The intravertebral distribution of bone density: correspondence to intervertebral disc health and implications for vertebral strength.

UNLABELLED: This study's goal was to determine associations among the intravertebral heterogeneity in bone density, bone strength, and intervertebral disc (IVD) health. Results indicated that predictions of vertebral strength can benefit from considering the magnitude of the density heterogeneity and the congruence between the spatial distribution of density and IVD health. INTRODUCTION: This study aims to determine associations among the intravertebral heterogeneity in bone density, bone strength, and IVD health METHODS: Regional measurements of bone density were performed throughout 30 L1 vertebral bodies using micro-computed tomography (µCT) and quantitative computed tomography (QCT). The magnitude of the intravertebral heterogeneity in density was defined as the interquartile range and quartile coefficient of variation in regional densities. The spatial distribution of density was quantified using ratios of regional densities representing different anatomical zones (e.g., anterior to posterior regional densities). Cluster analysis was used to identify groups of vertebrae with similar spatial distributions of density. Vertebral strength was measured in compression. IVD health was assessed using two scoring systems. RESULTS: QCT- and µCT-based measures of the magnitude of the intravertebral heterogeneity in density were strongly correlated with each other (p < 0.005). Accounting for the interquartile range in regional densities improved predictions of vertebral strength as compared to predictions based only on mean density (R (2) = 0.59 vs. 0.43; F-test p-value = 0.018). Specifically, after adjustment for mean density, vertebral bodies with greater heterogeneity in density exhibited higher strength. No single spatial distribution of density was associated with high vertebral strength. Analyses of IVD scores suggested that the health of the adjacent IVDs may modulate the effect of a particular spatial distribution of density on vertebral strength. CONCLUSIONS: Noninvasive measurements of the intravertebral distribution of bone density, in conjunction with assessments of IVD health, can aid in predictions of bone strength and in elucidating biomechanical mechanisms of vertebral fracture.

The effect of intravertebral heterogeneity in microstructure on vertebral strength and failure patterns.

UNLABELLED: The goal of this study was to determine the influence of intravertebral heterogeneity in microstructure on vertebral failure. Results show that noninvasive assessments of the intravertebral heterogeneity in density improve predictions of vertebral strength and that local variations in microstructure are associated with locations of failure in the vertebral body. INTRODUCTION: The overall goal of this study was to determine the influence of intravertebral heterogeneity in microstructure on vertebral failure. METHODS: Trabecular density and microarchitecture were quantified for 32 thoracic vertebrae using micro-computed tomography (µCT)-based analyses of 4.81 mm, contiguous cubes throughout the centrum. Intravertebral heterogeneity in density was defined as the interquartile range and quartile coefficient of variation of the cube densities. The vertebrae were compressed to failure to measure stiffness, strength, and toughness. Pre- and post-compression µCT images were analyzed using digital volume correlation to quantify failure patterns in the vertebrae, as defined by the distributions of residual strain. RESULTS: Failure patterns consisted of large deformations in the midtransverse plane with concomitant endplate biconcavity and were linked to the intravertebral distribution of bone tissue. Low values of connectivity density and trabecular number, and high values of trabecular separation, were associated with high strains. However, local microstructural properties were not the sole determinants of failure. For instance, the midtransverse plane experienced the highest strain (p < 0.008) yet had the highest density, lowest structure model index, and lowest anisotropy (p < 0.013). Accounting for the intravertebral heterogeneity in density improved predictions of strength and stiffness as compared to predictions based only on mean density (strength: R(2) = 0.75 vs. 0.61, p < 0.001; stiffness: R(2) = 0.44 vs. 0.26, p = 0.001). CONCLUSIONS: Local variations in microstructure are associated with failure patterns in the vertebra. Noninvasive assessments of the intravertebral heterogeneity in density--which are feasible in clinical settings--can improve predictions of vertebral strength and stiffness.

Biomechanical validation of finite element models for two silicone metacarpophalangeal joint implants.

Silicone implants are used for prosthetic arthroplasty of metacarpophalangeal (MCP) joints severely damaged by rheumatoid arthritis. Different silicone elastomer MCP implant designs have been developed, including the Swanson and the NeuFlex implants. The goal of this study was to compare the in vitro mechanical behavior of Swanson and NeuFlex MCP joint implants. Three-dimensional (3D) finite element (FE) models of the silicone implants were modeled using the commercial software ANSYS and subjected to angular displacement from 0 deg to 90 deg. FE models were validated using mechanical tests of implants incrementally bent from 0 deg to 90 deg in a joint simulator. Swanson size 2 and 4 implants were compared with NeuFlex size 10 and 30 implants, respectively. Good agreement was observed throughout the range of motion for the flexion bending moment derived from 3D FE models and mechanical tests. From 30 deg to 90 deg, the Swanson 2 demonstrated a greater resistance to deformation than the NeuFlex 10 and required a greater bending moment for joint flexion. For larger implant sizes, the NeuFlex 30 had a steeper moment-displacement curve, but required a lower moment than the Swanson 4, due to implant preflexion. On average, the stress generated at the implant hinge from 30 deg to 90 deg was lower in the NeuFlex than in the Swanson. On average, starting from the neutral position of 30 deg for the preflexed NeuFlex implant, higher moments were required to extend the NeuFlex implants to 0 deg compared with the Swanson implants, which returned spontaneously to resting position. Implant toggling within the medullary canals was less in the NeuFlex than in the Swanson. The differential performance of these implants may be useful in implant selection based on the preoperative condition(s) of the joint and specific patient functional needs.

Blood utilization in hip and knee arthroplasty: a cost-minimization study.

The non-utilization of crossmatched blood is an expensive waste of resources. We have audited blood utilization for all primary total hip and knee arthroplasty patients. We compared routine pre-operative crossmatching (Phase 1) with a policy of group, screen and save (G & S) only (Phase 2). The patient groups were similar in both phases. Pre- and post-operative haemoglobin results were not significantly different between Phase 1 and 2. No adverse transfusion reactions occurred. In Phase 1, 213 units were crossmatched pre-operatively, but only 127 (60%) were transfused. In Phase 2, 117 units were requested and all transfused. The G & S only policy proved to be a safe and practical option which improved the efficiency and cost-effectiveness of blood ordering. Based on a handling charge of 37.50 Pounds per unit of blood by the Regional Transfusion Centre, an estimated annual saving of over 8000 Pounds can be made in our directorate.