CHANGES IN KNEE PHENOTYPE IN CORONAL PLANE ALIGNMENT AFTER MEDIAL UNICOMPARTMENTAL KNEE ARTHROPLASTY DID NOT AFFECT CLINICAL OUTCOMES

Background Studies on TKA reported increased positive patient-reported outcomes when the coronal plane alignment of the knee (CPAK) phenotype was preserved. However, reports on outcomes related to the change in CPAK after UKA remain limited. Methods One hundred forty-five patients undergoing medial UKAs with pre- and postoperative full-body anteroposterior standing radiographs were included in the study. Angle in coronal plane alignment, including medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA), and arithmetic hip–knee angle (aHKA) and joint line obliquity (JLO) were calculated. Patients were grouped based on restored CPAK and altered CPAK. With a minimum 1-year follow-up, patient-reported outcome measures, including FJS-12, OKS, and KOOS-12, were evaluated and compared between both groups. Results Among 145 patients, those whose pre- and postoperative radiographs were not true anteroposterior views or had component rotation were excluded, leaving 76 patients who met the criteria. The mean age and follow-up time were 68.7 years and 15.5 months, respectively. The most common preoperative CPAK phenotypes were Type I (55.3%) and Type II (28.9%). Postoperatively, 35 patients (46%) were in the restored CPAK group and 41 (54%) in the altered CPAK group, most commonly from Type I to Type VII and from Type II to Type VIII, with no differences between the groups in preoperative MPTA, LDFA, Kellgren–Lawrence (KL), and Ahlbäck grade. However, both groups showed similarly significant improvements in FJS-12, OKS, and KOOS-12 scores from baseline. The altered CPAK group demonstrated a greater change in both MPTA and LDFA compared with the restored CPAK group ( Δ MPTA +2.59°±3.12° vs +1.43°±2.00°, p = 0.055; Δ LDFA +2.71°±3.78° vs +1.00°±3.27°, p = 0.038). Conclusion Both groups had similarly significant improvements in patient-reported outcomes at a minimum of 1-year follow-up. Changes in knee phenotype in coronal plane alignment after medial UKA did not affect clinical outcomes.