The value of preoperative planning for total hip arthroplasty.

To analyse the value and accuracy of preoperative planning for total hip replacement (THR) we digitised electronically and compared the hand-sketched preoperative plans with the pre- and postoperative radiographs of 100 consecutive primary THRs. The correct type of prosthesis was planned in 98%; the agreement between planned and actually used components was 92% on the femoral side and 90% on the acetabular side. The mean (+/- SD) absolute difference between the planned and actual position of the centre of rotation of the hip was 2.5 +/- 1.1 mm vertically and 4.4 +/- 2.1 mm horizontally. On average, the inclination of the acetabular component differed by 7 +/- 2 degrees and anteversion by 9 +/- 3 degrees from the preoperative plans. The mean postoperative leg-length difference was 0.3 +/- 0.1 cm clinically and 0.2 +/- 0.1 cm radiologically. More than 80% of intraoperative difficulties were anticipated. Preoperative planning is of significant value for the successful performance of THR.