Kinematic Alignment in Knee Replacement

Alignment is a decision, not a setting

A knee replacement resurfaces worn bone, but the components have to be positioned in space, and where they sit changes how the knee loads, tracks, and feels. That positioning is what alignment means, and it is decided before the operation rather than discovered during it.

Mechanical alignment is the reference standard. It sets the leg to a neutral axis regardless of what the knee looked like before arthritis, and the long survivorship record in the national joint registries was built on knees aligned this way. Those registries do not track alignment philosophy as a field, so that record is a starting point rather than a head-to-head comparison. Any other strategy is still measured against it, not against a marketing claim.

Restricted kinematic alignment

Knees are not all built to the same axis. Kinematic alignment starts from the knee’s own pre-arthritic joint line and aims to restore it rather than convert every leg to neutral. The reasoning is that ligaments were built around that original geometry.

The word that matters is restricted. Boundaries are set, typically a few degrees either side of neutral, and a knee that falls outside them is aligned mechanically instead. Restricted kinematic alignment can be performed by hand, and Dr. Patel does.

Personalized alignment, and why Dr. Patel uses the Mako System for it

Personalized alignment individualizes further than restricted kinematic alignment: rather than working to a boundary rule, the plan is built around the individual knee’s geometry and the way its soft tissues balance. Both are personalized strategies. The difference is how much of the plan comes from a rule and how much from the individual knee.

Dr. Patel executes it with robotic-arm assistance. His reasoning is the sagittal plane: how the femoral component sits in flexion, and how the tibia slopes front to back. Those can be cut by hand, and are, but with wider variation than he is willing to accept when the entire plan is built around them. A CT-based plan and robotic-arm assistance on the Mako System are what hold the plan to the tolerance he wants, which is the whole reason the technology is used here.

The robotic arm does not perform the operation. Dr. Patel controls it throughout, works to a plan he built and can revise, and sets the assistance aside whenever the knee in front of him calls for something different.

What is settled, and what is not

Mechanical alignment has the longer track record in the joint registries, and that is the honest starting point. Kinematic strategies are studied for early function and patient-reported outcomes, and the long-term data is still maturing.

So no alignment strategy is offered here as better. What can be said is that the alignment is chosen for your knee rather than set by default, and that you are entitled to ask which one is planned for you and why.

When mechanical alignment is the right call

A leg that has bowed or angled well outside the safe boundaries, significant deformity, previous surgery that has changed the anatomy, or ligaments that will not balance to the knee’s original geometry can all make mechanical alignment the better plan.

The plan can also change during the operation. If what the knee does under examination and trial does not match what was planned, the plan gives way. That is judgment being exercised, not a setback.