Abstract
A stem revision system was developed by a group of orthopedic surgeons and bioengineers. Implant specific instruments have been created to make the operation as easy as possible. The stem of the MRP prosthesis is conical and forged of a Titanium Aluminium Niobium alloy. It consists of 2 modular elements, a diaphysical and a trochantical part that can be supplemented by a head. Stem lengths from 140 mm and 200 mm are aviable with different length of diaphysical and prolongation elements so that each stem length could be realized in small steps. Also the anchoring of th diaphysical prosthesis elements in the bone makes a free construction of the total prosthesis to the femur with choice of the length and a variable adjustment of the rotation position of the neck of the femur prosthesis. Eight longitudinal ridges on the stem elements guarantee a rotation stability and the curved stems allow a reconstruction of the physiological antecurvation of th thigh also in case of fractures and segmental resections.
Since 1993 the members of the clinical working team implanted 1500 MRP prosthesis. We think that the best way for an optimal anchoring is the preservation of a great deal of the solid bone structures also in the section of the primary anchoring with partial bone resorption. The proximal anchoring of the femoral isthmus up to the middle third of the femur guarantees the most reliable long-term results. Indications for revision operations are given by resorptive bone defects up to a considerable bone loss on the proximal femur, for intraoperative stem fractures, for primary subtrochantar long distance fractures with simultaneous coxarthritis and for defect zones after bone tumor treatments. The very variable new design facilitates the revision operation and shortens the operation time.
The MRP prosthesis is able to bridge mechanically stable, damaged or missing parts of the proximal femur with revision operations and it makes an immediate partial loading possible for the patient. Defected zones of the bone fill with bone structures as a basis for the local anchored musculature. The modularity of the prosthesis lightens the revision operation.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
