Rehabilitation

 

A helping hand

A Scottish-based company has launched i-LIMB Hand to market. The bionic hand is the first such articulated, thought-controlled prosthetic device that is commercially available and represents a major advance in bionics and rehabilitative patient care. Callan Emery reports

The i-LIMB Hand looks uncannily life-like and moves extraordinarily like a human hand. When covered in a specially developed skin-like cosmesis you would be hard pushed to tell it apart from the real thing and with five individually powered digits and an articulating thumb, the lightweight i-LIMB hand has a dexterity that sets it far ahead of any other prosthetic hand, enabling an array of grip configurations, many of which have not been available to amputees before.

Myoelectric control

The bionic hand uses myoelectric controls to open and close the hand. Myoelectric controls utilise the electrical signal generated by the muscles in the remaining portion of the patient’s limb. This signal is picked up by electrodes that sit on the surface of the skin. Usually one electrode is placed on the top of the forearm and the other on the bottom.

Amputees usually have a sensation that their amputated hand still exists – referred to as “phantom” feelings. When the amputee thinks about opening or closing their amputated hand the muscles in the forearm flex. The electrodes pick up electrical impulses from the flexing muscles and relay them to a small, advanced computerised control system in the back of the hand which directs motors in the hand to open and close.

A built-in feedback system tells each finger individually when it has enough grip – in other words when to stop applying pressure on the object it is holding. The individual fingers lock into position until the amputee triggers an “open” signal, by thinking “open hand” and flexing the appropriate muscle on the forearm.

The i-LIMB Hand is anatomically correct both when resting and in motion – an innovation, Touch Bionics says, that has been much appreciated by patients, many of whom simply wish to blend back into society without others noticing their amputation

Cosmesis

Touch Bionics, working with partners, has developed a life-like skin covering, or cosmesis, for the hand. The company says, however, the challenge has been to find materials that can move and flex in the same way that human skin does.

Touch Bionics noted that some people like to show off their bionic hand and would prefer not to use it with a cosmesis glove. However, because of the need to provide a grip surface and to protect the hand from dust and moisture, the company has developed the i-LIMB Skin. This is a thin layer of semi-transparent material that has been computermodelled to accurately wrap to every contour of the hand.

Modular design

The modular construction of the i-LIMB Hand means that each part of each individually powered finger – called ProDigits – can be quickly removed by simply removing one screw. This means that a prosthetist can easily swap out fingers that require servicing and patients can return to their everyday lives after a short visit to the clinic.

Stuart Mead, chief executive of Touch Bionics spoke to Middle East Health in Dubai in January. He said the company has just reached its “first milestone of 100 patients in 17 countries, including Iran in the Middle East”.

He commented they “are in the process of getting health insurance companies to pay for the hand” and added that “some insurance companies in the United States are paying.” Mead explained that the company is developing a full prosthetic bionic arm “We are aware of Professor Todd Kuiken’s work with nerve reinervation and are watching this with interest (See The bionic arm page 28).”

“We are developing the i- LIMB System joint by joint over time – the wrist, the elbow and so on.” “We expect some of these products to come out in 2009,” Mead said. He said the hand would require annual servicing to upgrade the software, but that this was available under the 3- year warranty.

Asked about the dexterity of the hand and if it was possible, for example, to rotate the wrist through 360 degrees? He said 360 rotation is already available “but it is worth bearing in mind, that the average amputee simply wants to get back to normal function and blend in with society’s expectation of what is normal. This is our focus, we are not aiming for super-human functionality.”

New ISO standard for spinal disc prostheses

A new ISO standard – ISO 18192-1:2008 – will promote the development of safe and resistant prostheses for patients and constitute a useful tool for the medical industry.

ISO 18192-1:2008 will allow the uniform testing and comparison of this relatively new technology ensuring the performance of different prosthesis. Its consensus based methodology will provide
a reliable and concise reference. Within the medical industry, this standard will provide transparency, improve communication and level the playing field for competing suppliers. Surgeons will be able to rely on soundly based comparative information for different devices.

A new ISO standard will help ensure that spinal disc prostheses meet requirements for wear resistance. This is particularly important as once implanted these will need to absorb the impact from the body’s daily activities for years to come.

The development of prosthetic discs presents a number of challenges. The device must allow movement, provide stability, and be resistant to impact from a person’s daily activities. It should not be
destructive and exhibit great endurance.

The first part of what is intended as a multi-part standard outlines a test procedure for the relative angular movement between articulating components and specifies the pattern of the applied force, speed and duration of testing, sample configuration and test environment.


 Date of upload: 3rd April 2008

                                  
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