Biomedical subjects

D B Burr

Publications and source records attributed to D B Burr.

At least 109 records · Page 6Linked to original sources

PubMed1989

Structural adaptations of the femur and humerus to arboreal and terrestrial environments in three species of macaque.

One reason to measure cross-sectional structural properties of primate long bones is to define mechanically relevant complexes of traits that describe the adaptation of bone to different biomechanical environments. This can be effectively accomplished when congeneric species having different postural and locomotor behaviors are compared. This paper compares the cross-sectional geometry of the femur and humerus in three behaviorally different macaque species as a basis for defining such patterns. Cross-sectional moments of inertia in the standard anatomical planes were calculated at five locations along the diaphyses of the femur and humerus in Macaca fascicularis, M. nemestrina, and M. mulatta. The data suggest that the "barrel-shaped" femur is associated with behaviors for which long limbs and small body size are an asset. This may be associated with, but is not restricted to, leaping behaviors. The data also suggest that structural rigidity of the femur and humerus is greater per unit body weight in primates that spend significant amounts of time in terrestrial environments than in those that are more restricted to climbing in arboreal environments.

Analysis of Variance↗

PubMed1989

Mechanical and morphological effects of strain rate on fatigue of compact bone.

Compact bone specimens were cyclically loaded in uniaxial tension for one million cycles; loading was performed at either of two physiological strain rates (0.01 s-1 or 0.03 s-1) and a physiological strain range (0-1200 microstrain). Microdamage in loaded and nonloaded control specimens was then assessed histomorphometrically. Fatigue, evidence by stiffness loss, was observed at both strain rates and was significantly greater in specimens loaded at the high experimental strain rate than in specimens loaded at the low strain rate. Morphologically, this fatigue corresponded to increased numbers of microcracks in the bone. These data show that fatigue and resultant microdamage are realistic expectations of cyclic loading within the physiological strain range. The rate at which strains are developed influences the fatigue behavior of compact bone, suggesting that cyclic loading at high physiological strain rates, characteristic of vigorous activities, is more damaging to compact bone than loading at lower physiological strain rates.

Animals↗

PubMed1989

The effects of altered strain environments on bone tissue kinetics.

This study defines the alteration in bone tissue kinetics responsible for the "adaptive remodeling" response to altered strain environments. Adult beagle dogs were separated into three experimental groups: ulnar osteotomy, ulnar osteotomy with fracture fixation plate spanning the gap and sham surgery. Four sets of double fluorochrome labels were administered. Prior to sacrifice at 1, 3, and 6 months, strains were measured through rosette strain gages on the cranial and caudal surfaces of the intact radius. Histomorphometric analysis indicated that the increased bone mass in response to elevated strain results from increased activation frequency of modeling with more sites undergoing formation processes than resorption processes on periosteal and endocortical surfaces. Increased remodeling activation did not lead to increased bone mass. There was no evidence that elevated strain changes the individual vigor of osteoclasts or osteoblasts, or that the sigma period was altered by elevated strain.

Adaptation, Physiological↗

PubMed1989

Skeletal change in response to altered strain environments: is woven bone a response to elevated strain?

Studies demonstrate that geometric changes in bone architecture in response to altered mechanical strain occur through the formation of woven bone. The goal of this study was to test the hypothesis that these changes are partly the result of surgical manipulation rather than a true adaptive response to altered strain. Beagle dogs were subjected to either an ulnar osteotomy, an osteotomy with plate fixation, or sham operation. Strains on the radius were measured just prior to sacrifice 1, 3 or 6 months after surgery. Our results support the idea that woven bone can be a normal response to an abnormal strain environment if the mechanical challenge is intense enough; that elevated mechanical strains can cause the endocortical bone envelope to revert to a state of net formation; and that "adaptive remodeling" in adults in response to a change in mechanical strain may be a special case of modeling in which resorption is not required prior to formation at a particular skeletal site.

Adaptation, Physiological↗

PubMed1989

Bone growth and remodeling in Cayo Santiago--derived Macaca mulatta.

