Science, medicine, and the future: Artificial limbs - PMC

06 May.,2024

 

Science, medicine, and the future: Artificial limbs - PMC

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In recent years technical innovations have combined to make artificial limbs much more comfortable, efficient, and lifelike than earlier versions. Future innovations are likely to depend on the interaction between three powerful forces—amputees' demands, advances in surgery and engineering, and healthcare funding sufficient to sustain development and application of technological solutions. This article looks at the innovative new prostheses that are currently available and discusses future developments.

Methods

This paper is based on the clinical experience of the authors in Britain and the United States, a review of the literature, and information gathered from colleagues in rehabilitation medicine throughout the world.

Amputation: causes and impact

In developed countries the main cause of lower limb amputation is circulatory dysfunction. The prime reason for this is atherosclerosis, although up to a third of patients have concomitant diabetes. These people are usually in their sixth decade (or older), and most have additional health problems that limit their walking ability. In the United Kingdom there are about 5000 new major amputations a year.1

This is in sharp contrast with developing countries, where most amputations are caused by trauma related either to conflict or to industrial or traffic injuries. Global extrapolations are problematic, but a recent US study states that the amputation rate among combatants in recent US military conflicts remains at 14-19%2 and the devastation caused by land mines continues, particularly when displaced civilians return to mined areas and resume agricultural activities.3

An amputation is a permanent disfigurement. For some, the relief from pain or disease in the affected limb may be welcome, but, for those losing a sound limb, resentment is understandable. Despite modern prosthetics, some adaptation is required, and people vary in their ability to adjust to the change in body image and, sometimes, lifestyle.

Skeletal attachment of artificial limbs

Several decades ago, the Swedish physician Per Branemark astounded the dental profession by developing a surgical technique to permanently anchor artificial teeth into the jaw. Despite numerous outcries about the futility of such efforts at the outset, his methods are now accepted worldwide as a routine method of dental restoration. In the past few years he has turned his attention to achieving similar results for upper and lower limb amputees and has generated similar controversy.15 Preliminary results, and enthusiastic feedback from participating amputees, justify further exploration of this technique (fig ).

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If these prostheses prove successful long term (at least 10 years) direct attachment of an artificial limb to the skeleton may avoid difficulties inherent in creating custom-designed prosthetic sockets, where fitting comfort depends on volumetric matching to the amputation stump. Being a dynamic organ, the stump tends to shrink (atrophy) over time, though it may also swell with heat or weight gain, which can lead to chafing. With osseointegration, the prosthesis fit is unaffected by such volume changes.

The drawbacks of this technique are that it requires two stage surgery to attach the titanium implant to bone. The procedure carries the risk of osteomyelitis or infection at the abutment of the implant, and meticulous personal hygiene is a prerequisite in patient selection. On a practical note, the typical Western person with a lower limb amputation, elderly and with poor circulation, is not likely to be a candidate for such an involved surgical procedure. It is primarily the subset of younger individuals, often with traumatic amputations, for whom this technique holds the greatest promise.

Comparative trials of the technique are not possible. To date, the patients selected for the procedure have had high level, above knee amputations for which all other prosthetic fitting techniques had failed. However, three year follow up of several dozen participants suggests that amputees with an osseointegrated prosthesis quickly develop superior control over the limb, at least in part because of enhanced sensation, termed “osseoperception” by Branemark. This combination of increased comfort, perception, and control is expected to drive the next round of technological innovations, just as superior socket designs did previously.

Making artificial limbs lifelike

Although some amputees like the robotic appearance of prosthetic components, most prefer a limb that is lifelike and therefore inconspicuous. The same silicone materials that contribute to socket comfort have also been used to create incredibly realistic external coverings for both upper and lower limb devices.

The present state of the art is the creation of a carefully sculpted match for the opposite limb, with individual colouring to give a lifelike finish.16 Unfortunately, such custom made prosthetic “skins” are costly (about £2500 ($3500)), particularly since they need replacement after a few years because of unavoidable wear and tear from normal use.

