Micro CT Analysis and 3D Modelling of Fluid Permeability of Talar Subchondral Bone After Marrow Stimulation Techniques Demonstrates Superiority of Nanofracture Over Microfracture and Fine Wire Drilling

Abstract

Introduction/Purpose: The aim was to compare different bone marrow stimulation techniques and consequent fluid permeability of subchondral bone by assessing flow of radiopaque contrast agent using μCT image analysis and 3D modelling. Methods: Donated human tali specimens (n=12) were prepared by creating separate matched 10mm diameter chondral defects in each. Each defect underwent one of three surgical techniques: fine wire drilling, nanofracture or microfracture, addition of radiopaque contrast agent and imaged using a clinical μCT scanner. Using Slicer 3D software each μCT scan was segmented for bone and contrast agent regions in each surgical site of each sample. Each site was resolved into a cylinder and the ratio of segmented pixels of contrast agent against bone calculated. Results: μCT analysis indicated that 8/12 nanofracture regions demonstrated enhanced flow of contrast to at least the depth of the fracture site, with some additional lateral flow also observed. 8/12 microfracture regions demonstrated flow of contrast agent localised to the fracture site and preferential flow laterally. Only 1/12 samples with fine wire drilling demonstrated any fluid flow. In 11/12 samples that showed no permeation of contrast agent, a residual layer of contrast agent on the chondral surface was seen. Segmentation of each sample site showed a significant increase (n=12, p< 0.05) in fluid flow of the contrast agent in the nanofracture sites (11%) compared to microfracture (5%) and fine wire drilling (2%). Conclusion: Nanofracture showed significantly improved fluid permeability throughout the surrounding trabecular structure, when compared to microfracture and fine wire drilling. Microfracture allowed some fluid flow, but only confined to the immediate area around the fracture site, while fine wire drilling allows very little fluid flow at all. This study suggests that nanofracture should perhaps be the preferred mode of subchondral bone preparation for osteochondral lesions of the talus. Quantitative measurement of contrast permeability into talar subchondral bone by technique Nanofracture showed significantly improved fluid permeability throughout the surrounding trabecular structure, when compared to microfracture and fine wire drilling