The Coronal Plane Alignment of the Knee (CPAK) classification in Chinese patients with knee osteoarthritis

Abstract

<p>Introduction: Coronal Plane Alignment of the Knee (CPAK) is a pragmatic and comprehensive classification system for heathy and arthritic knees. This study aims to apply the CPAK classification in Chinese osteoarthritic knees.<br>Methods: Chinese patients undergoing total knee arthroplasty for primary knee osteoarthritis at an academic institution between January 2021 and January 2023 were included. Radiological analysis of the preoperative weight-bearing long- films was performed. The lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured. The patients were grouped into 9 CPAK phenotypes based on the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO).<br>Results: 500 knees (269 patients) were included, mean age was 70.0±6.4. Female-to-male ratio was 2.2:1. Mean aHKA was 4.1° varus ± 4.1°, mean JLO was 174.3°±3.2°. The most common CPAK phenotypes were type I at 48.6%, II at 23.2% and IV at 18.2%. No patients had an apex proximal JLO (phenotype VII, VIII and IX). Mean aHKA was significantly more varus in males at 4.9° (p<0.01). They also had significantly greater tibial and femoral varus (p<0.05) with a mean LDFA of 89.6°±2.9° and mean MPTA of 84.7°±2.3°. There were no significant differences in JLO. The percentage of phenotype I knees were greater in males (59.9% vs 43.4%, p<0.05), while phenotypes II (25.9% vs 17.2%, p<0.05) and III (5.0% vs 1.3%, p<0.05) were greater in females.<br>Conclusion: Chinese knees are more constitutional varus when compared to western European knees. There is a left and up shift of the lower limb alignment distribution on the CPAK matrix with 90% of patients falling within phenotypes I, II and IV.</p>