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Biomedical subjects

D R Carter

Publications and source records attributed to D R Carter.

At least 145 records · Page 8Linked to original sources
PubMed1980

Distant metastases in head and neck epidermoid carcinoma.

Autopsy findings and case histories of 64 cases of epidermoid carcinoma of the head and neck at the Denver Veterans Administration Hospital between 1967 and 1977 were reviewed. Forty percent of these cases had metastases below the clavicles at autopsy. Incidence of metastasis was related to size of the primary lesion. Correlation with nodal involvement was equivocal. Our data was combined with that of similar studies done by O'Brien in 1970 and Gowen in 1963 and resulted in a combined autopsy series of 247 cases. Overall, 47% had distant metastases at autopsy.

Carcinoma, Squamous Cell↗
PubMed1980

Tensile fracture of cancellous bone.

Excised specimens of cancellous bone from human femora were subjected to compressive or tensile testing, and the resulting force-displacement curves were recorded. The relationships between bone strength and apparent density were similar for specimens tested in these two loading modes. The modulus of elasticity was also comparable for the tensile and compressive specimens. Specimens loaded in compression absorbed considerable energy after the initial fracture because of progressive impaction of the trabeculae. In the specimens loaded in tension, the fractured bone fragments separated and therefore absorbed little additional energy after the initial failure. The energy absorption capacity was thus significantly lower for the tensile specimens. The results of this study show that the primary difference in mechanical properties of cancellous bone tested in tension and compression is the energy absorption capacity. This finding suggests that tensile and avulsion fractures of cancellous bone observed clinically are associated with minimal energy absorption and therefore may be precipitated by relatively minor trauma.

Aged↗
PubMed1980

Problems associated with tibial fractures with intact fibulae.

Of twenty-three patients more than twenty years old who were treated for a tibial shaft fracture without a concomitant fibular fracture, six (26 per cent) had delayed union or non-union and six (26 per cent) had varus malunion of the fractured tibia. Pain and roentgenographic changes developed in the ipsilateral ankle within two years of injury in two of these six patients with malunion. Of forty-five patients less than twenty years old with similar fractures, one had delayed union and twelve (27 per cent) had varus malunion. Pain in the ipsilateral ankle was observed in two of these twelve patients with malunion. In addition, a bent fibula was observed in thirteen patients who incurred their fractures when they were less than twenty but in no patients who were more than twenty years old at the time of fracture. Clinical observations were corroborated by biomechanical studies on an experimental model. These studies suggested that when the fibula remains intact, a tibiofibular length discrepancy develops and causes altered strain patterns in the tibia and fibula. These may lead to delayed union, non-union, or malunion of the tibia with the sequelae of joint disturbances. The lower incidence of complications in patients less than twenty years old may be due to the greater compliance of their fibulae and soft tissues.

Adolescent↗
PubMed1977

The compressive behavior of bone as a two-phase porous structure.

Compression tests of human and bovine trabecular bone specimens with and without marrow in situ were conducted at strain rates of from 0.001 to 10.0 per second. A porous platen above the specimens allowed the escape of marrow during testing. The presence of marrow increased the strength, modulus, and energy absorption of specimens only at the highest strain rate of 10.0 per second. This enhancement of material properties at the highest strain rate was due primarily to the restricted viscous flow of marrow through the platen rather than the flow through the pores of the trabecular bone. In specimens without marrow, the strength was proportional to the square of the apparent density and the modulus was proportional to the cube of the apparent density. Both strength and modulus were approximately proportional to the strain rate raised to the 0.06 power. These power relationships, which were shown to hold for all bone in the skeleton, allow meaningful predictions of bone tissue strength and stiffness based on in vivo density measurements.

Animals↗
PubMed1977

Compact bone fatigue damage: a microscopic examination.

