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.
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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.
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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.
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Advances in prosthetic technology
Prosthetic technology has advanced to a remarkable degree in the past two decades, driven largely by amputees' demand. Today, otherwise healthy individuals with mid-calf amputation should be able to participate in a full range of normal responsibilities, to walk without any perceptible limp, and to engage in recreational and sports activities.
Interface between stump and socket
The single most critical aspect of any prosthesis is the quality of the interface between the limb remnant (stump) and the artificial prosthesis. The portion of the prosthesis that fits snugly over the limb remnant, the “socket,” determines the amputee's comfort and ability to control the artificial limb. Since the 1980s prosthetic clinicians and researchers worldwide have made breakthroughs in design and materials that have greatly improved the connection between the socket and stump.Predicted developments
Direct skeletal attachment (osseointegration) of prostheses may be a routine option for some amputees
Amputee demand for more versatile, higher performance prostheses with more lifelike external coverings will fuel further innovation
The use of prostheses controlled by microprocessors to allow finely tuned movement will increase
Future use of new prosthetic components is liable to be controlled by funding constraints in both developed and developing countries
Currently, silicone elastomers are widely used to create a soft and slightly elastic inner liner, providing a thin, comfortable, and compliant barrier between the amputee's skin and the more rigid, weight bearing portions of the prosthetic socket.4,5 These socket liners, are usually tethered to the inside of the socket with a mechanical device, termed a shuttle lock, to provide suspension for the prosthetic limb. To remove the artificial limb, the amputee simply presses a concealed button, disconnecting the liner from the socket.
In recent years researchers have developed a variety of thicker gel materials that add a measure of cushioning and pressure dissipation while retaining the benefits of the original liners (fig (fig1).1). The same gel cushioning technology has also been adapted to bicycle seat coverings and similar non-prosthetic applications.
Dynamic response feet with plastic springs
Carbon fibre composites, developed by the aerospace industry, are increasingly being used in artificial limbs, largely because of their superior strength to weight characteristics. One of the most successful innovators has been Flex-Foot, founded by US researcher and amputee Van Phillips. By the 1990s, Flex-Foot's prosthetic foot designs based on carbon fibre springs were widely acknowledged to be the most effective at storing and releasing energy during walking and, in particular, recreational and competitive sports activities.6–8 The combination of enhanced socket comfort and prosthetic feet with dynamic response enable amputee medallists in the Paralympics to complete the 100 metre dash within about one second of the Olympic record.
Shock absorbing mechanisms to reduce impact forces
Once amputees worldwide began to regularly jog, run, and jump, it became apparent that the lack of shock absorption in artificial limbs was a limiting factor. Flex-Foot introduced the Re-Flex shin-foot design in 1993, coupling a spring loaded shock absorber with the dynamic response foot (fig (fig2).2). Recently, gait studies have confirmed that this type of component improves the biomechanical performance of artificial limbs, which may explain the enthusiastic acceptance of such devices by non-athletes too.9
Until this past decade, thigh amputees have been forced to hold their prosthetic knee in full extension throughout most of the stance phase of the gait cycle to prevent the leg from collapsing. This not only results in an unnatural gait but also eliminates the primary mechanism for shock absorption offered by the biological knee. To address this shortcoming, a growing number of prosthetic knee designs now include a “stance flexion feature.” The UK company Blatchford was the first to offer this capability, termed the “bouncy knee.”10 As the amputee bears weight on the limb a friction brake engages automatically and stabilises the knee, while a small rubber element allows a few degrees of motion to absorb shock and simulate knee flexion during the early stance phase.
Microprocessor controlled movement
The first artificial knee with an “on board” computer to improve the symmetry of amputees' gait across a wide range of walking speeds was developed by Blatchford in the early 1990s. Studies have confirmed that these “intelligent prostheses” offer amputees a more reliable gait pattern during the swing phase of the gait cycle, permitting them to walk with more confidence and in a more energy efficient manner.11,12
The Otto Bock C-Leg takes this a stage further, offering not only symmetry in the swing phase but also markedly improved security in the stance phase—that is, the knee will not buckle unintentionally during standing (fig (fig3).3). Sensors in the ankle and shin of the prosthesis continually assess the position of the leg in space as the amputee is walking. The data are fed into two microprocessors inside the knee, and the resistance from a hydraulic damper is adjusted up to 50 times a second, optimising knee stiffness throughout the entire gait cycle (fig (fig4).4). The ability of this knee to automatically increase knee stability within microseconds makes it much easier and safer for amputees to traverse uneven ground, to walk on sloped surfaces, and to walk down stairs.
Preliminary studies report that amputees have increased independence with such a responsive and stable electronic prosthesis, confidently tackling more difficult and varied activities than they did with other limbs.13,14 Based on the widespread success of more than 1000 C-Leg fittings to date, the clinical application of such prostheses with microprocessor control of stance and swing is expected to increase steadily. Such technology costs about four times as much as limbs with mechanical knee controls.
1. write a 2 sentence summary of what you learned from that article.