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A game of thrones and broken bones

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Science Translational Medicine  27 Sep 2017:
Vol. 9, Issue 409, eaao6885
DOI: 10.1126/scitranslmed.aao6885

Abstract

Repair of cranial bone trauma with degradable magnesium implants could reduce complications and eliminate the need for implant removal.

After watching Game of Thrones, it’s easy to understand the show’s popularity. All the elements of an epic are intertwined—drama, passion, brutality, dragons, and shocking character deaths. With the story set in medieval times, the characters would have benefited from better technologies to repair the abundance of cracked skulls. Today, surgical repair of cranial trauma involves fixing bone in place with metal screws and plates to promote regrowth. Current standards use inert, nondegradable metals, such as titanium. However, permanent materials increase the risk of infection and complications and can require a separate removal procedure. Bone surrounding a permanent implant can also weaken because it is shielded from stress. New implants that are both strong enough for bone repair and degradable could help eliminate these challenges.

Magnesium alloys offer a route to address the issues above because the human body readily absorbs magnesium. These alloys can also be designed with controlled degradation rates and mechanical properties sufficient for bone repair. Degradable magnesium alloys have already been used in humans, for example, in ankle fractures. Now, Naujokat and colleagues are testing these alloys for repair of cranial fractures in a miniature pig model. In a recent report, a region of bone was removed from each side of each pig’s cranium, then replaced and fixed in place, using plates and screws made of titanium at one injury site and magnesium at the other site. Irrespective of implant material, all injuries healed by week 15, without inflammation or toxicity. Interestingly, while real-time measurements revealed that the volume of the magnesium implants remained constant, signs of biodegradation were indicated by development of porous regions of lower density within the implants.

Although the magnesium implants were efficacious and well tolerated, titanium promoted greater contact of the implant with bone. Magnesium can form local gas pockets during degradation, which might explain these differences. Future studies will need to investigate the impact of contact area on the long-term strength of bone forming around degradable implants, compared with the interfacial contact desired for permanent implants. Ultimately, degradable implants might simplify and improve outcomes for cranial bone injuries; even so, clubbing blows to the head are still ill-advised.

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