This paper examines similarities between rhesus macaques and humans in growth and remodeling of the long bones of the extremities. Cross-sectional moments of inertia were measured in three locations of the femur, humerus and tibia of M. mulatta using photon absorptiometry. Differences between males and females were evaluated with respect to age and weight. Remodeling was assessed from histologic sections at the same locations. Sex differences in structural properties of the long bones occur only at mid-diaphysis. Differences reflect the greater need for powerful hindlimb propulsion in males. The growth rate in males is twice as fast as that in females. Several periods of growth acceleration were detected in both males and females. Intracortical remodeling in growing macaques is relatively slow and may be more like that in elderly humans than that in growing children.

Academies and Institutes↗

PubMed1988

Synovial membrane and cartilage changes in experimental osteoarthrosis.

The Hulth instability model was performed on 25 rabbit knee joints. Electron-microscopic, light-microscopic, and histomorphometric data demonstrated consistent chondrocyte alterations and cartilage destruction. The comparison between operated, sham, and control knees shows that surgical intervention without surgically induced instability is followed by changes in the synovial membrane and cartilage. The cartilage destruction is preceded by a synovial reaction, suggesting that the inflammatory response has an important role in the onset of cartilage damage in this model. The damage was more severe in the experimental knees, suggesting that mechanical instability is also a factor in cartilage destruction.

Animals↗

PubMed1988

Composition of the cement line and its possible mechanical role as a local interface in human compact bone.

Human compact bone may be viewed as a fiber reinforced composite material in which the secondary osteons act as the fiber reinforcements. The cement line, which is the interface between the 'fibers' (osteons) and extraosteonal bone matrix, may impart important mechanical properties to compact bone. The nature of these properties is not known partly because the composition of the cement line is unknown. This analysis examines the constituents of the osteon cement line using scanning electron microscopy and X-ray microprobe analysis to address its biomechanical functions as a local interface. The analysis suggests that the cement line is a region of reduced mineralization which may contain sulfated mucosubstances. This composition is consistent with the hypothesis that the cement line provides a relatively ductile interface with surrounding bone matrix, and that it provides the point specific stiffness differences, poor 'fiber'-matrix bonding and energy transfer qualities required to promote crack initiation but slow crack growth in compact bone.

Adult↗

PubMed1988

Stiffness of compact bone: effects of porosity and density.

Stiffness of compact bone is found to be highly and nonlinearly dependent on its porosity, its complement, bone volume fraction and apparent density. Elastic modulus decreases as a power (0.55) of increasing porosity and increases both as a power of increasing bone tissue volume (10.92) and increasing apparent density (7.4). These data indicate that small changes in the amount or density of compact bone tissue exert a more pronounced influence on its stiffness than would similar changes in trabecular bone.

Animals↗

PubMed1988

[Arthrotomy--a prearthrotic factor?].

UNLABELLED: Light-microscopic and electron microscopic findings of the synovial membrane and cartilage were compared, of rabbit knee joints on which arthrotomy and surgical induced instabilisation operation were performed. The joint opening was followed by an inflammation of the synovial membrane, and cartilage changes were similar in joints of arthrotomy and surgically induced instability. CLINICAL RELEVANCE: To prevent joints from further damage after arthrotomy or arthroscopy, joints should be spared from weight bearing during the time of synovial inflammation.

Animals↗

PubMed1987

Morphology of the osteonal cement line in human bone.

While current consensus suggests the absence of collagen in osteonal cement lines, the extent of cement line mineralization and the nature of the ground substance within the cement line are unclear. Samples of human radius were examined by using scanning electron microscopy, electron microprobe, and histochemical techniques. X-ray intensities were used to compare the amount of calcium, phosphorus, and sulfur in cement lines with amounts in surrounding lamellar bone. The results indicate that cement lines contain significantly less calcium and phosphorus, but significantly more sulfur, than surrounding bone matrix. The Ca/P ratio of cement lines was significantly greater than that of lamellar bone, suggesting that the mineral in cement lines may not be in the form of mature hydroxyapatite. No selective staining of the cement lines could be demonstrated by using periodic acid-Schiff, Sudan black B, or alcian blue critical electrolyte concentration techniques.