Silicone is also a relatively heavy material, so the search continues for a lightweight alternative, ideally offering greater flexibility and durability. Because of the costs involved, most amputees currently receive “semi-custom” external coverings that are mass produced industrially from less expensive materials and provide only a generic external appearance.

The potential of low cost, limited function prostheses

Modern industrial fabrication, particularly with injection moulded plastics, can create lightweight, low cost components with sufficient function for limited walking, and this might be quite sufficient for today's typical elderly amputee. Some designs may also be made moisture resistant and therefore suitable for use in the shower or on the beach. The lower manufacturing costs of such devices may permit their use in developing economies, where the cost of more complex technology is prohibitive. The Shower Limb, developed by Blatchford, is an example of this trend. The company has also developed a special line of plastic Atlas Prostheses designed specifically for use in tropical climates.

The International Committee of the Red Cross has established an initiative to produce low cost polypropylene plastic prostheses, made by unskilled local workers, for areas where conflict or environmental catastrophes have resulted in large numbers of traumatic amputations (see www.icrc.org). These devices are well accepted clinically, although some problems have been reported with their durability.17,18

Future developments

The future development of prostheses will depend greatly on demand. The market for low cost, limited function devices will continue to expand in an effort to meet the needs of the developing world as well as the funding restrictions that are increasingly common in all economies. At the same time, innovative technologies will continue to be adapted from the aerospace and computer industries and applied to high performance artificial limbs whose function will more and more closely approximate to the missing limb.

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Initially, prosthetic innovations are often used sparingly, primarily by amputees with private funding—particularly those who are competitive athletes. As experience is gained, manufacturers discover how to apply the same principles to moderate cost devices intended for less active individuals, and the performance of prostheses in general will gradually improve as a result.

Similarly, some of the newer materials and applications will be used for the benefit of amputees in developing countries, despite differences in the cause of amputation and people's needs. It is really financial constraints that limit the rate of advancement in prosthetic rehabilitation, and one of the greatest challenges for the new millennium will be to find the will and the way to fund widespread application of prosthetic innovations.

Additional information on limb prostheses

  • Bowker JH, Michael JW, eds. Atlas of limb prosthetics: second edition. St Louis, MO: Mosby, 1992

  • Internet Gateway. www.oandp.com

  • British Association of Prosthetists and Orthotists website. www.bapo.com/companies.htm

  • International Society for Prosthetics and Orthotics website. www.i-s-p-o.org

  • Limbless Association website. www.limbless-association.org

Footnotes

  Competing interests: JWM has been employed by Otto Bock. Since 1999, he has been an independent consultant in prosthetics and orthotics and therefore may have a consulting relationship with any of the companies mentioned in this article. He has received payment for organising educational programmes, speaking, or consulting from Otto Bock and from Flex-Foot, which was recently acquired by Ossur.

Using Prosthetic Limbs: Safety, Care, and Concerns

When an arm or other extremity is amputated or lost, a prosthetic device, or prosthesis, can play an important role in rehabilitation. For many people, an artificial limb can improve mobility and the ability to manage daily activities, as well as provide the means to stay independent.

There is a wide variety of prostheses that are designed to function -- and in many cases look -- like a natural arm, leg, hand, or foot. Although there are many different designs, most have similar parts. These include:

  • A socket into which the stump of the amputated limb fits
  • The suspension, which holds the prosthesis onto the stump
  • The shaft
  • The foot, hand, or hook
  • A covering for cosmetic appearances

The socket is often lined with foam or silicone to protect the stump. Special socks are also worn over the stump to ensure a proper fit and improve comfort.

Following are some of the most common types of prostheses:

Lower leg and foot. A number of prosthetic feet are available to simulate the action of a natural foot after an amputation below the knee. At least one available foot-ankle prosthesis is controlled by a microprocessor. It uses feedback from sensors to adjust joint movement, making walking more efficient and reducing the risk of falls.

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