Biomedical subjects

D B Burr

Publications and source records attributed to D B Burr.

134 records · Page 8Linked to original sources

PubMed1977

Sexual dimorphism and mechanics of the human hip: a multivariate assessment.

The present research was undertaken to determine the effects of sexual dimorphism in the human pelvis and femur on the mechanics of human locomotion. The analysis was based on six biomechanical variables determined from 25 male and 32 female skeletal remains from the Dickson Mound site. Discriminant function analysis indicates that the mechanical variables which primarily contribute to dimorphism are the moment arm of the gluteus medius and the torque produced by the abductors at the hip. These mechanical aspects of hip function produce greater pressure on the femoral head in females.

Anthropometry↗

PubMedDate not supplied

Calculating the probability that microcracks initiate resorption spaces.

This paper explores the assumptions and limitations of the probability calculation that led to the conclusion by Burr et al. (1985) that microcracks initiate new remodeling events. It also corrects several minor errors in the calculation in the original manuscript. The results show that the probability that cracks and resorption spaces are associated depends heavily on a factor, F, that accounts for the possibility that some osteons that contain both a crack and a resorption space share a cement line with an adjacent osteon to which the crack more properly 'belongs.' F in turn depends on (1) the measurement criteria for cracks and resorption spaces, (2) the osteon population density in the bone, and (3) the mechanism by which cracks initiate remodeling. The theoretical maximum number of osteons that can contain both a crack and a resorption space (nmax) increases as the number of resorption spaces (r), the number of cracks (c), and F increase, but decreases as the osteon population density (d) increases. A larger nmax makes a direct association between cracks and resorption spaces more difficult to demonstrate experimentally.

Animals↗

PubMedDate not supplied

Basic biomechanical measurements of bone: a tutorial.

Although bone densitometry is often used as a surrogate to evaluate bone fragility, direct biomechanical testing of bone undoubtedly provides more information about mechanical integrity. Like any other specialized field, biomechanics contains its own techniques and vocabulary. This article serves as a guide to biomechanical principles and testing techniques for bone specimens.

Animals↗

PubMedDate not supplied

Increased intracortical remodeling following fatigue damage.

We previously demonstrated that microcracks occurred in common with resorption spaces more often than expected by chance, and proposed that fatigue damage initiates remodeling events. However, it was possible that cracks accumulated at sites of preexisting resorption spaces and did not initiate new remodeling. The goal of this work was to determine whether osteonal remodeling follows the accumulation of microcracks, as expected if microcracks are responsible for initiation of bone remodeling, or if it precedes microdamage accumulation. A three-point bending load was applied to the left limb of 13 dogs for 10,000 cycles at 2 Hz with 2500 microstrain on the cranial radial surface. The right limb was loaded in the same manner eight days later, and the dogs sacrificed immediately after the second loading episode. A nonloaded groups (n = 7) was used as an external control. Radii were strained en bloc for microdamage; parameters related to bone resorption, microdamage accumulation, and the association of damage and resorption were collected. The data demonstrate a significant increase in new remodeling events subsequent to the generation of microdamage. This temporal relationship between microcracks and resorption spaces is inconsistent with the hypothesis that cracks localize at sites of preexisting resorption spaces. This demonstrates that bone remodeling occurs preferentially in fatigue-damaged regions, and supports a direct cause and effect relationship between the initiation of microdamage in bone and its repair.

Animals↗

PubMedDate not supplied

[Synovial membrane and cartilage changes in an arthrosis model. Instability and impact stress model].

UNLABELLED: Surgical instability and repetitive impulsive loading was used to generate degenerative changes in knee joints of rabbits. Light- and electronmicroscopy was carried out at synovial membrane and cartilage samples. The instabilised joints had early synovial inflammation, preceding overall cartilage changes. Synoviocytes were activated and showed more and dilatated cytoplasmatic organells. Invaded round cells--potentially cartilage degenerative--were seen. In the loading model no initial synovial inflammation could be seen. Focal cartilage changes were located at the weight bearing zone. Two different inductive pathways may be involved in cartilage breakdown comparing the two arthrosis models. Mechanical factors seemed to trigger cartilage changes in the loading model, an inflammatory synovial pathway is likely to initiate cartilage breakdown in the instability model. CLINICAL RELEVANCE: The synovial membrane has the key-position for the cartilage degeneration in posttraumatic joint affections. The therapeutic use of antiphlogistic substances is indicated to supreme inflammatory mediators from the synovial membrane. This therapeutic concept seemed not to be useful in primary mechanical induced osteoarthrosis.

Animals↗

PubMedDate not supplied

Effect of fatiguing exercise on longitudinal bone strain as related to stress fracture in humans.

Muscular fatigue in the training athlete or military recruit has been hypothesized to cause increased bone strain that may contribute to the development of a stress fracture. Under normal circumstances, muscles exert a protective effect by contracting to reduce bending strains on cortical bone surfaces. In vivo strain studies in dogs show that muscle fatigue following strenuous exercise elevates bone strain and changes strain distribution. However, a similar experiment has yet to be performed in humans. The purpose of this work was to test the hypothesis in humans that strenuous fatiguing exercise causes an elevation in bone strain. It was also hypothesized that this elevation is greater in younger people than in older people due to the decline in muscle strength and endurance that normally occurs with age. To test these hypotheses, strain in the tibiae of seven human volunteers was measured during walking before and after a period of fatiguing exercise. Neither hypothesis was sustained. Post-hoc analysis of the strain data suggests that strain rate increases after fatigue with a greater increase in younger as opposed to older persons. Although not conclusive, this suggests that it is strain rate, rather than strain magnitude, that may be causal for stress fracture.

Adult↗

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Proprioception, gait kinematics, and rate of loading during walking: are they related?

The cyclic nature of walking can lead to repetitive stress and associated complications due to the rate of loading (ROL) experienced by the body at the initial contact of the foot with the ground. An individual's gait kinematics at initial contact has been suggested to give rise to the ROL, and a repetitive, high ROL may lead to several disorders, including osteoarthritis. Additionally, proprioception, the feedback signaling of limb position and movement, may play a role in how the foot strikes the ground and thus, the ROL. Our goal was to explore the relationship between proprioception, gait kinematics and ROL. Thirty-eight women were recruited for gait analysis, and the gait characteristics 50 ms prior to and at initial contact were examined. Two proprioception tests, joint angle reproduction and threshold to detect passive motion were used to examine the subject's proprioceptive acuity. Our results indicate that individuals with a larger knee angle (i.e., greater extension) 50 ms prior to initial contact (IC) experience a higher ROL during gait and have poorer proprioceptive scores. However, it remains unclear whether poor proprioception causes a high ROL or if a high ROL damages the mechanoreceptors involved in proprioception, but the apparent relationship is significant and warrants further investigation.

Adolescent↗

PubMedDate not supplied

Meniscal function and the importance of meniscal regeneration in preventing late medical compartment osteoarthrosis.

The medial meniscus was totally removed in 22 patients who were followed up for more than ten years. Preservation of the meniscal rims enhances regeneration. There was no evidence of medial compartment damage in 91% of the patients by arthroscopic examination at ten years' follow-up examination. This finding suggests that meniscal rim regeneration can protect the joint from osteoarthrotic changes. Late medial compartment osteoarthrosis following medial meniscectomy in an otherwise normal knee is probably avoidable if surgical and postoperative treatment are designed to enhance regeneration of the meniscal rim.

Adult↗