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Biomedical subjects

J A Buckwalter

Publications and source records attributed to J A Buckwalter.

At least 19 recordsLinked to original sources
PubMed1992

The microstructural tensile properties and biochemical composition of the bovine distal femoral growth plate.

The tensile properties of distal femoral growth plates from 12-month-old cows were determined on uniformly prepared straight bone-growth plate-bone specimens (7 x 7 mm2 in cross-section) from predetermined anatomical sites on the physis. Each specimen was distracted to failure using a computer-controlled servo-hydraulic testing machine at a strain rate of 0.004 s-1. It was found that the exponential constitutive law, using finite deformation formulation for strain, provides an excellent description of the stress-strain behavior of all the specimens up to the point of failure. The ultimate stress and both tangent moduli (i.e., the toe region tangent modulus and the tangent modulus calculated at 75% of ultimate strain) varied with anatomical site. The anterior region was the strongest, followed by the posterior/lateral. The anterior and posterior/lateral regions were also the stiffest, whereas the posterior/medial and center regions were the weakest and most compliant. The bone-growth plate-bone specimen exhibited a low ultimate strain (13.8% +/- 6%) that did not vary significantly throughout the growth plate. This result suggests that disruption of the physis may occur in vivo even at the lower distractions currently recommended for the clinical chondrodiatasis procedure for leg lengthening. The biochemical composition of the growth plate in the anatomical regions correlated well with the tensile properties. There was a greater collagen content in the regions that were the stiffest and strongest. The gross morphology of the growth plate of the bovine distal femur is also described in this study. There is a regular pattern to the undulations of the physis at several dimensional levels. Histologic findings showed that orientation of the hypertrophic cell columns and transphyseal septa are aligned nearly parallel to the longitudinal axis of the diaphyseal shaft. This column orientation is not affected by the undulation of the primary contour of the physis, which at certain locations may be inclined as much as 60 degrees relative to the diaphyseal axis. The orientation of the hypertrophic cell columns appears to be one of the dominant microstructural features influencing the tensile behavior of the bone-growth plate-bone specimens.

Animals↗
PubMed1992

Occult sacral fractures in osteopenic patients.

The presentation, diagnosis, and treatment of occult sacral fractures in seventeen osteopenic patients were reviewed. Sixteen of the seventeen patients were elderly women, and the fracture usually occurred without trauma (fourteen patients). In ten patients, the sacral fracture was associated with a fracture of the pubic ramus. The sacral fractures were difficult to diagnose because nine patients also had a history of a malignant lesion of the pelvis with or without radiation treatment. Computed tomography and bone-scanning were diagnostic in all patients, but magnetic resonance imaging was not specific. Use of crutches or a walker, a reduction in activity, and use of non-narcotic analgesics allowed for the resolution of symptoms in all twelve patients who did not have mitigating conditions and permitted these patients to walk independently.

Adult↗
PubMed1991

Interspecies comparisons of in situ intrinsic mechanical properties of distal femoral cartilage.

We measured the in situ biomechanical properties of knee joint cartilage from five species (bovine, canine, human, monkey, and rabbit) to examine the biomechanical relevance of animal models of human knee joint injuries and osteoarthritis. In situ biphasic creep indentation experiments were performed to simultaneously determine all three intrinsic material coefficients (aggregate modulus, Poisson's ratio, and permeability) of the cartilage as represented by the linear KLM biphasic model. In addition, we also assessed the effects of load bearing on these intrinsic properties at "high" and "low" weight-bearing regions on the distal femur. Our results indicate that significant differences exist in some of these material properties among species and sites. The aggregate modulus of the anterior patellar groove within each species is the lowest among all sites tested, and the permeability of the patellar groove cartilage is the highest and does not vary among species. Similarly, the Poison's ratio in the patellar groove is the lowest in all species, except in the rabbit. These results lead to the conclusion that patellar groove cartilage can undergo greater and faster compression. Thus, under high compressive loads, the cartilage of the patellar groove surface can more rapidly compress to create a congruent patellofemoral joint articulation. For any given location, no differences were found in the aggregate modulus among all the species, and no correlation was found between aggregate modulus and thickness at the test site. Thus, in the process of selecting a suitable experimental animal model of human articular cartilage, it is essential to consider the significant interspecies differences of the mechanical properties.

Analysis of Variance↗
PubMed1991

Effects of osteochondral defect size on cartilage contact stress.

