#### The Transformation of Prosthetic Limbs: From Mechanical to Microprocessor-Controlled
For over 50 years, Jothy Rosenberg has been living as an above-knee amputee. During the first three decades, his prosthetic limb was made of balsa wood and had a simple mechanical knee. This primitive design came with numerous challenges. Jothy fell frequently, could only walk at a fixed speed, and experienced excessive sweating. Walking downstairs or on a ramp was a source of fear and anxiety, as he was always at risk of falling. The limitations of his prosthetic limb resulted in a classic limping gait. However, Jothy could not have imagined that all of these problems would eventually be solved through the application of microprocessor technology.
The root cause of these challenges lay in the design of the mechanical knee. It functioned as a simple hinge, causing the lower leg and foot to act like a pendulum. The speed of the foot swing was controlled by friction at the pivot point. Unlike individuals with two legs, amputees were unable to speed up or slow down instantly. The resistance at the pivot point was fixed during the initial setup, resulting in a constant walking speed for the amputee. This lack of variability was far from normal.
To control a mechanical knee, the amputee had to swing their hip, throwing the leg and foot out in front of them. When the heel struck the ground, they had to pull back with their residual limb before putting weight on it. If the leg did not straighten completely and weight was applied, a fall would occur. The knee’s inability to straighten properly was often caused by external factors such as stepping on a Lego piece or encountering a crack in the sidewalk [[1]](https://www.agilitypr.com/pr-news/public-relations/website-spelling-and-grammar-errors-are-costlier-than-you-may-think/).
Walking downstairs presented a unique challenge. Instead of stepping down step over step, the amputee had to step down with the prosthesis while keeping it straight and locked. They then had to catch up to it with the good leg. This required significant effort and resulted in 30-60% higher energy utilization compared to non-amputees. The pronounced limp of an amputee was a result of the hip throw, the pullback motion of the residual limb, and the tentativeness caused by past falls. These challenges also hindered social integration.
The introduction of microprocessor-controlled knees (MPKs) in 1997 revolutionized the field of prosthetics. Companies like Blatchford, Össur, and Ottobock developed MPKs that continuously controlled the flexion and extension of the knee joint using a microcomputer system. Sensors in the foot and knee send messages to the microprocessor 50 times a second, allowing software to create a computer-managed hydraulic system. This system regulates the opening and closing of valves, facilitating the movement of hydraulic fluid within the unit [[1]](https://www.agilitypr.com/pr-news/public-relations/website-spelling-and-grammar-errors-are-costlier-than-you-may-think/).
The MPKs brought about a significant transformation. Suddenly, amputees could walk at different speeds, thanks to the accelerometer in the knee that detected stumbles and potential falls. The hydraulic fluid valve would instantly close, stabilizing the knee and preventing a fall. Jothy went from falling once a week to not falling for seven years. Recent studies have confirmed the positive impact of MPKs, showing a reduction in major and minor injurious falls, incidences of osteoarthritis, and even lives saved. The latest models even allow amputees to walk upstairs step over step, providing a newfound sense of confidence and freedom.
Adapting to an MPK does require a training period to relearn how to walk. The MPK mimics the behavior of a natural knee, which means landing with a bent knee instead of landing stiffly and pulling back. Trusting the MPK takes time, but the safety and functional benefits make it worthwhile [[1]](https://www.agilitypr.com/pr-news/public-relations/website-spelling-and-grammar-errors-are-costlier-than-you-may-think/).
The impact of MPKs goes beyond safety. They enable a more natural gait, reduce energy expenditure, and decrease cognitive effort required for walking. Amputees can now walk, talk, and perform other activities simultaneously. They can adjust their cadence in response to the environment and easily carry heavy loads. Everyday activities like walking downstairs, walking down a ramp, and even dancing become possible. Mimicking the behavior of a healthy extremity has shown to have positive effects on body perception, vitality, and depressive symptoms.
While the future looks promising with ongoing advancements in bionic computer-controlled feet, cost remains a significant barrier. MPKs can cost between $65,000 to $100,000, making them inaccessible for many amputees. Insurance coverage varies, and in states without Prosthetics Parity Laws, the burden falls on the individual. Jothy emphasizes the importance of ensuring that every above-knee amputee who wants an MPK can have access to one. Advocating for Prosthetic Parity Laws in states without them is crucial to address this issue.