Quantification of the microstructural anisotropy of distraction osteogenesis in the rabbit tibia

Abstract

A longitudinal orientation of fibers and trabeculae has been observed histologically within distracted callus. This study quantified the intensity and angle of orientation of trabeculae within a distracted callus. Sixteen New Zealand white rabbits underwent unilateral tibial callus distraction with an external fixator across a mid-diaphyseal osteotomy. Included were: a seven-day postoperative latency period, ten days of distraction at 0.5 mm every 12 hours, and 20 days of post-distraction consolidation before euthanasia. Tibiae were removed, stripped of soft tissue, sectioned, and processed for decalcified histology. Micrographs of mid-coronal sections of the callus were evenly divided into 12 regions and underwent Fast Fourier Transform (FFT) analysis of the digitized image to determine the angle and intensity of the orientation of the bony trabeculae within the callus. The microstructure of the regenerate callus demonstrated an angle of orientation that uniformly matched that of cortical bone in all of regions of the callus and an intensity of orientation which approached that of cortical bone.

Figure 1

Photomicrograph of a mid-coronal section through the distracted callus of a rabbit tibia, and twelve areas for trabecular orientation analysis.

Figure 2

A 6µm mid-coronal plane section is taken from the distracted callus to be histologically prepared. The digitized photomicrograph of the section is then divided into twelve areas described by their coordinates in either cortical (C1 and C2) or medullary (M) longitudinal zones, and in the proximal (P), proximal middle (PM), distal middle (DM) or distal (D) transverse zones.

Figure 3

Once a field is selected from the digitized photomicrograph, the program gray- rescales the area (left), generates a Fast Fourier Transform power spectrum (middle), and finally produces an intensity histogram to graphically represent the distribution of oriented angles within the area (right).

Figure 4

The averaged angle of orientation of the trabeculae within the 12 areas in the distracted callus, described by their coordinates in either cortical (C1 and C2) or medullary (M) longitudinal zones, and in the proximal (P), proximal middle (PM), distal middle (DM) or distal (D) transverse zones.