Contact stress distributions were studied in vitro for 13 dog knees, with full-thickness osteochondral defects drilled in the weight-bearing area of both femoral condyles. Diameters of the circular defects were concentrically enlarged from 1 to 7 mm. Digitally-imaged Fuji film was used to record cartilage contact stress distribution on femoral condyles for each increment of defect diameter. All specimens showed at least some tendency for contact stress concentration at the rim of the defects. However, detailed distributions had large interspecimen variability and, within a given specimen, contact stress distributions became progressively more nonuniform around the defect rim as the diameter was enlarged. Averaged over the full series of 26 condyles, circumferential mean cartilage contact stress around the defect rim was only moderately higher (by 10-30%) than intact surface's peak local contact stress [series average = 6.2 mega pascals (MPa)]. Maximal rim stress concentration occurred for 2 mm defects, there being a consistent trend toward mild rim stress decrease with further defect enlargement. Such modest contact stress elevations, per se, are probably insufficient to inhibit defect repair or to cause degeneration of surrounding cartilage. However, near the defect rim (for all diameters), the radial component of the gradient of contact stress (i.e., radial-direction variation of contact stress) was consistently elevated by an order of magnitude above that for intact, condyle articular cartilage.

Animals↗
PubMed1991

Magnetic resonance imaging of myxoid containing tumors.

Myxoid tissue forms part of many benign and malignant soft-tissue tumors. The advent of percutaneous needle biopsy has made it important to be aware of the diagnostic implications of biopsy samples containing myxoid tissue. To determine whether the magnetic resonance imaging (MRI) characteristics could help establish the diagnosis, we compared the MR images of 11 tumors containing myxoid tissue with the resected tumor tissue. In our small series of these rare tumors, the MRI characteristics allowed differentiation of intramuscular myxomas from malignant neoplasms containing myxoid tissue. Intramuscular myxomas meet the following conditions: (a) they are well circumscribed; (b) they arise within muscle; (c) T1-weighted images demonstrate uniform, decreased signal intensity; (d) T2-weighted images demonstrate uniform increased signal intensity; (e) contrast-enhanced images exhibit an inhomogeneous increase in signal intensity. If any of these conditions is not met, then a malignancy containing myxoid tissue should be suspected.

Adult↗
PubMed1991

Experimental studies on repair of large osteochondral defects at a high weight bearing area of the knee joint: a tissue engineering study.

There is a vast clinical need for the development of an animal model to study the fundamentals of healing of injured or diseased diarthrodial joints (knee, hip, shoulder, wrist, etc). Current prosthetic replacements do not offer acceptable treatment for injuries and diseases of these joints in young active individuals. New clinical treatment modalities, based on sound biologic principles, are sought for the development of repair or healing tissues engineered to have similar biomechanical properties as normal articular cartilage. In this paper we present a brief review of this need, and propose a grafting procedure which may lead to a successful animal model for studies of long term repair of major osteochondral defects. This grafting procedure uses an autologous periosteum-bone graft or an autologous-synthetic bone replacement graft. We have applied these grafts for in vivo repair of large surgically created defects in the high weight bearing area of the distal femoral condyle of mature New Zealand white rabbits. Further, an interdisciplinary study, including histochemistry, biochemistry (composition and metabolic activities), and biomechanics (biphasic properties), was performed to assess the feasibility of our animal model to generate viable repair tissues. We found our grafting procedure produced, 8 weeks postoperatively, tissues which were very similar to those found in normal articular cartilage. However, our histological studies indicate incomplete bonding between the repair tissue and the adjacent cartilage, and lack of an appropriate superficial zone at the articular surface. These deficiencies may cause long term failure of the repair tissue. Further studies must be undertaken to enhance development of a strong bond and a collagen-rich surface zone. This may require the use of growth factors (e.g., transforming growth factors beta) capable of simulating extra collagen production, or the use of serum derived tissue glue for bonding. At present, we are pursuing these studies.

Animals↗
PubMed1991

Is there a link between fluoridated water and osteosarcoma?

To test the hypothesis that fluoride is a risk factor for osteosarcoma, a case control study compared the complete residential fluoride histories of osteosarcoma patients with matched hospital-based controls. Fluoridation was not found to be a risk factor for osteosarcoma in the study population. The trend in the data from this small sample study suggests the hypothesis that a protective effect may exist against the formation of osteosarcoma for individuals consuming fluoridated water.

Adolescent↗
PubMed1990

Calcium pyrophosphate dihydrate crystal deposition patterns in the triangular fibrocartilage complex.

To define the patterns of calcium pyrophosphate dihydrate (CPPD) crystal deposition in the triangular fibrocartilage complex (TFCC), we examined the wrists of five adult, fresh-frozen cadavers using light and scanning electron microscopy and the wrist radiographs of 10 patients with a clinical diagnosis of CPPD disease. The radiographs consistently showed mineral deposits near or on the proximal and distal surfaces of the radial half of the TFCC. Light and electron microscopy showed that CPPD crystals formed distinct clusters sharply demarcated from uninvolved fibrocartilage. The density of crystal packing within clusters varied with the sharpness of demarcation of the clusters from the surrounding tissue. TFCC defects were consistently found in the vicinity of CPPD crystals, and degeneration of the articular cartilage on the ulnar half of the proximal surface of the lunate was associated with CPPD crystal deposition in the radial half of the TFCC. These observations suggest that degenerative tears of the TFCC and degeneration of the articular cartilage of the lunate are associated with CPPD crystal deposits in the TFCC.

