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Biomedical subjects

R B Martin

Publications and source records attributed to R B Martin.

At least 109 records · Page 6Linked to original sources
PubMed1984

The effects of exercise on the bones of postmenopausal women.

The effects of walking and aerobic dancing on the bones of 73 recently postmenopausal women have been compared by photon absorptiometry of the distal radius with a control group who did not exercise. The period of observation was six months. Results showed that the control group and the walking group lost statistically significant amounts of bone mineral content (1.6%, and 1.7% respectively), but that the dancing group did not (0.8%). The control group did not show a significant increase in the bone width (0.9%), but both the dancing (1.3%) and walking (1.6%) groups did. Changes in the cross-sectional moment of inertia of the radius were estimated for each subject based on bone mineral content and bone width values. Both exercise groups experienced significant increases in this variable, while the control group did not. Plasma oestrogen levels were not influenced by exercise. The results support the hypothesis that mechanical loading due to exercise may be effective in preventing postmenopausal osteoporosis.

Biomechanical Phenomena↗
PubMed1984

Non-invasive measurement of long bone cross-sectional moment of inertia by photon absorptiometry.

The use of the Norland-Cameron Bone Mineral Analyzer (BMA) to measure the cross-sectional moment of inertia of the mineral in a long bone is described and data regarding the usefulness and precision of the method are presented. The correlation coefficients between BMA-measured CSMI and that obtained from cross-sectional geometry were 0.99 both for a series of aluminum tubes and five bones of different sizes. The BMA-measured CSMI was linearly correlated with the CSMI digitized from cross-sections of a series of human ulnas at the r = 0.92 and 0.95 level in the AP and ML directions, respectively. The BMA-measured CSMI also correlated well with the torsional and bending behavior of ulnar specimens. Finally, a method for estimation the CSMI of a long bone section from BMA readings of mineral content and bone width is described. A linear correlation of r = 0.98 with the CSMI digitized from sections of human radii is demonstrated.

Biomechanical Phenomena↗
PubMed1984

Finite element studies of some juxtarticular stress changes due to localized subchondral stiffening.

A finite element analysis was undertaken in concert with an animal model of mechanically-induced osteoarthritis. The numerical model was used to explore stress transmission anomalies associated with localized subchondral stiffening due to implantation of small cylindrical plugs immediately below the subchondral plate of sheep. The quasi-static, plane strain computational formulation included solution of the non-linear intra-articular contact problem, and was validated by comparison with a corresponding analytical solution and with the in vivo experimental results. The numerical results showed that stress aberrations due to metal implant insertion were felt most greatly in the bone immediately surrounding the implant, but that nominal compressive stress elevations up to about 50% could also be induced in the overlying deep hyaline cartilage layer. This localized cartilage stress elevation following the insertion of a metal plug could be seriously affected by a number of factors, including the positioning of the implant, variation in the area of intra-articular contact, or the elastic modulus of the cancellous bone and/or subchondral plate. Experimentally-observed fibrous encapsulation also reduced the cartilage stress elevation effect, but later bony remodelling and the development of a corticalized shell around the implant encapsulation served to re-elevate the local cartilage stresses.

Animals↗
PubMed1984

Architectural changes in the proximal femur following prosthetic insertion: preliminary observations of an animal model.

A study was made of the changes occurring in the proximal femur following unilateral total hip replacement in fourteen sheep. Implants were observed 0-12 months post-operatively. Contralateral implants inserted at sacrifice served as controls. The paired specimens were cut into five transverse sections and stereologically analyzed. The following phenomena were seen during the post-operative year: (a) calcar resorption; (b) encapsulation of the prosthetic cement in fibrous sheath; (c) interruption of the trabecular network between the cement-stem system and the cortex; (d) increase in the cross-sectional moment of inertia of the cortical shell. These changes form a consistent pattern of biological responses to the implant, the details of which are important because they suggest failure mechanisms and demonstrate the inadequacy of simple analytical models based on static pictures of the bone-implant composite structure. Failure modes may depend on the initial degree of bone-cement interdigitation. Concentric layers of fibrous tissue surrounded by layers of dense bone were formed where interdigitation was not extensive. Where interdigitation was maximal, a band of bony resorption separated the cement-bone complex from the endosteal trabecular bone. Increased levels of bone-cement interdigitation would not appear to influence the ultimate outcome, but, rather, only the mode of failure of the prosthetic attachment.

Animals↗
PubMed1983

Osteoarthrosis: sex-specific relationship to osteoporosis.

Examination of an Eskimo skeletal series demonstrated at least two etiologically distinct groups of joint deterioration divided along sex lines. Low bone mineral content (BMC) among women and high BMC among men were associated with osteoarthrosis on the tibial plateau. This finding contradicts conventional wisdom based on clinical observation, which suggests that reduced skeletal mass prevents osteoarthrosis.

Adult↗
PubMed1983

The effects of composition, structure and age on the torsional properties of the human radius.

A standard site in the distal shaft of the radius is commonly used to monitor the skeletal status of aging individuals by photon absorptiometry. Since the adjacent metaphysis of this bone is a common site for fractures, it is important to know whether bone mineral content (BMC) is a good indicator of mechanical integrity. In concert with previous studies, the BMC of the scan site declined significantly (p less than 0.005) with age in women but in men showed no change to age 90. In spite of the loss of BMC, there was no decrease in torsional rigidity in women. In men torsional rigidity increased significantly (p less than 0.05) with age even though BMC did not change. Thus, measurements of BMC alone do not adequately reflect the mechanical integrity of a clinically significant skeletal site, and assessment of skeletal health based on such criteria may be misleading.

