KSSTA - 2026-04-09 - Journal Article
Inverse kinematic alignment outperforms adjusted mechanical alignment in varus TKA at 5 years.
Winnock de Grave P, Roosens O, Vermue H, Luyckx T, Gunst P, Claeys K
Topics
Key Takeaway
In varus TKA patients at 5 years, inverse kinematic alignment produced a clinically meaningful 4-point higher Oxford Knee Score (44.2 vs 40.2) and 19-point higher Forgotten Joint Score (78.5 vs 59.4) compared to adjusted mechanical alignment.
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Summary
This retrospective matched cohort compared robotic-assisted iKA versus aMA in varus knee TKA patients, matching on age, sex, BMI, preoperative HKA, OA severity, and baseline PROMs. iKA preserved native tibial anatomy (MPTA change -0.4° vs -2.7° in aMA) and required less distal medial femoral resection (6.4 vs 7.6 mm). At 5 years, iKA produced superior OKS (44.2 vs 40.2), FJS (78.5 vs 59.4), and MET scores (7.8 vs 6.4), all reaching statistical significance.
Key Limitation
The small sample size of 45 patients per group is underpowered to detect differences in low-frequency outcomes such as revision, aseptic loosening, or component failure, which are the critical durability endpoints at 5 years.
Original Abstract
PURPOSE
Varus knee phenotypes might benefit more from patient-specific alignment strategies in total knee arthroplasty (TKA) since they deviate more from the mechanical, orthogonal planes. The aim of this study was to compare 5-year functional outcomes following robotic-assisted TKA using inverse kinematic alignment (iKA) versus adjusted mechanical alignment (aMA), specifically in patients with preoperative varus alignment.
METHODS
In this retrospective matched cohort analysis, two groups of 45 patients with preoperative varus alignment who received robotic-assisted TKA using either iKA or aMA were recruited. Patient groups were directly matched based on age, sex, height, weight, body mass index, preoperative hip-knee-ankle angle, type and severity of osteoarthritis, preoperative Oxford Knee Score (OKS) and EuroQol 5 Dimensions (EQ.-5D). Clinical outcomes were assessed using the OKS, the Forgotten Joint Score (FJS) and the Metabolic Equivalent of Task (MET) scale at 5-year postoperative. Radiographic and intraoperative data were compared.
RESULTS
Postoperative medial proximal tibial angle (MPTA) was higher in aMA (89.4° ± 0.8°) compared with iKA (86.7° ± 1.4°; p < 0.001), with a greater change of MPTA in aMA compared to iKA (-2.7° ± 1.6° vs. -0.4° ± 0.5°; p < 0.001). Distal medial femoral resections were larger in aMA (7.6 ± 1.1 mm) compared with iKA (6.4 ± 0.9 mm; p < 0.001). Patient-reported outcomes at 5 years postoperatively favoured iKA, with higher postoperative OKS (44.2 ± 3.8 vs. 40.2 ± 6.5; p = 0.001) and FJS (78.5 ± 19.9 vs. 59.4 ± 27.7; p = 0.001) compared to aMA. Similarly, the MET score was significantly higher in the iKA group (7.8 ± 2.1) compared with the aMA group (6.4 ± 2.5; p = 0.002).
CONCLUSIONS
In varus patients, iKA demonstrated superior 5-year functional outcomes compared to aMA with consistently higher OKS, FJS and MET scores. iKA better preserved the native tibial anatomy and medial femoral anatomy.
LEVEL OF EVIDENCE
Level III.