A retrospective comparison of Coronal Plane Alignment of the Knee

Background: Unicompartmental arthritic degeneration is treated by unicompartmental knee arthroplasties (UKA). The two current standards are mechanical alignment, where knee placement is perpendicular to the leg's mechanical axis and kinematic alignment, that consists of aligning the knee with the angles specific to the patient's innate bone structure. The purpose of this study was to compare knee alignment between mechanical and kinematic UKA. Methods: A retrospective study at Medstar Washington Hospital Center from 2015 to 2022 identified 156 cases of knee arthroplasties. Of these, 95 had mechanical alignments and 61 had kinematic alignments. Patients were evaluated post-surgically for Coronal Plane Alignment of the Knee (CPAK). Analysis of post-operative joint x-ray imaging was performed, and the mechanical medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured. The arithmetic hip knee ankle angle (aHKA) and joint line obliquity (JLO) were calculated. Results: The CPAK results for mechanically aligned group demonstrated an average MPTA of 87.12 (f3), LDFA average of 86.04 (f3), aHKA average of 0.62 (f4) and JLO average of 172.57 (f4). The CPAK results for the kinematically aligned group demonstrated an average MPTA of 86.96 (f3), LDFA average of 84.67 (f3), aHKA average of 2.09 (f4), and JLO average of 171.1 (f4). A two-sample t-test on this data demonstrates statistically significant p-values of 0.004 for LDFA, 0.03 for aHKA, and 0.02 for JLO all below the 0.05 significance level. Both cohorts only contained CPAKs alignment types I and III. Conclusion: This study demonstrated that there is a statistically significant difference in knee alignment when comparing mechanically versus kinematically aligned knees which suggests that there is an advantage for patients that undergo kinematically aligned knee replacements.