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

Objectives: 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.

Patients and methods: 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.

Results: 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%).

Conclusion: 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.