Quantification of the effect of osteolytic metastases on bone strain within whole vertebrae using image registration

Abstract

ABSTRACT:The vertebral column is the most frequent site of metastatic involvement of the skeleton with up to 1/3 of all cancer patients developing spinal metastases. Longer survival times for patients, particularly secondary to breast cancer, have increased the need for better understanding the impact of skeletal metastases on structural stability. This study aims to apply image registration to calculate strain distributions in metastatically involved rodent vertebrae utilizing mCT imaging. Osteolytic vertebral lesions were developed in five rnu/rnu rats 2-3 weeks post intracardiac injection with MT-1 human breast cancer cells. An image registration algorithm was used to calculate and compare strain fields due to axial compressive loading in metastatically involved and control vertebrae. Tumor-bearing vertebrae had greatly increased compressive strains, double the magnitude of strain compared to control vertebrae (p ¼ 0.01). Qualitatively strain concentrated within the growth plates in both tumor bearing and control vertebrae. Most interesting was the presence of strain concentrations at the dorsal wall in metastatically involved vertebrae, suggesting structural instability. Strain distributions, quantified by image registration were consistent with known consequences of lytic involvement. Metastatically involved vertebrae had greater strain magnitude than control vertebrae. Strain concentrations at the dorsal wall in only the metastatic vertebrae, were consistent with higher incidence of burst fracture secondary to this pathology. Future use of image registration of whole vertebrae will allow focused examination of the efficacy of targeted and systemic treatments in reducing strains and the related risk of fracture in pathologic bones under simple and complex loading. ß

Mechanical assessment of the effects of metastatic lytic defect on the structural response of human thoracolumbar spine

“…However, our findings, as well as the findings of clinical, experimental, and computational studies, suggest the disruption of the vertebral cortex and the degree of cortical involvement to be associated with a high probability of risk for vertebral body collapse . Although our study has focused on the effect of lytic lesions on the pre‐fracture structural response of the FSU, the remarkable change in the structural response of the lytic vertebra, as shown in a recent small animal study, demonstrate the highly damaging effect of cortical involvement on the structural response of the affected vertebra . Current work in our Laboratory is leveraging this model to elucidate the effect of torsional and bending loading on the structural response and consequent failure mechanisms of lumbar and thoracic spine segments with clinically relevant defect patterns …”

Elastic Full‐Field Strain Analysis and Microdamage Progression in the Vertebral Body from Digital Volume Correlation

“…A deeper understanding of the internal elastic full‐field strain distribution was achieved. In fact, despite that a number of studies used DVC to investigate the vertebral global fracture under compression , the elastic strain distribution is still unexplored. The results clearly showed how local strain built up from the elastic regime and highlighted those internal weaker regions that could result in microdamage initiation and progression up to vertebral failure (Figures ).…”

“…In that study, a new image registration algorithm was developed to spatially resolve strain in whole bones (rat vertebrae) using micro‐computed tomography (CT) images. Since then, a number of studies investigated the full‐field strain distribution in vertebral bodies without and with the adjacent intervertebral discs , as well as entire vertebrae under compressive loading. In Ref.…”

“…Also, the influence of strain directionality and local levels of strain on microdamage evolution in the vertebra has not been investigated. Hardisty et al [36] is the only study to date to report the microdamage in metastatic and healthy vertebrae (rat models) associated with full-field strain from DVC, but only for the axial strain. That work reported an average axial strain at failure of À27 000 microstrains for the healthy group (five specimens) but no information of the critical strain values in different locations of the vertebrae.…”

Effect of the metastatic defect on the structural response and failure process of human vertebrae: An experimental study

“…The deleterious effect of lytic lesions on the risk of vertebral failure was recently demonstrated in an animal model for vertebral lytic metastasis (Hardisty et al, 2012;Hojjat et al, 2010). The occurrence of the lesion resulted in the doubling of compressive strains compared to the control vertebrae with the development of stress concentration at the dorsal aspects of the vertebrae indicating increased structural instability.…”