The placement of a total knee arthroplasty (TKA) in cases of valgus can be performed through an anteromedial or anterolateral approach. The hypothesis of this study was that the anterolateral approach during robotic TKA reduced residual medial laxity of the knee. The main objective of this study was to evaluate the impact of the surgical approach on ligament balancing in robotic TKA for valgus knees ≤192 °, as evidenced by the residual laxity after final implant placement. The secondary objectives were to compare post-operative radiological parameters, the need for tibial tuberosity osteotomy, and complications between the two approaches.

This was a single-center, multi-operator, comparative study based on a historical-prospective cohort. A total of 81 consecutive patients who underwent Mako® Stryker robotic TKA for valgus knee ≤192 ° were included. Two groups were formed based on the surgical approach: anteromedial (AM) or anterolateral (AL). To homogenize the groups, a 1:1 propensity score matching was performed based on age, gender, and deformity. Residual laxity, evaluated in millimeters, was measured at the end of the procedure with the definitive implants, using the Mako Total Knee SmartRobotics™ software measurements in four stress positions: extension (0−10 °) varus and valgus, then flexion (85−95 °) varus and valgus. Postoperatively, a radiological analysis of the coronal alignment of the TKA, patellar tilt and translation was performed, along with an analysis of complications.

After matching, 37 patients were included in each AL and AM group. The groups were comparable in terms of age, gender, coronal deformity, and ASA score; however, BMI was statistically higher in the AL group (29.0 versus 26.6; p = 0.002). Residual laxity in extension was not statistically different between AL versus AM groups, respectively in medial 1.6 mm versus 2.1 mm (p = 0.326) and in lateral 1.6 mm versus 1.6 mm (p = 0.384). Laxity asymmetry in extension was lower in the AL group versus AM group (0.05 mm versus 0.5 mm; p = 0.031). In flexion, there was no significant difference regarding residual laxity in medial (AL 1.5 mm versus AM 2.4 mm; p = 0.07) and in lateral (AL 2.9 mm versus AM 2.9 mm; p = 0.344). Laxity asymmetry in flexion was greater for the AL approach than for the AM approach (−1.4 mm versus −0.5 mm; p = 0.02).

There was no difference regarding postoperative coronal alignment of the implants. Patellar tilt was greater with AM (1.7 ° versus −3.8 °; + in lateral tilt; p < 0.001). Patellar translation was not different between groups. At follow-up, there were 6 complications in the AM group and 4 in the AL group (p = 0.237). Anterior tibial tuberosity osteotomy was performed in 6 versus 1 case respectively for AL and AM (p = 0.107).

In comparing residual laxity in robotic TKA for valgus knees ≤192 °, the main finding was that the surgical approach does not significantly impact knee residual laxity. Despite small differences, the anterolateral approach yields a knee laxity profile close to the native knee, with better management of patellar tilt, without increasing the complication rate. Moreover, the Mako workflow does not dictate the choice of surgical approach, remaining equally feasible for both AM and AL approaches.

IV.