Robotic Assisted Primary Total Knee Arthroplasty for Severe Varus Knee Utilizing an Unconstrained Prosthesis: a retrospective study

Background Recent findings indicated that robotic-assisted primary total knee arthroplasty (TKA) utilizing an unconstrained prosthesis for severe varus knee (SVK) showed excellent clinical outcomes. The surgical techniques are valuable to be explored. Methods Patients with SVKs and intact medial and lateral collateral ligaments underwent robotic assisted primary TKAs by using the unconstrained posterior stabilized (PS) prostheses. The osteotomy principle was that the more severe the varus degree, the thinner the resection. Tibial resection was assessed on the lateral plateau, and medial plateau defects were managed with cement, bone grafts, or augments, depending on defect size and depth. The femoral external rotation angle was determined using the transepicondylar axis (TEA) and posterior condylar angle (PCA), rather than the conventional 3°. Radiographic evaluations included the hip-knee-ankle angle (HKAA), PCA, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior tibial slope (PTS), patella tilt angle (PTA), and Insall-Salvati ratio (ISR). Clinical evaluations comprised the range of motion (ROM) and the Hospital for Special Surgery (HSS) knee score. Results Postoperative improvements were significant for HKAA, LDFA, PCA, MPTA, PTS, and PTA compared to preoperative values: 178.52 ± 1.79° vs. 156.34 ± 1.85°, 90.03 ± 0.39° vs. 83.92 ± 0.42°, 6.53 ± 0.89° vs. 3.32 ± 0.02°, 90.15 ± 0.47° vs. 71.84 ± 0.73°, 5.35 ± 2.02° vs. 7.53 ± 1.34°, and 2.2 ± 1.48° vs. 15.7 ± 6.35°, respectively ( P  < 0.05). The ISR showed no significant difference. Postoperative joint line changes were controlled at 1 ± 1.2 mm. Both ROM and HSS scores demonstrated significant improvements at the last follow-up ( P  < 0.01). Conclusions The techniques include reducing femoral and tibial resections, controlling patient-specific femoral external rotation, and reconstructing tibial bone defects are effective to manage the SVK utilizing an unconstrained prosthesis, yielding excellent clinical results.