Preoperative templating of femoral components on plain X-rays. Rotational evaluation with synthetic X-rays on ORTHODOC.

INTRODUCTION: Preoperative femoral templating for total hip arthroplasty (THA) has been performed by antero-posterior radiographs of both hips which should be taken with the femur rotated internally to reduce the effect of femoral anteversion. However, there is no criterion to evaluate the optimal rotated radiograph. Here, we quantitatively investigated 50 femora whether the thickness of the lesser trochanter (TLT) was useful when evaluating the femoral rotation, and assessed the effect of prosthetic templating on the inappropriate rotated radiographs.

MATERIALS AND METHODS: We assessed 50 femora of 46 consecutive osteoarthritic patients using "synthetic X-ray" based on computer tomography (CT) images, which can be displayed as virtual plain radiographs with any magnification and any projected direction such as plain radiographs. We made four femoral radiograph groups of different rotation prepared (neutral, 15 degrees, 30 degrees, and 45 degrees external rotation), and measured the TLT. We also templated femoral stem on the different rotated synthetic X-ray of each patient, and investigated the effect of inappropriate rotated radiograph by the measurement of the position and the size of the stem.

RESULTS: Seventy-four percent of the neutral rotational group had less than 5 mm of the TLT. While 30 degrees and 45 degrees external rotation group had few cases with less than 5 mm of the TLT. Compared to the neutral group, smaller stem size was selected in more than 80% cases of 30 degrees and 45 degrees external rotational group, and the stem position in these two groups was more than 5 mm proximally.

CONCLUSION: We suggest that when templating femoral stem, this criterion "the TLT is less than 5 mm" reduces some risks by inappropriate rotated radiograph.