CORR Insights®: Differences in Femoral Torsion Among Various Measurement Methods Increase in Hips With Excessive Femoral Torsion

摘要

Femoral torsion refers to the angle of offset between the proximal and distal portions of the femur in the transverse plane, typically defined distally by the condylar axis and proximally by the center of the femoral head and another anatomic landmark. Excessive internal rotation has been described as both a risk factor for lateral patellar instability [ ] and as a predisposing factor for femoroacetabular impingement (FAI) [ ]. For patellar instability, clinicians typically look for maltorsion of more than 15 as an indication for surgical intervention [ ]. However, using a measurement to determine the proper course of treatment is predicated on the idea that the clinician has access to a reliable measurement method and a reliable normal range of measurements for comparison. Many different imaging techniques have been used to reliably measure femoral torsion, including biplanar radiography [ ], CT [ ], ultrasound [ ], and MRI [ ]. Additionally, there are many ways to identify anatomic landmarks for defining the proximal and distal axes that are used to measure femoral torsion. Therefore, while the intra and interrater reliability has been strong using most measurement methods and modalities, the actual measurement of femoral torsion can vary greatly depending on the type of imaging and measurement definition used to obtain the measurement. For example, Kuo and colleagues [ ] found a mean difference of 13.5 in femoral torsion values when comparing biplane radiography with CT in normal adult cadavers. In the current paper by Schmaranzer and colleagues [ ], five different methods for defining the rotation of the proximal femur were compared using CT scans of patients with hip pain and physical findings suggestive of FAI. The authors found that inter and intrarater reliability was strong for each measurement method, but differences between torsion values increased when a more-distal definition of the proximal axis was used, and in patients who had more-severe maltorsion [ ]. Similar results were previously found in a study that compared different measurement methods for CT images in average adult human cadavers [ ], although this study did not include a wide range of torsional values within its sample. Another study [ ] reported good reliability in femoral torsion values using radiography and CT in children.