Restricted kinematic total knee arthroplasty provided better functional outcomes and higher satisfaction rates for Asians of genu varum with apex distal joint line over unrestricted kinematic total knee arthroplasty.

Background: Coronal Plane Alignment of the Knee (CPAK) phenotypes I, II, and IV can achieve favorable soft tissue balance following kinematic total knee arthroplasty (KA-TKA). Given that this classification was developed from a Caucasian population, limited studies have evaluated clinical outcomes following restricted vs unrestricted KA-TKA in South-East Asian patients, this study aimed to: (1) outline the prevalence of CPAK types in a South-East Asian population, (2) compare clinical outcomes of patients undergoing restricted versus unrestricted KA-TKA.

Methods: Prospectively collected data from 232 patients who underwent KA-TKA between 2015 and 2018 were reviewed. The prevalence of CPAK in our cohort was determined using preoperative medial proximal tibial (MPTA) and lateral distal femoral (LDFA) angles measured from long-limb radiographs. Unrestricted calipered KA-TKA targeted equal bone cuts while restricted KA-TKA utilized intraoperative navigation to restrict tibia varus to 4°. Patients were assessed preoperatively, at 6 months, and 2 years using the Knee Society Score, Oxford Knee Score, and Short-Form 36. Postoperative satisfaction and expectation fulfillment were recorded. Intra- and interclass correlation of all radiographic measurements and both parametric and non-parametric statistical analysis were used.

Results: The prevalence of CPAK in our cohort: I (47.8%), II (30.6%), III (9.1%), IV (7.8%), V (3.9%), VI (0.9%), VII (0%), VIII (0%) and IX (0%). Intra- and interclass correlation of radiographic measurements were excellent at 0.98 (95%CI: 0.95-0.99, P < 0.01). Subgroup analysis of CPAK I patients demonstrated that restricted KA-TKA had better KSS objective (P = 0.04), a higher proportion of satisfied patients (P = 0.02) at 6 months, and better OKS (P = 0.03) than unrestricted KA-TKA.

Conclusion: CPAK I was the most prevalent phenotype in an Asian population. CPAK I patients undergoing restricted KA-TKA had better functional outcomes and satisfaction rates than those who underwent unrestricted KA-TKA. Future studies should focus on evaluating outcomes of different alignment strategies to personalize treatment for Asian CPAK phenotypes.