Primary Total Knee Arthroplasty Using a Functional Alignment Concept with Kinematic Versus Inverse Kinematic Technique: Does it Make a Difference?

Abstract

There is an increasing trend toward a functional alignment in total knee arthroplasty (TKA). Functional alignment can be performed using a kinematic technique, FA(k), or an inverse kinematic approach, FA(ik). The purpose of this study was to compare the results of kinematic versus inverse kinematic techniques during primary TKA using a functional alignment concept. A retrospective review was conducted of patients undergoing robotic-assisted TKA with 1-year follow-up, excluding patients who had a body mass index (BMI) greater than 45 or valgus deformity by coronal plane alignment of the knee (CPAK) classification. The cohorts included 166 FA(k) and 146 FA(ik) cases with similar demographics, CPAK, and comparable preoperative tibial and femoral angles. Intraoperative data included coronal alignment of the femoral and tibial components and final hip-knee-ankle (HKA). Postoperative outcomes included Forgotten Joint Score (FJS), Visual Analog Scale (VAS) pain, and Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS JR). The FA(ik) group had less varus on the final tibial component (3.0 versus 4.5°, P < 0.00005) and less varus at final HKA compared to the FA(k) technique (0.92 versus 2.6°, P < 0.00005). There was no difference in postoperative KOOS JR or VAS scores. Preoperative FJS in the FA(ik) group improved from 12.4 to 60.2, P < 0.0001. Preoperative FJS in the FA(k) group improved from 17.7 to 66.7, P < 0.0001. Regression analyses demonstrated that FA(k) was an independent predictor of higher FJS, with patients being less aware of their total knee arthroplasty. This study demonstrated improvement in PROMs with both FA(k) and FA(ik) techniques. The FA with kinematic technique led to greater varus of both tibial coronal alignment and final HKA compared to inverse kinematics. The FA(k) demonstrated higher FJS with patients less aware of their knees during sitting, walking, and hiking.