Impact of changes in native coronal plane alignment of the knee (CPAK) on patient-reported outcome measures (PROMS). A bilateral single implant study.

Background: A contemporary trend favours a restricted kinematic alignment (rKA) strategy, incorporating safe boundaries to restore a variable percentage of a patient's natural alignment.This study aims to compare preoperative and postoperative coronal plane knee alignment (CPAK) in patients undergoing bilateral TKA with SAIPH implants (MatOrtho, UK). The concept was to control the implant (same prosthesis both sides), patient (bilateral model) and assess what effect any surgical alteration in alignment had on patient's outcomes measured by patient-reported outcome measures (PROMS) and patient satisfaction. Method: A total of 70 patients and 140 knees who underwent bilateral sequential TKA with a SAIPH implant between 2012 and 2022 were included in this study. PROMS, clinical assessment, pre and postoperative CT scans and plain x-rays were obtained. The CPAK phenotype, lateral distal femoral angle, medial proximal tibial angle, joint line obliquity (JLO), and arithmetic Hip-Knee-Ankle (aHKA) angle were measured pre and postoperatively. Results: Postoperative CPAK phenotype recreation was achieved in 27.9 %, while in 72.1 % it was not. PROMS did not significantly differ when CPAK phenotype was not recreated. Additionally, isolated changes to aHKA or JLO did not significantly impact outcomes, nor was a TKA that recreated the native coronal alignment more likely to be the patient's preferred side. Conclusion: Tailoring alignment approaches to individual patient characteristics may be crucial for optimal functional outcomes but in this study, we were not able to show a difference between those with CPAK recreated versus those who did not have native CPAK recreated following TKA when using PROMS as the outcome measure.