Closing capacity of segmental radius defects in rabbits.

In the research of synthetic bone graft substitutes, the relevance for bone regeneration can be confirmed in a critical-sized model. In this study the rabbit radial defect was investigated as an ingenious model of critical size, due to its defect immobilizing intact ulna. In addition, the influence of poly(DL-lactic-co-glycolic acid) (PLGA) on bone regeneration was determined. Sixteen, 4-month-old rabbits received bilateral segmental radial defects of 15 or 20 mm. The osteotomy ends were marked with small titanium pins. Half of the group received injected PLGA microparticle/carboxymethylcellulose implants. Implantation time was 12 weeks. Evaluation consisted of radiographs after surgery and sacrifice, microcomputed tomography and histology. The radiographs revealed that the created defects were significantly smaller after sacrifice. Further a number of radii showed fibrocartilaginous interposition. Both findings indicated instability of the created defect. All evaluation techniques revealed that 15 and 20 mm were not of critical size, as most defects were more or less regenerated. PLGA microparticles did not influence bone regeneration significantly. In conclusion, 15- and 20-mm radius defects in 4-month-old rabbits were not a suitable model for bone regeneration as these defects were neither critical size nor stable. PLGA-microparticle degradation did not influence bone regeneration.