The accuracy of sizing of the femoral component in total knee replacement

Femoral sizing in total knee replacement is important. Either undersizing or oversizing may result in deleterious effects to the clinical outcome after the surgery. There has been no study on the precision and accuracy of femoral sizing and the effect of measurement at different landmarks over the distal femur. This study assesses the intra-observer and inter-observer error of femoral sizing and identifies the effect of the placement site of the anterior referencing tool on femoral sizing.

Five investigators with different clinical experience measured the femoral size of 10 cadaveric specimens twice using three anterior referencing tool. The measurement of the femoral size was repeated at nine designated points on the anterior cortex of the cadaveric femora.

Excellent intraobserver and interobserver agreements were obtained using the three anterior referencing tools. When the size on which the majority agreed was regarded as the actual size of the specimen, measurement at the nine designated points on the anterior cortex showed a deviation from the actual size from 6.2 to 46.2 %. Placing the femoral sizer stylus at the middle and 2 cm above the proximal margin of the anterior femoral condyle yielded the highest precision and accuracy.

Regardless of the experience of the surgeons, measurement of the femoral size using the three anterior referencing tools is very accurate. Placing the stylus of the femoral sizer at the middle and 2 cm above the proximal margin of the anterior femoral condyle best reflects the actual size of the femur.

Experimental study.