Search PubMed⌕ Search

Biomedical subjects

D B Burr

Publications and source records attributed to D B Burr.

At least 127 records · Page 7Linked to original sources
PubMed1984

Effects of mechanical loading on the tissues of the rabbit knee.

We studied changes in subchondral bone and articular cartilage in an animal model of osteoarthrosis. In this model we applied repetitive impulsive loads to rabbits' knees. Their legs were held in short leg splints so the rabbits were unable to dampen the peak applied load with ankle flexion. After sacrifice, at 1 day to 6 weeks, we studied proximal tibial load-bearing cartilage histologically, biochemically, and with radioactive sulfate uptake. We also studied the subchondral bone under that cartilage histologically, histomorphometrically, with bone scan (99mTc pyrophosphate), and by tetracycline labeling. An increase in 99mTc labeling of the subchondral bone was the first reliable change observed. This was followed by an increase in tetracycline labeling, bone formation, and a decrease in porosity, which has been associated with relative stiffening of bone. Horizontal splitting and deep fibrillation of the overlying articular cartilage followed the early bone changes. All of these changes preceded changes in content and characterization of cartilage proteoglycans or increased chondrocyte activity as manifested by incorporation of radioactive sulfate. In this model the early bone changes preceded changes in the articular cartilage. The deep splitting of articular cartilage occurred prior to metabolic alteration of that tissue.

Animals↗
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

Hypothesis: joints can heal.

Although cartilage has a limited capacity for intrinsic repair, cells extrinsic to the cartilage can provide a mechanism for repair if the proper conditions exist. The new chondroid material produced, although not histologically or biochemically identical to mature hyaline articular cartilage, can nevertheless in many circumstances permit normal joint function and prevent further joint deterioration. The evidence suggests that joint healing results from establishing a source of cells, normalizing joint pressures, and encouraging joint motion. Much of the controversy surrounding the question of whether joints can heal results from a failure to view joint function, rather than cartilage appearance, as the most important component of the healing process, and to appreciate the significant role played by mechanical factors in promoting this response.

Cartilage, Articular↗
PubMed1984

Intracast muscle stimulation prevents bone and cartilage deterioration in cast-immobilized rabbits.

Tibial articular cartilage and the knee meniscus from cast-immobilized rabbits whose quadriceps were electrically stimulated for 17 days were compared with those from cast-immobilized rabbits without muscle stimulation. Cartilage from non-stimulated rabbits showed evidence of deep fibrillation and loss of Safranin O metachromasia. Scanning electron microscopy (SEM) showed large areas of cavitation and cartilage erosion. Cartilage from cast-immobilized muscle-stimulated rabbits demonstrated no fibrillation, pitting, or surface erosion at either the light microscopic or SEM levels. Electrical muscle stimulation prevented bone loss by significantly increasing bone turnover rate. These observations suggest that electrical muscle stimulation can prevent bone and cartilage deterioration in short-term cast-immobilized limbs.

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

How do trabeculae affect the calculation of structural properties of bone?

One difficulty that arises in an analysis of the cross-sectional properties of bone is whether to include the cancellous bone in the analysis. The purpose of this paper is to determine how different amounts of cancellous bone affect the measurement of structural properties of bone cross-sections. Thirty-two tibial and femoral cross-sections were chosen at random from a series of cross-sectioned nonhuman primate bones. Geometrical properties were calculated for the cross-sections, and torsional and bending stress analyses were performed. The results suggest that the effect of including cancellous bone in the analysis is closely related to the amount of bone, where it lies within the cross-section, and the type of analysis performed. Including cancellous bone in calculations of structural properties of bone cross-sections may cause the strength and stiffness of the bone to be exaggerated.

Animals↗
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

Measurement accuracy of proximal femoral geometry using biplanar radiography.

Experimental testing indicates that the neck-shaft angle of the proximal femur can be reliably measured from biplanar radiographs, but torsion cannot. Calculated torsion varies significantly from true torsion as a function of the error created by femoral rotation, while the calculated neck-shaft angle is invariant with respect to rotation even though the calculated neck-shaft angle is mathematically dependent on calculated torsion. Theoretical considerations support this finding and demonstrate for the first time why it is true. This study demonstrates that clinical measurements of frontal plane hip deformities using existing biplanar radiography are quite accurate, but clinical measurements of torsional abnormalities are unreliable. These errors can be minimized if investigators specify the angle of the lateral X-ray beam on the anteroposterior film using methods described in this paper and if patient position is radiographically verified. The magnitude and types of errors inherent in biplanar radiography should be considered in planning preoperative strategies and in postoperative assessments of hip geometry.

