Micro-computed tomography assessment of fracture healing: Relationships among callus structure, composition, and mechanical function

Abstract

Non-invasive characterization of fracture callus structure and composition may facilitate development of surrogate measures of the regain of mechanical function. As such, quantitative computed tomography- (CT-) based analyses of fracture calluses could enable more reliable clinical assessments of bone healing. Although previous studies have used CT to quantify and predict fracture healing, it is unclear which of the many CT-derived metrics of callus structure and composition are the most predictive of callus mechanical properties. The goal of this study was to identify the changes in fracture callus structure and composition that occur over time and that are most closely related to the regain of mechanical function. Micro-computed tomography (μCT) imaging and torsion testing were performed on murine fracture calluses (n=188) at multiple post-fracture timepoints and under different experimental conditions that alter fracture healing. Total callus volume (TV), mineralized callus volume (BV), callus mineralized volume fraction (BV/TV), bone mineral content (BMC), tissue mineral density (TMD), standard deviation of mineral density (σTMD), effective polar moment of inertia (Jeff), torsional strength, and torsional rigidity were quantified. Multivariate statistical analyses, including multivariate analysis of variance, principal components analysis, and stepwise regression were used to identify differences in callus structure and composition among experimental groups and to determine which of the μCT outcome measures were the strongest predictors of mechanical properties. Although calluses varied greatly in the absolute and relative amounts of mineralized tissue (BV, BMC, and BV/TV), differences among timepoints were most strongly associated with changes in tissue mineral density. Torsional strength and rigidity were dependent on mineral density as well as the amount of mineralized tissue: TMD, BV, and σTMD explained 62% of the variation in torsional strength (p<0.001); and TMD, BMC, BV/TV, and σTMD explained 70% of the variation in torsional rigidity (p<0.001). These results indicate that fracture callus mechanical properties can be predicted by several μCT-derived measures of callus structure and composition. These findings form the basis for developing non-invasive assessments of fracture healing and for identifying biological and biomechanical mechanisms that lead to impaired or enhanced healing.

Adult Stem Cell Mobilization Enhances Intramembranous Bone Regeneration: A Pilot Study

“…Based on our data, it is now possible to make a realistic estimate of the sample size needed for further studies. We estimate 16 to 17 mice/ group/time point would be an appropriate sample size to detect a 60% difference in mean BV/TV with a power of 0.8, which is consistent with sample sizes needed in some other bone repair models such as fracture [44]. Even though we found a difference of approximately 60% with a smaller sample size in our study, a post hoc analysis indicates the power of the experiment was on the order of 0.5.…”

“…The sample size utilized in this study is based on and consistent with sample sizes used in other bone repair models [44]. After the conclusion of this study, power analyses were performed for assessing one of the key outcomes in Experiment 3, bone volume per total volume (BV/TV), assuming a power of 0.8, with alpha = 0.05, and expecting a 60% difference between groups (Power and Sample Size Calculations 3.0.43; http://biostat.mc.vanderbilt.edu/Power SampleSize).…”

Cone-beam CT to assess bony fusion following anterior cervical interbody fusion

“…Besides the subchondral sclerotic bone changes at the pressure areas of the cage wall with the endplates, different stages of the bone fusion process were shown in the periphery of the cage: bone apposition adjacent to the endplates, appearance of hazy densities indicating matrix calcification/mineralization, and finally formation of trabecular bone within the disc space. Appreciation of the amount and width of these changes was possible with this cross-sectional technique, not demonstrated before with radiography nor with classical CT. With regard to predicting ACIF outcomes, CBCT may demonstrate the amount of bone mineralization is visible, as there are the hazy densities visible before a stable bone bridge is formed [10,11].…”

Loss of Gi G-Protein-Coupled Receptor Signaling in Osteoblasts Accelerates Bone Fracture Healing

“…The newly formed fracture callus tissue was spatially segmented from the native cortical bone in the 2D tomograms. (20,21) Briefly, the outside of the callus was manually delineated and refined through an automated intensity matching procedure to contour the outer boundary. The periosteal surface of the native cortical bone was manually delineated to define the callus and cortical boundaries, thus isolating the callus volume of interest (Supporting Fig.…”

“…For these calculations, both TV and BV were normalized by the length of the callus. (20) Histological, immunohistochemistry, and quantitative PCR assessments of the callus tissue were performed as described. (9,10,22) (Details are available in the Supporting Information-Methods and Supporting Tables 1 and 2.…”