How Does Surgical Technique Affect Fluid Permeability? A Laboratory Study Comparing Nanofracture, Microfracture and Fine Wire Drilling Approaches

CATEGORY: Basic Sciences/Biologics; Ankle; Arthroscopy; Sports INTRODUCTION/PURPOSE: Current surgical practice for the treatment of osteochondral lesions in the ankle involves using one of three techniques to promote blood flow from subchondral bone tissue to the defect site, improving the rate of healing. These different techniques: - fine-wire drilling, nanofracture and microfracture, involve disrupting the trabecular bone. However, the size and method of these techniques means this varies in terms of penetration depth and diameter. Additionally, each technique causes differing degrees of damage to the trabecular structure, and the ability of fluid to flow through the porous structure. The aim of this study was to compare the influence of the different techniques on the fluid permeability of the tissue following by assessing the flow of radiopaque contrast agent using μCT image analysis. METHODS: Fresh-frozen cadaveric tali specimens (n=12) were prepared through creating a 10mm diameter chondral defect in three different regions of each talus. Each region then underwent one of three surgical techniques: 1) Fine wire drilling, 2) Nanofracture or 3) Microfracture, undertaken by a single surgeon.0.1 ml radiopaque contrast agent (Omnipaque(TM) 300) was then added to each region and imaged using a clinical μCT scanner (SCANCO Medical AG, 73.6 μm resolution) The amount of contrast agent that permeated through each different region was assessed through imaging processing. RESULTS: The μCT analysis indicated that across the 12 samples, eight nanofracture regions demonstrated flow of contrast agent to the depth of the fracture site or deeper. Some lateral flow was also observed in these sites. Eight microfracture regions demonstrated that the flow of contrast agent was localised to the fracture site and a preferential flow laterally. In only one sample, did a fine wire drilling region demonstrate any fluid flow. In this sample, contrast agent had permeated through the drilling site to the bottom and some sub-site permeation was observed. However, in all samples that showed no permeation of contrast agent through the fracture site, there was a layer of contrast agent on the chondral surface or minor permeation through to the sub- chondral surface. CONCLUSION: Nanofracture showed improved fluid permeability throughout the surrounding trabecular structure, when compared to microfracture and fine wire drilling. Microfracture appears to allow some fluid flow, but this is confined to the immediate area around the fracture site, while fine wire drilling appears to allow almost no fluid flow through the surrounding trabecular tissue. This conclusion is reinforced by previous literature that concluded the damage to the structure of the trabecular tissue is reduced when using nanofracture, compared to the other two techniques.