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Development of a modular lightweight tumour endoprosthesis with novel textile attachment points for the refixation of previously detached muscle groups

Poster presented at 18th EFORT Congress, Sports Activities & Orthopaedic Practice 31 May to 02 June 2017, Vienna
Entwicklung einer modularen Tumor-Endoprothese mit neuartigen textilen Anbindungsstellen zur Refixation zuvor abgelöster Muskelgruppen
: Grunert, Ronny; Schmidt, Michael; Kopper, Michael; Töppel, Thomas; Rädel, Thomas; Hanus, Sybille; Prietzel, Torsten

Poster urn:nbn:de:0011-n-4526194 (332 KByte PDF)
MD5 Fingerprint: d4446fe90ef7e09d8d19fbe64ca2c14d
Created on: 23.6.2017

2017, 1 Folie
European Federation of National Associations of Orthopaedics and Traumatology (EFORT Congress) <18, 2017, Vienna>
Poster, Electronic Publication
Fraunhofer IWU ()
tumor endoprosthetics; lightweight construction; Textile Attachment

In tumor endoprosthetics, implants are applied to reconstruct the proximal femur. The main problems of these implants are often the high weight and the biomechanically not optimal attachment of soft tissue. The aim of this work is to solve these problems in order to develop a long-term stable biomechanically correct implant of a proximal femoral replacement.
Based on lightweight construction concepts from vehicle construction, a topology optimization was performed with an existing modular implant basic body. The additive manufacturing process laser beam melting (metallic 3D printing) was applied to produce the implant with the material TiAl6V4. The individual modules were coupled by a specially designed polygon interface. To disconnect the interface, a joining instrument was used which applies a force at two defined points and thus elastically deforms the internal contour of the interface. This allows the reversible joining of the mo- dular components. In order to fix the muscles anatomically correctly, textile attachment points made of multifilament polyester were produced by embroidery. These were firmly bonded to the implant by a polyethylene extrusion of the neck module. The shaping of the plastic molding was possible by the creation of an injection molding tool. In order to determine the fatigue strength of the implant, a test was carried out in a laboratory certified for this purpose. Furthermore, the developed implant functional model was implanted in a body donor.
A functional model of a modular implant was produced. On the basis of a topology optimization, the new implant has a mass reduction of 400 g compared to a proximal femoral set, which was assembled from the MML system (AQ Implants GmbH, Germany). The greatest savings potential was found in the trochanter module (weight reduction by 55%). The load-bearing structures consisted of TiAl6V4, whereas the shell of the neck module was made of polyethylene. The reversible coupling was implemented by a polygonal interface. The force closure took place by switching off the external force effect and thus the deformation of the round bore hole into an elliptical geometry, which resulted in a "jamming" of the spigot. According to ISO 7206 the fatigue strength of the implant was determined. The test implantation at a body donor showed that the implant can be placed under realistic conditions. The suture fixation of the muscles to the textile attachment points was significantly simplified.
The technological feasibility of a novel biomechanically optimized implant could be demonstrated. The innovations shall contribute that the implant reflects the original biological situation as realistically as possible. By means of the embroidery technique, textile structures can be produced which, in terms of their properties such as bursting pressure, pore size and thickness etc., basically correspond to the textile-technological requirements profile in the sense of the soft tissue attachment. The embroidered structures for soft tissue attachment can be injection molded with plastic without loss of strength. In further tests it has to be investigated if the modular attachment points of the implant are susceptible to corrosion. Furthermore, it should be evaluated whether the modular components of the proximal femoral replacement can also be applied for the design of a femoral total prosthesis.