Preoperative templating of femoral components on plain X-rays

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°, 30°, and 45° 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 positon 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° and 45° 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° and 45° 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.