Purpose of the study: Data are scarce in the literature on lower limb length discrepancy (LLD) after total hip arthroplasty (THA). This parameter is difficult to evaluated intraoperatively with conventional instruments. In addition LLD after THA is often poorly tolerated and can be a source of legal suites. The purpose of this work was to evaluate the contribution of navigation for controlling lower limb length during implantation of a THA.

Material and method: Sixty-five THA were implanted in 63 patients, aged 35–81 years, using a passive navigation system based on a function reference system which controlled the position of the implants and the length of the operated leg. Limb length and femur length were measured radiographically on both sides before and after surgery. The horizontality of the acetabular U lines was measured on the AP view of the pelvis. An independent radiologist made all measurements.

Results: The precision of the radiographic measurements was < 3 mm. The precision of the navigation system was < 3 mm. Subjectively, 56 of the 63 patients did not have a feeling of LLD preoperatively. No un programmed difference > 3 mm in leg length between the before and after THA measurements was noted. Preoperatively, seven patients complained of lower back pain related to LLD and three had a compensated shoe measuring 5 to 10 mm. These latter three patients had a horizontal pelvis (< 1) after THA. In all cases, the overall length correction was achieved by adapting the length of the neck.

Discussion: In our opinion, not all radiologically determined and/or clinically perceived LLD should be corrected. Care must be taken to ensure that permanent preoperative hip flexion does not perturb limb length measurements.

Conclusion: The navigation system used in this series for the implantation of THA was able to control operated limb length with precision.