Inverse kinematic alignment outperforms adjusted mechanical alignment in varus TKA at 5 years

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.

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.

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).

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 III.