LegWorks

Adaptive Mechanical Prosthetics

Andrew Kuzemczak
August 13, 2025

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TL;DR

The All-Terrain Knee provides stability, a natural gait, and adaptable swing and stance control entirely through mechanical systems, avoiding electronics or hydraulics while remaining durable, low-maintenance, and affordable.
LegWorks operates a hybrid social enterprise model, selling in high-income markets to sustain the business while distributing subsidized or free devices in low-resource regions, enabling broad global access to advanced prosthetic technology.
By improving walking efficiency and reducing compensatory movements, the AT-Knee enhances patient mobility and confidence, supports independence, increases participation in work and daily life, and reduces long-term healthcare and societal costs.

Hi friend,

Welcome back to Future Human! As I mentioned in our last letter, I’ve been buried in logistics for the arrival of our new M1 med students. After a whirlwind—but very rewarding—weekend, I’m happy to report that all 109 of them have been properly welcomed and are now deep in orientation. With that box checked, my summer research wrapped up and presented, I’m writing this edition from the sunny beaches of Stone Harbor, NJ, soaking in a few days with my college best friends before M2 year kicks off. Enjoy every moment while it lasts!

Honestly, this summer vacation (last one forever?) has been pretty spectacular. NYC summers do not disappoint, my work at Weill Cornell was fantastic, and time with friends felt practically non-stop. My only regret? I probably should have squeezed in a few more Anki cards—but that’s a problem for Future Andrew.

Now, if you’ll excuse me, it’s time to put fingers to keyboard so I can return to the epicenter of culture and class at the Jersey Shore.

So with that, let me ask you:

What if walking for the disabled didn’t have to be a compromise between stability, speed, and cost—no matter where in the world you live?

The Story

It started with a question: what if mobility was treated as a basic human right, rather than a privilege determined by where someone happened to be born? In too many places, above-knee amputees were left with devices that were unstable, uncomfortable, or unaffordable—often all three. Engineers, entrepreneurs, and advocates had tried to solve this before, but the solutions rarely reached those who needed them most.

One of the people unwilling to accept that reality was Jan Andrysek, a prosthetics engineer who had been experimenting with new designs since his graduate student days. His earlier devices, like the MiniMac and GeriMac, had won awards for innovation but were still too costly for low-resource settings. He began working on a different kind of prosthetic knee—one that was purely mechanical, durable, stable, and affordable enough to be used anywhere in the world.

That invention became the All-Terrain Knee (AT-Knee), and the effort to bring it to the world became LegWorks. The company was co-founded by Andrysek, global health entrepreneur David Green, social enterprise leader Emily Mochizuki Lutyens, and Brandon Burke, an above-knee amputee whose experience shaped product design and advocacy. Together, they took on the seemingly impossible challenge of building a sustainable, access-driven prosthetics business that could serve both high- and low-resource markets.¹

Andrysek, an assistant professor at the University of Toronto, designed the AT-Knee to deliver stability, durability, and a natural gait without relying on electronics or hydraulics—keeping costs low and maintenance simple.

Initial field testing in El Salvador quickly expanded to trials in Chile, Myanmar, and beyond, often in partnership with humanitarian organizations searching for better alternatives to standard-issue knees. In trials across 10 countries, 95% of early users preferred the AT-Knee over more expensive existing technologies. Developed with a $100,000 Grand Challenges Canada seed grant in 2012, their product consistently outperformed existing options on challenging terrain.²

LegWorks formally launched with support from Holland Bloorview, Grand Challenges Canada, and other funders, building out manufacturing and distribution to bring the AT-Knee to scale.

“We want to make high-quality and well-functioning prosthetic devices affordable and accessible for the many individuals whose needs are currently left unmet”

Jan Andrysek, CTO of LegWorks

Its social enterprise model enables the company to serve both high-income markets—where sales help sustain the business—and lower-income regions, where cost-subsidized devices can be distributed at scale. It's a model we see often in access-focused firms, it can crumble if the balance between revenue-generating and subsidized markets starts to tip.¹

Andrysek’s work is grounded in the belief that prosthetic innovation should focus equally on functionality and equity of access. His contributions have earned global recognition, including his 2019 induction into the American Institute for Medical and Biological Engineering (AIMBE) College of Fellows, placing him among the top 2% of biomedical engineers worldwide.³^,⁴

The Tech

Let’s explore some high level hardware–good luck to you all. LegWorks built the All-Terrain Knee (AT-Knee) around two coordinated, fully mechanical systems that make the joint “phase-aware” without electronics or hydraulics. The first governs stability when the limb is on the ground (stance). The second shapes how the limb swings through the air (swing).

At the end of each step—late terminal swing—the knee approaches extension. LegWorks’ AutoLock is engineered to sense that condition and automatically engage a mechanical lock just before heel strike. With the lock active, the knee resists unintended flexion during initial contact and loading response, helping the user accept weight without the knee “giving way.” Crucially, the knee stays locked through stance for safety, then unlocks mid-stance to set up an efficient roll-over and prepare the limb for toe-off and the next swing. Because it’s purely mechanical, all of this happens without batteries, firmware, or hydraulic fluids—minimizing maintenance complexity, benefiting those in under-resourced areas.

