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Instant Cage Making with PMMA
31 July 2014
24 October 2014
23 March 2015 (online)
We were pleased to read the inspiring paper on cage making by Christopher Brenke et al. 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.
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.
- 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