JOA - 2026-05-19 - Journal Article
Limited Femoral Joint-Line Alteration and Preserved Extension Lateral Laxity Enhanced Early Outcomes in restricted kinematic alignment TKA.
Lee DW, Ro DH, Han HS
Topics
Key Takeaway
In robotic cruciate-retaining rKA TKA, LDFA change <2.3° and ELG ≥3.0 mm were the strongest predictors of superior 2-year KSKS and FJS, respectively.
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Summary
This retrospective study of 69 robotic-arm-assisted cruciate-retaining rKA TKAs examined whether magnitude of alignment correction and intraoperative gap characteristics predicted 2-year PROMs. Multivariable ANCOVA identified smaller HKA change and smaller LDFA change as independently associated with higher 2-year KSKS (p=0.001 and p=0.013), while ELG ≥3.0 mm predicted higher FJS (AUC 0.658) and FMG ≥1.5 mm predicted lower WOMAC stiffness (AUC 0.716). All PROMs improved postoperatively with no revisions at 2 years.
Key Limitation
The sample size of 69 cases is underpowered for multivariable modeling with multiple gap and alignment variables, increasing the risk of spurious associations and limiting generalizability.
Original Abstract
BACKGROUND
Restricted kinematic alignment (rKA) total knee arthroplasty (TKA) seeks to restore native alignment while limiting excessive correction. The influence of alignment change magnitude and intraoperative gap characteristics on early patient-reported outcome measures (PROMs) after robotic rKA TKA remains unclear.
METHODS
This retrospective cohort study included 69 robotic-arm-assisted cruciate-retaining TKAs performed using an rKA protocol. Intraoperative medial and lateral extension and flexion gaps-extension medial gap (EMG), extension lateral gap (ELG), flexion medial gap (FMG), and flexion lateral gap (FLG)-were recorded automatically. Pre- and postoperative hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA) were measured using a validated deep learning model. Multivariable analyses of covariance evaluated associations between demographics, baseline alignment, alignment changes, gap characteristics, and PROMs at one and two years.
RESULTS
All PROMs improved postoperatively. Smaller changes in HKA and LDFA were independently associated with higher two-year Knee Society Knee Scores (KSKS) (P = 0.001 and P = 0.013). Greater ELG was associated with a higher two-year Forgotten Joint Score (FJS) (P = 0.001), whereas greater FMG was associated with lower two-year Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and stiffness scores (P = 0.011 and P = 0.002). Receiver operating characteristic (ROC) analysis identified changes in LDFA <2.3° (area under the curve [AUC] 0.622) and changes in HKA <8.4° (AUC 0.541) as thresholds associated with higher KSKS. An ELG ≥ 3.0 mm predicted higher FJS (AUC 0.658), and FMG ≥1.5 mm predicted lower WOMAC stiffness (AUC 0.716). No revisions occurred.
CONCLUSION
In robotic cruciate-retaining rKA TKA, minimizing femoral joint-line alteration and preserving controlled lateral extension laxity, along with mild medial flexion laxity, were associated with modestly improved early outcomes. These findings are exploratory and require validation in larger cohorts with longer follow-up.