Once the limb leaves the ground, the knee must flex and then extend again in time for a clean heel strike. Constant-friction knees apply the same damping regardless of speed, which can force users to adopt a single “comfortable” cadence. The VCC instead uses a spring–friction architecture that adjusts damping with angular velocity. At slower paces, lower damping permits easy flexion and smooth extension. As cadence increases, the effective damping rises to prevent the knee from whipping forward, maintaining controlled extension and reducing terminal impact. The result is swing that “self-tunes” to the user’s speed without dials, chips, or pumps.

Still with us? Let’s continue.

This dual system is quite critical. The AutoLock prioritizes stability right where falls are most consequential—during weight acceptance—while the VCC preserves step-to-step adaptability. That division of labor mirrors what high-end microprocessor and hydraulic systems attempt electronically, but here it’s achieved with just carefully engineered linkages, springs, and friction interfaces. The practical upside is reliability (no charging), environmental tolerance (dust, humidity, rain are less of a concern than for electronics), and serviceability with simple tools–again all to the benefit of those in under-resourced areas.

In a 2022 study in Cambodia, Andrysek and colleagues compared the AT-Knee’s VCC to constant-friction knees. Users walked about 15% faster with the VCC and showed shorter swing-phase times and more symmetrical knee flexion at both normal and fast speeds—signals that swing control was adapting appropriately to cadence and helping restore a more balanced pattern.⁵

What this feels like for the user. On level ground, AutoLock provides a steady platform at heel strike, then releases as the body moves over the foot. On slopes or uneven terrain, the same mechanics damp sudden speed changes and resist unexpected knee collapse. Day to day, that consistency can translate into fewer compensations, a broader comfortable speed range, and greater confidence in new environments—delivered by a knee that’s intentionally simple under the hood.

The Market

The global prosthetics market represents both a rapidly growing business opportunity and a pressing humanitarian need. In 2025, the market for prosthetic devices is valued at roughly $2.3 billion, with growth driven by factors such as an aging population, rising rates of diabetes and vascular disease, and increased survival after traumatic injuries. Yet while the technology has advanced dramatically in high-income countries, access remains profoundly unequal. In many parts of the world, advanced prosthetic knees—often priced in the range of $5,000 to $50,000—are unavailable to the majority of amputees, especially those living in rural or low-resource settings. Instead, individuals must rely on basic, often uncomfortable devices that limit mobility and independence.⁶

LegWorks operates at the intersection of these two realities, with a mission and model designed to bridge the gap. The company’s dual-structure approach includes a for-profit arm selling the All-Terrain Knee to clinics and patients in high-income markets, and a nonprofit arm working with NGOs, governments, and global health organizations to make the device affordable—or free—in low-income countries. By cross-subsidizing its humanitarian distribution with commercial sales, LegWorks is able to reach patients who would otherwise have no access to such technology, without sacrificing the quality or durability of the product.

This approach directly challenges the prevailing dynamics of the prosthetics industry, where innovation tends to target a small segment of wealthier patients. The All-Terrain Knee is priced dramatically lower than comparable high-functioning prosthetic knees, while still offering key features—like variable cadence walking and auto-lock stance control—that are typically found only in far more expensive, electronically controlled systems. In doing so, LegWorks positions itself uniquely against both traditional medical device manufacturers and newer startups that focus on advanced designs.

Co-founder David Green, a social entrepreneur with a long track record of “compassionate capitalism” ventures, helped shape this hybrid business model. His previous work includes Aurolab, which became a major producer of low-cost intraocular lenses for cataract surgery, and Sound World Solutions, which developed affordable, high-quality hearing aids. In each case, Green applied a principle that cutting-edge technology can be made accessible to those who need it most, without depending solely on charitable donations. LegWorks carries that same philosophy into the prosthetics space, aiming for scale and sustainability rather than one-off interventions.

As the global prosthetics market grows—and as more attention is paid to inclusive innovation—LegWorks’ model offers a blueprint for how medtech startups can balance commercial viability with social impact.

The Sick

Walking may seem simple, but it’s a complex, highly coordinated sequence of movements known as the gait cycle. Each step involves the two main phases mentioned in our tech section: stance—about 60% of the cycle—when the foot is on the ground supporting body weight, and swing—about 40%—when the foot lifts off and the leg moves forward for the next step. The knee is central to both. In stance, it must remain stable and extended to prevent collapse; in swing, it must flex and extend smoothly to clear the foot and ensure a fluid stride.⁷

For individuals with transfemoral amputation—where both the lower leg and the knee joint are lost—the challenge is far greater than for those with below-knee amputations. Without a natural knee, walking requires significantly more energy and skill. When prosthetic knees are unresponsive or lack adaptability, amputees often develop compensatory gait patterns: hip hiking, where the pelvis lifts on the prosthetic side; circumduction, swinging the leg outward in a semicircle; and vaulting, rising on the toes of the intact limb. These strategies can help clear the foot during swing, but they come at a cost—increased fatigue, reduced efficiency, and long-term strain on the hips, lower back, and sound limb.⁸^,⁹

