Device body, Prosthesis

A surgical procedure by which a medical device or prosthesis is placed either temporarily or permanently in the human body. 

Metallic devices have been used to repair and replace parts of the human body for centuries. Archaeological evidence clearly indicates that surgical procedures were performed in several ancient civilisations. The use of surgical metal implants in humans was first recorded in 1562 when a gold prosthesis was used to close a defect in a cleft palate. ... 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

Titanium alloys generally show a combination of strength and biocompatibility which makes them suitable for medical devices (prosthesis, surgical instruments). The high strength Ti-6Al-7Nb alloy has several orthodontic applications. Only a limited number of alloys have the necessary combinations of properties needed for successful use in the human body. Titanium and its alloys, stainless steels and cobalt-chromium alloys are the workhorse alloys in the medical device industry. 

Miscellaneous. Many other organs sometimes become diseased or defective, and some artificial device has been used to replace them. For example, the gastrointestinal (GI) tract has often been replaced, totally or partially, by some type of plastic tubing. Such a prosthesis does not perform the normal GI tract functions but merely connects existent, nondiseased tubular parts in the body. Many materials have been used such as polyamides, polyesters, polysilicones, and polyethylene. In a similar manner, various ducts have been replaced by plastic tubing. Finally, the bladder, trachea, ureter, and similar organs have been replaced by nonfunctional plastic tubing (]J. 

An orthopedic prosthesis is an internal or external device that replaces lost parts or functions of the neuroskeletomotor system. In contrast, a orthopedic orthosis is a device that augments a function of the skeletomotor system by controlling motion or altering the shape of body tissue. For example, an artificial leg or hand is a prosthesis, whereas a calliper (or brace) is an orthosis. This chapter addresses only orthoses and external orthopedic prostheses internal orthopedic prostheses, such as artificial joints, are a subject on their own. 

The power for active hand and arm prostheses can come form the body (Body-powered Prosthesis), or from external sources (Externally-powered prosthesis) [90-97]. Gross body movement controls a body-powered prosthesis. The movement of the shoulder, upper arm, or chest is captured by a harness system, which is attached to a cable that is connected to a terminal device (hook or hand). For some levels of amputation or deficiency, an elbow system can be added to provide the amputee additional function. An amputee must possess at least one or more of the foUowing gross body movements glenohumeral flexion, scapular abduction or adduction, shoulder depression and elevation, and chest expansion in order to control body-powered prosthesis. In addition, sufficient residual limb length and sufficient musculature must exist. 

Many amputees who wear a body-powered prosthesis develop increased control due to a phenomenon called extended proprioception [ 90]. Extended proprioception gives the wearer feedback as to the position of the terminal device. The subject will know whether the hook is open or closed by the extent of pressure the harness is exerting on his or her shoulder area without having to visually inspect the operation. Many amputees do not like the cosmetic appearance of the hook and control cables and they request a natural-like part of the body replacement. 

A prosthesis is a device that has been designed to replace a missing part of the body or to make a part of the body work better. An artificial limb or part is called a prosthetic device. Doctors have had to amputate limbs to save injured patients lives for thousands of years (Figure 20-9). Perhaps you have seen a cartoon or a movie of a pirate who had a peg leg—a wooden stump from the knee down. Or perhaps you have seen fictional movies or television shows about a bionic man or woman. Significant improvements in prosthetic devices have been made in the past decade, and the future looks even better. 

As is the case for all portable devices, power is scarce. Choice of power source defines a prosthesis, in that it determines the choice of actuator. If the power source is to be the person, i.e., body power, then the actuator is the person s own musculature and the prosthesis should not require excessive effort to use. Mechanical mechanisms need to be efficient and frictional losses need to be minimized to avoid tiring the user over the course of a day. If the artificial limb is externally powered (i.e., uses a power source other than the body, usually electric storage), the limb should be able to run for a day from the same power source without needing to be replaced or recharged. In addition, it is desirable for the power source to be contained within the prosthesis. 

In a body-powered device, the jjerson uses his or her own muscular power to operate the prosthesis, usually via a cable link called a Bowden cable (Fig. 32.4). A Bowden cable consists of two parts, an outer housing and an inner tension cable. The housing is fixed at both ends and serves as a flexible bridge between two points, maintaining a constant length regardless of any motion. The cable is free to slide within the housing. 

The basic configuration of Bowden cables in prostheses has changed little over the intervening years and is stiU in use today. In fact, if prehensile function is the primary goal of the prosthetic fitting, the device of choice for most persons with amputations is a body-powered, Bowden-cable-operated prosthesis with a split hook-shaped terminal device. This is in spite of all the technological advances in electronics, computers, and dc motor technology that have occurred since the end of World War H. 

FIGURE 32.6 Photograph of a person with a unilateral transhumeral (above-the.eIbow) amputation using a body-powered prosthesis. This picture clearly shows the elbow lock control cable (strap and cable on the anterior of the humeral section of the prosthesis). In a transhumeral prosthesis this cable is needed to switch control from the elbow to the terminal device. When the elbow is locked, the terminal device is under the control of the control cable when the elbow is unlocked, then the elbow is under the control of the control cable. 

A prosthesis is a device that replaces a missing body part or augments a partial one an individual who measures, fits, and modifies the prosthesis is referred to as the prosthetist. Legs, arms, feet, and hands are the most commonly known artificial devices. 

Interaction with the patient begins well before any surgery, with the physician determining if replacement of the natural body part is required. If a surgical procedure such as amputation is required, the physician, nurse, and social workers must prepare the patient emotionally and physically. The prosthetist, physician, and physical therapist consult with the patient to determine the size, shape, and material most appropriate for the appropriate device. The physical therapist evaluates factors such as strength and ability to wear the prosthesis and works with the patient to increase physical strength as appropriate for the device involved. 

Prosthetic Limbs. Over the years, prosthetic limbs consisted of combinations of springs and hinges to increase motion and function. Prosthetic Umbs use a socket to fit over the remaining part of the limb and provide a link between the body and the prosthesis. Additional straps and belts are often used to attach the device to the body with soft, socklike material used in between to protect the area of contact from excessive pressure and friction. The main body of the prosthesis is often made from material such as carbon fiber, popular for its light weight, strength, and durability. These properties require less exertion of effort by the patient, and the device appears more natural. 

Prosthesis Artihcial device that replaces a missing body part or augments an injured part also known as prosthetic device. 

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