Kinematic Alignment for Total Knee Replacements

Implant Materials and Composition

All of our knee replacements are Cobalt Chromium. The plastic is a highly specialised polyethylene. The composition of the implant is designed to increase longevity. Under an electron microscope, the surface of a CoBalt Chromium implant is extremely smooth. In a knee replacement, there is no metal touching metal, as the plastic sits between it.

For more information of knee replacement composition - visit this link.

How a Normal Knee Moves

Unlike a standard hinge, a normal knee bends, straightens, opens and closes (laterally), is tighter medially, and also rotates. This is what the implant design is for - the medial pivot design mimics the behaviour of a normal knee. When coupled with kinematic alignment, this is designed to increase the natural feeling of a knee. To achieve kinematic alignment, patient specific technology is used. For all of our total knee replacements, a disposable instrument set is used so it is brand new for each and every knee that is performed.

Preserving Ligaments and Soft Tissue

Yes, the aim of a kinematically aligned knee is to not cut or detach any of the surrounding ligaments, tendons or capsular structures. Like with all knee replacements with a medial pivot design, the ACL and PCL, which reside within the knee, are removed, in order to position the prosthesis. The surrounding ligaments, the LCL and MCL, including the Popliteus, ITB and capsular structures are not damaged or released.

Kinematic vs Mechanical Alignment — What Is the Difference?

Mechanical alignment was developed in the era of the earliest knee implant designs. The goal is a straight leg: the bone cuts are made perpendicular to the mechanical axis of the limb, so that the hip, knee and ankle line up at 180 degrees. Every knee is prepared to the same target, regardless of what that person's knee looked like before arthritis. Because most people's joint lines are not naturally perpendicular to this axis, achieving the target frequently requires releasing or lengthening the surrounding ligaments to make the knee balance around the new, altered joint line.

Kinematic alignment takes the opposite starting point. Rather than imposing a single universal target, it asks: where was this patient's joint line before arthritis wore it away? The bone cuts then reproduce that pre-arthritic geometry, resurfacing the knee to its own constitutional alignment. The natural obliquity of the joint line is preserved, the ligaments remain at their native tension, and releases are minimised or avoided altogether.

In practical terms, the differences are these. Target: mechanical alignment aims for a neutral 180-degree axis for everyone; kinematic alignment restores each patient's own pre-arthritic anatomy. Joint line: altered in mechanical alignment; preserved in kinematic alignment. Soft tissue: mechanical alignment often requires ligament releases to balance the knee; kinematic alignment works with the ligaments as they are. Consistency: mechanical alignment treats every knee the same; kinematic alignment treats every knee — even the left and right knee of the same person — as unique.

Neither technique is "new". Mechanical alignment has the longest track record and remains widely used. Kinematic alignment has now been studied for more than two decades, and published survivorship studies at 10 to 15 years report comparable implant survival between the two approaches. The registry data available so far does not show a longevity penalty for kinematic alignment, while proponents report a more natural-feeling knee in appropriately selected patients. It is a factual difference in philosophy: one standardises the limb, the other individualises the implant position.

Who Is Kinematic Alignment Suitable For?

Kinematic alignment is suitable for the majority of patients undergoing total knee replacement. Patient selection still matters. Those with significant pre-existing deformity, prior fracture malunion, or ligament instability may be better served by a more conventional alignment strategy, or a hybrid of the two.

This is why every knee in my practice is assessed with a 3-dimensional scan before surgery. The patient-specific planning process simulates the surgery in a 3D environment first, confirms the intended alignment is safe for that individual anatomy, and produces cutting guides manufactured for that patient alone. The decision between kinematic and conventional alignment is made deliberately, before the operation, based on each patient's imaging — not as a default applied to everyone.

Does Alignment Affect How Long a Knee Replacement Lasts?

Published studies following kinematically aligned knee replacements over 10 to 15 years report survivorship comparable to mechanically aligned replacements. Longevity of any knee replacement depends on multiple factors — implant design and materials, fixation, infection prevention, patient weight and activity, and surgical accuracy — rather than alignment philosophy alone.

For the full Australian registry picture — survivorship at 15 and 20 years, the main causes of revision, and which patient factors change the risk profile — see the companion article on the longevity of a total knee replacement.

Frequently Asked Questions