IMPROVEMENT OF CUP POSITION FOR TOTAL HIP ARTHROPLASTY USING A NEW MECHANICAL GUIDE

Abstract

Purpose: Dislocation is a short-term complication frequently encountered after implantation of a total hip arthroplasty (THA). Different strategies can be used to limit the influence of technical, particularly surgical, factors. The position of the acetabular element is a key factor, particularly the anteversion angle and the abduction angle. The purpose of this work was to determine the precision, the reproducibility, and the ease of use of a new mechanical guide for insertion of the acetabular cup.

Material and methods: After calculating the sample size necessary to achieve 90% statistical power for a 5% type I error, we had five surgeons who regularly implanted THA implant 310 press-fit hip cups on a plastic anatomic model of the pelvis. A new mechanical guide was developed using the constant direction of gravity as the reference frame. We determined the precision of acetabular cup implantation, its reproducibility, and ease of use compared with that of the Müller mechanical guide during in vitro implantation of 310 cups via a posterolateral approach that allowed the usual vision of the operative field.

Results: The error of cup anteversion relative to the reference set at 15 was 10.4±5.0 (range 3–21) for the Müller guide and 0.4±0.7 (range 1–3) for the new guide. Cup abduction, relative to the reference set at 45, was −4.7±2.3 (range 7–11) for the Müller guide and 0.3±0.5 (range 0–3) for the new guide. Mean time for positioning the cup was comparable with the two guides (mean 6s for the Müller guide and 5s for the new guide).

Discussion: The precision and reproducibility of cup positioning obtained with the new guide are better than those obtained with mechanical guides currently available on the market (p< 0.00001 with the Müller guide). They are more comparable with values found in in vitro studies using computer-assisted surgery techniques. Use of the new guide was also found to be rapid and simple.

Conclusion: The excellent results obtained with this new mechanical guide, as assessed in terms of cup position for THA, should be confirmed with in vivo trials.