility. The images can then be used in treatment planning for patients with femoroacetabular impingement, according to researchers from Orthopedic University Hospital Balgrist in Zurich, Switzerland.

In the study published online March 8 in the journal Radiology, the researchers, led by Reo Sutter, MD, recruited 63 asymptomatic volunteers and 63 symptomatic patients to assess the range of femoral antetorsion using MRI. All subjects underwent standard imaging plus two additional rapid transverse sequences of the proximal and distal femur for antetorsion measurements. Twenty volunteers had a repeat MRI performed on the same leg. Measurements were taken by two independent readers.

Researchers found that the MRI assessments could be made in approximately 80 seconds; both readers had the same value and the different MRIs had similar findings.

Patients with pincer-type FAI, which occurs when the acetabulum has too much covering of the femoral head, had significantly higher femoral antetorsion than did patients with cam-type FAI, which is characterized by abnormalities in the femoral head and neck.

This study’s findings could make it useful for orthopedic surgeons to know what angle is present before performing osteochondroplasty of the proximal femur and acetabular rim section in patients with FAI, the researchers wrote. “However, on the basis of the wide range of femoral antetorsion angles we found in the population of volunteers, there is no single cutoff value that separates a normal versus abnormal antetorsion.”