Perry, John; (2000) A Non Invasively Extendible Endo-prosthetic Replacement. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

An endo-prosthetic replacement (EPR) has been developed that can be lengthened under control from outside the body. This EPR is for use with child bone tumour cases and is to be surgically implanted to replace a section of bone, usually including a joint, which has been resected as part of the treatment for a bone tumour occurring in one of the long bones of a limb. The EPR includes an extendible module that can be adapted for individual patients by the addition of alternative types of artificial joint to suit various tumour sites. The extendible module may be lengthened at frequent intervals during the child's growth years to maintain limb length symmetry. The non-invasive method of lengthening is considered to be a marked improvement on current methods that require a surgical operation each time an extendible EPR requires to be lengthened. Placing the limb into a rotating magnetic field actuates extension. This field acts on a small magnet sealed within the extendible module of the EPR and induced rotation of this magnet drives reduction gearing that turns a power screw to extend telescopic sections. The extension force is sufficient to overcome the expected resistance of body tissues and the extension may be in sufficiently small increments to avoid pain or excessive joint stiffness. Extension can be reversed if necessary. This study considers alternative extension methods and details the reasons for the final selection of the magnetic drive. The study then covers the detailed design of the various elements of the system including a compact and robust gearing mechanism and the equipment that generates the rotating magnetic field. The complete system has been constructed in prototype form and the study is concluded with tests demonstrating that the magnetic drive is capable of reliably extending the telescopic sections of the EPR against simulated in-vivo loading.

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