Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: A 2-4-year follow-up study in rabbits

Biodegradation of hydroxyapatite (HA)/poly(L‐lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u‐HA) or calcined HA (c‐HA). Composite rods of u‐HA/PLLA and c‐HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning‐electron microscopy (SEM), and transmission‐electron microscopy (TEM) 2–4 years later. For u‐HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u‐HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross‐sectional area after 4 years decreased by 23.3 ± 8.4%. The mean ratio of bony ingrowth to the initial cross‐sectional area around the shrunken rods was 6.7 ± 1.3 %. The viscosity molecular weight of PLLA reduced from 2 × 105 to less than 1 × 103. Thus, most of the PLLA had released from the rods. The c‐HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 66B: 539–547, 2003