The Coronal Plane Alignment of the Knee Classification May be Unreliable With Advanced Knee Arthritis.

Background: Kinematic alignment (KA) seeks to restore native, prearthritic alignment, including the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO). Advanced osteoarthritis may alter these parameters through erosion, subchondral collapse, or insufficiency fracture, potentially misrepresenting the native coronal plane alignment of the knee (CPAK) phenotype. Therefore, we sought to evaluate concordance in CPAK phenotype parameters between the severely arthritic knee and the contralateral healthy knee within the same patient. Methods: We performed a radiographic review of 578 patients with bilateral, weight-bearing, long-leg radiographs obtained prior to total knee arthroplasty. The inclusion criteria required a Kellgren-Lawrence grade 4 knee (arthritic) and a contralateral Kellgren-Lawrence grade 0 or 1 knee (healthy). Absolute side-to-side differences were calculated for aHKA, JLO, medial proximal tibial angle, and lateral distal femoral angle, with additional stratification based on the predominant compartment of arthritic degeneration (medial or lateral). Results: Ninety patients met the inclusion criteria. The mean absolute differences between healthy and arthritic knees were 3.5° for aHKA, 2.3° for JLO, 2.4° for medial proximal tibial angle, and 1.7° for lateral distal femoral angle. CPAK concordance between healthy and arthritic knees was limited, with matching phenotypes in only 41% of patients with medial arthritis and 50% with lateral arthritis. Conclusions: Advanced knee osteoarthritis may lead to permanent bony changes that alter the measured CPAK phenotype. Replicating this pathologic alignment during kinematic alignment total knee arthroplasty could result in unintended component malposition. Careful preoperative radiographic assessment is essential to identify and account for these deformities.