Tibia-neutral functional alignment with femoral varus adjustment of up to 3° in robotic-assisted total knee arthroplasty: a preliminary prospective study using gait analysis of the bony mechanical axes
Year: 2026
Type: preprint
Abstract: Background Robotic-assisted total knee arthroplasty allows bone cuts to be adjusted in 1° increments, but how much adjustment is acceptable remains unclear. Our standard strategy is a tibia-neutral functional alignment: the tibial component is fixed perpendicular to the mechanical axis, and only the coronal alignment of the femoral component is adjusted, within 3° of varus, to balance the knee in varus–valgus, extension and flexion. The aim of this study was to evaluate this strategy using gait analysis of the bony mechanical axes. Methods Twelve knees in 10 women with varus knee osteoarthritis who underwent robotic-assisted total knee arthroplasty with this strategy were studied. Two-dimensional to three-dimensional registration of biplanar full-length radiographs and computed tomography was combined with three-dimensional motion analysis to compare the mechanical axes of the femur and tibia, the dynamic weight-bearing line, and knee moment during gait before and after surgery. Paired t-tests or Wilcoxon signed-rank tests (according to normality), two-way repeated-measures analysis of variance, and Pearson or Spearman correlation coefficients were used. Results The femoral component was placed in a mean of 1.8° of varus and the tibial component at a mean of 0.0°. Joint line obliquity was within the neutral range in 11 of 12 knees. The waveforms of the tibial mechanical axis and the dynamic weight-bearing line were similar in shape to those before surgery, and the change in the varus direction decreased. The peak knee adduction moment decreased from 4.0 to 2.8%BW·Ht (p < 0.001). However, the greater the varus angle of the femoral component, the larger the knee adduction moment (r = − 0.772). Conclusions Femoral adjustment within 3° of varus appears appropriate in terms of joint line obliquity and gait kinematics. However, femoral varus increases the knee adduction moment; varus should therefore be limited to the amount required for balance, with 3° as the upper limit. Trial registration Not applicable (prospective observational study: IRB number 2020 − 0448).
Source: Research Square
Institution: Niigata University Medical and Dental Hospital
Language: English
Subfield: Surgery
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7225742450