Traditionally, a postoperative neutral mechanical alignment was the gold standard in total knee arthroplasty (TKA) and mechanically aligned TKA has achieved good long-term survival. However, recent study demonstrated the variety of coronal alignment in non-arthritic population and raises a question whether post-operative neutral alignment is not a target for all patients. To resolve this issue, a couple of personalized alignment such as kinematic alignment, restricted kinematic alignment, inverse kinematic alignment, and functional alignment has been proposed. Furthermore, recently introduced robotic technologies accelerate the surgery based on the personalized alignment in TKA. The purpose of this study is to compare the clinical outcome of mechanically aligned navigation-assisted TKA and functionally aligned robotic-assisted TKA.
A total of 121 bicruciate-stabilized (BCS) TKA was included in this study. Fifty-nine knees were navigation-assisted TKA and sixty-two knees were robotic-assisted TKA. In navigation group, the target alignment was neutral mechanical alignment of which distal femur and proximal tibia was cut perpendicular to the mechanical axis. In robotics group, image-free handheld robotics was used. The initial intraoperative plan started from neutral mechanical alignment. After gap evaluation using robotics, the plan of implant position was manipulated to minimize the soft tissue imbalance while limb alignment must fall within ± 3 degrees of neutral in coronal plane. After surgeon approved the final plan, femur and tibia were cut using robotically controlled handheld bur. A long-standing anteroposterior radiograph was used to measure pre and postoperative hip-knee-ankle angle (HKA). To evaluate patient-reported outcome measures, 2011 Knee Society Score (KSS) was recorded before and 1-year after surgery. Unpaired t-test was used to evaluate differences between navigation and robotics. The level of significance was set at p < 0.05 for all tests. This study was approved by the institutional review board.
Preoperative patient demographics (age, gender, BMI, disease, ROM, HKA and 2011 KSS) were not different between groups. Postoperative HKA was significantly varus in robotics group (navigation, 179.4 ± 2.2°; robotics, 178.4 ± 2.7°). The mean postoperative 2011 KSS for objective knee indicators, symptoms, patient satisfaction and functional activities were significantly better in robotics group (72.9 vs 74.5, 18.8 vs 20.9, 26.5 vs 29.8, 59.9 vs 69.1, respectively). Postoperative extension and flexion angle were not different between groups.
Functionally aligned robotic-assisted BCS TKA showed better postoperative 2011 KSS items of objective knee indicators, symptoms, patient satisfaction and functional activities compared to that of mechanically aligned navigation-assisted BCS TKA. On the other hand, postoperative ROM was comparative between groups. Personalized alignment using robotics potentially provides better clinical outcome than uniform mechanical alignment for all cases. Differences between navigation and robotics such as limb alignment, soft tissue balance, bone resection volume, joint line obliquity may affect the results. Further study to investigate which factor affect this result is necessary.