Femoral head-neck offset (femoroacetabular impingement)
Femoral head-neck offset is a measurement for characterization of hip morphology.
Usage
Femoral head-neck offset is used for quantitative characterization of the femoral head-neck junction, in particular in the setting of suspected femoroacetabular impingement for the detection of cam morphology and preoperative planning.
Measurement
The distance between the tangent of the femoral neck and a tangent cutting the femoral head is obtained with both tangents paralleling the femoral neck axis.
In addition, a head-neck offset ratio can be determined by dividing the femoral head-neck measurement by the femoral head diameter . This can be done radiographically from lateral views of the hip or with CT or MRI
Interpretation
Radiographically a femoral head-neck offset ratio <0.17 is considered indicative for cam morphology .
Femoral offset measurements in the anterosuperior position in MRI yielded the smallest values with a suggested threshold of 6-7 mm with sensitivities and specificities in the 55-65% range .
See also
