Three poly(L-lactides) with different molecular weights were synthesiz
ed. Small blocks (3 X 3 X 2 mm) and rods (25 X 3 X 2 mm) were produced
either by injection moulding (amorphous parts, M(vis) 200 000 and 120
000, respectively) or machined out of a solid as-polymerized polylact
ide block (crystalline parts, M(vis) 429 000) and implanted into the d
orsal muscle of rats. After 1 to 116 wk the rats were killed and the i
mplants were recovered. Histological preparation was carried out using
the cutting-grinding technique. All three polylactides had incorporat
ed well, forming a collagenous fibrous layer. Crystalline block polyla
ctide remained stable in form and structure over the whole observation
period. Amorphous injection-moulded specimens developed a rough surfa
ce within weeks, then deep resorptive lacunae after ca. 1 yr and becam
e totally degraded (M(vis) 120 000) or nearly totally degraded (M(vis)
200 000) after 2 yr. This velocity of biodegradation seems to meet th
e requirements for an absorbable material for osteosynthesis. Long-ter
m implantation into rodents brings the problem of foreign-body tumorig
enesis independent of the chemical nature of implants (the Oppenheimer
effect). Observations in this study and in the literature are discuss
ed.