gms | German Medical Science

German Congress of Orthopaedics and Traumatology (DKOU 2015)

20.10. - 23.10.2015, Berlin

Novel osteosynthesis implant system for electrical stimulation of femoral neck fractures – Monopolar inducible screw system (MISS)

Meeting Abstract

  • presenting/speaker Andreas Obermeier - Klinikum rechts der Isar, Technische Universität München, Klinik für Orthopädie - Muskuloskeletale Forschung, München, Germany
  • Markus Rennich - Klinikum rechts der Isar, Technische Universität München, Klinik für Orthopädie - Muskuloskeletale Forschung, München, Germany
  • Viktor Lacatusu - Klinikum rechts der Isar, Technische Universität München, Klinik für Orthopädie - Muskuloskeletale Forschung, München, Germany
  • Heribert Stephan - Neue Magnetodyn GmbH, München, Germany
  • Axel Stemberger - Klinikum rechts der Isar, Technische Universität München, Klinik für Orthopädie - Muskuloskeletale Forschung, München, Germany
  • Rüdiger von Eisenhart-Rothe - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany
  • Rainer Burgkart - Technische Universität München, Klinikum rechts der Isar, Klinik für Orthopädie und Sportorthopädie, München, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2015). Berlin, 20.-23.10.2015. Düsseldorf: German Medical Science GMS Publishing House; 2015. DocPO21-918

doi: 10.3205/15dkou709, urn:nbn:de:0183-15dkou7094

Published: October 5, 2015

© 2015 Obermeier et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.


Outline

Text

Objectives: Fracture of the femoral neck is one of the most common fractures with about 130,000 fractures per year in Germany. In general, a quick surgical intervention is required to keep the femoral heads vital and avoid hip endoprostheses for the patients. This type of fracture can be stabilized with a dynamic hip screw or a 2/3-screw fixation by using classical osteosynthesis screws. Through use of a well-known low-frequency magnetic field therapy, in conjunction with activatable implants, the bone structure can be electrical stimulated. In order to enhance the fracture healing, a novel implant system was developed, optimized for the electric stimulation of femoral neck fractures. This implant system, the monopolar inducible screw system (MISS), generates an optimized field distribution along the femoral neck.

Methods: During the design a miniaturized secondary inductive energy source was integrated into a hollow implant screw. This inductivity was calculated and mounted by contacting one electrical output to the shaft and a second led to an isolated contact in the head of the screw. Then, one or two further osteosynthesis screws can be connected via a plug contact during surgical procedure, representing the second electric pole for electric stimulation. This new construction produces a bone growth stimulating electric field at the implant, activated by an external low frequency magnetic field. Finite element simulations were calculated to estimate the field distribution. Electrical measurements prove the electrical parameters for the therapy and evaluate field distributions in vitro. Optimization of the electrode-tissue interface with different implant surface modifications were investigated by electrical impedance spectrometry to improve stimulation conditions at 20 Hz.

Results and Conclusion: Electrical measurements met the target therapeutic induction voltage for electric osteotherapy of about 800 mV, at 20 Hz and 4 mT magnetic flux of the external field. FEM-Simulation indicated homogeneous electric field distribution between the screw shafts, hence enabling various fracture situations along the femur neck to be electrically stimulated. Measurements in pig femurs gave the initial information regarding currents and resistance in bone tissue. Electric field measurements in vitro confirmed homogenous distributions. The impedance spectroscopy measurements showed significant differences in the impedance of the implant-tissue interface, ranging from 125 to 5,700 Ohm at 20 Hz, dependent on surface modifications. Non-anodized titanium or titanium-niobium oxynitride coatings was shown to be the most appropriate surfaces. With the MISS-system it is now possible to apply the known potential positive effect of osteoblast stimulation by electromagnetic fields with a single, compact implant. Consequently, this implant system can support clinicians in hip joint saving procedures. The integration of this technology into other implants such as the dynamic hip screw is under consideration.