For Sale or License – Next Generation Knee Concept and Technique
As an increasing number of studies show dissatisfaction post total knee arthroplasty (TKA) coupled with overwhelming growth projected for active patients within the ASC market, there is an opportunity to deliver a next-generation implant designed to meet the growing needs and demands.
Several manufacturers have attempted to solve this dissatisfaction with instruments that align the prosthesis based on ligament tension regardless of the other factors critical to locomotion. Even fewer manufacturers have attempted to design an articular surface based on normal knee kinematics to help solve the quandary of dissatisfaction. Regardless of action or intent, all manufacturers share these common issues when it comes to TKA:
- – Promoting a reproducible surgical technique to place the prosthesis in the proper alignment specific to each patient’s anatomy
- – Understanding the relationship of the collateral ligaments as they relate to proper knee kinematics and how to treat the structures intraoperatively
- – And most importantly, the ability to design an implant that fully behaves as the normal knee does through both active and passive flexion. We own the rights to a patent which aims to solve these issues that plague current knee systems (Patent# 9,833,324).
Management / Surgeon Team
- Eric L. Muller – BSBE; 10+ years, Stryker, Wright Medical, MicroPort Orthopedics
- J. David Blaha, MD –Surgeon developer of MicroPort (formerly Wright Medical) Advance Medial-Pivot and Evolution Medial-Pivot Knee Systems
Most total knee prostheses are predicated on two assumptions:
- The normal knee is symmetric. That is, both the medial and lateral compartments have the same stability and ligament tension.
- The motion is guided by the ligaments of the knee. Based on this principle, the articular surfaces of the knee cannot restrict the motion of the femur and tibia lest there be high forces (caused by the ligaments as they guide the motion) at the fixation interface that would cause the implants to loosen from the bone. Based on these two assumptions, most total knee prostheses have similar (in most cases identical) condylar geometries in the medial and lateral compartments. Femoral components are designed with a “J-curve” (that is a decreasing radius of curvature) and the corresponding tibial component surface does not conform to the femoral. In order to provide stability for the arthroplasty, ligaments must be tensioned in the process of “ligament balancing”. Accordingly, most prominent surgeons profess from the podium that total knee arthroplasty is a “soft tissue procedure”. Both of the above assumptions are incorrect.
The knee is not symmetric.
Analysis of human knees in living patients using MRI analysis and the study of cadaveric knee joints have added significantly to the understanding of the kinematic and stability behavior of the living knee. Most significant is the understanding that during the majority of flexion, the medial compartment of the knee (medial femoral condyle, medial meniscus and tibial plateau) moves largely as a simple ball-in-socket joint, whereas the lateral compartment (lateral femoral condyle, lateral meniscus and lateral tibial plateau) moves such that the contact point changes from anterior to posterior (front to back) in an arcuate path dependent largely on the longitudinal rotation of the tibia beneath the femur. Thus the contact area or point (imaginary point at the center of contact pressure) between the medial condyle of the femur and the medial tibia remains almost stationary while the lateral condyle contact point on the lateral tibia moves during activity. Stability at the medial side of the knee is provided by the conformity between the femoral condyle and the concave tibial surface with the attached medial meniscus such that the construct resists anterior-posterior (AP) displacement, while the lateral side of the knee with its convex surface and less firmly attached meniscus does not provide a high degree of AP constraint but is free to move in and anterior-posterior manner with knee flexion. This kinematic behavior provides that at the medial interface acts as the center of rotation for internal/external rotation of the tibia while the lateral femoral condyle moves anteriorly and posteriorly. An elongated distal contour of the medial femoral condyle creates the cam-effect and screw-home motion at the last 10-15° of extension. The anterior-posterior mobility of the lateral compartment allows the unique motion in flexion beyond 115 degrees. Images below show the medial and lateral compartments, respectively.
Ligaments do not guide knee motion.
Ligaments do not guide the motion of the knee because, for the majority of the range of motion of the knee, they are in the low stiffness “toe-region” of their stress-strain curve. The collateral ligaments resist external loads that would force the knee into a varus (bowlegged) or valgus (knock-kneed) position. The cruciate ligaments act similarly to resist externally applied anterior or posterior forces on the knee. However, when the knee is moving in the flexion-extension plane, the ligaments are simply not taught enough to affect knee joint motion.
The knee has three ranges of motion.
The behavior of the knee in the terminal 20 degrees of extension and after 115 degrees of flexion differs from the motion in the mid-range of motion. In full extension, a cam-like effect of the distal medial condyle (i.e., not a ligament effect) moves the femur away from the tibial surface, tightens the medial and lateral collateral ligaments, and creates an external rotation of the tibia called “screw-home”. Beyond 115 degrees of flexion the lateral tibial contacts the posterior lateral tibial surface in a rolling and sliding motion that moves the lateral femoral condyle off the back of the tibia (“roll-off”) and allows full flexion while decompressing the contents of the popliteal fossa. Thus the knee has three ranges of motion: full-extension, midrange flexion, and full-flexion all controlled by the geometry of the surfaces with the ligaments acting to resist externally applied loads but not themselves causing motion.
