Becker’s Executive Briefing, Sponsored by Medacta USA

Kinematic Alignment – The Cost-Effective Strategy for Achieving Superior Outcomes

We’ve all heard the data; total knee arthroplasty (TKA) is one of the fastest-growing procedures, by 2030 TKA will increase by 189% to approximately 1.28 million procedures¹. These are opportunistic tailwinds for surgeons, not just more patients requiring TKA, but rapid growth in surgeon ownership models in Ambulatory Surgery Centers (ASCs), and improvements in technology and surgical devices. Healthcare efficiency has become a major driver, requiring surgeons to carefully evaluate and refine every aspect of their practice.

We also all know that TKA is a successful procedure that significantly improves postoperative pain scores. Yet over the past 40 years, unfortunately, a distinct subset of patients have been dissatisfied with their outcome after surgery^2,3. The leading complaints tend to relate to feeling tight, instability, anterior pain, and patellofemoral issues⁴. The one common denominator for most surgeons performing TKA is that nearly all utilize the mechanical alignment (MA) technique. Perhaps MA is a root cause for dissatisfaction, especially when all objective measurements, including x-ray standards, stable exam, achieving neutral cuts, etc., indicate a successful procedure.

Industry has attempted to respond with so-called novel devices to help improve patient outcomes. A leading trend has been the push toward robotically assisted surgery to improve the accuracy of component positioning. These technologies, while fascinating, incur heavy costs with disposables, exorbitant facility contracts, and longer surgical times. Despite increased cost, robotically assisted TKA has not shown improved outcomes^5,6,7.

Perhaps a different direction is the calipered Kinematic Alignment (KA) technique, which is one of the fastest-growing and most-discussed in TKA. It is simple, straightforward to implement, and does not require expensive robotics. In fact, the technique is more accurate than robotic TKA⁸. The overall premise of KA is to match the patient’s prearthritic anatomy through femoral and tibial resurfacing to allow the patient to have their native kinematics and gait restored, all while eliminating the pain they experienced before surgery.

The benefits of Kinematic Alignment are immense and could have major implications for eliminating the dissatisfaction previously seen in TKA globally:

1. Studies repeatedly demonstrate higher forgotten joint scores and other PROMs versus mechanical alignment^9,10,11
2. It is cost-effective, reproducible, and simple to implement in practice
3. Mid-term and long-term data demonstrate similar survivorship to prior conventional techniques^12,13

I personally came to KA after decades of practicing Mechanical Alignment. I switched from an MA technique with an ultra-congruent conventional knee system to calipered KA with the GMK Sphere medial ball-in-socket knee system. Evaluating my first 327 KA TKA, I saw improved KOOS-jr scores, more patients reaching minimally clinically important difference (MCID), a higher percentage of patients achieving the patient-acceptable symptom state (PASS), a lower manipulation rate, and improved patient satisfaction. We published the early results, including our learning curve with the technique¹⁴.

When Medacta launched the GMK SpheriKA, the world’s first knee system specifically optimized for KA, I began implanting these instead of the GMK Sphere. Since switching, I’ve seen even further improvements. especially evident in difficult-to-satisfy patients, who I have noticed are typically females with CPAK III phenotype (CPAK classification system¹⁵).

Interestingly, I’ve realized that my rate of having to release, lengthen, or otherwise balance the MCL was roughly 26% with my previous MA technique, the same percentage of patients in the CPAK I classification. As we continue to enhance our understanding of native phenotypes, you see we cannot simply use MA to make the patient’s leg “straight” without performing soft tissue release. With KA and the GMK SpheriKA, my soft tissue release rate is 0%.

Kinematic Alignment is here to stay. Medacta International has championed the development of products and systems to support this technique. The technique workflow is seamless and supported by a wide range of instrumented options, including conventional or Efficiency single-use KA instruments, the MyKnee KA patient matched guides, or NextAR Augmented Reality to achieve KA. It is important to note that Medacta’s GMK Sphere and GMK SpheriKA knee systems are two of the only systems on the market cleared for Kinematic Alignment with the FDA. Leveraging these novel technologies allows for a more efficient procedure, a smaller surgical footprint, and more streamlined processes, which drives these procedures into the ASC. No other system is as efficient and has such a positive financial impact for all stakeholders in the outpatient space.

