Coronal plane alignment of the knee phenotypes and ankle joint coronal plane alignment patterns in Egyptian population.

BACKGROUND: In an era leaning toward a personalized alignment of total knee arthroplasty, coronal plane alignment of the knee (CPAK) phenotypes for each population are studied; furthermore, other possible variables affecting the alignment, such as ankle joint alignment, should be considered. AIM: To determine CPAK distribution in the North African (Egyptian) population with knee osteoarthritis and to assess ankle joint line orientation (AJLO) adaptations across different CPAK types. METHODS: A cross-sectional study was conducted on patients with primary knee osteoarthritis and normal ankle joints. Radiographic parameters included the mechanical lateral distal femoral angle, medial proximal tibial angle, and the derived calculations of joint line obliquity (JLO) and arithmetic hip-knee-ankle angle (aHKA). The tibial plafond horizontal angle (TPHA) was used for AJLO assessment, where 0° is neutral (type N), < 0° is varus (type A), and > 0° is valgus (type B). The nine CPAK types were further divided into 27 subtypes after incorporating the three AJLO types. RESULTS: A total of 527 patients (1054 knees) were included for CPAK classification, and 435 patients (870 knees and ankles) for AJLO assessment. The mean age was 57.2 ± 7.8 years, with 79.5% females. Most knees (76.4%) demonstrated varus alignment (mean aHKA was -5.51° ± 4.84°) and apex distal JLO (55.3%) (mean JLO was 176.43° ± 4.53°). CPAK types I (44.3%), IV (28.6%), and II (10%) were the most common. Regarding AJLO, 70.2% of ankles exhibited varus orientation (mean TPHA was -5.21° ± 6.45°). The most frequent combined subtypes were CPAK type I-A (33.7%), IV-A (21.5%), and I-N (6.9%). A significant positive correlation was found between the TPHA and aHKA (r = 0.40, P < 0.001). CONCLUSION: In this North African cohort, varus knee alignment with apex distal JLO and varus AJLO predominated. CPAK types I, IV, and II were the most common types, while subtypes I-A, IV-A, and I-N were commonly occurring after incorporating AJLO types; furthermore, the AJLO was significantly correlated to aHKA.