Varus/valgus alignment of the femoral component in total knee arthroplasty

The position of the femoral component in 362 total knee replacements was assessed radiologically. A subgroup of 32 knees, 18 of which had perfect alignment and 14 with imperfect alignment underwent CT scout scans of the femur from which the mechanical axis of the femur could be measured. Radiologically 92% of all components were implanted within 3 degrees of the target value. There was close correlation between the CT and X-ray measurements in the subgroup. Deviation from the mechanical axis was 1.16 degrees (range -2.5 to +2) in the perfectly aligned knees, validating both surgical technique and radiological assessment. Causes for inaccuracy in femoral placement and future likely developments are discussed.