Adult↗

PubMed1987

Early vascular changes in rabbit subchondral bone after repetitive impulsive loading.

The sequence of vascular and bony changes that precedes experimental osteoarthrosis was observed in rabbits. The subchondral bone underlying the weight-bearing portion of the medial tibial condyle and the talocalcaneal joint were examined after two, three, and six weeks of 50-ms and 500-ms repetitive loading at 1 Hz for 40 minutes each day. Vascular alterations were evident in the subchondral bone of the talocalcaneal joint after three weeks of a 50-ms load regime. A 10% increase in bone mass and a significant increase in the number of small diameter vessels were observed after six weeks. No changes were observed in the tibial subchondral bone, consistent with the measured attenuation of load distal to this joint. No changes were observed in either tibial or calcaneal subchondral bone in the 500-ms load group. Impulsive loading promotes early vascular changes in subchondral bone, which are developed in response to both the magnitude and the rate of loading.

Animals↗

PubMed1986

Comparison of joint degeneration models. Surgical instability and repetitive impulsive loading.

We used surgical instability and repetitive impulsive loading in rabbits to initiate degenerative changes in knee joints. Synovial membrane and cartilage samples were examined by light and electron microscopy. Early synovial inflammation at three days postoperatively preceded cartilage destruction in the instability model. Synovial inflammation was only apparent after eight weeks in the loading model and increased subsequently to cartilage destruction. Cartilage breakdown was focal and limited to the weight-bearing area. Comparison of the histological data of the two arthrosis models suggests that different inductive mechanisms may be involved in cartilage degeneration, but in both models the inflammatory changes appeared to be secondary to mechanical factors.

Animals↗

PubMed1985

Cortical bone maintenance and geometry of the tibia in prehistoric children from Nubia's Batn el Hajar.

The relationship between advancing age in adults and patterns of cortical bone maintenance has been extensively documented for archaeological populations (Dewey, et al., 1969; Van Gerven et al., 1969; Perzigian, 1973). Most recently, this research has been expanded to include a more thorough consideration of the geometric properties of bone in relationship to adult age changes (Martin and Atkinsin, 1977; Ruff and Hayes, 1983). To date, however, few studies have documented subadult patterns of cortical bone maintenance in archaeological populations and none have incorporated the relationship between patterns of cortical bone loss and gain and the changing geometric properties of growing bone. Using a sample of 172 tibias from children excavated from the Medieval Christian site of Kulubnarti, located in Nubia's Batn el Hajar, the present research examines the relationship between percent cortical area, bone mineral content, and cross-sectional moments of inertia. Among these children, bone mineral content increases steadily from birth in spite of a reduction in percent cortical area during early and late childhood. It appears, therefore, that tissue quality of the bone is not adversely affected by the reduction. Furthermore, the reduction in percent cortical area in later childhood corresponds to a dramatic increase in bending strength measured by cross-sectional moments of inertia. Thus, whether this cortical reduction is due entirely or in part to either normal modeling or nutritional stress, the tissue and organ quality of the bone is not adversely affected.

Aging↗

PubMed1985

Effects of age and sex on the amount and distribution of mineral in Eskimo tibiae.

The bone mineral content (BMC), bone width, and cross-sectional moment of inertia (CSMI) of 141 Alaskan Eskimo tibias were measured using photon absorptiometry. The effects of age and sex on the bones' structural properties were studied. It was found that in women, BMC decreased by 50% between the third and sixth decades, but that of the males did not decline significantly with age. This was true of the CSMI as well, for bending in both the anteroposterior (AP) and mediolateral (ML) planes. This result is different than that in some other prehistoric native American populations, where tibia CSMI increases with age in both sexes. The CSMI values were significantly higher in men than in women. Also, in men the AP CSMI was 55% larger than the ML CSMI; in women this difference was only 25%, and declined with age. Since the tibia is preferentially loaded in the AP plane by locomotor activities, the platycnemic differences between the sexes may reflect sex-related differences in activity which become more pronounced with age. The non-destructive method for obtaining data on the cross-sectional geometry of dry bones which is described here may be useful in studying other archaeological collections.

