No difference in clinical outcomes between functionally aligned cruciate-retaining and posterior-stabilized robotic-assisted total knee arthroplasty.

PURPOSE: To compare the clinical outcomes of subjects undergoing primary robotic-assisted total knee arthroplasty (RA-TKA), following functional alignment (FA) principles, with cruciate-retaining (CR) or posterior-stabilized (PS) bearing designs, at a minimum of 24 months of follow-up. METHODS: This observational, retrospective study included 167 consecutive patients undergoing RA-TKA with cemented PS and cementless CR implants performed with a CT-base robotic-arm assisted system (Mako, Stryker), following FA principles, between 2017 and 2020. Patients were followed up with a clinical and radiographic assessment and were administered the Forgotten Joint Score-12 (FJS-12), Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR), and the 5-level Likert scale (5-LLS). RESULTS: Three TKA revisions were performed (2 PS, 1 CR); therefore, a total of 164 knees with a mean age of 71.7 years (SD 8.9) were considered (80 cemented PS; 84 cementless CR). No statistically significant differences were recorded between study groups relative to FJS-12, KOOS-JR, and 5-LLS at a minimum of two year follow-up (FJS-12 89.3 ± 9.2 vs 87.5 ± 12.8, p-value 0.46; KOOS-JR 88.8 ± 10.0 vs 86.7 ± 14.0, p-value 0.31; 5-LLS 4.5 ± 0.7 vs 4.5 ± 0.8, p-value 0.34). CONCLUSION: No significant outcome differences were reported between patients undergoing PS and CR RA-TKA at a minimum of two year follow-up. RA-TKA achieves excellent clinical results and high satisfaction scores, regardless of the implant design used.

Joint line is restored in robotic-arm-assisted total knee arthroplasty performed with a tibia-based functional alignment.

INTRODUCTION: Functional alignment (FA) in total knee arthroplasty (TKA) has been introduced to restore the native joint line obliquity, respect the joint line height and minimize the need of soft tissue releases. The purpose of this study was to assess the intraoperative joint line alignment and compare it with the preoperative epiphyseal orientation of the femur and tibia in patients undergoing robotic-arm-assisted (RA)-TKA using FA. MATERIALS AND METHODS: This retrospective study included a consecutive series of patients undergoing RA-TKA between February 2019 and February 2021. The joint line orientation of the femur and tibia in the three-dimensions was calculated and classified on preoperative CT-scans and compared with the intraoperative implant alignment. The tibial cut was performed according to the tibial preoperative anatomy. The femoral cuts were fine-tuned based on tensioned soft tissues, aiming for balanced medial and lateral gaps in flexion and extension. RESULTS: A total of 115 RA-TKAs were assessed. On average, the tibial component was placed at 1.8° varus (SD 1.3), while the femur was placed at 0.8° valgus (SD 2.2) and 0.6° external rotation (SD 2.6) relative to the surgical transepicondylar axis. Moderate to strong, statistically significant relationships were described between preoperative tibial coronal alignment and tibial cut orientation (r = 0.7, p < 0.0001), preoperative femoral orientation in the coronal and axial planes and intraoperative femoral cuts alignment (r = 0.7, p < 0.0001 and r = 0.5, p < 0.0001, respectively). One case (0.9%) of slight tibial component varus subsidence was reported 45-days post-operatively, but implant revision was not necessary. CONCLUSIONS: The proposed robotic-assisted functional technique for TKA alignment, with a restricted tibial component coronal alignment, based on the preoperative phenotype and femoral component positioning as dictated by the soft tissues, provided joint line respecting resections. Further studies are needed to assess long-term implant survivorship, patient satisfaction and alignment-related failures.