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Biomedical subjects

R R Pelker

Publications and source records attributed to R R Pelker.

34 records · Page 2Linked to original sources
PubMed1986

Indium-111 platelet scintigraphy for the diagnosis of acute venous thrombosis.

Platelets labeled with indium-111 have been used successfully as a marker of active thrombosis in man. To establish the diagnostic accuracy of platelet scintigraphy in comparison to contrast venography in the diagnosis of acute lower limb venous thrombosis, we evaluated 103 consecutive patients divided into two groups. Platelets were labeled by the indium-111 oxine method. Patients from group I (n = 73, 56 had venograms) were asymptomatic and underwent platelet scintigraphy 1.1 +/- 0.6 days (mean +/- 1 SD) after a major orthopedic procedure. Patients from group II (n = 30, all had venograms) were symptomatic and underwent platelet scintigraphy 1.2 +/- 1.7 days after venography. In group II, 15 patients with positive findings on contrast venography were treated with intravenous heparin; five others with positive venograms did not receive heparin until platelet scintigraphy was completed. Both platelet scintigraphy and contrast venography were evaluated by two blinded observers. Only studies with blinded agreement of both platelet scintigraphy and contrast venography were included in the analysis. Sensitivity and specificity of platelet scintigraphy for the whole limb were 93% and 97% in group I and 42% and 67% in group II. The lower sensitivity in group II was most likely attributable to therapy with heparin. These results demonstrate that platelet scintigraphy, a test that permits imaging for up to five days after a single injection, correlates favorably with contrast venography in patients who have not received heparin and may be used as a surveillance test in high-risk patients. The role of platelet scintigraphy in acutely symptomatic patients requires further evaluation.

Aged↗
PubMed1985

Chemotherapy-induced alterations in the biomechanics of rat bone.

The effects of methotrexate and doxorubicin (Adriamycin) on intact and fractured bone were studied in a rat model. Methotrexate, 0.1 mg/kg i.p., was administered five times a week, or doxorubicin, 1 mg/kg i.v., was given once a week. Animals were killed and evaluated at 4, 8, 12, and 16 weeks after surgical production of a unilateral femoral osteotomy and initiation of the chemotherapeutic program. Both intact and fractured bones were tested to failure in rapid torsion, and the torque, angular deformation, stiffness, and energy were measured. There was a significant alteration in the strength of the healing osteotomies in doxorubicin- and methotrexate-treated animals compared with the control group. The torsional strength of intact bone was not significantly altered by either drug protocol over the period of this observation.

Animals↗
PubMed1985

Effects of short-term cyclosporin-A on biomechanical properties of intact and fractured bone in the rat.

Cyclosporin-A is a new immunosuppressant drug being used widely for solid organ transplantation. The systemic effects of Cyclosporin-A on the skeletal system have not previously been defined. This study examined the effects of Cyclosporin-A on biomechanical properties of intact bone and fracture repair in a rat model. Closed midshaft femoral fractures were produced over a preplaced intramedullary pin. Cyclosporin-A, dissolved in olive oil and administered by gavage, was begun the day following surgery and continued for 14 consecutive days at a dose known to prolong solid organ allograft survival in rats (7 mg/kg/day), and a second group of control animals received comparable volumes of plain olive oil under identical circumstances. Groups of both experimental and control animals were killed at 4, 8, 12, or 16 weeks following fracture, after which both intact and fractured femurs were tested to failure in torsion. As judged by torque, angular deformation, stiffness, and energy absorption, Cyclosporin-A did not significantly alter the biomechanical properties of fracture repair or intact bone turnover. Based on current biomechanical data, we can find no reason to discourage the short-term clinical use of Cyclosporin-A in patients with or without fractures. Histomorphometric studies are required to accurately assess the biologic effects of this drug on bone biology and to complete the analysis of skeletal toxicity.

Animals↗
PubMed1985

Effect of freezing on histologic and biomechanical failure patterns in the rabbit capital femoral growth plate.

Ten pairs of proximal femora were harvested from 8-week-old New Zealand white rabbits. Experimental shear fractures were then created in vitro, and load-displacement curves were recorded. One specimen from each animal was tested within 4 h of death, whereas the contralateral specimen was frozen for 10 to 20 days and thawed prior to testing. Histologic sections of the fractured specimens were studied. No statistically significant differences could be demonstrated between the fresh and the frozen/thawed specimens in either the histologic patterns or the shear load or stress to failure.

Analysis of Variance↗
PubMed1985

Wave propagation across a bony discontinuity simulating a healing fracture.

Stress wave propagation in a long bone with a progressively increasing defect in the bony cortex, simulating a healing fracture, was studied by recording the outputs of bonded semiconductor strain gages, proximal and distal to the defect. Statistically significant relations were found between the relative size of the discontinuity and the transmission coefficient, dispersion and transit time across the fracture. We also showed that the stress wave in a bone could be monitored from the vibration response of a traction pin, placed in a magnetic field. The results may be helpful for the development of new methods to measure the rate of fracture healing, as well as aiding our understanding of the dynamic loading of bone.

Femoral Fractures↗
PubMed1985

Dimensions of the rabbit femur during growth.

In the rabbit, the femur grew rapidly in length during the first 4 weeks of life of the animal. Growth continued at a slower rate up to 8 to 10 weeks of age and then reached a plateau. A similar growth pattern (rapid increase followed by a plateau) was seen for the dimensions of the femoral head, neck, and shaft. Significant growth differences between the left and right femurs did not occur.

Age Factors↗
PubMed1984

Effects of freezing and freeze-drying on the biomechanical properties of rat bone.

