Prosthetic components

Resorption of bone in the medial neck places the forces of continued weight bearing on the bone cement in that area and may lead to medial and/or distal migration of the femoral cement and prosthetic component ... 

Implantable prosthetic bearings may be constructed from a composite material having a first layer and a second layer (20). The first layer has an articulating surface defined therein, whereas the second layer has an engaging surface defined therein for engaging either another prosthetic component or the bone itself. The first layer is constructed of a UHMWPE, whereas the second layer is constructed of a copolymer of ethylene and an acrylate. 

Partial or complete replacement of natural organs with prosthetic components will someday be commonplace. For instance, the design of the total artificial heart, which has had limited clinical success, involved an application of many fundamental principles already discussed as they relate to hemodynamics, biomaterials, and control. Most would agree, however, that the materials-blood-tissue interface is the nidus for some of the most serious problems preventing the development of a safe and reliable artificial heart. This reinforces the importance of investigating at the molecular level the complex interactions that occur between artificial surfaces and the physiological environment. 

The major factors limiting the effective life of a total replacement synovial joint are loosening of one or more of the prosthetic components, a variety of medical problems (e g. infection) and wear. Most internal prostheses now consist of metallic and polymeric components and it is the penetration of the former into the latter which is the subject of this paper. 

Typical conditions, to which gamma-sterilized prosthetic components may be subjected, are summarized as follows ... 

The origins of consolidation-related oxidation are not clear yet, but the processing conditions of the UHMWPE bar or sheet, together with the influence of the machining of the prosthetic component, have been proposed as contributing factors. Poor consolidation of the UHMWPE powder during processing. 

Typical GC/MS analysis of the soluble fraction extracted from a retrieved UHMWPE prosthetic component. 

Thus it is apparent that while the user-prosthesis interface is a major impediment to the advancement of prosthetic technology, there is much room for improvement in the prosthetic components themselves. The limitations of current systems are not due to a lack of innovative design but rather are due to the very severe nature of the physical constraints that are placed on the designer and the inability of current technology to match the power and energy density of natural muscle. 

The typical prosthesis control system consists of a Bowden cable with appropriate terminal fittings. The terminal fittings are used to anchor one end of the cable to a body-harness, and the other end to the prosthetic component to be controlled. Between the two end points, the cable crosses the prosthetic joint to be controlled and the physiolog-... 

Third, this fitting highlights the severity of the control interface problem when faced with amputations at this level. Everything is used—conventional harness control and biomechanical switches, using the chin, are extensively used in the control of the body-powered prosthetic components. These same chin motions are used to control externally powered components through the use of electromechanical switches and linear transducers. 

In proportional control, the amountfintensity of a controlled output variable is directly related (proportional) to the amount of the input signal. For example, the output speed of a dc motor is proportional to the amount of voltage applied to its terminals. This is why dc motors are said to be speed controlled. This is also the reason why most of today s commercially available prosthetic components are speed controlled—it is simple. Output speed is proportional to the amount of input signal. Proportional control is used where a graded response to a graded input is sought. 

Processing steps take time Any delay in the response of the output to a change in the input of greater than about 100 /ts is perceptible to the human operator as a sluggish response. Any delay in response reduces the overall system bandwidth. Parker and Scott (1985) suggest that delays between input and output should not exceed 200 fxs, and even this can be unacceptable for use with high performance prosthetic components. 

Weir, R. F. ff., Heckathome, C. W., and Childress, D. S. (2001). Cineplasty as a Control Input for Externally Powered Prosthetic Components. Journal of Rehabilitation Research and Development, vol. 38, no. 4, pp. 357-363, July/August. 

Formation of Sebiff s bases is also postulated in the ease of decaibo lation at keto acids by amino compounds (Langenbeek s artificial carboxylases). Recently bacterial amino acid decarboxylases have also been shown to contain an active carbonyl in their prosthetic component—phosphorylated pyridoxal (84).i... 

Abstract— Pistoning is said to be one of the major indicators of optimal suspension of lower limb prosthesis. Mannfac-tnrers of prosthetic components have always tried to come np with new innovative snspension systems to lessen pistoning. Some have attempted to decrease the pistoning by targeting the skin-liner interface and others have been working on the surface between liner and hard socket. 

One of the greatest concerns about the use of PE in joint replacement bearing surfaces is the wear of the material and the effect the wear debris has on the surrounding tissues. For many years, it has been demonstrated that this wear debris leads to osteolysis and loosening of the prosthetic components [21, 25]. Wear of the polyethylene or loosening of the implants, which may be related to wear debris, remains a common reason for revision surgery after total hip [26, 27] or total knee arthroplasty [28]. 

Fig. 12.62. Total hip replacement. Longitudinal oblique 12-5 MHz US image obtained over the anterior aspect of the hip joint in a patient with a hip prosthesis. The prosthetic components are well depicted with US, including the acetabular part (Ac), the head (H) and the neck (N). Posterior reverberation artifacts are manifest (arrowheads). A discrete amount of fluid (asterisk) distends the anterior recess of the pseudocapsule. IPs, iliopsoas muscle...

Not all researchers use the same definition of osteolysis in their radiographic analyses, complicating the comparison of results between smdies. Some researchers identily radiolucencies around the margin of an implant as a linear lytic defect [52], whereas in other smdies, only a focal lesion or cyst is classified as osteolysis [46]. Of greatest clinical concern are unstable or expansile lesions (so-called balloon lesions ) that grow over time and lead to aseptic loosening of a prosthetic component. 

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