In many low-resource settings, cost constraints lead to the widespread use of constant-friction knees. While durable and affordable, these devices only function at a single walking speed and fail to adjust to real-world variations in pace or terrain. This limits mobility and makes walking less natural. The All-Terrain Knee was designed to break this compromise. Its Variable Cadence Controller (VCC) adjusts automatically to different walking speeds, allowing for smoother, more responsive swing-phase movement. Meanwhile, the AutoLock mechanism engages at the end of each swing phase to stabilize the knee during weight-bearing, then disengages mid-stance to prepare for the next step.⁵

The impact on patients is profound. By enabling a more symmetrical, stable, and energy-efficient gait, the All-Terrain Knee reduces reliance on compensatory movements, helping amputees walk faster, with less effort, and over more varied terrain. For many users, this doesn’t just mean improved biomechanics—it means reclaiming the ability to move confidently through daily life, whether navigating a crowded urban street, climbing a hill, or walking to work. In settings where mobility often determines access to education, employment, and community participation, these gains translate directly into independence and opportunity.

The Economy

The economic consequences of lower-limb amputation extend far beyond the initial surgery. For individuals without access to functional prosthetic knees, mobility limitations reduce the ability to work, attend school, and engage in life, while compensatory gait patterns increase the risk of secondary musculoskeletal injuries. These effects accumulate over time, imposing both direct and indirect costs on individuals, families, and health systems.⁷^,⁸^,⁹

In low- and middle-income countries (LMICs), the challenge is particularly acute. Constant-friction knees dominate these markets due to their low upfront cost and durability, but their limited adaptability restricts walking speed and efficiency. Based on a 2022 study conducted by the University of Toronto in collaboration with Cambodia’s Department of Prosthetics and Orthotics, the All-Terrain Knee’s Variable Cadence Controller (VCC) improved gait speed and symmetry compared to constant-friction devices, demonstrating that meaningful performance gains can be achieved without raising costs or introducing maintenance complexity. By reducing reliance on compensatory movements, the AT-Knee helps amputees expend less energy and avoid long-term strain, making it a practical and scalable solution for resource-limited health systems.⁵

Even in high-income settings, the economic stakes are substantial. One study at a U.S. urban safety-net hospital found that the mean hospitalization cost for patients with above-knee amputations totaled $114,292 over two years, with 64% of these costs uncompensated. Lifetime healthcare costs for patients undergoing amputation can reach $509,275—nearly three times higher than limb reconstruction procedures—driven largely by the recurring expenses of prosthetic purchase and maintenance. Conventional mechanical above-knee prostheses cost $10,000–$15,000, while high-end microprocessor knees can range from $25,000–$50,000 or more. Over a 10-year horizon, microprocessor knees have been shown to reduce direct healthcare costs by approximately $3,676 per year and indirect costs by $909 per year, primarily by preventing falls and injuries.¹⁰^,¹¹^,¹²^,¹³

The All-Terrain Knee, estimated under $4,000, dramatically lowers the barrier to high-function mobility in both low-resource and high-income contexts. By combining affordability with advanced gait performance, the AT-Knee allows patients to regain independence more quickly, return to work or school, and reduce ongoing healthcare expenses. In LMICs, this means that amputees who would otherwise be confined to minimal mobility can participate in the workforce, contribute to their families’ income, and avoid the long-term costs associated with poor-functioning prosthetics.

Ultimately, the economic impact of the All-Terrain Knee is multidimensional. It reduces direct healthcare costs, mitigates long-term injury and energy burdens, and unlocks productivity for patients who might otherwise face lifelong economic marginalization. By making advanced prosthetic functionality broadly accessible, LegWorks is not just improving mobility—it is enabling meaningful participation in economic and social life across diverse global contexts.

My Thoughts

There’s something undeniably inspiring about hardware that performs at world-class levels without a single line of code or a battery in sight. The All-Terrain Knee is a masterclass in mechanical ingenuity: springs, friction, and clever linkages working in perfect harmony to sense stance, modulate swing, and lock at precisely the right moment. It’s almost magical to watch a purely mechanical system replicate functions we usually associate with microprocessors or hydraulics, yet do so with incredible reliability and minimal maintenance. This kind of design excites me even more than electronics-driven solutions, because it shows that elegance, durability, and accessibility can coexist. In a world where access often depends on wealth or infrastructure, hardware that is inherently simple, resilient, and effective can reach people everywhere—urban hospitals, rural villages, and everything in between. The future of prosthetics isn’t just digital; sometimes, the raw beauty of hardware is the most revolutionary technology of all.

To more lives saved,

Andrew

I always appreciate feedback, questions, and conversation. Feel free to reach out on LinkedIn @andrewkuzemczak.