The Impact of Mechanical and Restricted Kinematic Alignment on Knee Anatomy in Total Knee Arthroplasty

Background: Total knee arthroplasty (TKA), aiming at neutral mechanical alignment (MA), inevitably modifies the patient's native knee anatomy. Another option is kinematic alignment (KA), which aims to restore the original anatomy of the knee. The aim of this study was to evaluate the variations in lower limb anatomy of a patient population scheduled for TKA, and to assess the use of a restricted KA TKA protocol and compare the resulting anatomic modifications with the standard MA technique. Methods: A total of 4884 knee computed tomography scans were analyzed from a database of patients undergoing TKA with patient-specific instrumentation. The lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and hip-knee-ankle angle (HKA) were measured. Bone resections were compared using a standard MA and a restricted KA aiming for independent tibial and femoral cuts of maximum +/- 5 degrees deviation from the coronal mechanical axis and a resulting overall coronal HKA within +/- 3 degrees of neutral. Results: The mean preoperative MPTA was 2.9 degrees varus, LDFA was 2.7 degrees valgus, and overall HKA was 0.1 degrees varus. Using our protocol, 2475 knees (51%) could have undergone KA without adjustment. To include 4062 cases (83%), mean corrections of 0.5 degrees for MPTA and 0.3 degrees for LDFA were needed, significantly less than with MA (3.3 degrees for MPTA and 3.2 degrees for LDFA; P < .001). Conclusion: The range of knee anatomy in patients scheduled for TKA is wide. MA leads to greater modifications of knee joint anatomy. To avoid reproducing extreme anatomy, the proposed restricted KA protocol provides an interesting hybrid option between MA and true KA. (C) 2017 Elsevier Inc. All rights reserved.