A comparison of in-vitro and in-vivo degradation of poly(D,L-lactide) bio-absorbable intra-medullary plugs

Poly(D,L-lactide) has been evaluated as a material for the manufacture of intra-medullary plugs to be used in total hip arthoplasty. Plugs were manufactured by compression moulding and subjected to in-vitro and in-vivo degradation. In-vitro hydrolysis was carried out by immersion in phosphate buffered saline (Ringer's solution) at 37 degreesC and rates of degradation were relatively rapid with molecular weight halving after 30 days. In-vivo degradation was assessed by implantation into dogs followed by retrieval at intervals up to 24 months. Molecular weight was found to reduce to half the original value in about 190 days. It is thought that this difference in degradation rate is because of diffusional control of the overall process, Histology showed that the implanted plugs were resorbed over 24 months.