Long-term zoledronic acid treatment increases bone structure and mechanical strength of long bones of ovariectomized adult rats.

Zoledronic acid (ZOL) is a highly potent heterocyclic bisphosphonate which has been shown to inhibit bone resorption in short-term experiments in young growing animals. In this investigation we have evaluated the effects of a 1-year administration to mature, ovariectomized (OVX) rats as a model for postmenopausal osteoporosis in order to elucidate (1) the temporal changes in urinary biochemical markers of bone turnover and femoral bone mineral density (BMD), (2) to measure changes of static and dynamic histomorphometric parameters and mechanical strength, and (3) to assess the preventive effects of chronic treatment with ZOL on these parameters. In urine, deoxypyridinoline increased after OVX and was significantly reduced by ZOL administration, indicative of a reduced bone collagen turnover. These changes were accompanied by alterations of tibial cancellous bone: trabecular bone volume and parameters of bone architecture were significantly augmented by ZOL and bone formation rates fell as a consequence of suppressed bone turnover, but were still measurable. No signs of "frozen bone" or osteomalacia could be detected. BMD of the whole femurs rose in sham-operated control animals (SHAM) during the entire experimental period, whereas in OVX animals, BMD plateaued after 32 weeks at a lower level. ZOL at a low dose (0.3 mg/kg/week s.c.) did not alter whole femur BMD, but at higher doses (1.5 and 7.5 mg/kg/week s.c.) BMD increased to the level of the SHAM group. A distinct pattern was noted for the distal quarter of the femur, a region rich in cancellous bone: BMD initially increased in all treatment groups except the OVX group, and at a later stage fell again at a comparable rate irrespective of treatment. Mechanical stability, as assessed by a 3-point bending test, was significantly increased by all doses of ZOL and exceeded OVX and sham-operated controls. The effects on mechanical properties were observed at a low dose which did not measurably increase femoral BMD after 1-year treatment. Multiregression analysis revealed a significant positive correlation between maximum load and BMD, and a significant negative correlation of maximum load with labeled perimeter, a marker of bone formation and turnover. No significant correlation was found with urinary deoxypyridinoline, a marker of bone resorption. The data show that mechanical testing detects improvements of functional bone quality following low dose bisphosphonate treatment which are not identified by standard DXA measurements of BMD.

Skeletal changes in the ovariectomised ewe and subsequent response to treatment with 17 beta oestradiol.

The ewe has been suggested as a suitable large animal model for assessment of therapeutic agents for the treatment of osteoporosis. In this study we asses the response of ewe bone mineral parameters, using dual energy x ray absorptiometry (DXA), after ovariectomy. Regular DXA analysis was performed over a period of 75 weeks followed by a period of dosing with 17 beta oestradiol. Total body bone mineral density (BMD) was reduced in ovariectomised animals 15 weeks post operatively. BMD remained lower than control animals for the entire pre dose period. Subsequently, dosing with 17 beta oestradiol prevented further loss of bone over a period of 38 weeks. Several complicating factors were noted during the study including seasonal BMD variation, a correlation between fat/lean ratio and total body BMD together with a reversible reduction in bone mineral content as a result of lactation. Also changes in BMD were associated with age at ovariectomy.

Mechanical implications of collagen fibre orientation in cortical bone of the equine radius.

Mechanical test specimens were prepared from the cranial and caudal cortices of radii from eight horses. These were subjected to destructive tests in either tension or compression. The ultimate stress, elastic modulus and energy absorbed to failure were calculated in either mode of loading. Analysis was performed on the specimens following mechanical testing to determine their density, mineral content, mineral density distribution and histological type. A novel technique was applied to sections from each specimen to quantify the predominant collagen fibre orientation of the bone near the plane of fracture. The collagen map for each bone studied was in agreement with the previously observed pattern of longitudinal orientation in the cranial cortex and more oblique to transverse collagen in the caudal cortex. Bone from the cranial cortex had a significantly higher ultimate tensile stress (UTS) than that from the caudal cortex (160 MPa vs 104 MPa; P < 0.001) though this trend was reversed in compression, the caudal cortex becoming relatively stronger (185 MPa vs 217 MPa; P < 0.01). Bone from the cranial cortex was significantly stiffer than that from the caudal cortex both in tension (22 GPa vs 15 GPa; P < 0.001) and compression (19 GPa vs 15 GPa; P < 0.01). Of all the histo-compositional variables studied, collagen fibre orientation was most closely correlated with mechanical properties, accounting for 71% of variation in ultimate tensile stress and 58% of variation in the elastic modulus. Mineral density and porosity were the only other variables to show any significant correlation with either UTS or elastic modulus. The variations in mechanical properties around the equine radius, which occur in close association with the different collagen fibre orientations, provide maximal safety factors in terms of ultimate stress, yet contribute to greater bending of the bone as it is loaded during locomotion, and thus lower safety factors through the higher strains this engenders.

The response of equine cortical bone to loading at strain rates experienced in vivo by the galloping horse.

