Biodegradable osteosynthesis material for stabilization of midface fractures: experimental investigation in sheep

The most frequently tested biodegradable osteosynthesis materials have up t o now largely consisted of poly-L-lactide (PLLA). The PLLA polymers appear to have sufficient mechanical strength for fracture treatment in the midfac e, but their degradation does not seem to be uniform enough to allow their clinical use. During the degradation process the disintegration products el icit a foreign body reaction due to non-uniform degradation rates. The fore ign body reaction is sometimes combined with a fluctuant swelling at the im plantation site. Implants injection-moulded from 90:10 PLLA/PGA (polyglycol ic acid) have a more uniform degradation rate and seem to lead to a milder foreign body reaction. We bridged Le Fort I osteotomies in sheep using a sy stem of injection-moulded PLLA/PGA 90:10 plates and screws and compared it with 2 mm AO miniplates and mini-screws made from titanium. Light microscop y evaluation showed that the PLLA/PGA copolymer system experienced its high est mechanical stress at the transition from screw head to screw shaft. Nev ertheless, the fragments fixed with the copolymers were on the whole only s lightly less stable than those fixed with the titanium system. The foreign body reaction solely due to co-polymer degradation was not severe, consider ing the fibrous tissue response that was found associated with the titanium components. The study does show that the copolymer investigated is adequat e for clinical use as a biodegradable osteosynthesis material, at least in low stress bearing areas.