Healthy knee joints are essential in maintaining an active lifestyle, but as the largest joint in the body, according to the American Academy of Orthopedic Surgeons (AAOS), the knee is also one of the most vulnerable to injury. In fact, knee injury is one of the most common reasons people see their doctor, with more than 10.4 million U.S. patients seeking treatment for common knee injuries like sprains and ligament tears each year.

The need to treat chronic knee pain, prevent injury, speed up the recovery process, and push the boundaries of physical and athletic performance has led to an increased use of common braces like functional knee braces, unloader braces, and neoprene sleeves. These braces have been around in substantively the same form for a very long time and their use has become widespread. But are these devices doing enough?

While the use of common knee braces is well-known, and their role as prevention and management devices for injury and disease is well established, such devices mainly serve the functions of providing lateral stability or correcting alignment of knee joint structures. As technology has advanced, the prospect of going beyond structural support or alignment-correction to also augment muscular strength of the legs is now much more tangible.

Within this application lies the potential for the technological augmentation of knee joint function for both healthy and injured individuals, making any type of movement from fundamental activities of daily living to weightlifting to cross-country skiing easier to accomplish or even enhance. A particular category of this novel and relatively new knee bracing technology is the knee extensor assist (KEA) design.

What Is KEA Technology?
Recently, companies have begun utilizing assistive device and exoskeleton technology to not just help individuals with movement disability, but also to improve healthy knee function, enhance abilities, and reduce fatigue. So how do these systems work?

KEA designs can be described as either passive or active in nature. Devices that use active KEA technology, like powered exoskeletons, are often contained within total walking assist systems. This technology is capable of fully supporting the user in upright and walking positions with minimal to no muscular exertion from the user, typically utilizing battery cells to power actuators.

While powered exoskeletons offer remarkable opportunities, they come at a cost. Relying on large battery cells and motors to transmit power makes these devices cumbersome to wear. Due to their heavy weight and large size, along with their inability to rapidly respond to the wearer’s intended movement, active KEAs have limited use for sports and athletic activity. Additionally, active KEAs are costly (typically between $70,000 -$120,000), making them largely inaccessible to the general public.

Passive KEAs on the other hand, produce the necessary energy for assisting knee extension through the wearer’s own movement. In other words, no large battery packs or motors are required. However, the key here is that unlike powered exoskeletons, which can be used for even complete paraplegia, the user must have sufficient muscular control to initiate movement and energy storage. This is because energy is stored when the user bends their knees (although they can use gravity to help), and released as the user begins to straighten their legs.

Because passive KEAs use mechanical systems without batteries or motors, these braces are comparatively lightweight and compact, and moreover, drastically lower in cost. A number of passive KEA bracing options exist, relying on traditional spring devices, such as metal coils and heavy elastomer cords, to provide muscular assistance.

How Does KEA Technology Provide Muscular Assistance?
Today’s passive KEA options that employ latex bands or medical tubing utilize elasticity to assist joint movement. When the knee is bent, the tubing is elongated and put under pressure. That pressure is then alleviated when the user straightens their knee, restoring energy to the movement. A few notable devices on the market that rely on elasticity based mechanisms include the Townsend Extension Assistance Mechanism and SKO Extension Assist by Becker Orthopedic.

Other KEA knee braces store energy when the knee is bent in traditional metal coil springs. A few notable devices on the market that rely on metal spring mechanisms include the sport-specific Ski Mojo, Ultraflex Systems’ Power Unit, and Cadence Biomedical’s Kickstart.

While passive KEA technology offers users muscular assistance not provided by a traditional brace, today’s passive, elastic, and metal spring-based KEA designs are often limited in their ability to produce force. For example, current device options seldom produce enough force to assist the wearer during intense every-day movement, like rising from a seated position (where up to seven times your body weight is transferred through your knees) or participating in sports (where even greater forces can be transferred through the knees). This leaves room for technological improvements that can further enhance the wearer’s ability during athletic activity and contribute to measurable differences in knee joint capabilities.

How Can KEA Technology Be Improved?
What does the future of KEA technology look like? The answer is in a novel form of hydraulics.

In order to further develop KEA technology for increased assistance, engineers face the challenge of creating a rotary-to-linear coupling that stores a large amount of force on a miniature scale. When looking to incorporate powerful and compact energy suspension systems (like those found in bicycle suspension or aircraft landing gear systems) into a knee brace, material selection becomes extremely important.

Traditional spring materials, including elastics, polymers, and metals (to name a few) cannot be made small and powerful enough to do the job inside a traditional knee brace. Liquid springs, however, which rely on the compression of fluid to store energy, can provide such force. Incorporating this type of hydraulic system into knee braces not only provides added assistance, but also functions as a shock-absorption system to reduce joint compression while bearing weight.

The combination of liquid spring technology with carefully designed bionic hinges allows KEA braces to become more lightweight, compact, and extremely powerful. This kind of powerful KEA mechanism can then be used to assist the quadriceps during knee extension, which can boost natural strength and power, thus preventing muscle fatigue and injuries.

With the addition of hydraulics and other future improvements in KEA technology, a new era of protective, performance, and capacity-enhancing braces is emerging. This technology can benefit anyone from athletes to those managing knee osteoarthritis to individuals living with poor muscle control as a result of stroke or brain injury. Going forward, watch out for KEA technology to offer a wide range of individuals the chance at a more active and healthy life, free from knee pain and with reduced risk of common debilitating knee injuries.

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As the co-founder, president, and CEO of Spring Loaded Technology, Chris Cowper Smith thrives at the interface of research and development to foster the creation of new “bionic” bracing products that have the potential to improve patients’ quality of life. A published and award-winning scientist, Smith is recognized for his strong track record in bridging the gap between science and business while working closely with industry professionals, clinicians, researchers, patients, and customers.