The behaviour of cortical bone under load is strain rate-dependent, i.e. it is dependent on the rate at which the load is applied. This is particularly relevant in the galloping horse since the strain rates experienced by the bone are far in excess of those recorded for any other species. In this study the effect of strain rates between 0.0001 and 1 sec-1 on the mechanical properties of equine cortical bone were assessed. Initially, increasing strain rates resulted in increased mechanical properties. Beyond a critical value, however, further increases in strain rate resulted in lower strain to failure and energy absorbing capacity. This critical rate occurred around 0.1 sec-1 which is within the in vivo range for a galloping racehorse. Analysis of the stress-strain curves revealed a transition in the type of deformation at this point from pseudo-ductile to brittle. Bones undergoing brittle deformation are more likely to fail under load, leading to catastrophic fracture and destruction of the animal.

Pathway of ultrasound waves in the equine third metacarpal bone.

The velocity of ultrasound waves through bone has been used widely as a non-invasive method for assessing bone quality. Accurate measurement of velocity depends on accurate assessment of the distance travelled by the sound wave. It has been argued that the sonic pathway is deflected around the marrow cavity and so does not follow a straight line through the bone; therefore, correction factors have been developed to account for the extra distance travelled. This hypothesis was examined in vitro using sections from the equine third metacarpal bone. Two 1 MHz transducers used with the transmitting transducer energized by a 600 V electrical spike generator produced a 0.1 microsecond pulse width and the received signal was recorded on a delayed time-base oscilloscope, from which the velocity was calculated. Two distinct peaks were apparent in the received signal, corresponding to a direct cortical transmission wave and a direct medullary transmission wave. This observation was confirmed quantitatively using models of the third metacarpal made from homogeneous materials that allow accurate determination of the transit times of each component of the signal. Perspex was used to mimic cortical bone, with water as the mimic for the contents of the medullary canal; these materials were chosen because they have transmission velocities similar to the materials they were mimicking. The results confirmed that the pathway went straight through the bone with a time lag in the medullary wave due to the slower transmission velocity of the marrow. To ensure that the cortical wave is always received, transducers larger than the medullary width should always be used.

A contact method for the assessment of ultrasonic velocity and broadband attenuation in cortical and cancellous bone.

A portable system using a direct contact for the measurement of ultrasonic velocity and broadband attenuation in bone is described (contact ultrasonic bone analyser, CUBA). Soft-tissue compensation is performed using an ultrasonic pulse-echo technique. CUBA has been successfully validated using reference materials, the precision of velocity and broadband attenuation measurements being typically 0.2% and 0.5% respectively. The clinical reproducibility has been assessed on the equine third metacarpal bone. The reproducibility of velocity measurement is typically 0.5% for cortical bone and 1% for cancellous bone. For broadband attenuation the reproducibility is typically 7% for cortical bone and 6% for cancellous bone. The lower reproducibility of the attenuation data is attributed to the high sensitivity to variations in the material properties of bone with small changes in transducer positioning. Coupling difficulties through an intact equine coat have been overcome and the system may now be assessed in the clinical environment, in both human and animal populations.

Hardness, an indicator of the mechanical competence of cancellous bone.

Hardness and calcium content in compact bone are strongly related. Variation in Young's modulus is produced mainly by variations in mineralisation. Therefore, there should be a relationship between hardness and Young's modulus. We demonstrate this. The calcium content of cancellous bone and adjacent compact bone in several species shows little difference, the cancellous bone having approximately 10% less calcium. The hardness of cancellous bone in Bos is approximately 12% less than that of adjacent compact bone, and the calcium is approximately 2% less. These lines of evidence make it unlikely that the Young modulus of cancellous bone material is much different from that of compact bone. Similar evidence suggests that the yield stress of cancellous bone is similar to that of adjacent compact bone.

Can biosensors help to protect drinking water?

A large proportion of drinking water is abstracted for treatment from lowland rivers--about 30% in the UK--and this water is at particular risk from sudden and poisonous industrial or agricultural pollution. To cover the range of potential pollutants it may be possible to use biosensors as broadband monitors for toxins. The underlying assumption is that some biological processes, when challenged with a toxin, will be affected in a way analogous to that of man, and that therefore on-line scrutiny of such processes will provide early warning of substances liable to be detrimental to human health. Suitable processes for study might involve multi-cellular organisms, whole cells or enzymes. To date, most practical work has concentrated on fish, but enzymes and single cells hold out the promise of quicker response and, possibly, easier maintenance.

Medical student use of objectives in basic science and clinical instruction.

The purpose of this study was to investigate the long-term use of objectives by medical students who were experienced with objectives and immersed in a basic science and clinical curriculum referenced to objectives. The investigators examined: the extent to which medical students used objectives, the manner in which they used objectives as they progressed through the curriculum, and the factors that influenced their use of objectives. Questionnaires mailed to two classes of students yielded a 77 percent (n = 103) response rate. Students reported that objectives were essential early in the curriculum, but they became gradually less useful as the curriculum proceeded. The two factors showing most influence on the students' use of objectives were the relation of objectives to testing and the quality of the objectives. Curricular implications and questions to be addressed in future research were discussed.