Repair of microdamage in osteonal cortical bone adjacent to bone screw

Abstract

Up to date, little is known about the repair mode of microdamage in osteonal cortical bone resulting from bone screw implantation. In this study, self-tapping titanium cortical bone screws were inserted into the tibial diaphyses of 24 adult male rabbits. The animals were sacrificed at 1 day, 2 weeks, 1 month and 2 months after surgery. Histomorphometric measurement and confocal microscopy were performed on basic fuchsin stained bone sections to examine the morphological characteristics of microdamage, bone resorption activity and spatial relationship between microdamage and bone resorption. Diffuse and linear cracks were coexisted in peri-screw bone. Intracortical bone resorption was significantly increased 2 weeks after screw installation and reach to the maximum at 1 month. There was no significant difference in bone resorption between 1-month and 2-months groups. Microdamage was significantly decreased within 1 month after surgery. Bone resorption was predisposed to occur in the region of <100 µm from the bone-screw interface, where had extensive diffuse damage mixed with linear cracks. Different patterns of resorption cavities appeared in peri-screw bone. These data suggest that 1) the complex microdamage composed of diffuse damage and linear cracks is a strong stimulator for initiating targeted bone remodeling; 2) bone resorption activities taking place on the surfaces of differently oriented Haversian and Volkmann canals work in a team for the repair of extensive microdamage; 3) targeted bone remodeling is a short-term reaction to microdamage and thereby it may not be able to remove all microdamage resulting from bone screw insertion.

Figure 1. Microdamage in peri-screw bone stained with basic fuchsin.

Diffuse damage was contacted with bone edge (large arrow), behind which larger linear cracks (small arrows) were visible. Linear cracks often mixed with diffuse damage (arrow heads) in the area adjacent to the bone-screw interface.

Figure 2. Resorption cavities in peri-screw bone (1 month after surgery).

A) cutting cavities (arrow) were covered by a thin layer of basic fuchsin stained tissue and contacted with microdamage; B) closing cavity (arrow) was covered by a thick seem of osteoid, on which there was a single layer of cuboidal osteoblasts attached.

Figure 3. The distribution frequency of bone resorption cavities in different areas of peri-screw bone.

The distribution patterns were similar in 2-weeks, 1-month and 2-months groups. In the region of 500 µm from the bone-screw interface, about 40% of the resorption cavities were located in the area of <100 µm from bone edge.

Figure 4. The morphology of microdamage and bone resorption cavities in peri-screw bone.

A) microdamage adjacent to the bone-screw interface was composed of diffuse damage and linear cracks (1 day after surgery). The microcracks not only cut through osteocyte lacunae and canaliculi in bone matrix, but also destroyed the surface of Haversian canal (arrows); B) cutting cavities (arrows) in damaged bone (2 weeks after surgery); C) closing cavities (arrows) in damaged bone (2 months after surgery). Extensive osteocyte lacunar-canalicular network was visible in newly formed bone beneath the osteoid (top arrow).

Figure 5. Huge bone resorption cavities in the cross section of peri-screw bone.

A) irregular and bifurcated resorption cavity (arrow) in damaged bone; B) Huge resorption cavity (long arrow) with cutting zone (short arrow) in damaged bone and closing zone (arrow head) behind (1 month after surgery).