Kinematic and Mechanical Alignment Randomized Trial

Total Knee Arthroplasty (TKA) is recognized as a highly effective procedure for alleviating pain and restoring function in patients with knee arthritis. Despite its high success rate, approximately 20% of patients remain dissatisfied with the outcomes, primarily due to loss of functional outcomes, persistent pain, and reduced knee range of motion. This has sparked a debate on the optimal surgical alignment technique in TKA-whether mechanical alignment (MA), or personalized alignment philosophies such as kinematic alignment (KA) or restricted kinematic alignment (rKA) provides superior patient outcomes.

MA traditionally targets a neutral 180-degree hip-knee-ankle (HKA) axis, as it was taught traditionally that this approach focuses on the longevity and stability of the implant. However, this one-size-fits-all philosophy overlooks individual anatomical differences. Personalized alignments such as KA customize the placement of prosthetic components to replicate each patient's unique knee geometry and ligament tensions. Personalized alignment philosophies aim to achieve a more natural knee motion, which may enhance patient satisfaction. The precision provided by robotic-assisted surgery has increasingly facilitated the implementation of personalized alignment philosophies in TKA. Recent evidence suggests that while MA and KA yield comparable outcomes in terms of knee functionality and motion, KA may improve satisfaction and the natural feel of the knee in certain groups, particularly those without severe preoperative deformities. There is also the emerging approach of restricted kinematic alignment (rKA) which aims to provide a compromise by aligning the prosthesis within safe anatomical limits, thus avoiding the extremes of anatomical variation. This approach tailors the surgery more closely to the individual's anatomy without the risks associated with the broader variances permitted in pure KA. Hypothetically, KA and rKA techniques should more closely replicate natural knee biomechanics and improve waking gait. There are advantages and disadvantages to these alignment philosophies which should be addressed with high-quality research. While there have been several previous randomized trials on MA vs KA and its variations, the evidence is still unclear with meta-analyses having conflicting findings.

Patients will be randomly assigned to either mechanical alignment or restricted kinematic alignment. All participants will receive robot-assisted TKA using the Stryker Mako surgical robot and Stryker implants. Perioperative care, postoperative pain medications, and rehabilitation will be standardized according to local standard care.

Inclusion criteria

• Adult aged 18 years or older
• Knee osteoarthritis requiring total knee arthroplasty
• Provide informed consent

Exclusion criteria

• Inability to provide informed consent (e.g. cognitive disability, language barrier)
• Revision knee surgery
• Simultaneous bilateral knee surgery
• Recent lower extremity surgery or trauma interfering with gait assessment
• A CT scan cannot be obtained prior to surgery
• Inability or unwillingness to comply with the study protocol