Kinematic alignment versus conventional techniques for total hip arthroplasty: A retrospective case control study

Background: Residual complications of conventionally implanted hip components have only been partially reduced by improved implant design and higher surgical precision, and their occurrence is poorly predicted by the radiographic standing/supine cup orientation. This has raised awareness that conventional techniques may not aim for the correct component orientation target, and the lumbo-pelvic kinematics, which influences the functional acetabular orientation, may be of interest to further improve THA clinical outcomes. This has led to the development of the Lumbo-Pelvic kinematic alignment (KA) technique for THA that aims to anatomically position and kinematically align hip implants (acetabular and femoral, total and resurfacing components), in order to optimise prosthetic hip biomechanics and hopefully improve prosthetic function, patient satisfaction, and components' lifespan. Therefore, we conducted a case control investigation to assess the early-term safety and efficacy of this new technique by answering the following questions: does the KA technique for THA: (1) better restore the native hip anatomy, (2) generate a different radiographic supine cup position, and (3) improve clinical outcomes in comparison to the conventional mechanical alignment technique?

Hypotheses: Using KA technique allows there is no statistically significant difference between the pre to postoperative differential for acetabular medial and vertical offsets, femoral offset, and leg length.

Methods: We led a case control retrospective study with prospectively collected clinical data. Forty-one consecutive unselected KA-THAs performed with manual instrumentation were paired with 41 mechanically aligned THAs. The 1-year clinical outcomes and radiographical measurements were compared.

Results: Compared to the mechanical alignment technique, the KA technique resulted in a more anatomical restoration of the prosthetic hip centre of rotation with a lower delta pre- to post-operative horizontal acetabular offset (1.47mm for KA versus -5.1mm for MA, p=0.001), and with 74% of KA versus 50% of MA cups (p=0.044) being within 15% of native anatomy for the horizontal acetabular offset. In addition, the KA technique resulted in a higher cup anteversion (22°±7° vs 15°±8°, p<0.001) but similar cup inclination (41°±6° vs. 42°±7°, p=0.25), a similar proportion of cups within the Lewinnek zone (65% vs. 70%, p=0.8), similar excellent functional outcomes (delta Oxford score pre- to follow-up of 24.3 and 23.5 points for KA and MA groups, respectively, p=0.88), similar patient satisfaction scores of 95.4/100 and 89.5/100 for KA and MA groups, respectively, and the same absence of aseptic complications.

Conclusion: The KA technique for THA has been demonstrated to be safe, efficacious, and not inferior to the conventional MA technique at early-term. As the concept of the KA technique for THA is only at an early stage, its influence on mid to long-term clinical outcomes remains to be determined and further refinements of the concept are yet to be made.

Level of evidence: III; case-control retrospective study.