Effect of absorbable hydroxyapatite/poly-DL-lactide rods on experimental fracture healing

In order to investigate the effect of a new institute-designed absorbable hydroxyapatite microparticles/poly-DL-lactide (HA/PDLLA) fracture fixation devices on experimental fracture healing, 25 rabbits with a transverse transcondylar osteotomy of the distal femur were fixed intramedullary by a HA/PDLLA rod (4.5 mm in diameter, 30-40 mm in length). The follow-up time lasted 1, 2, 4, 6 and 12 week(s). Roentgenographic, histological and ultrastructural analyses were conducted. The results showed that all osteotomies united within 6 weeks without delay. No accumulation of inflammatory cells was seen. Ultrastructural studies showed that polymorphonuclear neutrophils and macrophages were observed mainly at the 1st week, but only few were noted at the 2nd week. The inflammatory and debridement stages were not prolonged. Large amount of active fibroblasts and some chondroblasts were observed at the 2nd week, suggesting a fibrous callus stage. The main cellularity at 4th week was osteoblasts and osteocytes. Part of osteocytes had already entered the static stage at the 6th week. Our experiment showed that the HA/PDLLA had good biocompatibility, sufficient mechanical strength and caused no delay to the fracture healing.