Adolescent↗
PubMed1983

Lower extremity loads stimulate bone formation in the vertebral column: implications for osteoporosis.

Senile osteoporosis is a growing national health problem. The purpose of this study was to determine whether loads applied through the lower extremity would stimulate bone formation in the vertebral column, the site of most osteoporotic fractures. Female white New Zealand rabbits were divided into experimental (EG) and control (CG) groups. The right hind leg of the EG was repetitively loaded to 1.5 X body weight, 20 min/day for three weeks; the CG was "sham loaded". Bone formation in both groups was labeled using tetracycline. Labeled osteons, resorption spaces, surface bone formation, and porosity were measured in cross-sections from the right and left tibias and humeri, right femurs, and L6, L1, T12, T1, and C7 vertebrae. This experiment demonstrates that repetitive loading of the lower extremity increases osteonal bone formation in the vertebral column of rabbits extending at least up to the cervical spine, but not into the forelimbs. This finding supports the concept that exercise involving repetitive loading of the lower limbs (eg, walking) could be used to treat or prevent age-related osteoporotic changes in the vertebrae.

Aged↗
PubMed1982

Femoral mechanics in the lesser bushbaby (Galago senegalensis): structural adaptations to leaping in primates.

One method used to examine the relationship between behavioral strategies and anatomical adaptation is to study the results of mechanical stress associated with a given behavior and compare this with skeletal adaptations to other behaviors. This comparative approach is appropriate for highlighting combinations of features that are specializations to specific types of behavior. The purpose of this paper is to compare femoral mechanics in Galago senegalensis with previously collected data for macaques and humans as a basis for discussing structural adaptations in the primate hindlimb to leaping. The stiffness and load carrying capabilities of the femoral diaphyses of 27 G. senegalensis were analyzed using the SCADS computer program. The data suggest that the galago femur is well adapted to sustain large sagittal plane compressive loads rather than large bending loads. The straightness of the femoral shaft and large midshaft area moments of inertia prevent buckling from these large compressive loads. Calculations indicate that the ratio of critical buckling load to body weight in galago is 31 times that in macaques and 55 times that in humans. The femur of this saltatory primate is morphologically adapted to resist buckling when subjected to large compressive loads, while those of macaques and humans are better adapted to resist bending moments caused by ground reaction forces acting on the extended limb. The differences between galago on the one hand and macaques and humans on the other suggest that relatively smaller moments about the hip and relatively larger moments about the knee accompany more quadrupedal and bipedal walking, while habitual leaping is associated with relatively larger moments about the hip. These data reinforce the apparent similarity of the mechanical effects of quadrupedal and bipedal locomotion on the femur and dissimilarity with femoral mechanics in habitually saltatory primates.

Adaptation, Physiological↗
PubMed1982

A hypothetical mechanism for the stimulation of osteonal remodelling by fatigue damage.

This paper presents a theory describing mechanisms by which repetitive stress initiates remodelling in compact bone. The theory is based on the observation that the lamellar structure of osteons arrests and traps microcracks produced by cyclic loading. Debonding of an osteon by a crack may produce changes in the Haversian canal wall adjacent to the crack which initiate a new secondary osteon. The repair of damaged areas by secondary osteons prevents the accumulation of microdamage due to repetitive loading and protects compact bone from fatigue failure.

Biomechanical Phenomena↗
PubMed1981

Lanthanide probes in biological systems: characterization of luminescence excitation spectra of terbium complexes with proteins.

Upon irradiation in the ultraviolet region aromatic chromophores may transfer energy to a nearby Tb3+, which in turn emits a green phosphorescence. This paper reports the characterization of the ultraviolet excitation spectra of aromatic chromophores capable of transferring energy to Tb3+ by monitoring of the green Tb3+ emission in the 540-550 nm region. Results are included for complexes containing phenyl, hydroxyphenyl, indole, and catechol chromophores. Characteristic excitation spectra are presented for the aromatic chromophores occurring as side chains in proteins. Though it is preferable to compare entire excitation spectra, the ratio of intensities at 292 to 276 nm, R, is suggested as a useful diagnostic criterion. Numerical R valves are indicative of the following aromatic side chains as the energy donor to Tb3+: R less than 0.2, unionized tyrosine; R = 0.5 to 1.0, tryptophan; and R less than 1.8, ionized tyrosine. The phenylalanyl chromophore displays a definitive excitation spectrum at shorter wavelengths. For ovotransferrin R = 0.9 and comparison of the full excitation spectra suggests that it contains comparable contributions from both ionized tyrosine and tryptophan side chains. Some difficulties in obtaining reliable excitation spectra are described. An analysis of inner-filtering of incident light reveals that for an absorbance less than 0.8 the excitation spectrum is broadened and flattened compared to the absorption spectrum. At maximum absorbances greater than 0.8 false maxima may appear to both sides of a real maximum. Two spurious maxima in an excitation spectrum were generated in a Tb3+ complex and compared to the correct excitation spectrum of the same complex obtained at lower absorbance.

Animals↗