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The Evolution of Total Knee Arthroplasty (TKA)

Over the past 50 years, TKA has become one of the most common orthopedic procedures in the world due to its high success rate and survivorship. Multiple studies and clinical registries indicate that these procedures are capable of survivorship past 20 years. There have been many incredible advancements since the inception of TKA. Some notable examples include minimally invasive surgical approaches, implant refinements, 3D printed technology, and robotic surgical systems. These advancements have contributed to the widespread acceptance of knee replacement. As such, over 1 million patients in the U.S. receive a knee replacement annually.

Forget About Your Knee Replacement: It Means You Are Satisfied

Despite its successes, TKA has not experienced the same patient satisfaction as another common joint replacement procedure - hip replacement. A rating system known as the Forgotten Joint Score (FJS) can capture the patient’s feedback on this subject. The FJS system is likely one of the most crucial patient-reported outcome measurements because it focuses on a critical aspect of joint replacement – returning to everyday life and forgetting that you even have an artificial joint. Although knee replacement has shown widespread success in eliminating joint pain and allowing patients to move more freely, knee replacement satisfaction levels still trail hip replacement satisfaction. Patients cannot always explain it, but a commonly cited reason for lower satisfaction is that their knee feels ‘unnatural.’

Is It Technology or Something Else?

Technology has enabled surgeons to be more precise, efficient, and effective than ever. Software and robotics have led to an unprecedented level of precision and data acquisition. These advancements have all had positive effects, but clinical data is mixed on whether these advancements translate to significant changes in patient satisfaction. So, if precision isn’t the root cause of dissatisfaction, what else can we look to?

Mechanical Alignment: The (Historically) Gold Standard TKA Technique

Historically known as the gold standard technique for knee replacement, the mechanical alignment technique requires the surgeon to position the implants perpendicular to a patient’s hip-knee-ankle angle (HKA), also known as the weight-bearing axis of the patient’s leg. It is the most employed (and studied) approach globally. The technique has many variances through soft tissue balancing and bone resection to ensure the patient achieves a neutral HKA axis (180°).It is important to note that this technique sometimes requires surgeons to perform soft tissue releases, elevating or gently cutting medial or lateral ligament fibers to ensure equal tension in both knee compartments. As such, the patient leaves the operating room with a straight leg, an optimal X-ray standard, and objective positioning marks.

Kinematic Alignment: The Fastest Growing Technique in TKA Today

To diagnose the root cause of lower satisfaction levels, we must investigate all the variables affecting patient satisfaction. Some surgeons have recognized that mechanical alignment could be part of the root cause. This approach, not technology or implant design, has been the common denominator in knee replacement for decades. Several modified approaches have been developed over the past 50 years, but none have grown as exponentially as the kinematic alignment (KA) technique. The idea is simple: resurface the patient’s bony anatomy and minimize soft tissue releases. The technique’s rationale comes from the fact that every patient has different knee anatomy. Are the patient’s legs slightly bowed or knock-kneed? Kinematic alignment will ensure the leg is restored to its native angle, whereas mechanical alignment forces each leg in to a neutral stance. Proponents of the KA technique say that each patient’s anatomy is restored, which should theoretically also restore native joint forces, ligament tensions, and kinematics. A novel concept, this technique essentially places each component in a personalized alignment instead of a ‘standardized’ position.

"Kinematic alignment represents a shift of thinking; reproduce the patient’s native anatomy and kinematics, instead of focusing on an arbitrary standard (MA) "

Industry focus on kinematic alignment has continued to surge in popularity, particularly in the past five years. A key reason for the surge is improved forgotten joint scores (the critical metric) and positive surgeon feedback. Perhaps nothing has spread the concept of kinematic alignment faster than peer discussions among surgeons. More and more studies are published each year demonstrating that kinematic alignment deserves consideration in a surgeon’s practice. The bottom line? The knee replacement industry is facing a critical moment: we may be witnessing a transition to personalized arthroplasty.

What Does the Future Look Like?

Is kinematic alignment the watershed moment for TKA? Time will tell. The most exciting aspect of this rising trend is that surgeons are beginning to question the wisdom of conventional knee replacement. That may be just the start –the KA technique was developed using implants and instrumentation designed explicitly for Mechanical Alignment. There are some promising opportunities for manufacturers to create KA-specific instrumentation to simplify the technique and make it even more reproducible for every surgeon. Since KA requires positioning implants to each patient’s individual anatomy, there is also a significant opportunity to refine the implant designs and further reinforce the concept of patient-specific knee replacement.

The Watershed Moment: Personalizing Patient’s Knee Replacements

The watershed moment for knee replacement is not robotics, software, or other technology that enhances precision. The industry has already accomplished significant achievements in precision. The watershed moment is improving the accuracy of each surgery by changing the target. kinematic alignment represents a shift of thinking; reproduce the patient’s native anatomy and kinematics instead of focusing on an arbitrary standard (MA).The data looks promising: early and mid-term studies are already demonstrating improved forgotten joint scores. In turn, more and more surgeons are switching their techniques, further reinforcing the trend. The concept represents a substantial opportunity to improve patient outcomes with zero additional costs to the healthcare system, which is a victory for every party involved in the patient’s continuum of care.