Positional stability of polylactide pins with various surface textures in sheep tibia.

Resorbable pins with a smooth or textured surface were produced from poly(L-lactide) P(L)LA poly(L/D-lactide) 95/5% P(L/D)LA, and poly(L/DL-lactide) 95/5% P(L/DL)LA by injection molding. The pins were implanted in sheep tibiae to establish whether the pin surface geometry and the polymer composition used for the pin preparation affect their positional stability in bone; i.e., can the pin design and its ability to swell in body fluids protect against loosening. Three of the 32 P(L)LA pins with a smooth surface loosened but none of the P(L/D)LA and P(L/DL)LA pins with a smooth surface did. This may indicate that expansion of the pin upon swelling protects against loosening, even if the pin's surface geometry is not optimal. None of the pins with a textured surface were loose, independent of the polymer used for the pin preparation. The textured surface of these pins allowed the ongrowth of new bone and hence, implant anchoring, secured the positional stability of the implant in the bone.