Restoration of Preoperative Coronal Plane Alignment of the Knee Phenotypes and Clinical Outcomes Following Mechanically Aligned Total Knee Arthroplasty

Abstract

Objectives: This study aimed to determine the proportion of patients who exhibited a change in their coronal plane alignment of the knee (CPAK) classification after mechanically aligned (MA) total knee arthroplasty (TKA) and compare postoperative clinical outcomes between patients who restored their preoperative CPAK classification and those who did not.Materials and Methods: This was a retrospective cohort study including 194 knees from 143 patients who underwent MA TKA between December 2021 and June 2024. Radiographic parameters, including pre- and postoperative lateral distal femoral angle and medial proximal tibial angle, were measured using long-leg standing radiographs to determine the CPAK classification. Postoperative Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, range of motion (ROM), and surgical complications were recorded.Results: The most common preoperative CPAK classification was type I (40.7%), followed by type II (22.7%) and type IV (14.9%). Furthermore, 36 (18.6%) knees were restored to their preoperative CPAK classification. No significant differences in postoperative ROM (flexion: 115° vs. 110°, p = 0.445; extension: 5° vs. 5°, p = 0.770) and WOMAC scores (13.56 ± 9.58 vs. 18.12 ± 10.64, p = 0.251) were observed between the restored and non-restored groups. The surgical complication rates were 2.7% and 5.7% in the restored and non-restored groups, respectively.Conclusion: A fixed MA TKA target may alter patients’ CPAK classification postoperatively, with only a limited proportion achieving restoration of their preoperative CPAK classification. Restoration of the preoperative CPAK classification did not significantly influence clinical outcomes.