Impact of personalized alignment technique on implant components position in total knee arthroplasty

Introduction Due to substantial rates of dissatisfaction in patients with mechanical alignment in total knee replacement, surgeons began searching for alternative techniques to improve functional outcome. In the recent decade, kinematic alignment that is not based on the mechanical axis of the femur has become the most popular alternative to mechanical alignment. Kinematic alignment technique development has led to creation of a personalized alignment technique. Purpose To compare postoperative implant positions in full-length standing lower-leg radiographs between kinematic alignment and mechanical alignment groups of patients. Materials and methods A prospective, single-center, randomized, controlled study was performed in 139 patients with grade 3–4 knee osteoarthritis (Kellgren – Lawrence). We collected data from 76 cases of mechanical alignment (66 women and 10 men) and 83 cases of personalized alignment group (60 women and 23 men). There were no patients with significant post-traumatic or other deformities of the lower limb which can alter the results in the study. All measurements were done on digital full-length standing X-rays of the lower legs with special MediCAD software. Results The positions of the implant components in mechanical and personalized alignments did not differ significantly in many parameters after operations, despite the fact that the alignment was based on completely different principles. There were no differences between the average values of the angles after operations with mechanical and anatomical axes of the femur in both study groups (the difference was 0.1° at p = 0.595). The only difference in the groups was the position of the tibial component in relation to the horizontal surface in the standing position: in personalized alignment, the angle was 0.9°, and in mechanical alignment it was 2.4° valgus ( p < 0.001). Discussion The absence of significant difference in the postoperative leg alignment and implant position except in the joint line orientation between the groups demonstrates possibility to achieve good leg alignment with both techniques. In the personalized alignment group, the joint line orientation in the coronal plane was found nearly parallel to the ground which can result in a more balanced weight distribution compared to mechanical alignment. Conclusion In patients who receive total knee replacement with the personalized technique, the postoperative lower limb alignment was found within the safe boundaries of 3° from the mechanical axis while the joint line orientation in the coronal plane was significantly closer to be parallel with the ground compared with mechanical alignment group.