Effects of bone density alterations on strain patterns in the pelvis: application of a finite element model.

Insufficiency fractures occur when physiological loads are applied to bone deficient in mechanical resistance. A better understanding of pelvic mechanics and the effect of bone density alterations could lead to improved diagnosis and treatment of insufficiency fractures. This study aimed to develop and validate a subject-specific three-dimensional (3D) finite element (FE) model of a pelvis, to analyse pelvic strains as a function of interior and cortical surface bone density, and to compare high strain regions with common insufficiency fracture sites. The FE model yielded strong agreement between experimental and model strains. By means of the response surface method, changes to cortical surface bone density using the FE model were found to have a 60 per cent greater influence compared with changes in interior bone density. A small interaction was also found to exist between surface and interior bone densities (< 3 per cent), and a non-linear effect of surface bone density on strain was observed. Areas with greater increases in average principal strains with reductions in density in the FE model corresponded to areas prone to insufficiency fracture. Owing to the influence of cortical surface bone density on strain, it may be considered a strong global (non-linear) indicator for insufficiency fracture risk.

Automated CT-based analysis to detect changes in the prevalence of lytic bone metastases from breast cancer.

The spinal column is the most frequent site of bone metastasis in patients with breast cancer. It is important to understand how the pattern of vertebral lesions may be affected by the introduction of modern cancer therapies. The purpose of this study was to characterize changes in the radiological appearance of spinal column metastases over the past decade using highly automated Computed Tomography (CT) based computational analysis methods. Two case series studies were performed using CT scans of patients with confirmed spinal metastases secondary to breast cancer: Cohort A with CT scans acquired between 1998 and 2001 and Cohort B with CT scans acquired between 2004 and 2007. Diseased vertebrae were classified as lytic, blastic, or mixed based on CT scan intensity through an automated 3D computer algorithm. The relative incidence of lytic vertebral metastases decreased in comparing Cohort B to Cohort A (12% vs. 49%) with a corresponding increase in mixed lesions (51% vs. 18%) Significant associations were found between the percentage of lytic lesions in number of diseased vertebrae measured per patient and lack of bisphosphonate use (RR = 2.6) and for membership in Cohort A vs. Cohort B (RR = 5.9). This work highlights a change in the CT appearance of vertebral metastases from breast cancer during the past decade toward a lower proportion of lytic disease. Observation of patient therapies suggests that differences in radiological assessment may be linked, at least in part, to bisphosphonate use. These findings have important implications for both clinical practice and research strategies involving vertebral metastases.

A biomechanical assessment of the coupling of torsion and tension in the human scapholunate ligament.

The mechanical behaviour of human scapholunate ligaments is not well described in the literature with regard to torsion. In this study, intact scapholunate specimens were mechanically tested in torsion to determine whether a simultaneous tensile load was generated. Human intact scapholunate specimens (n = 19) were harvested. The scaphoid and lunate bones were potted in square chambers using epoxy cement, while the interposing ligament remained exposed. Each specimen was mounted rigidly in a specially designed test jig and remained at a fixed axial length during all tests. Specimens were subjected to a torsional load regime that included cyclic preconditioning, ramp-up, stress relaxation, ramp-down, rest, and torsion to failure. Torque and axial tension were monitored simultaneously. The relationship between torsion and tension was determined. Graphs of torque versus tension were generated, from which outcome measures were extracted. Tests demonstrated a clear relationship between applied torsion and the resulting generation of tension for the ligament during ramp-up (torsion-to-tension ratio, 38.86 +/- 29.00 mm; linearity coefficient R2 = 0.89 +/- 0.15; n = 19), stress relaxation (torsion-to-tension ratio, 23.43 +/- 15.84 mm; R2 = 0.90 +/- 0.09; n = 16), and failure tests (torsion-to-tension ratio, 38.81 +/- 26.39mm; R2 = 0.77 +/- 0.20; n = 16). No statistically significant differences were detected between the torsion-to-tension ratios (p = 0.13) or between the linearity (R2) of the best-fit lines (p > 0.085). A strongly coupled linear relationship between torsion and tension for the scapholunate ligament was exhibited in all test phases. This may suggest interplay between these two parameters in the stabilization of the ligament during normal motion and for injury cascades.

Lateral compression fracture of the pelvis represents a heterogeneous group of complex 3D patterns of displacement.

Although clinical and radiological criteria exist to direct the non-operative and operative treatment of other types of pelvic injuries, none exist for lateral compression (LC) fractures. The purpose of this study is to describe the patterns of injury in LC fractures through quantitative 3D radiographic analysis. It is hypothesised that LC fractures represent a spectrum of injuries with a combination of translational and rotational displacements. CT data from 60 patients with unilateral lateral compression fractures were obtained. Quantification of translations and rotations of the fractures was performed using 3D visualisation software. Fractures initially diagnosed as LC actually represent a spectrum of displacement patterns, ranging from a minimally displaced hemipelvis to complex combinations of displacements. Fractures were grouped based on pattern of rotation and translation into 5 distinct groups. 3D analysis of displacement patterns demonstrated a complexity in LC fractures which may explain the variations seen in outcomes associated with this injury.

Quantitative characterization of metastatic disease in the spine. Part I. Semiautomated segmentation using atlas-based deformable registration and the level set method.

Quantitative assessment of metastatic disease in bone is often considered immeasurable and, as such, patients with skeletal metastases are often excluded from clinical trials. In order to effectively quantify the impact of metastatic tumor involvement in the spine, accurate segmentation of the vertebra is required. Manual segmentation can be accurate but involves extensive and time-consuming user interaction. Potential solutions to automating segmentation of metastatically involved vertebrae are demons deformable image registration and level set methods. The purpose of this study was to develop a semiautomated method to accurately segment tumor-bearing vertebrae using the aforementioned techniques. By maintaining morphology of an atlas, the demons-level set composite algorithm was able to accurately differentiate between trans-cortical tumors and surrounding soft tissue of identical intensity. The algorithm successfully segmented both the vertebral body and trabecular centrum of tumor-involved and healthy vertebrae. This work validates our approach as equivalent in accuracy to an experienced user.