Femur↗
PubMed1979

Density variation in the humeral cortex of Macaca.

The purpose of this research was to describe patterns of density variation throughout the cortex of the humeral shaft in Macaca and to attempt to explain these variations in terms of the gross anatomy and mechanical function of the bone. One hundred ninety transverse sections were taken from five sites along the humeral diaphyses of 38 Macaca. The density at eight positions around each section was measured using radiographic and densitometric techniques. Analysis of variance indicated significant (p less than 0.02) differences among cross-sectional levels and positions within each level. No sexual dimorphism in density could be demonstrated, although sexual dimorphism in density has been reported for the femora of this same sample. This relationship between humerus and femur parallels that found in humans. Density increased distally in the humerus, probably due to major areas of muscle attachment. Comparison with similar data from the femur of Macaca indicated unexpected differences in density pattern which may underlie differences in the strength and mechanics of the upper and lower extremities.

Absorptiometry, Photon↗
PubMed1979

Patterns of variability in mineralization of the primate femoral diaphysis.

The purpose of this research was to study intra- and interspecific variability in mineral density in the femoral diaphysis of nonhuman primates. Four hundred five sections were taken from five sites along the femoral diaphysis of 34 macaques (Macaca sp.), 24 squirrel monkeys (Saimirisciureus), and 23 tamarins (Saguinus labiatus). The mineral density at eight positions around each section was measured. Analysis of variance indicated significant (p less than 0.05) interactions among species, sex, cross sectional levels, and positions within each level. Both Macaca and S. sciureus showed sexually dimorphic patterns of mineral distribution. S. labiatus exhibited no sexual dimorphism in distribution, but was sexually dimorphic in density magnitude. No significant dimensional differences in density were found among species, though significant differences in pattern were evident. Highly significant differences (p less than 0.01) were found among cross sectional levels and among positions within the levels within each species.

Absorptiometry, Photon↗
PubMed1979

Percentage ash content of nonhuman primate long limb bones.

Trotter and Hixon ('76) and Vose and Roach ('72) presented conflicting data about percentage ash content of the long limb bones of M. mulatta and M. nemestrina. The suggestion of Trotter and Hixon ('76) that this discrepancy was due to methods of preparing the bone prior to ashing, rather than to species differences, was tested using data collected by Gong ('72) on the volumetric composition of nonhuman primate bone. Masses of the various chemical fractions of bone reported by Gong ('72) were used to compute ash content as a percentage of total dry weight and ash content as a percentage of fat-free dry weight. Good agreement was found between ash content as a percentage of total dry weight and the data of Vose and Roach ('72); good agreement was also found between ash content as a percentage of fat-free dry weight and the data of Trotter and Hixon ('76). This suggests that the data of Vose and Roach ('72) conflict with those of Trotter and Hixon ('76) because Vose and Roach ('72) failed to defat the bones prior to ashing. No actual species differences exist in the ash content of bones of M. mulatta and M. nemestrina. The data of Trotter and Hixon ('76) are most likely a more adequate reflection of both the magnitude and the regional similarity of ash content in nonhuman primate bone.

Animals↗
PubMed1978

Etiological differences in patterns of psycholinguistic development of children of IQ 30 to 60.

We compared the psycholinguistic abilities of 131 mentally retarded children (IQs 30 to 60) of different etiological classifications (Down's syndrome, biologically brain damaged, environmentally caused retardation, unknown cause) and characterized each etiology according to the different patterns of psycholinguistic skills exhibited by the children. Level of skills was determined by the Illinois Test of Psycholinguistic Abilities, which was administered to each subject. Down's syndrome children exhibited significantly lower verbal-auditory skills than visual-motor skills. The environmentally caused retardation group showed no significant differences in development of psycholinguistic channels. Down's syndrome children had significantly lower verbal-auditory abilities than did the other etiological groups of severely retarded children. Etiological differences in the visual-motor channel were less marked.

Adolescent↗