LATE DEGRADATION TISSUE-RESPONSE TO POLY(L-LACTIDE) BONE PLATES AND SCREWS

Patients with fractures of the zygomatic bone were treated with high m olecular weight poly(L-lactic) acid (PLLA) bone plates and screws. Thr ee years after implantation four patients returned to our department w ith a swelling at the site of implantation. At the recall of the remai ning patients we found an identical type of swelling after the same im plantation period. To investigate the nature of the tissue reaction, e ight patients were reoperated for the removal of the swelling. The imp lantation period of the PLLA material varied from 3.3 to 5.7 years. Mi croscopic evaluation and molecular weight measurements were performed. The excised material showed remnants of degraded PLLA material surrou nded by a dense fibrous capsule. Ultrastructural investigation showed crystal-like PLLA material internalized by various cells. The results of this investigation suggest that the PLLA material slowly degrades i nto particles with a high crystallinity. The intra- and extracellular degradation rate of these particles is very low. After 5.7 years of im plantation, these particles were still not fully resorbed.