Phenotyping of the Turkish population according to Coronal Plane Alignment of the Knee classification: A retrospective cross-sectional study

This study aimed to phenotype healthy individuals and patients with arthritic knees in the Turkish population according to the Coronal Plane Alignment of the Knee (CPAK) classification. The retrospective cross-sectional study included 207 healthy individuals (109 males, 98 females; mean age: 32.9±8.4 years; range, 20 to 45 years) with a total of 414 knees (Group 1) and 296 patients (155 females, 141 males; mean age: 54.5±7.9 years; range, 43 to 80 years) with a total of 408 arthritic knees (Group 2) who met the inclusion criteria and underwent evaluation using digital long-leg radiographs between January 2019 and July 2023. Mechanical lateral distal femoral angle and medial proximal tibial angle were measured. Subsequently, the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated. Based on the results obtained, participants in both groups were categorized according to the CPAK classification. In Group 1, the mean aHKA was 0.3°±2.5°, and the mean JLO was 175.2°±3.5°. In Group 2, the mean aHKA was -1.4°±3.9°, and the mean JLO was 174.6°±3.7°. The most common CPAK type in healthy individuals (Group 1) was type 2 (41.5%), followed by type 3 (14.7%) and type 1 (14.5%). In arthritis patients (Group 2), the most common CPAK type was type 2 (31.6%), followed by type 1 (28.2%) and type 3 (13.5%). The CPAK classification serves as an important guide for categorizing lower extremity alignment. In the Turkish population, healthy individuals most commonly exhibited CPAK type 2, 3, and 1 alignments, respectively, while osteoarthritic patients predominantly displayed CPAK type 2, 1, and 3 alignments.