Functional knee positioning in patients with valgus deformity undergoing image-based robotic total knee arthroplasty: Surgical technique.

Background: Functional knee positioning (FKP) represents an innovative personalized approach for total knee arthroplasty (TKA) that reconstructs a three-dimensional alignment based on the optimal balance of soft tissue and bony structures, but it has mostly been described for varus knee deformity.

Surgical technique: Valgus deformities present specific challenges due to altered bone remodeling and soft tissue imbalances. Using robotic assistance, FKP enables precise intraoperative assessment and correction of compartmental gaps, accommodating each individual's unique anatomy and laxities. The distal femoral cut is calibrated for 9 mm resection at the intact medial femoral condyle and adjusted on the lateral side to accommodate bone wear, while the tibial plateau resection aims for 8 mm from the medial side and 4-6 mm from the lateral side. Intraoperative evaluations of mediolateral laxities are performed at extension and 90° flexion. Adjustments are made to femoral and tibial cuts to balance gaps, aiming for 0 mm in posterior stabilized implants and minimal discrepancies in cruciate-retaining designs with lateral gap looser in flexion.

Discussion: FKP emphasizes soft tissue-driven adjustments with the use of robotic platforms. Hence, intact soft tissue envelope of the knee is essential. This technique holds significant promise for managing valgus deformities in TKA, but further research is needed to evaluate its functional outcomes.