Flexural fatigue tests of bovine bone specimens produced fracture surfaces that were transverse on the tension side and oblique on the compression side. Similar fracture patterns were produced by bending tests with a single applied loading. Microscopic examination of flexural fatigue specimens prior to complete established that fatigue fracture is caused by the progressive accumulation of diffuse structural damage. The microdamage observed on the tension side consisted primarily of separation (or debonding) at cement lines and interlamellar cement bands. Tensile cracks in interstitial bone were also observed. The major damage modes on the compression side were oblique cracking and longitudinal splitting. The fatigue fracture patterns observed for the bone specimens correspond to the types of fatigue fractures observed clinically. Compact bone fatigue fractures in areas of longitudinal tensile stresses are generally seen as transverse lesions, whereas fatigue fractures in areas of longitudinal compressive stresses are normally oblique fractures. The diffuse nature of the observed fatigue damage is consistent with the hypothesis that microdamage caused by mechanical loading may serve as a stimulus for in vivo bone remodeling.

Animals↗
PubMed1976

Bone compressive strength: the influence of density and strain rate.

The compressive strength of bone is proportional to the square of the apparent density and to the strain rate raised to the 0.06 power. This relationship is applicable to trabecular and compact bone, and provides clinical guidelines for predicting bone strength on the basis of x-ray and densitometric examination.

Animals↗
PubMed1976

Postyield behavior of subchondral trabecular bone.

Cylindrical specimens of bovine subchondral trabecular bone were tested to uniaxial compressive strain levels of 75% to study energy absorption during pore collapse. Stress-strain curves were characterized by macroscopic yield at about 8% strain followed by a significant horizontal pore collapse regime. Energy absorption occurred largely in this postyield regime. Yield strength and energy absorption capacity were found to increase linearly with specimen apparent density. Microstructural analysis of the deformed specimens verfied that the mechanism for energy absorption was primarily fracture and buckling of trabeculae. The results suggest that during fracture, the collapse of trabecular bone (and the consequent absorption of energy) serves to attenuate stresses transmitted through the skeleton and thus protect vital structures such as the brain.

Animals↗
PubMedDate not supplied

Observations of convergence and uniqueness of node-based bone remodeling simulations.

Some investigators have indicated that mathematical theories and computational models of bone adaptation may not converge and that the density solutions from such simulations are dependent on the initial density distribution. In this study, two-dimensional finite element models were used to investigate the effect of initial density distribution on the final density distribution produced using a node-based bone remodeling simulation. The first model was a generic long bone, and the second was a proximal femur, For each model, we conducted time-dependent, node-based, linear rate-law bone remodeling simulations. Five initial density conditions were used with the generic long bone and three with the proximal femur. Remodeling simulations were performed, and the largest average nodal density differences at the end of the simulations were 0.000010 g/cm3 and 0.000006 g/cm3 for the generic long bone and proximal femur models, respectively. Results illustrate that, for a given set of loads and a given finite element model, the node-based bone adaptation algorithm can yield a unique density distribution. In conjunction with previous studies, this finding suggests that uniqueness of the density solution is dependent on both the mathematical theory and the computational implementation.

Algorithms↗
PubMedDate not supplied

Mechanobiologic influences in long bone cross-sectional growth.

We developed a computer model to simulate the interaction of biological and mechanobiological factors in the development of the cross-sectional morphology of long bones. The model incorporated a strong influence of biologically induced bone formation during early development. In addition, an assumed mechanical loading history during growth and development corresponding to age-related changes in body weight and muscle mass was applied. Based on the bone stress stimulus generated by the assumed loads, mechanically induced apposition and resorption rates were calculated at the periosteal and endosteal surfaces using a previously developed bone modeling theory. These methods successfully emulated the growth-related changes seen in long bone diaphyseal structure as well as changes observed in mature bones during aging. The simulations recreated the rapid increase in bone dimensions during development, stabilizing at maturity, and then the gradual, age-related subperiosteal expansion and cortical thinning. Throughout the growth, development, and aging simulations, the values of the bone radii, area, moments of inertia, and apposition rates corresponded well with measurements documented by other researchers.

Adaptation, Physiological↗