Science fiction becomes
The world is about to become a better place for above-knee amputees with
the development of two revolutionary bionic knees. Callan Emery speaks
to the Icelandic company leading the innovation.
is a revolution going on in the development of prosthetics, which is
making the bionic man of the future a reality of the present.
Through an interdisciplinary and precise fusion of electronics,
mechanics and human physiology prosthetics are being developed that are
opening a whole new realm of lifestyle enhancements and capabilities for
An Icelandic-based company, Ossur, is leading this bionic revolution
with two award winning products – the Rheo Knee and the Power Knee.
Ossur received the 2005 Frost & Sullivan Technology of the Year Award
for the European medical devices market for its pioneering Rheo Knee and
the company received Popular Science magazine’s 2005 Best of What's New
Award in the Personal Health category for its revolutionary Power Knee,
the first powered prosthesis for above-knee amputees.
The Rheo Knee
The Rheo Knee is the first artificially intelligent knee system having
the ability to learn and adapt to its user's movements in real-time,
resulting in continually improved and optimised performance.
Claire Staniforth, research analyst with Frost & Sullivan, explained:
“Based on over three years of intensive R&D, the Rheo Knee is the first
in a new generation of microprocessorcontrolled, swing and stance knee
systems that incorporate artificial intelligence, giving the system the
ability to learn how the user walks and eventually pre-empt each step.
This breakthrough in technology will lead the way for the next
generation of prosthetics, focused on precisely copying the
biomechanical motion of human joints and limbs.”
The Rheo Knee functions by using a dynamic learning matrix algorithm (DLMA)
– software based artificial intelligence to learn the individual’s
walking style and provide a mechanism for continual monitoring and
optimisation of swing control, allowing the user to walk comfortably and
safely at a range of speeds.
The crucial drawback with traditional hydraulic knee control joints has
been the build up of drag within the system, which results in fatigue
for the user. However, the Rheo Knee solves this issue through advanced
technology using magnetic fields, magnetorheological (MR) fluid, and
This is how it works: the angle of and load borne through the artificial
knee joint are monitored at a rate of 1,000 times per second using
electronic sensors. Changes in value are accompanied by related
alterations in the viscosity of the MR fluid within the knee. A computer
chip creates and regulates the intensity of the magnetic field, causing
changes in MR fluid viscosity about the joint that facilitates optimal
motion control. With application of the magnetic field, carbyliron
spheres are drawn together in electromagnetic chains. As the knee
rotates into flexion or extension, fine rotary blades shear the particle
chains to create resistance.
The result is minimised fluid drag within the knee restoring more
natural pelvic position during preswing and reducing fatigue levels –
thereby conserving the energy levels of the amputee and enabling longer
periods of joint use.
Through advanced sensing and processing, the Rheo Knee provides multiple
safeguards against inadvertent stance release. The knee must be fully
extended, momentarily still, and achieve 20% of the average maximum
extension moment during each step to release.
The microprocessor continually samples the sensors’ force measurements
and is always aware of how the user is loading the prosthesis.
Disturbances in the user’s path are automatically recognised by the
force sensors. Stance support is instantaneously activated to protect
the user from a potential stumble and fall. By detecting these patterns
in their earliest stages, the Rheo Knee can take the preventive actions
to reduce the likelihood of a fall.
Kim De Roy, product manager, R&D at Ossur (Iceland) told Middle East
Health that the Rheo Knee is available globally, but can only be
proscribed and fitted by a prosthetist who has been certified to do so
The Power Knee
Users of the revolutionary Power Knee say it feels as if the knee is
doing the walking for you.
The Power Knee is the first powered prosthesis for lower limb amputees.
It is artificially intelligent. It predicts and responds to changes in
terrain and incline, and restores gait dynamics, thereby allowing its
user to cover greater distances while using less energy. The Power Knee
replaces true muscle activity, effectively bending and straightening the
leg at the knee. Importantly and for the first time, amputees will be
able to ascend stairs and ramps foot-over-foot and facing forward.
The knee also facilitates level-ground walking, climbing inclines and
the simple act of sitting down and standing up from a chair.
By gathering sensory information one step ahead of the prosthesis, the
Power Knee is able to anticipate and pro-actively work in step with
daily activities, such as climbing stairs and inclines.
It works like this: an amputee takes their first step with their good
leg, which has sensor equipment attached on the foot accurately
measuring motion, load and position of the limb at a rate of 1,350 times
per second. This information is transmitted to the knee’s artificial
intelligence which determines the appropriate function and calculates
the precise amount of power needed to generate it.
The knee’s generated power replaces lost muscle function enabling
complex movements as well as restoring symmetry, balance and power to
the amputee’s gait. “The Power Knee is different from the Rheo Knee in a
number of ways,” De Roy explained. “The most obvious one being that it
Please keep in mind that not all above-knee amputees have the same
needs; rather, these needs are determined based on their age and
activity level, type of amputation, etc.
Which knee is best suited to a particular amputee’s needs can only be
determined by a qualified prosthetist who is not only familiar with, but
certified to recommend and fit these knees. In other words, the Power
Knee is not ’more advanced’ than the Rheo Knee, it is different and
addresses particular needs which are not universal to all above-knee
“Learning how to use a Power Knee is a totally different experience than
adapting to the Rheo Knee,” De Roy pointed out. “The larger part of Rheo
Knee users manage to quickly learn how to use the Rheo Knee, thanks to
the system’s unique capability to adapt to the way the user walks. The
Power Knee is more training intense, since users are trying to perform
activities which they might not have done in a long time.
Outcome will partly depend on the patient’s desire and commitment,
which, as we know, is different for each individual and often limited by
physical condition of the user.” The Power Knee is in limited launch in
certain parts of the world and, like the Rheo Knee, requires an Ossur-certified
prosthetist to fit it. De Roy said: “The timeframe for global
availability of the Power Knee is yet to be determined.
Patient care, education and training are the keys to a successful
fitting on the Power Knee and we are therefore building a team of Power
Knee experts, which will be responsible for global Power Knee fittings
in the upcoming months. “However, each request, irrespective of the time
or place, will be addressed and preparations will be initiated by the
team to assure a successful clinical outcome for each fitting.”
The bionic man is here. As Ossur aptly points out: “From sensation to
motion, the prosthetic limb is now a true active extension of the
amputee which interacts with the environment. Through sensing,
processing, and learning, the prosthesis is now equipped to move with
the amputee and adapt to the individual’s path, enhancing the
fundamental human needs of comfort, security and independence.”
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