Kinematic alignment technique for total hip arthroplasty

Abstract

Concept born from the observation that 1) systematic conventional techniques for implanting hip components are still affected by some complications that technological improvements have not entirely solved, and 2) the increasing awareness that abnormal lumbo-pelvic kinematics are responsible for clinically detrimental poor functional cup orientation and components' interaction (edge loading and articular impingement) that occur during activities of daily living. Following on from this, the kinematic alignment (KA) technique for total hip replacement (THR) has been developed and consists of personalising the implantation of components, with the intention of restoring the pre-arthritic hip joint anatomy: centre of rotation, acetabular anteversion, and proximal femur anatomy. The acetabular component orientation will be adjusted from its native orientation (transverse acetabular ligament) for patients with poor functional acetabular orientation due to an abnormal spine-hip relationship (≍10 to 35% of patients). As the majority of conditions that lead to hip degeneration are automatically corrected when anatomically replacing a hip, there is little-to-no risk of reproducing the hip anatomy, with the exception of developmental disease. The cup adjustment aims, by reaching a compromise, to optimise the components' interaction between the standing and the sitting positions. The intended benefits of the KA technique for THR are primarily to reduce risk of prosthetic instability and failure as a result of the improved functional components' interaction, and secondarily to improve functional performances and patient satisfaction due to the anatomical implantation and subsequent physiological prosthetic hip kinematics. A parallel may be drawn between the KA technique for THR and the concept of “restricted KA technique for total knee replacement”, as in both techniques component positioning primarily aims to reproduce the native joint anatomy, with only a fraction of patients requiring component orientation adjustment in order to compensate for a biomechanically sub-optimal pre-operative joint condition. Planning a KA-THR is simple (physical examination and radiographic measurements to distinguish between hip and spine users, in order to define the individual spine-hip relationship), and surgery can be reliably performed free hand. As the pre-operative individual spine-hip relationship is also influenced by the stiff osteoarthritic hip (hip-spine syndrome), further research is needed to refine the indication and the level of cup orientation adjustment.