Gavriel Feuer

Prediction of point-of-failure in a high-energy femoral neck fracture model with finite element analysis: Are models supported by biomechanical evidence?

Vertical shear fracture models represent a new direction for analyzing fracture risk that has been understudied to date. Vertical shear fractures have not been thoroughly analyzed using finite element modeling, thus it is unclear whether these models can accurately predict the location of these fractures. This study showed that patient specific finite element modeling is able to accurately predict the location of fracture in a vertical shear model of the human femur.

Dynamic mechanical properties of human ribs

In order to characterise the mechanical behaviour of bones under various loading conditions, it is important to determine the effect of strain rate on the load carrying capacity and fracture behaviour of various members of our skeletal system. This study aims to understand the mechanical behaviour of human thoracic ribs through the application of a variety of strain rates. In this experiment, embalmed ribs were tested in a three-point bending mode under three different rates of deformation ranging from 0.05 to 8 mm/s. Mechanical parameters such as maximum bending moment, maximum deformation, bending stiffness and energy absorption capacity were determined. The maximum bending moment and stiffness showed an increase by 53% and 8%, respectively, at the highest rate of deformation compared to the lowest. The ultimate deformation and energy absorbed also increased by 26% and 66%, respectively, in this range of deformation rate. This data confirm that bone is viscoelastic in nature and exhibits different mechanical properties that are a function of strain rate.

Regional Variations in Shear Strength and Density of the Human Thoracic Vertebral Endplate and Trabecular Bone

Background Previous studies investigated the overall mechanical strength of the vertebral body; however, limited information is available on the biomechanical properties of different regions within the vertebral endplate and cancellous bone. In addition, the correlation between mechanical strength and various density measurements has not been studied yet. Methods Thoracic (T10) vertebrae were harvested from fifteen human cadaveric spines (average age: 77 years old). Twelve cylindrical cores of 7.2 mm (diameter) by 3.2 mm (height) were prepared from each vertebral body. Shear was produced using a stainless steel tubular blade and measured with a load cell from a mechanical testing machine. Optical and bulk densities were calculated before mechanical testing. Apparent, material, and ash densities were measured after testing. Results Material density and shear strength increased from anterior to lateral regions of both endplate and cancellous bone. Endplate shear strength was significantly lower in the anterior (0.52 ± 0.08 MPa) than in the lateral region (2.72 ± 0.59 MPa) (p=0.017). Trabecular bone maximum load carrying capacity was 5 times higher in the lateral (12 ± 2.74 N) (p=0.09) and 4.5 times higher in the central (10 ± 2.24 N) (p=0.2) than in the anterior (2 ± 0.60 N) regions. Mechanical strength positively correlated with ash density, and even moreso with material density. Conclusion Shear strength was the lowest at the anterior region and highest at the lateral region for both endplate and cancellous bone. Material density had the best correlation with mechanical strength. Newer spinal implants could optimize the loading in the lateral aspects of both endplate and cancellous bone to reduce the likelihood of screw loosening and the subsidence of disc replacement devices. This study was reviewed by the SUNY Downstate Medical Center IRB Committee; IRB#: 533603-2.

Influences of the vertebral endplate microvasculature on the development of degenerative disc diseases: A preliminary study

An average of 70% of all Americans will suffer from one episode of low back pain (LBP) in their lifetime [1]. Senescence of the avascular nucleus pulposus with decreased transport of nutrients is thought to lead to degenerative disc diseases (DDD) and low back pain [2-5]. We investigated the relationship between aging, cartilage endplate microvasculature, and the level of disc degeneration. Lumbar discs with adjacent endplates were harvested from three fresh young bovine and three embalmed human cadaveric spines. After tissue processing, histology, and staining, microscopic features of endplate vascular channels were visualized under light microscopy and measured using ImageJ. Our preliminary data showed a 15% decrease in the vascular channel count at the interface between subchondral bone and cartilage endplate from the bovine to the elderly human specimens. Moreover, we observed a 67% increase in endplate thickness and a 70% decrease in cross sectional vascular area in the human subjects.

Evaluation of contraction of packable dental composites using photoelasticity

A novel technique was developed to compare the effectiveness of restorative dental composite materials to avoid contracting after they are cured.

Shear Properties of Cancellous Bone from Osteoporotic Sheep Treated with Synthetic Bone Mineral

The aim of this study was to determine whether a calcium phosphate-based synthetic bone mineral (SBM) could increase bone strength by preventing bone loss induced by estrogen deficiency and accelerated by a combination of a low mineral diet plus corticosteroid injections in a large animal (ovine) model. Twenty-eight sheep were randomly allocated to four different groups: sham-operated, ovariectomy, SBM without fluoride (-F), and SBM with fluoride (+F). After eight months of treatment the sheep were sacrificed. There was a significant difference in the peak load, shear stress, stiffness, and density of the cancellous bone between the four different groups. Specifically, when the SBM with fluoride was compared to the ovariectomy group there was a significant improvement in peak load (p<;0.05), shear stress (p<;0.05), stiffness (p<;0.05), and density (p<;0.01) in the cancellous bone.

Effect of deformation rate on the flexural strength of human ribs

In order to characterize the mechanical behavior of bones under various loading conditions, it is important to determine the effect of strain rate on the load carrying capacity and fracture behavior of various members of our skeletal system. In this study we tested five groups of human rib samples at five different loading rates. The ultimate stress for the two groups tested at the highest deformation rates increased compared to groups tested at the lowest deformation rates as did the elastic modulus. Ultimate strain decreased between the group loaded at 0.4 mm/s compared to the group loaded at 50 mm/s. These data show bone to be viscoelastic in nature and its mechanical properties to change with a variation in the strain rate.

A non-contacting sensor to measure the stress wave generated magnetic field in bone: A preliminary study

Bone is piezoelectric in nature and therefore capable of transforming mechanical stress into an electric charge. These moving charged particles produce a magnetic field. A magnetic sensor may be able to detect this field and thus may provide a measure of the stress wave amplitude in the bone. Such a sensor can potentially measure the properties of bone in-vivo.

Effect of Strain Rate on the Bending Properties of Human Ribs

To fully characterize the mechanical behavior of bones under various loading conditions, it is important to determine the effect of strain rate on the load carrying capacit and fracture behavior of various members of our skeletal system. In this study embalmed human ribs were tested in a three-point bending mode under deformation rates of 0.05 mm/s, 0.5 mm/s, and 8 mm/s. Mechanical parameters such as maximum bending moment, maximum deformation, bending stiffness, and energy absorption capacity were determined. The maximum bending moment and stiffness showed an increase by 53 and 8 percent, respectively, at the highest rate of deformation compared to the lowest. The ultimate deformation and energy absorbed also increased by 26 and 66 per cent, respectively, in this range of deformation rate. This data confirms that bone is visco-elastic in nature and exhibits different mechanical properties that depend on the deformation rate.Copyright