[Ultrastructural investigation of experimental fracture healing: effect of fixation with plates of various materials].

The right tibiae of 45 new zealand rabbits were osteotomized and internally fixed with plate of methylmethacrylate (MMA) or stainless steel (SS) with or without compression. The animals were divided into 3 groups, 15 in each. The ultrastructure of the specimens are as follows. Repair of the fractures immobilized with MMA plate went through a typical course of secondary healing, showing obvious periosteal, contact and medullary callus. The fibroblasts, chondroblasts and osteoblasts were numerous and very active throughout the healing period, demons treating an extremely active synthesis and secretion function. Findings in fractures fixed with SS plate without compression manifested atypical secondary healing. The early callus was mainly of contact and medullary one, the periosteal callus set in rather late. The fibroblasts were active, but not the osteoblasts, and even less in some chondroblasts. Fractures fixed with SS plate with compression healed primarily on the plate side, while the opposite side showed fissure healing, like that without compression. Intramedulla repair looked similar to that of fissure healing. Although the fibroblasts and osteoblasts were much like that in the group without compression, no chondroblasts came into action. All these biological differences are supposed to be response to the magnitude of stress at the fracture site.