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The release of damaged prosthesis from it's cemented position in human bone
Kadoura, Ahmed Mohamed
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Original surgery to replace a joint in the body with an implant is known as arthroplasty. There are cases where it is necessary to replace the implant with a revision surgery, because it has worn out or infection may have developed. Revision surgery is a long and complex procedure because the orthopaedic surgeon has to remove the implant that had been cemented in the bone cavity as well as the bone cement. A major problem is the hardness of the bone cement. Several methods are used in order to remove it, requiring excessive strength and sharp tools, that pose a danger to the human body long surgery time, from 3 - 4 hours. In this study, modern methods were used attempting to soften bone cement by heating it using heating equipment (a hair dryer and a heat gun), by bombarding it with ultrasonic waves and finally applying mechanical vibrations. The heating of the bone cement did not give satisfying results, as the temperature needed for melting or softening the bone cement was very high, which is not tolerable in operations, especially dealing with the human body. The use of ultrasonic waves in trying to separate the implant from the bone cement did not give any positive results either. The exposure of bone cement to ultrasonic waves in a wide range of frequencies and for a long period of time resulted in some heating effect but did not produce any change in its mechanical or chemical properties. Mechanical vibration produced a significant difference in results with the similar samples used in the first phase (heating) and the second phase of testing (the use of ultrasonic waves). After choosing an effective vibration source (a hammer drill), an adaptor was developed for securing the "implant test" samples and ensuring that the source of vibration would apply an axial tension on the implant as it were cemented in the bone cavity. The results were very positive, in that firstly and foremost the implant was separated from the bone cavity together with the body of the cement, i.e. leaving no remnants or leftovers in the inner surface of the bone where it was cemented. The frequency of vibration for best results was found to be 40 Hz and the time period of vibration for the complete extraction of the "implant" with the cement attached to it, did not exceed 22 seconds.