A revolution is under way in prosthetic rehabilitation, and tiny computers – microprocessors – are leading the way, most notably in the development of knee componentry for above knee replacement limbs.
Even the most sophisticated pneumatic and hydraulic mechanical knees lack one essential ingredient: the ability to “sense” and react quickly to changes in the wearer’s gait and operating environment.
While variable cadence is possible with those components, changes in walking speed occur only gradually. But with computerized (AKA “smart”) knees such as the Rheo Knee®, C-Leg®, Smart Adaptive knee and others, these cadence changes can occur almost instantly, producing a more natural and energy efficient gait. Sensors constantly channel information to the microprocessor about what the limb is doing – for example, a sudden increase in walking speed or a step onto different terrain.
In real time the decision-making chip signals the swing-phase control to react so the limb will be ready for heel strike at the appropriate instant and place. Then at heel strike, the microprocessor signals the knee to restrict flexion until late stance phase, providing needed stability for full weight bearing, then gradually allows flexion in preparation for toe-off. Smart knees can further detect danger of falling or slipping and react to keep the knee from contributing to a fall.
Beyond functional considerations, computerized knees can substantially enhance the amputee comfort factor, so essential for sustained prosthetic success. Comfort begins in the socket, of course, but there is a dynamic component as well: In optimizing each gait step, smart knees minimize abnormal or excessive muscle use, and thus energy expenditure, employed to stabilize or move the prosthesis. Another benefit is mental relaxation as these intelligent systems enable wearers to walk in one amputee’s words, “without having to think about it” and thus concentrate on other things.
This attribute is particularly valuable when walking on stairs, on a changing slope or in other circumstances requiring alternating stability and mobility. Mechanical knees cannot make that adjustment, requiring the wearer to look down and consciously adjust foot and body position.
Since the first microprocessor-controlled (MPC) knees appeared more than a decade ago, the technology has improved substantially, yet we’re still only scratching the surface. New materials and manufacturing processes will provide lighter, more durable components, while software enhancements and research into direct neural control promise ever-more-responsive performance from existing and future designs.
With these exciting developments, will there still be a place for mechanical knee systems? Most assuredly, for these advanced systems are far from appropriate for all amputees. For one thing, though MPC systems have been shown to provide substantial quality of life improvement for patients as low as Functional (K) Level 2, a great number of older and less-vigorous amputees will be unable to appreciate the capabilities of these advanced systems. In addition, the high cost of this prosthetic technology and third-party reimbursement resistance will likely be with us for some time, limiting access for many. Nevertheless, smart prostheses are the future of limb rehabilitation, and that future is truly exciting.
The life of a lower-amputee patient many times is filled with sacrifice. Activities such as a round of tennis or golf, shopping and hiking that were once so easy to engage in become more difficult. Over the past decades, LeTourneau Prosthetics has helped thousands of lower amputee patients overcome barriers that are keeping them from the life they want.