A method for patient-specific evaluation of vertebral cancellous bone strength: in vitro validation.

BACKGROUND: In the context of osteoporosis, important determinants of the fracture risk are the apparent strength and stiffness of cancellous bone, as well as its brittleness and energy absorption capacity. Standard medical imaging, however, cannot measure these mechanical properties directly. Consequently, an estimation of the risk for fracture is made by correlating relative density or mineral density at a skeletal site with statistics of fracture occurrence, which provides limited and partial indications on fracture risks. A better method for evaluating the patient-specific mechanical properties of cancellous bone is therefore required. METHODS: In order to asses the mechanical properties of vertebral cancellous bone, we developed a finite element parametric model of lattice trabecular architecture that, in the future, will be suitable for use with bone imaging modalities. The model inputs are apparent morphological parameters (trabecular thickness and trabecular separation) and the bone mineral density. We conducted uniaxial compression tests on 36 canine vertebral cancellous bone specimens (C7 and L1) to validate model predictions of strength and stiffness in vitro. FINDINGS: Predictions of strength and stiffness matched the experimental results within relative absolute errors of 17.7% and 12.8%, respectively (average of differences between model-predicted and measured values, divided by the average of measured values). We also employed the model for evaluation of strength and stiffness of human L1 and L5 vertebrae and found mean strength of 1.67 MPa (confidence interval 0.42 MPa) and mean elastic modulus of 190 MPa (confidence interval 50 MPa), which are well within the range of previously reported apparent strength and stiffness properties. INTERPRETATION: The present model can be used to improve medical imaging-based evaluation of the spine in osteoporotic individuals by providing more specific information on the individual bone's susceptibility to fracture once clinical bone scans will be able to provide more reliable measures of trabecular thickness and separation.

How to select the elastic modulus for cancellous bone in patient-specific continuum models of the spine.

Patient-specific finite element (FE) modelling is a promising technology that is expected to support clinical assessment of the spine in the near future. To allow rapid, robust and economic patient-specific modelling of the whole spine or of large spine segments, it is practicable to consider vertebral cancellous bone in the spine as a continuum material, but the elastic modulus of that continuum material must reflect the quality of the individual vertebral bone. A numerical parametric model of lattice trabecular architecture has been developed for determining the apparent elastic modulus of cancellous bone Ecb in vertebrae. The model inputs were apparent morphological parameters (trabecular thickness TbTh and trabecular separation TbSp) and the bone mineral density (BMD), which can all be measured in vivo, using the spatial resolution of current clinical quantitative computed tomography (QCT) commercial whole-body scanners. The model predicted that Ecb values between 30 and 110 MPa represent normal morphology and BMD of human spinal cancellous bone. The present Ecb to TbTh, TbSp and BMD relationships pave the way for automatic generation of patient-specific continuum FE spine models that consider the individual's osteoporotic or other degenerative condition of cancellous bone.

Different malaria control activities in an area of Liberia--effects on malariometric parameters.

The epidemiology of malaria was studied in a West African mining town (Yekepa) and three surrounding zones defined as Close, Middle and Far areas. Malariometric parameters were investigated in children two to nine years of age at the end of the rainy season. In Yekepa, vector control measures and intense suppression of malaria with drugs had created an almost hypoendemic situation with a spleen rate of 11%. In Close area, vector control was applied to some extent and malaria drugs were frequently used for treatment; the spleen rate was 40%. In Middle area, a mobile clinic provided sporadic malaria treatment to small children, but the clinic did not reach out to Far area. The spleen rates were 95 and 99%, respectively. Three species of Plasmodium were found in all areas. The prevalences in Far area were P. falciparum 82%, P. malariae 39% and P. ovale 9%. The crude parasite rates increased from 13% in Yekepa to 92% in Far area, whereas haematocrit levels decreased from 37.6 to 35.2, respectively. Plasmodium falciparum seropositivity, as measured by indirect immunofluorescence, was 74% in Yekepa and 99% in Middle and Far areas. Total IgG concentrations ranged from 18 g1(-1) in Yekepa to 33 g1(-1) in Far area. Three main anopheline species were found in the zones outside Yekepa. Their relative frequencies in Far area were Anopheles funestus 45%, A. hancocki 37%, and A. gambiae 18%. The local inoculation rates gradually increased outwards from Yekepa from less than 0.01 to 0.17 inoculations per man and night at the beginning of the dry season.(ABSTRACT TRUNCATED AT 250 WORDS)