Combined kinematic cup alignment reduces the rate of impingement and edge loading compared to mechanical and anatomical alignment. An in-vitro case-control study

Introduction: In recent years, different alignments have been described for acetabular components in total hip arthroplasty (THA), to reduce the risk of impingement and edge loading. Currently there are 3 main options: mechanical (40 degrees inclination/15 degrees anteversion relative to the anterior pelvic plane), anatomic (40 degrees inclination/anteversion parallel to the transverse ligament) and combined kinematic (according to spinal -pelvic parameters). There are no studies comparing all three in terms of impingement and edge loading. We therefore performed a retrospective case-control in-vitro study comparing risk of impingement and edge loading between the three alignments. Hypothesis: The study hypothesis was that combined kinematic alignment incurs significantly less risk of impingement and edge loading than do the other two types of alignment. Methods: Using a THA planning system, we simulated the 3 alignments for 90 patients undergoing THA with a ceramic-on-ceramic bearing between November 2019 and January 2022; for each simulation, we recorded any prosthetic impingement or edge loading. The study endpoint was the rate of prosthetic impingement or edge loading between the 3 alignments. Results: With the mechanical alignment, 31% of patients (28/90) showed risk of impingement and 22% (20/90) risk of edge loading. With the anatomic alignment, 31% of patients (28/90) showed risk of impinge-ment and 23.3% (21/90) risk of edge loading. With the combined kinematic alignment, 12.2% of patients (11/90) showed risk of impingement and 8.9% (8/90) risk of edge loading. Pairwise comparison showed that the combined kinematic alignment was associated with significantly less impingement and edge loading than the mechanical alignment (respectively, p = 0.03 and p = 0.022) or the anatomic alignment (respectively, p = 0.03 and p = 0.014), while the mechanical and anatomic alignments did not differ. Conclusion: A combined kinematic cup alignment in THA significantly reduced the risk of impingement and edge loading compared to mechanical and anatomic alignments. Level of evidence: III, retrospective case-control study. (c) 2022 Elsevier Masson SAS. All rights reserved.

Automated summary

In recent years, different alignments have been described for acetabular components in total hip arthroplasty (THA) to reduce the risk of impingement and edge loading. This study compared the risk of impingement and edge loading between mechanical, anatomic, and combined kinematic alignments. The results showed that the combined kinematic alignment significantly reduced the risk compared to mechanical and anatomic alignments.