Current total knee designs rely on ligament tension.
Knee prosthetic implants ideally seek to match the kinematic and stability behavior of a healthy living knee. Paramount is maintaining stability of the joint through the full range of motion. Currently available knee prosthetic implants rely heavily on tension in the medial and lateral collateral ligaments
with or without tension in the posterior cruciate ligament to drive kinematics and stability. It is conventionally understood that adjusting (through “ligament balancing”) and maintaining tension in these ligaments throughout flexion is essential to providing stability of the joint. However, in the total knee arthroplasty procedure it is difficult to achieve the desired tension in these ligaments and lack of the desired tension or excessive tension leads to a result unacceptable to the patient. Insufficient ligament tension leads to joint instability and a result unacceptable in terms of function to the patient, and in extreme cases dislocation of the joint. Excessive ligament tension leads to restrictions in range of motion and the potential for ligament failure. Moreover, most designs fail to provide a full range of flexion movement because the type of stability and motion found in the normal knee (referenced above) is not provided by the articulation and ligamentous tension.
Instability is the reason that many patients are unhappy with the results of total knee arthroplasty. The difficulties in correctly tensioning ligaments so that they stabilize articular surfaces that are non- conforming is the reason for instability. Despite changes in design and new technology for assessing ligament tension in the operating room, many patients are still unhappy. The solution is not to continue to tweak the design and implantation technique of non-conforming implants in hopes that a new iteration will have a better result. The solution is not to decrease patient expectations to that they are satisfied with a total knee arthroplasty that does not have the stability of the normal. The solution is to mimic the normal knee that achieves stability through the geometry of the articular surfaces.
New patented design to mimic the asymmetric motion and stability of the normal through articular congruence.
PATENT # 9,833,324 – REALIZING FULL FLEXION POTENTIAL
The present invention, a knee prosthetic implant for total knee arthroplasty relies on the conformation of interfacing surfaces during the full range of motion (i.e., all three ranges of motion identified previously) to provide a large range of motion of the joint, and stability throughout flexion but not relying primarily on ligament tension to provide such. These features are provided through sets of cooperating convex and concave facet surfaces within the prosthesis joint compartment which cooperate in the ranges of motion.
In full extension as the separate facet on the distal medial condyle lefts the femur away from the tibia thus tensing the medial collateral ligament.
In the midrange of motion, the spherical condyle on the
medial side maintains motion and stability by the “ball-in-
socket” geometry. The lateral side is free to contact anteriorly or posteriorly to accommodate the longitudinal rotation position of the tibia relative to the femur.
In full flexion a lateralized cam and post moves the lateral side to the posterior part of the tibial plateau mimicking the “roll-off” function of the normal knee. This term of “full flexion” is realized with this
device and has not been conceptualized or patented until now. Full description of the concept may be found in US Patent # 9,833,324.
TOTAL KNEE ARTHROPLASTY MARKET
The US total knee arthroplasty (TKA) market is nearly $3.5B with companies such as Zimmer Biomet, DePuy Synthes, and Stryker owning a combined market share of 85%. As larger companies like Zimmer Biomet have consolidated their businesses, hospitals networks and systems alike are employing similar strategies with the goal being to limit suppliers in hopes to gain better pricing. In doing so, many smaller orthopedic medical device companies are finding it increasingly challenging to gain access into health systems. With both CMS and commercial payors (BCBS, Aetna, etc.) demanding high-quality, low-cost care, the market is considering site of service changes to meet the demand. These new sites of service include hospital outpatient departments (HOPDs) and ambulatory surgery centers (ASCs). HOPDs are effectively extensions of hospitals and much of the consolidation activities driven by health systems will most likely impact access to this site of service as it does in the hospital setting. ASCs are different in that in many cases they are not owned or have any affiliation with a hospital system or network. They act independently and are able to negotiate separate supplier and payor agreements. A study performed by Kingery et al. found nearly 70% of patients were considered eligible for outpatient joint procedures (BMI < 40, low or no comorbidities, no sleep apnea). In addition to this, market researchers note that by 2026, 51% of joints will be performed in an outpatient setting.
As noted by market research and trends, there will be a substantial increase in the total joint procedures by 2026. This is a reflection of the total number of outpatient procedures, but not by location. As of 2017, there were more than 200 ASCs performing outpatient total joints. This number is up from 25 ASCs in 2014. This trend is an indicator that TKA are becoming more prevalent in the ASC as more surgeons become trained on minimally invasive technology and pain management techniques. In addition, insurance companies are more willing to setup reimbursement within ASCs as more studies are demonstrating success for appropriately selected patients.
J. David Blaha, MD
Email – firstname.lastname@example.org Phone – (734) 883-4447