Preoperative evaluation of bone quality and bone density using a novel CT/microCT-based hard-normal-soft classification system.

PURPOSE: To obtain more objective presurgical measurements of clinical interest, this study proposes a new method of measuring and classifying bone density. MATERIALS AND METHODS: The density of bovine bone blocks of different qualities was first measured in Hounsfield units (HU) using computed tomography (CT). Next, bone cylinders corresponding to each examined area were retrieved. Bone quality was then measured by both histomorphometric microCT and by subjective evaluation of bone quality during drilling. RESULTS: A statistically significant correlation was found between CT and microCT measurements. Based on this evidence, a new method of classifying bone density/quality into three classes of clinical interest was developed: hard/dense, normal, and soft (HNS). These statistical data also enabled the creation of a formula to convert ordinary CT values expressed in HU into bone volume percentages (BV%) to objectively measure bone density based on the HNS system. CONCLUSION: Stable implant placement depends upon measurements of bone quality/density that are site-specific, objective, and quantitative. To meet these standards, this paper reports an innovative method of classifying bone quality/density and then objectively measuring bone density based on this HNS classification system, using a simple, innovative mathematical formula that converts HU values into measurements of bone volume.