Femoral head-neck offset (femoroacetabular impingement)
Femoral head-neck offset is a measurement for characterization of hip morphology.
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.
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 2-4. This can be done radiographically from lateral views of the hip 2-4 or with CT 5 or MRI 6
Radiographically a femoral head-neck offset ratio <0.17 is considered indicative for cam morphology 2-5.
Femoral offset measurements in the anterosuperior position in MRI yielded the smallest values with a suggested threshold of 6-7 mm 6 with sensitivities and specificities in the 55-65% range 6.
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