Clinical Outcome, Postoperative Alignment, and Implant Survivorship After Kinematically Aligned Total Knee Arthroplasty

Overview

This chapter reviews the clinical outcome, postoperative alignment, and implant survivorship after kinematically aligned (KA) total knee arthroplasty (TKA) based on results of international randomized controlled trials (RCTs), case-control studies, meta-analyses, and single-surgeon case series. The first section describes differences in patient-reported outcome scores and range of motion between patients treated with KA TKA and mechanical alignment (MA) TKA. Featured are a chronologic review of the findings of RCTs, a matched cohort of patients treated with calipered KA and MA performed with manual instruments and a medial pivot implant design published by the author of this chapter, and meta-analyses. Many studies used inclusion restrictions and postoperative correction restrictions in the KA cohort that biased the results against KA TKA and in favor of MA TKA. The second section discusses differences in KA and MA postoperative limb and joint line alignment and the accuracy of the calipered KA technique. The third section reports the mid- and long-term implant survival after KA TKA and discusses the differences in the rate of reoperations other than for infection between the KA and MA TKA. The contrary and unexpected finding of negligible long-term risk of tibial component failure from a varus mechanism after KA TKA is highlighted. The explanation for the negligible risk is the lack of correlation between the degrees of varus alignment and component migration, low knee adduction moment during gait, and restoration of native tibial compartment forces after KA TKA, which MA TKA does not achieve. The educational objective is to provide compelling evidence that the KA target results in a better clinical outcome and that the calipered technique accurately restores the patient’s prearthritic joint lines. Surgeons that perform KA TKA can expect a low risk of mid- and long-term implant failure and a negligible risk of varus failure of the tibial component that is lower than MA TKA.

Differences in Clinical Outcome Between Kinematically Aligned and Mechanically Aligned Total Knee Arthroplasty

Persistent patient dissatisfaction and residual symptoms after mechanically aligned MA TKA contrast with the generally favorable reports of high implant survival. ^, These features of disappointment, unchanged by purported advances in implant design and more consistent neutral limb alignment from the use of intraoperative navigation and robotic technologies, show the intrinsic limitations of the MA technique. Modern views conclude that changing the native joint line, kinematics, and laxities, which is inherent to the MA technique, impede optimal clinical outcomes. For all modern arthroplasties except the knee, reconstruction of the patient’s functional phenotypes, prearthritic joint surfaces, soft tissue envelopes, and joint laxities is recognized as the primary goal. Over the past decade, improvements in the understanding of knee kinematics and the importance of restoring the flexion-extension axis encouraged the evaluation of other alignment techniques and the use of medial pivot or stabilized implant designs. These experiences brought insight and strategies for achieving higher function scores and satisfying even the highly active patient. ^{, ,}

The calipered KA technique reduces the risk of patient disappointment after TKA. KA restores the patient’s prearthritic joint lines regardless of preoperative knee deformity without ligament release and does so by reestablishing the tibial compartment forces, ligament lengths, and laxities of the native knee. ^, KA is now a 15-year-old surgical technique that individualizes component placement, targeting anatomic surface landmarks within the knee, which is substantially different from the MA targets of the center of the hip, knee, and ankle. The international orthopedic community is highly interested in KA because of the generally favorable results of the published RCTs, case-control studies, and meta-analyses, discussed further in this chapter, in which the differences between kinematically aligned and mechanically aligned total knee arthroplasty have been analyzed.