Why KA Makes Sense as an Implant Design Philosophy

Kinematic Alignment (KA) ‘s increasing popularity highlights that knee replacement surgeons always look for ways to improve their surgical decision-making and achieve better patient results. This growth also underscores the importance of collaborations between the medical industry and surgeons so that they can have access to the most accurate alignment instrumentation and patient-friendly implant designs.

KA has proven effective in numerous randomized control trials, retrospective analyses, and outcome studies. When combined with various knee implant systems, KA has resulted in better patient outcomes than mechanical alignment. Recent studies suggest that implant design plays a significant role in determining patient outcomes. While several types of knee systems are available, including CR, Medial 1:1 Ball-in-socket, Medially Congruent (MC), and Posterior Stabilized (PS), most of them have similar trochlear angles, averaging 6-7° valgus. This is primarily because these implants were designed for placement using mechanical alignment (MA) to approximate the quadriceps line of force, which is the proximal determinant of the Q-angle that controls patellofemoral tracking and kinematics.

The accuracy of KA performed with manual instruments, as verified by a caliper, more accurately resects the distal and posterior femur and resurfaces the patient’s pre-arthritic knee than robotics8. Because KA restores the pre-arthritic femoral valgus angle and quadriceps vector, the orientation and medial-lateral location of the prosthetic trochlear groove are different than when the femoral component is set with the mechanical alignment (MA). Although KA results in a closer restoration of native knee trochlear groove morphology than the MA technique¹⁶, there is room for improvement since all prosthetic trochlea to date are designed with a narrow groove angle specific for the MA technique^17,18. For example, a study of osteoarthritic knees using 4,116 CT scans determined the difference between the native trochlear groove angle and 45 available knee systems. The prosthetic trochlear groove angle averaged 6° valgus for most knee systems average while the native knee’s angle was significantly wider, ranging from -5° ± 4° varus to 6° ± 5° valgus. Since only about 58% of knee systems’ have a prosthetic trochlear groove angle that restores the patients’ native trochlear groove improving the femoral component’s design = to accommodate more varied trochlear anatomy could benefit a wider range of patients undergoing TKA¹⁹.

A wider prosthetic trochlear groove is especially important in the small subset of approximately 10% of patients with a valgus limb and valgus joint line obliquity (so-called CPAK III). In these patients, the prosthetic trochlear groove could be medial to the quadriceps line of force (QLF), especially with KA, and adversely affect patellar tracking as the patella could ride too lateral abutting the lateral ridge of the femoral component.

Medacta recognized the necessity of widening the prosthetic trochlear groove as an additional step toward improving patient outcomes. Their bioengineers analyzed the MySolutions database, which consisted of over 150,000 native knee CT scans, to identify the optimal angle and lateral coverage for the prosthetic trochlear groove. They performed the morphologic analysis using the KA technique, referencing the three kinematic axes of the knee, instead of the MA technique because KA is associated with higher outcome scores and better patient satisfaction.

The collaboration between the engineers and surgical consultants worldwide resulted in the GMK SpheriKA, which has a 20° valgus prosthetic trochlear groove angle widened from the 6° angle of its predecessor, the GMK Sphere. The reasons for modifying the GMK Sphere are that its medial 1:1 ball-in-socket congruency and a flat lateral articular surface provide better patient outcome scores and knee flexion than a posterior stabilized design²⁰, and because it restores native knee tibial internal-external rotation required for optimal patellofemoral kinematics²¹.

The SpheriKA has an enhanced prosthetic trochlea that accommodates the wide range of valgus femoral component placements needed to resurface the pre-arthritic knee with the KA technique and offers better lateral bone coverage. A preliminary study showed that the GMK SpheriKA better suits patients with the more variable anatomies and helps to facilitate patellofemoral tracking in nearly all cases, compared to only 69% with an MA-designed 6° valgus femoral component²².

We are optimistic that the combination of the FDA-approved Kinematic Alignment Platform with the GMK Sphere launched in 2018, along with an upgrade to the GMK SpheriKA in 2024, will lead to a new path in knee replacement that will enhance the surgeon’s ability to provide better clinical outcomes to their patients.

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