JOA - 2026-05-20 - Journal Article
Neutralization of Joint Line Obliquity Improves Early Joint Function in Valgus Coronal Plane Alignment of the Knee Phenotypes After Primary Total Knee Arthroplasty.
Bayram JM, Al-Abbasi G, Chopra S, Wallace D, Mahmood FF, Holloway NJ, Ohly NE, Clarke JV
Topics
Key Takeaway
In valgus CPAK phenotypes (III and VI), neutralizing joint line obliquity after mechanical alignment TKA was associated with a 4.19-point higher 6-week Oxford Knee Score in CPAK III and 1.10-point improvement per degree of delta JLO in CPAK VI, while CPAK V knees lost 1.13 OKS points per degree of apex-proximal JLO shift at one year.
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Summary
This study asked whether postoperative changes in CPAK phenotype, aHKA, and JLO after manual cemented mechanical alignment TKA differentially affect Oxford Knee Scores and satisfaction across constitutional CPAK phenotypes. Multivariable regression in 621 patients showed that changing CPAK phenotype overall improved 6-week OKS (β=1.97) and 1-year satisfaction (OR 2.84), but subgroup analysis revealed this benefit was driven by valgus phenotypes (CPAK III and VI) responding to JLO neutralization, while CPAK V knees showed worse 1-year OKS with increasing delta JLO (β=-1.13). These findings indicate that a single mechanical alignment strategy produces heterogeneous outcomes depending on constitutional phenotype.
Key Limitation
The 6-week OKS endpoint reflects acute recovery rather than durable functional outcome, and the phenotype subgroups (especially CPAK V and VI) are likely underpowered for the regression estimates reported.
Original Abstract
BACKGROUND
The debate between kinematic and mechanical alignment (MA) 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.
METHODS
A retrospective cohort of 1,000 manual cemented MA 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 (aHKA), and joint line obliquity (JLO) categories and their deltas, with Oxford Knee Scores (OKS) and satisfaction at six weeks and one year.
RESULTS
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).
CONCLUSION
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.