Neutralization of Joint Line Obliquity Improves Early Joint Function in Valgus Coronal Plane Alignment of the Knee...

The debate between kinematic and mechanical alignment centers on whether constitutional coronal plane alignment should be preserved or "corrected." This study examined whether changes in coronal plane alignment of the knee (CPAK) following manual total knee arthroplasty (TKA) were associated with patient-reported outcomes across constitutional phenotypes.

A retrospective cohort of 1,000 manual cemented mechanical alignment TKAs was assessed, with 621 included and grouped by constitutional CPAK phenotype. Multivariable regressions assessed associations of postoperative changes in CPAK, arithmetic hip-knee-ankle angle, and joint line obliquity (JLO) categories and their deltas, with Oxford Knee Scores (OKSs) and satisfaction at six weeks and one year.

Overall, changing CPAK phenotype was associated with a higher 6-week OKS (β = 1.97, 95% CI [confidence interval] = 0.24 to 3.71, P = 0.026) and increased odds of 1-year satisfaction (OR [odds ratio] 2.84, 95% CI = 1.10 to 6.80, P = 0.023). In constitutional CPAK III knees, changing JLO category (β = 4.19, 95% CI = 0.02 to 8.36, P = 0.049) and increasing delta JLO (β = 0.49, 95% CI = 0.02 to 0.97, P = 0.041) were associated with a higher 6-week OKS. Similarly, in CPAK VI knees, increasing delta JLO (β = 1.10, 95% CI = 0.35 to 1.85, P = 0.005) was associated with a higher 6-week OKS. Conversely, CPAK V knees demonstrated a lower 1-year OKS with increasing delta JLO (β = -1.13, 95% CI = -2.13 to -0.14, P = 0.026).

Although changing CPAK phenotype was associated with superior early outcomes overall, this was primarily driven by valgus phenotypes (CPAK III and VI) benefitting from JLO neutralization. In contrast, CPAK V knees performed worse with an apex proximal shift. These findings suggest universal TKA alignment strategies may not be optimal, warranting analyses to define phenotype-specific targets.