Adult↗

PubMed1985

Bone remodeling in response to in vivo fatigue microdamage.

It has been suggested that osteonal remodeling is triggered by bone microdamage. The validity of this theory rests on the assumption that loading within the physiological range will produce substantial microdamage with relatively few load cycles. The object of the first experiment was to determine threshold values required to consistently produce fatigue microdamage in vivo. The left forelimb of five groups of dogs, characterized by different strain levels and different numbers of load cycles, were loaded in three point bending. The number of microscopic fields which contained some microdamage was calculated as a percentage of the total number of fields. This experiment indicated that loads producing strains as low as 1500 microstrain on the radius and 1400 microstrain on the ulna for 10,000 cycles will produce significant bone microdamage. A second experiment was performed to verify this threshold and to determine whether microcracks are associated with the initiation of bone remodeling. Procedures in this experiment were the same as those in the first, except that all dogs were loaded in such a way as to produce strains on the radius of 1500 microstrain for 10,000 cycles, and the dogs were sacrificed 1-4 days after loading. The loaded limb demonstrated significantly more microdamage than the control limb (p = 0.03). Moreover, we observed 44 times as many microcracks in association with resorption spaces as expected by chance alone. These data support the hypothesis that fatigue microdamage is a significant factor in the initiation of intracortical bone remodeling.

Animals↗

PubMed1985

Structural and mechanical indicators of limb specialization in primates.

The structural mechanics of femora and humeri from primates representing a wide spectrum of habitual locomotor activities were examined to determine how cross-sectional properties vary with functional specializations of the extremities. Average bending rigidities of the midshaft of humerus and femur were measured in 60 individuals of four nonhuman primate species (Macaca nemestrina, Macaca fascicularis, Presbytis cristata, Hylobates lar) using single-beam photon absorptiometry. Linear regression analyses of the loge transformed data were used to assess the relative usage of the forelimb and hindlimb in propulsion and weight bearing, and to evaluate deviations from generalized mammalian quadrupedalism. The results suggest that average bending rigidities of the humerus and femur in primates reflect the extent to which the forelimb and hindlimb are used differently in locomotion; deviations of average bending rigidity from geometric similarity indicate functional variations from generalized mammalian quadrupedalism and the ratio of humeral to femoral bending rigidity can be used to identify trends towards hindlimb or forelimb dominance in locomotion and can be employed in general to determine how the limb was used.

Animals↗

PubMed1984

Graduate education and the role of the physical anthropologist in biomedical teaching and research.

There is a place for the physical anthropologist in biomedical teaching and research because of the special and unique skills possessed by this individual. However, eventual success in the health sciences environment requires the student to obtain the knowledge and background for functionally oriented teaching and research. Students interested in a biomedical teaching and research career must prepare themselves methodologically and theoretically. This requires: (1) teaching qualifications, (2) an increased emphasis on methodology and technology, (3) an increased emphasis on research and experimental design, (4) appropriate interdisciplinary courses which provide the background for both teaching and research, (5) increased interaction with graduate faculty active in research, and (6) the latitude to adapt the graduate program to meet these specific needs. Students who finish their graduate training with a marketable skill, and who can apply their unique talents to a specialized area, will have broad appeal in the job market and will considerably strengthen their career opportunities.

Anthropology, Physical↗

PubMed1984

Primate cortical bone microstructure: relationship to locomotion.

Mechanical factors are implicated in the control of osteonal (Haversian) remodeling. Twenty primate species, representing a diverse range of locomotor behaviors, have been examined to determine whether the arrangement of secondary osteonal bone at femoral mid-diaphysis reflects behaviorally related biomechanical influences. The proportion of bone cortex occupied by secondary osteons (percent osteonal bone) is related to the biomechanical environment of these femora. Percent osteonal bone delineates groups which correspond to other skeletal and kinesiological categorizations of primate locomotion and distinguishes among arboreal quadrupedal, terrestrial quadrupedal, suspensory, and bipedal primates.

Animals↗