Image-based radiodensity profilometry measures early remodeling at the bone-callus interface in sheep

Fast automated creation of digital twins for virtual mechanical testing of ovine fractured tibiae

Virtual mechanical testing with image-based digital twins enables subject-specific insights about the mechanical progression of bone fracture healing directly from imaging data. However, this technique is currently limited by the need for commercial software packages that require manual input to create finite element (FE) models from computed tomography (CT) scans. The purpose of this study was to develop automated image analysis algorithms that can create subject-specific models from CT scans without a human in the loop. Two competing techniques were developed and tested on an imaging dataset consisting of 26 intact and 44 osteotomized ovine tibiae. In both techniques, the raw image was cropped to an efficient bounding box, downsampled, segmented by an element-formation threshold, and cleaned up for efficient FE analysis using voxel-based meshes. The key difference between contour-free (CFT) and snake-reliant (SRT) techniques was threshold- and contour-based segmentation of images, respectively, before bounding box detection. The contours were detected using a snake that balanced desired aspects of the contours through energy minimization. Virtual torsion tests were performed and the results were validated by comparison to ground-truth experimental data. The CFT and SRT models produced nearly identical predictions of virtual torsional rigidity and both methods reliably replicated the physical tests. Models generated by SRT were faster to solve, but model preparation and solution combined was faster by CFT. Automatic digital twin creation by CFT is therefore recommended except where other downstream analyses require systematic spatial data sampling of the bone, which is only achieved by SRT.

Risk of fragility fracture is aggravated during bone regeneration processes in osteoporotic sheep

INTRODUCTION

Bone regeneration processes are associated with a systemic skeletal change in bone quality, increasing the risk of fragility fractures. This condition may be aggravated in osteoporotic patients due to their limited osteogenic capacity. This work evaluates the impairment of the bone quality in osteoporotic sheep during a bone regeneration process. It provides a deeper understanding about the complex multiscale dynamics of bone mineral density, microstructure and chemical composition across different bone tissues, locations and time points.

MATERIALS AND METHODS

Osteoporosis was induced in fifteen Merino sheep. A critical-size defect was then created in the sheep's right hind metatarsus and subsequently regenerated using distraction osteogenesis. The animals were randomly sacrificed during bone regeneration, either on days 40 or 100 after surgery. Computed tomography, micro-computed tomography and chemical composition analyses were conducted on different bone tissues (cortical, trabecular and woven) at several skeletal locations (the operated metatarsus, the contralateral one and the iliac crest) to assess the individual bone quality changes relative to the non-osteoporotic time point.

RESULTS

After osteoporosis induction, the trabecular tissue experienced a 6.4% reduction in the bone mineral density, while no significant changes were reported in cortical tissue quality. During bone regeneration, the operated bone increased significantly the woven ossification whilst the cortical mineral density decreased by 18.7%. Simultaneously, an early deterioration in the microstructure and chemical composition of the trabecular bone was observed in the iliac crest, persisting over time in non-operated trabecular regions.

CONCLUSIONS

Osteoporosis causes uneven degradation to trabecular tissue quality across different bone locations. Furthermore, the bone regeneration process via bone transport in osteoporotic subjects leads to a systemic skeletal disorder that further impairs the bone quality, surpassing the damage caused by osteoporosis alone. This impairment appears to be intensified by the pre-existing osteoporotic condition.

3D-printed bioceramic scaffolds for bone defect repair: bone aging and immune regulation

The management of bone defects, particularly in aging populations, remains a major clinical challenge. The immune microenvironment plays an important role in the repair of bone defects and a favorable immune environment can effectively promote the repair of bone defects. However, aging is closely associated with chronic low-grade systemic inflammation, which adversely affects bone healing. Persistent low-grade systemic inflammation critically regulates bone repair through all stages. This review explores the potential of 3D-printed bioceramic scaffolds in bone defect repair, focusing on their capacity to modulate the immune microenvironment and counteract the effects of bone aging. The scaffolds not only provide structural support for bone regeneration but also serve as effective carriers for anti-osteoporosis drugs, offering a novel therapeutic strategy for treating osteoporotic bone defects. By regulating inflammation and improving the immune response, 3D-printed bioceramic scaffolds may significantly enhance bone repair, particularly in the context of age-related bone degeneration. This approach underscores the potential of advanced biomaterials in addressing the dual challenges of bone aging and immune dysregulation, offering promising avenues for the development of effective treatments for bone defects in the elderly. We hope the concepts discussed in this review could offer novel therapeutic strategies for bone defect repair, and suggest promising avenues for the future development and optimization of bioceramic scaffolds.

