Comparison of Functional Recovery Between Restricted Inverse Kinematic Alignment and Adjusted Mechanical Alignment with Robotic-assisted Unilateral Total Knee Arthroplasty. a Randomized Controlled Trial.

Nowadays, total knee arthroplasty (TKA) for the treatment of osteoarthritis patients generally aims to achieve a neutral alignment of the leg. This involves cutting the bones perpendicular to the mechanical axis in both the femur and tibia. This method is called mechanical alignment TKA (MA TKA), which is widely popular and is often considered the standard technique for TKA. It has shown satisfactory long-term outcomes. However, despite advancements in materials and surgical techniques, MA TKA still requires bone and soft tissue adjustments to correct alignment, which may involve releasing soft tissues. This can result in post-surgical pain or dissatisfaction, with up to 20% of patients reporting dissatisfaction despite improved knee pain compared to pre-surgery. Furthermore, 1 in 4 of these dissatisfied patients do not wish to undergo a revision surgery, as the MA TKA method is a "one-size-fits-all" approach that aims to achieve equal and parallel gaps between the femur and tibia components without respecting individual soft tissue balance and the original alignment of each patient's leg. However, adjusted mechanical alignment technique, an adaptation of conventional MA technique with under-correction of constitutional coronal deformity, within a limit of ± 3° (HKA -3° to 3) has been introduced according to the constitutional deformity and coronal plan alignment of the knee concept.

In 2006, Howell introduced kinematic alignment TKA (KA TKA) as an alternative, with the goal of restoring the patient's natural kinematic axis and reducing the incidence of pain related to TKA rather than focusing on equal medial and lateral joint line gap and neutral mechanical axis like in mechanical alignment technique. KA TKA is considered a more personalized approach because it aims to replicate the knee's pre-arthritic alignment and movement, believing that each patient's knee has a unique alignment. This approach has gained increasing interest in recent years, with studies reporting good short- to mid-term clinical outcomes. However, the KA technique is more complex because we cannot always know the pre-arthritic alignment of individual patients and measuring soft tissue tension remains imprecise.

Later, Dr. Pascal-André Vendittoli proposed the restricted kinematic alignment TKA (rKA TKA) technique to restore natural knee movement while avoiding excessive correction of coronal alignment by maintain the HKA axis within ± 3 degrees (safe zone). By maintaining some of the constitutional deformity, this technique reduces the need for excessive soft tissue or ligament releases. In 2020 Winnock et al, introduced the Inversed kinematic technique (iKA) or tibia-referenced technique by resurfacing the tibia with equal medial and lateral resections maintaining the native tibial joint line obliquity before distal femoral bone. When combines these KA principles with robotic-assisted TKA, enhancing the accuracy of soft tissue balancing and the overall effectiveness of the procedure.

In 2020, McEwen et al. compared the use of robotic-assisted KA with MA in the same patients who underwent bilateral knee surgery using different techniques. They found that clinical outcomes, including range of motion and knee scores, were not significantly different at any time point. However, Elbuluk conducted a similar comparison, specifically robotic-assisted (MAKO) KA versus MA, and found that the KA group had less pain and better knee scores, including a higher Forgotten Joint Score. Later, Abhari conducted a study comparing robotic-assisted (MAKO) restricted KA with non-robotic MA TKA and found that the robotic-assisted (MAKO) restricted KA group had superior clinical outcomes and knee scores, including the Forgotten Joint Score, KOOS, WOMAC, Knee Society Score, as well as greater patient satisfaction. However, there are still limited prospective RCTs that study differences in outcomes, especially performance-based outcomes between restricted inverse kinematic alignment (restricted iKA) versus adjusted mechanical alignment (aMA). Therefore, the researchers aim to conduct a study comparing the efficiency of performance-based outcomes as a primary focus, including patient-reported outcome questionnaires, ROM, VAS for postoperative pain, postoperative morphine consumption within 24 hours, postoperative lower limb alignment (HKA axis), operative time, blood loss, and complications. The goal is to further advance the development of knee replacement surgery.