JOA - 2026-05-07 - Journal Article
Does the Magnitude of Change in Coronal Plane Alignment of the Knee Affect Clinical Outcomes in Functional and Mechanical Alignment Total Knee Arthroplasty?
Kawaguchi K, Young SW, Tay ML, van Rooyen R, Walker ML, Farrington WJ, Bayan A
Topics
Key Takeaway
Functional alignment restored the preoperative CPAK phenotype in 42.9% of cases versus 10.3% with mechanical alignment, and in the MA group, greater deviation from native JLO was negatively correlated with Forgotten Joint Score.
Summary Depth
Choose how much analysis to show on this article page.
Summary
This substudy of a prospective single-blinded RCT compared coronal plane alignment changes (delta aHKA, delta JLO, CPAK phenotype restoration) between functional and mechanical alignment TKA in 236 patients, correlating alignment change magnitude with FJS and OKS at 1 and 2 years. FA produced significantly smaller alignment changes and restored the native CPAK phenotype in 42.9% versus 10.3% with MA. In the MA group only, a dose-response relationship showed greater JLO deviation correlated with lower FJS; no such relationship existed in the FA group.
Key Limitation
CPAK phenotype restoration rate and dose-response findings are derived from a single center with a surgeon experienced in FA, making it unclear whether these alignment-outcome relationships hold across surgeons with varying FA proficiency.
Original Abstract
INTRODUCTION
Changes to native coronal plane alignment of the knee (CPAK) phenotypes following total knee arthroplasty (TKA) may influence outcomes, particularly with mechanical alignment (MA). This relationship has not been evaluated with functional alignment (FA). This study compared the magnitude of coronal alignment change between MA and FA and whether this influenced patient-reported outcomes.
METHODS
This substudy analyzed data from a prospective, single-center, single-blinded randomized controlled trial involving 236 patients (119 FA and 117 MA). Long-leg radiographs were used to calculate the arithmetic hip-knee-ankle angle (aHKA), joint line obliquity (JLO), and CPAK phenotype pre- and postoperatively. Alignment change was assessed using absolute differences (delta aHKA, delta JLO), and a dose-response analysis was conducted. Clinical outcomes included the Forgotten Joint Score (FJS) and Oxford Knee Score (OKS) at 1- and 2-year follow-up.
RESULTS
The FA resulted in smaller changes in alignment compared to MA (delta aHKA P = 0.01; delta JLO P = 0.01) and more frequent restoration of the preoperative CPAK phenotype (42.9 versus 10.3%, P = 0.01). In the MA group, restoration of the CPAK phenotype was associated with significantly higher FJS, while no such relationship was observed in the FA group. A dose-response relationship was identified in the MA group: greater changes in JLO were negatively correlated with FJS. This correlation was not seen with FA.
CONCLUSION
Functional alignment more closely preserved native coronal alignment and restored CPAK phenotypes compared to mechanical alignment. In MA cases, larger deviations from the native JLO and CPAK phenotypes were associated with poorer patient-reported outcomes. These findings suggest anticipating alignment changes may support optimal strategy selection in TKA.