Templating in uncemented THA. On accuracy and postoperative leg length discrepancy

This study examines the accuracy of digital templating in uncemented total hip arthroplasty (THA), i.e., whether the templated components where actually inserted during surgery. The surgical outcome was evaluated on the basis of limb length equality.

We retrospectively examined digital x-rays of 41 patients scheduled for uncemented THA. These were templated using templating software. The template was compared to the surgical choice of implant registered in the patients' journal. Postoperative x-rays were evaluated for limb length equality. The data underwent statistical analysis to assess accuracy.

The acetabular component was templated accurately in 7.3%, while 41% was within +/- 1 component size difference, and 73% was within +/-2 size differences. The femoral stem was templated accurately in 34%, while 76% was within +/- 1 component size difference, and 90% was within +/-2 size differences. The neck length was templated accurately in 29%, while 88% was within +/-1 component size difference, and 100% was within +/-2 size differences.Fifty four percent of patients experienced radiologic equalization within +/- 5 mm, and 85% within 10 mm. Fifteen percent had leg length discrepancy of more than 10 mm postoperatively. There was no systematic tendency to overestimate or underestimate leg length peroperatively.

We find that the accuracy of digital templating in uncemented THA is acceptable for the femoral stem, but somewhat inferior for the acetabular shell and poor for neck length. Templating is a useful tool in preoperative planning, but cannot be regarded as a blueprint for the operative choice.