Don't mind the gap: reframing the Perren strain rule for fracture healing using insights from virtual mechanical testing

Aims

The "2 to 10% strain rule" for fracture healing has been widely interpreted to mean that interfragmentary strain greater than 10% predisposes a fracture to nonunion. This interpretation focuses on the gap-closing strain (axial micromotion divided by gap size), ignoring the region around the gap where osteogenesis typically initiates. The aim of this study was to measure gap-closing and 3D interfragmentary strains in plated ovine osteotomies and associate local strain conditions with callus mineralization.

Methods

MicroCT scans of eight female sheep with plated mid-shaft tibial osteotomies were used to create image-based finite element models. Virtual mechanical testing was used to compute postoperative gap-closing and 3D continuum strains representing compression (volumetric strain) and shear deformation (distortional strain). Callus mineralization was measured in zones in and around the osteotomy gap.

Results

Gap-closing strains averaged 51% (mean) at the far cortex. Peak compressive volumetric strain averaged 32% and only a small tissue volume (average 0.3 cm3) within the gap experienced compressive strains > 10%. Distortional strains were much higher and more widespread, peaking at a mean of 115%, with a mean of 3.3 cm3 of tissue in and around the osteotomy experiencing distortional strains > 10%. Callus mineralization initiated outside the high-strain gap and was significantly lower within the fracture gap compared to around it at nine weeks.

Conclusion

Ovine osteotomies can heal with high gap strains (> 10%) dominated by shear conditions. High gap strain appears to be a transient local limiter of osteogenesis, not a global inhibitor of secondary fracture repair.

Adaptive Image Segmentation Reveals Substantial Cortical Bone Remodeling During Early Fracture Repair

The goal of this study was to develop an image analysis algorithm for quantifying the effects of remodeling on cortical bone during early fracture healing. An adaptive thresholding technique with boundary curvature and tortuosity control was developed to automatically identify the endocortical and pericortical boundaries in the presence of high-gradient bone mineral density (BMD) near the healing zone. The algorithm successfully segmented more than 47,000 microCT images from 12 healing ovine osteotomies and intact contralateral tibiae. Resampling techniques were used to achieve data dimensionality reduction on the segmented images, allowing characterization of radial and axial distributions of cortical BMD. Local (transverse slice) and total (whole bone) remodeling scores were produced. These surrogate measures of cortical remodeling derived from BMD revealed that cortical changes were detectable throughout the region covered by callus and that the localized loss of cortical BMD was highest near the osteotomy. Total remodeling score was moderately and significantly correlated with callus volume and mineral composition (r > 0.64, p < 0.05), suggesting that the cortex may be a source of mineral needed to build callus.

Embracing ethical research: Implementing the 3R principles into fracture healing research for sustainable scientific progress

As scientific advancements continue to reshape the world, it becomes increasingly crucial to uphold ethical standards and minimize the potentially adverse impact of research activities. In this context, the implementation of the 3R principles-Replacement, Reduction, and Refinement-has emerged as a prominent framework for promoting ethical research practices in the use of animals. This article aims to explore recent advances in integrating the 3R principles into fracture healing research, highlighting their potential to enhance animal welfare, scientific validity, and societal trust. The review focuses on in vitro, in silico, ex vivo, and refined in vivo methods, which have the potential to replace, reduce, and refine animal experiments in musculoskeletal, bone, and fracture healing research. Here, we review material that was presented at the workshop "Implementing 3R Principles into Fracture Healing Research" at the 2023 Orthopedic Research Society (ORS) Annual Meeting in Dallas, Texas.