Abstract: Objective To compare the distribution of coronal plane alignment of the knee(CPAK)phenotypes between patients with knee osteoarthritis(KOA)and asymptomatic controls,and to identify the phenotypic characteristics of CPAK distribution in patients with KOA. Methods This retrospective study included 2,166 individuals who underwent standing full-length lower-extremity radiography at The First Affiliated Hospital of Soochow University between January 1, 2019 and December 31, 2024. Among them, 1,785 patients were diagnosed with KOA as the primary diagnosis, who underwent total knee arthroplasty(TKA), involving 1,418 knees, and 486 patients who underwent unicompartmental knee arthroplasty(UKA), involving 551 knees. In addition, 381 normal controls were included. Medial proximal tibial angle(MPTA), lateral distal femoral angle(LDFA), arithmetic hip-knee-ankle angle(aHKA), and joint line obliquity(JLO)were measured, and CPAK phenotypes were assigned according to the established CPAK classification system. Preoperative anatomical parameters and CPAK phenotype distributions were compared among the control, TKA, and UKA groups. In patients with available postoperative images, preoperative-to-postoperative changes in anatomical parameters and CPAK phenotypes were further analyzed. Results CPAK phenotype distribution differed significantly among the three groups (P<0.001). The predominant phenotypes were type Ⅲ(281 knees, 36.88%)and type Ⅱ(216 knees, 28.35%)in the control group, type Ⅰ(605 knees, 42.67%)and type Ⅳ(286 knees, 20.17%)in the TKA group, and type Ⅰ(232 knees, 42.11%)and type Ⅱ(119 knees, 21.60%)in the UKA group. Preoperative MPTA, LDFA, aHKA, and JLO also differed significantly among the three groups(P<0.001). Postoperative imaging follow-up was available for 768 patients(858 knees)in the TKA group and 222 patients(265 knees)in the UKA group. CPAK phenotype distribution changed significantly from preoperative to postoperative in both groups(Bowkers symmetry test, both P<0.001), and postoperative phenotype distribution differed significantly between the two groups(P<0.001). Postoperatively, the TKA group mainly shifted to type Ⅳ(242 knees, 28.21%)and type Ⅴ(248 knees, 28.90%), whereas the UKA group remained predominantly type Ⅰ(102 knees, 38.49%)and type Ⅱ(83 knees, 31.32%). Conclusion CPAK phenotypes may help characterize KOA-related coronal alignment features and morphological changes before and after surgery; however, its value in assessing KOA risk and surgical decision-making still requires further validation in prospective studies.

Key words: Knee osteoarthritis, Total knee arthroplasty, Unicompartmental knee arthroplasty, Coronal plane alignment of the knee phenotypes, Lower limb alignment