The effects of various preservation techniques on the biomechanical properties of bone have been investigated in a rat model. Freezing of the specimens to -20 degrees C, -70 degrees C, and -196 degrees C did not adversely affect the strength of long bones tested in torsion or of vertebral bodies tested in compression. Freeze-drying did not markedly affect the compression properties of the vertebral specimens; however, it did produce a significant deleterious reduction in the torsional strength of the long bones.

Animals↗
PubMed1984

Radiation-induced alterations of fracture healing biomechanics.

The effects of irradiation on the normal temporal progression of the physical properties of healing fractures were studied in a rat model. Fractures were surgically produced in the femur, stabilized with an intramedullary pin, and irradiated. One group of rats was exposed to 2,500 rads in divided doses over 2 weeks, beginning 3 days after fracture, and compared to a control group with fractures which were not irradiated. Animals were sacrificed at periodic intervals and the bones were tested to failure in torsion. The torque, stiffness, and energy increased and the angle decreased for the nonirradiated specimens in the expected fashion. This progression was deleteriously altered in the irradiated femurs.

Animals↗
PubMed1984

Biomechanical and histological correlations in growth plate failure.

An experimental model using immature bovine femora and tibiae was used to determine the varying patterns of failure in and around the physis when the direction of stress was varied. Compression, tension, shear, and torque were individually applied. The results showed that the histologic failure pattern did vary with each type of applied load. Compression resulted in failure in the zone of provisional calcification and the metaphysis rather than the previously hypothesized germinal zone. Tension loads caused failure in the upper zone of columnation. Failure in between the upper zone of columnation and lower zone of hypertrophy was caused by shear loads. Torque resulted in failure through all zones.

Animals↗
PubMed1984

Proximal femoral epiphysiolysis in the neonate.

Seven neonates with eight proximal femoral epiphysiolyses were reviewed. Pain elicited by leg motion was the common diagnostic finding in all. Radiography showed lateralization of the shaft similar to congenital hip dysplasia. However, the acetabular index was normal in all but one child. Arthrography confirmed the diagnosis, showing a located proximal femoral epiphysis and a laterally displaced, externally rotated proximal metaphysis. Treatment usually consisted of traction followed by abduction splinting. The long-term results were excellent in six fractures. Growth complications included angular deformation (bowing) in one patient and coxa vara due to localized premature epiphysiodesis in one patient. Duplication of the lesion in stillborn cadavers showed that the fracture was usually a type 1 physeal injury traversing the entire physis beneath both the capital femur and the greater trochanter. The periosteal sleeve was intact posteriorly and still attached to the proximal physis. However, in two instances there was comminution (rather than crushing) of the epiphysis, physis, and metaphysis medially, which might explain the residual varus deformation and premature growth arrest seen infrequently as complications of this particular proximal femoral injury. An experimental animal model also duplicated these morphologic observations.

Birth Injuries↗
PubMed1983

Stress wave propagation in bone.

The traveling wave characteristics for a single compressive pulse were studied in fresh and embalmed human long bones. The stress wave was generated by the longitudinal impact of a steel ball on one end of a bone and was monitored by bonded strain gages. The dynamic properties, namely velocity, attenuation coefficient and dispersion were correlated with the mineral density, porosity, and cross-sectional area of the specimens. Statistically significant relationships were found between several of these parameters. These stress wave propagation characteristics are important for our understanding of the dynamic loading of bone and they may also provide a basis for the development of noninvasive techniques for studies of diseased or fractured bone.

Bone and Bones↗
PubMed1983

Biomechanical properties of bone allografts.

The biomechanical properties of allograft bone can be altered by the methods chosen for its preservation and storage. These effects are minimal with deep-freezing or low-level radiation. Freeze-drying, however, markedly diminishes the torsional and bending strength of bone allografts but does not deleteriously affect the compressive or tensile strength. Irradiation of bone with more than 3.0 megarad or irradiation combined with freeze-drying appears to cause a significant reduction in breaking strength. These factors should be considered when choosing freeze-dried or irradiated allogeneic bone that will be subjected to significant loads following implantation.

Animals↗
PubMedDate not supplied

Shear fractures through the capital femoral physis of the skeletally immature rabbit.

Shear fractures were created through the capital femoral physes of rabbits 2, 4, 6, 10, and 14 weeks of age. Biomechanically, the load to complete failure (i.e., fracture) increased with maturation. The load to failure increased with increasing area of the capital femoral physis. The shear stress increased with age and then began to plateau at 10 weeks of age. Histologically, the zone of failure involved the columnar zone in the specimens from rabbits 2-6 weeks old, progressed to the junction of the columnar and hypertrophic zones in the specimens from 10-week-old rabbits, and occurred within the zone of hypertrophy in the specimens from 14-week-old rabbits. Fractures progressed from a type I physeal fracture in the specimens from rabbits 4-6 weeks old to a type II physeal/metaphyseal fracture in the specimens from older animals, with the metaphyseal fragment increasing in size with increasing chondroosseous maturation of the specimen.

Aging↗
PubMedDate not supplied

Histologic patterns of capital femoral growth plate fracture in the rabbit: the effect of shear direction.

Growth plate fractures were produced in vitro in the rabbit capital femoral physis by applying shear loading parallel to the physeal complex in four different directions. Load-displacement curves were recorded and histologic sections were prepared from each specimen. Different histologic patterns were observed with different directions of shear loading. The histologic level within the growth plate through which the fracture propagated varied with each specimen and with the different directions of shear loading. The "classical" pattern of failure through the hypertropic cellular zone of the physis was not uniformly seen. The mechanical patterns of failure also varied with the direction of shear loading. The shear strength of the physeal complex was significantly greater with anterior to posterior loading than with posterior to anterior loading. The possible factors contributing to this mechanical anisotropy are discussed, and the literature on related studies is reviewed.

Animals↗