Copy to clipboard 
The results of meniscus repair surgery are largely successful, but many patients continue to experience pain and joint impairment after the procedures. Partial meniscectomies offer short-term results but don’t address the underlying clinical condition that can lead to the progression of osteoarthritis and the eventual need for a knee replacement.
Increasing numbers of orthopedic companies are tackling this unmet clinical need with meniscus replacement implants geared toward treating younger patients who seek an effective treatment for persistent knee pain following tears. Doing so requires a mix of advanced materials and creative design concepts.
Restoring Stabilization
OrthoPreserve’s Defender is a meniscus replacement implant that acts as a biomechanical substitute for native tissue, serving as a way to restore the knee’s anatomy and function.
“Defender was designed around anatomic congruence, meniscus-like mechanical behavior and stable fixation at the same locations as the natural meniscus,” said OrthoPreserve CEO Jonathan Schwartz. “The goal was to recreate native load distribution and joint stabilization rather than having the implant act like a generic spacer. Shape, compliance and fixation were developed together to function as a system.”
Meniscal injuries place high amounts of stress on articular cartilage, accelerating degeneration and arthritis. Defender aims to change the biomechanics that drive that disease progression.
“While the implant is meant to be inert, the intent is to provide long-term joint preservation through biomechanical restoration,” Schwartz said. “Defender is designed to restore a physiologic load distribution and reduce focal contact stresses and pressures that are associated with cartilage breakdown.”
The implant’s most important properties are fatigue resistance, controlled compliance, low wear in a hydrated environment, and long-term mechanical stability under millions of load cycles.
“It’s engineered to deform, dissipate energy, and recover under cyclic loading, similar to native meniscus behavior,” Schwartz said. “Reinforced architecture and fixation manage hoop stresses and maintain alignment through repeated motion and long-term use.”
Materials science plays an important role in maintaining that level of durability. Defender features a self-lubricating hydrogel surface that’s combined with oriented reinforcement fibers, resulting in an implant with wear and fatigue resistance that maintains meniscus-like mechanics over time.
“The performance of the material has been evaluated through high-cycle mechanical, wear and aging tests designed to reflect real knee loading conditions,” Schwartz said.
In January 2025, OrthoPreserve was granted FDA Breakthrough Device Designation and enrollment in the Total Product Life Cycle (TAP) Program, which are intended to accelerate the development of devices that offer effective treatments of debilitating health conditions.
“The designations reflect the significant unmet need in symptomatic meniscus-deficient patients and the potential for Defender to offer more than incremental improvement,” Schwartz said. “TAP enrollment also signals FDA alignment and support on an efficient, evidence-driven development path.”
TAP enrollment has changed OrthoPreserve’s approach to Defender’s commercialization pathway. “It has pushed earlier alignment with FDA and other stakeholders — payors, physician societies, patients — on what evidence matters most and how it should be generated,” Schwartz said. “It’s helped focus development on the highest-impact risks, endpoints and validation activities earlier in the lifecycle.”
Bringing an anatomically specific, load-bearing implant to scale is no easy process, and OrthoPreserve has focused on optimizing manufacturing processes from the start, including maintaining tight geometric tolerances, consistent mechanical properties and durable integration of fixation features.
OrthoPreserve is preparing to move Defender into clinical evaluation, with a pilot trial targeted for 2026 and a potential FDA approval pathway toward the end of the decade.
“The anatomical design of the implant restores the normal stabilization and cushioning functions of the meniscus to relieve symptoms and preserve knee joint health,” Schwartz said. “If Defender performs in the clinic as it has in the lab, it could redefine what’s possible for patients living in the gray zone between meniscus surgery and joint replacement.”
Predictable Mechanical Behavior
Phoenix Kinetics designed its meniscus replacement implant, NUsurface, to re-establish load sharing and protect articular cartilage in a way that mimics the meniscus’ primary mechanical role.
NUsurface is a polycarbonate/urethane composite that’s intended to optimize load-bearing capacity that approaches native meniscal tissue, exhibit durability under long-term cyclic loading and maintain conformity to the tibial plateau and femoral condyle through the knee’s full range of motion.
The material’s elastic modulus is tuned to distribute loads naturally, without stress-shielding cartilage, while still withstanding the 1 to 3 million load cycles per year that an active adult knee experiences.
In developing NUsurface, Phoenix Kinetics intentionally mimicked the load distribution function of a native meniscus while diverging from its viscoelastic behavior.
Phoenix Kinetics President and CEO Ryan Belaney said the composite provides consistent mechanical behavior across loading rates, which proved advantageous for predictable long-term performance. The geometric design — thickness, curvature and peripheral geometry — was optimized to restore natural contact pressures across the joint surface.
“Importantly, we’re not trying to perfectly replicate every aspect of native tissue,” Belaney said. “We’re restoring the primary mechanical function: load sharing to relieve pain and protect articular cartilage.”
One of NUsurface’s defining features is that it requires no fixation.
“The non-fixation approach was both our biggest engineering challenge and our most important innovation,” Belaney said. “Without fixation, we had to solve for positional stability entirely through geometry and material friction characteristics.”
Phoenix Kinetics conducted extensive finite element modeling and cadaveric testing to define a peripheral geometry that seats properly in the meniscal compartment and resists extrusion. Material selection was equally critical, according to Belaney.
“The coefficient of friction against cartilage had to be high enough for stability, but low enough to avoid adhesion or damage,” he said. “The payoff is significant: no bone tunnels, preserved anatomy and true replaceability if it’s needed years later.”
To function in the knee’s dynamic environment, NUsurface relies on what Belaney calls “controlled compliance.”
“The material deforms under load, conforming to joint surfaces during compression and then returning to its designed shape when unloaded,” he said. “It’s able to maintain its position through motion while actively participating in load sharing.”
Low-friction interfaces and geometry that follows the native meniscal footprint accommodate rotation and translation. Belaney said the behavior has been validated in vitro under simulated gait conditions and, more importantly, in five years of clinical follow-up showing maintained position and function.
Phoenix Kinetics is completing a De Novo submission for NUsurface during the first half of this year and wants to undergo FDA review and clearance by the end of year. The company is prepping for commercial readiness through surgeon training, payer engagement and building KOL networks at major centers such as Mayo Clinic, Rush, Ohio State, Brigham & Women’s and Stanford.
Belaney cited 15 years of safety data and the unmet clinical need for meniscus replacement solutions in the 45- to 65-year-old demographic to back his belief that NUsurface is positioned for regulatory success and rapid adoption.
It’s another example that less is sometimes more in efforts to develop minimally invasive ways to solve meniscus tears.
