Accuracy of Image-less Navigation for Functional Cup Positioning in Total Hip Arthroplasty

Introduction: Malpositioning of the acetabular cup component during total hip arthroplasty (THA) can be associated with significant post-operative complications including dislocation, impingement, increased wear rates. Computer-assisted navigation has the potential to improve the accuracy of cup positioning during THA. The purpose of this study was to compare acetabular cup position and post-operative leg length discrepancy (LLD) in patients who underwent primary THA using posterior approach.

Methods: Between August 2016 to October 2017, all THA with (n=79) or without (n=93) the assistance of an imageless navigation device (Intellijoint HIP^®) were analyzed. Post-operative weight-bearing radiographs were analyzed using TraumaCad (version 2.5) for anteversion, inclination and LLD. Goal for cup placement was functional 40° inclination and 20° anteversion. Functional LLD was measured as compared to pre-operative radiographs and compared to contralateral side. Proportion of cups within Lewinnek’s safe zone, proximity to a pre-operative target of and the LLD >5 mm was assessed.

Results: The mean age was 54.9 ± 9.6 years (30 – 72) and 57.6 ± 12.5 years (20 – 85) in control and navigated groups, respectively. Mean orientation in the navigated group was 20.6°± 3.3° (17 - 25) of anteversion and 41.9°± 4.8° (30 - 51) of inclination, vs. 25.0°± 11.1° (10 - 31) and 45.7°± 8.7° (29 – 55) in control group, where were statistically significant (p=0.005 and p=0.0), respectively. In the navigated group, significantly more acetabular cups were placed within Lewinnek’s safe zone (anteversion: 78% vs. 47%, p=0.005; inclination: 92% vs. 67%, p=0.002). There was no significant difference in mean LLD in navigation and control groups (3.1 ± 1.5 mm vs. 4.6 ± 3.4 mm, p=0.36), although fewer LLDs >5 mm were reported in the navigated group (7.1%) than in controls (31.4%, p=0.09).

Conclusion: The use of computer-assisted navigation improved the accuracy with which acetabular cup components were placed and may represent an important method for limiting post-operative complications related to cup malpositioning.