Comparison of post-operative pain and early rehabilitation functional vs mechanical alignment in bilateral robotic-arm assisted total knee arthroplasty

Total knee arthroplasty is a time-tested and successful surgery for arthritis of the knee joint. However, despite advances in implant design and refinement of surgical techniques, 20% of patients are still dissatisfied. The overall complication rate is less than 1%. There are many factors which may be responsible for patient dissatisfaction, but one of the common complaints is the patient feels "his/her knee does not feel like the native knee". This could be due to alteration in knee kinematics, resulting in dissatisfaction.

In manual or conventional-Jig based TKR, the target limb alignment is a joint line that is 90 degrees or perpendicular to the mechanical axis of the lower limb. This technique is also known as MECHANICAL ALIGNMENT. Mechanically aligned knees have good survivorship but may compromise the kinematics of the knee leading to pain and reduced function.

Functional alignment is an alternative alignment strategy in which surgeons attempt to restore the pre-operative knee kinematics by placing components to target an joint line that is a few degrees oblique (varus or valgus) to the mechanical axis of the knee, thus restoring the original balance of the knee. This is particularly important in those patients with "constitutional varus" of the knee, where the limb alignment was 1+ degrees of varus. Putting these knees in mechanical alignment (0 degrees) disrupts knee kinematics.

Functional alignment is possible and accurate with robotic-arm assisted TKR, in which the surgeon can visualise every bone cut which is pre-planned. Components are placed in a safe-zone to recreate the balance of the knee, without excessive soft-tissue releases.

The hypothesis of our study is that functional alignment is associated with less soft tissue releases, less dissection, and improved knee kinematics leading to reduced pain, improved early rehabilitation after the surgery.

A lot of confounding factors come into play when trying to compare FUNCTIONAL versus MECHANICAL alignment in different individuals. This is because of differences in the native limb or pre-arthritic limb alignment, OA wear patterns, weight and BMI of the patients etc. This is the reason behind this novel methodology, where patients undergoing bilateral simultaneous TKR will receive two globally accepted and time tested alignment strategies. One knee is randomized to receive functional alignment and the other knee is mechanically aligned. Both strategies are followed widely across the world. The patients thus provide internal controls against which the comparison can be done, without any confounding variables influencing the outcomes.