J Neurol Surg A Cent Eur Neurosurg 2015; 76(03): 255-256
DOI: 10.1055/s-0034-1543962
Letter to the Editor
Georg Thieme Verlag KG Stuttgart · New York

Instant Cage Making with PMMA

Gerald Huschak
1   Department of Anesthesiology and Intensive Care Medicine, University of Leipzig, Medical Faculty, Leipzig, Germany
Laura Weichsel
2   Department of Neurosurgery, Spine Center Baden, Mittelbaden Hospital, Baden-Baden, Germany
Andre Beier
2   Department of Neurosurgery, Spine Center Baden, Mittelbaden Hospital, Baden-Baden, Germany
Thomas Hoell
2   Department of Neurosurgery, Spine Center Baden, Mittelbaden Hospital, Baden-Baden, Germany
› Author Affiliations
Further Information

Publication History

31 July 2014

24 October 2014

Publication Date:
23 March 2015 (online)

Dear Editor,

We were pleased to read the inspiring paper on cage making by Christopher Brenke et al.[1] We report on virtually the same idea that we developed along with Gerald Fehling 10 years ago, working at that time at the Bergmannstrost Hospital in Halle/Saale, Germany. [Fig. 1] shows the metal form with a silicone inlay. Polymethylmethacrylate (PMMA) was injected after evacuation with a larger syringe ([Fig. 2]). The cages could be formed in a good shape and removed easily from the silicone inlay. The injection nose ([Fig. 3]) could be removed by hand. Up to three cages were made with a single shot. The cages were bubble free, and biomechanical tests revealed sufficient and comparable results to those reported by Brenke et al.

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Fig. 1 Metal form with the silicone inlay. The holes (left panel) display the injection site for the polymethylmethacrylate.
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Fig. 2 Opened metal form after injection. The cages were readymade. The larger syringe was used to evacuate the silicone inlay.
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Fig. 3 Section of the self-made cage with the injection nose. After breaking the nose away, the cage is ready for use.

We filed a German patent successfully, but the European application failed due to a handwritten English patent by a student. We later changed the application to a German Gebrauchsmuster (patent-like intellectual property right that protects inventions). The company interested in marketing the device lost interest in developing the cage commercially due to the unfortunate patent situation. The cages made from PMMA technically work well, but we did not leave them implanted in the patient because we were not sure about the legal issues at that time.

During the past 10 years, prices of cages have declined by a third. However, the cost of a PMMA cage is still attractive. Legal issues may still lead to uncertainty in the user community. The key concern is that the responsibility for implant safety went from a company to the surgeon and the hospital, and most of them may not be willing to take on this responsibility.

  • References

  • 1 Brenke C, Pott P, Schwarz ML, Schmieder K, Barth M. Development of a low-cost polymethylmethacrylate stand-alone cervical cage: technical note. J Neurol Surg A Cent Eur Neurosurg 2014; 75 (4) 317-322