High accuracy of knee alignment following well-balanced image-based robot-assisted total knee arthroplasty; radiographic validation of implant position and knee alignment.

Abstract

Image based robotic assisted knee replacement surgery enables surgeons to achieve patient-specific alignment through intraoperative ligament balancing and implant positioning. The purpose of this study was to validate the accuracy of the implant position and lower limb alignment using full-leg weight-bearing postoperative radiographs. This retrospective study included 69 patients receiving total knee arthroplasty (TKA) with the use of a MAKO robot and patella-in-place balancer between 01/2023 and 04/2024. All patients received a Triathlon® CS prosthesis with functional alignment philosophy. Coronal parameters (mechanical hip-knee-ankle-angle (mHKA), lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA)) and sagittal alignment parameters (femoral flexion and tibial slope) were collected from the intraoperative plan and compared with pre- and postoperative weight-bearing full leg radiographs (FLR). Preoperative mean mHKA of 2.4° ± 6.2° varus corrected to 2.2° ± 2.7° varus intraoperatively and 1.4° ± 3.2° varus postoperatively; with no significant differences intra-to postoperatively. LDFA increased significantly from 87.8° ± 3.2° to 90.1° ± 2.2° intraoperatively, but did not differ significantly on postoperative radiographs. Original MPTA angle was preserved intraoperatively at 87.7° ± 1.7°, but increased by 0.9° postoperatively (p = 0.005). Femoral flexion decreased after surgery from 5.8° ± 3.9° to 3.9° ± 2.8° (p < 0.001). Tibial slope decreased intraoperatively from 8.6° to 6.7° (p < 0.001), with no further postoperative change. Functional alignment philosophy in combination with a patella in place balancing device in reliably reproduced the targeted limb alignment and implant positioning, with postoperative measurements closely matching intra-operative values across all alignment subgroups. There was no soft-tissue laxity asymmetry detected that had meaningful effect on alignment outcomes, supporting this technique as a precise and consistent surgical strategy.