Adult↗
PubMed1989

Articular cartilage and intervertebral disc proteoglycans differ in structure: an electron microscopic study.

Articular cartilage and the intervertebral disc tissues have different material and biological properties and different patterns of aging and degeneration. To determine if the proteoglycans of these tissues differ in structure, we used the electron microscopic monolayer technique to compare baboon articular cartilage proteoglycans with baboon annulus fibrosus, transition zone, and nucleus pulposus proteoglycans. Intervertebral disc and articular cartilage proteoglycans differed significantly. Articular cartilage contained large proteoglycan aggregates formed from hyaluronic acid central filaments, multiple monomers, and large nonaggregated monomers. These molecules were identical to those of nasal cartilage, growth plate cartilage, chondrosarcomas, or menisci. In contrast, the intervertebral disc tissues contained only nonaggregated proteoglycan monomers and clusters of monomers without apparent central filaments. Intervertebral disc nonaggregated monomers were shorter and more variable in length than those from articular cartilage, and nucleus pulposus nonaggregated monomers were even shorter and more variable in length than transition zone and annulus fibrosus monomers. These observations suggest that significant differences in proteoglycan metabolism exist between articular cartilage and intervertebral disc.

Animals↗
PubMed1989

Leak after vertical banded gastroplasty.

We have reported the case of a morbidly obese patient who became gravely ill during the first day after vertical banded gastroplasty. The diagnosis of a leak from the stomach was established by a Gastrografin swallow, and ten additional operations were done before the patient was discharged on the 135th postoperative day.

Adult↗
PubMed1989

A posterior surgical approach to the proximal part of the humerus.

At least eight centimeters of the posterior aspect of the proximal region of the humeral diaphyseal cortex can be exposed through the interval between the lateral head of the triceps and the deltoid muscle. No nerves or major blood vessels are exposed in the dissection, although care must be taken to protect the axillary and radial nerves during the exposure. The safety of this approach was confirmed in fourteen upper extremities of seven adult cadavera, and it was used successfully for an excisional biopsy of an osteoid-osteoma in the proximal third of the posterior part of the humeral cortex of an eleven-year-old boy.

Cadaver↗
PubMed1988

Electron microscopic studies of cartilage proteoglycans.

Proteoglycans, molecules consisting of glycosaminoglycan chains bound to protein, form a significant part of the cartilage extracellular matrix. Biochemical and biophysical methods describe the average composition and physical properties of these polydispense molecules. Electron microscopy reveals the structure and dimensions of individual proteoglycans. Examination of individual molecules can confirm or challenge concepts of their structure developed from studies of their chemical composition and physical properties, and may suggest new directions for biochemical investigation. Electron microscopy has confirmed that cartilage proteoglycans exist on two levels of organization: monomers consisting of central protein core filaments with attached glycosaminoglycan chains and aggregates consisting of central hyaluronate filaments with multiple attached monomers. Most aggregated monomers have a thin segment which attaches to the hyaluronate filament and probably represents primarily the keratan sulfate rich region of the protein core, and a peripheral thick segment that represents the chondroitin sulfate rich region and in some monomers part of the keratan sulfate rich region. Proteoglycans vary considerably in size, charge and composition. Direct visualization of proteoglycan aggregates and nonaggregated monomers has helped explain the structural basis of this polydispensity. Monomers vary in protein core length, number of glycosaminoglycan chains and length of the glycosaminoglycan chains. Aggregates vary in hyaluronate filament length, spacing between monomers, number of monomers per aggregate, and aggregated monomer length. In most populations of aggregates, from most tissues, variability in the number of monomers per aggregate produces most of the difference in aggregate size. Link proteins, small proteins that bind to monomers and hyaluronate, help determine aggregate size and the proportion of monomers that aggregate. Experiments in vitro show that link protein can increase aggregate size four fold, make the spacing between aggregated monomers more regular and increase the proportion of monomers that aggregate ten fold. With increasing age, cartilage proteoglycan monomers become shorter, more variable in length, have shorter chondroitin sulfate chain clusters and have a shorter thin segment which may result from an increase in keratan sulfate content. Study of monomers newly synthesized by calf and steer chondrocytes suggests that the age related changes in monomer structure result largely from changes in proteoglycan synthesis or intracellular processing. Aggregates also change with age. They become shorter, have fewer monomers per aggregate and have shorter aggregated monomers. In addition, the proportion of monomers that aggregate decreases. These age related changes in proteoglycan aggregation may result from a decreasing concentration of functional link protein or from accumulation of fragments of the protein core containing the hyaluronic acid binding region.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1988

Leaks occurring after gastric bariatric operations.

A leak from the stomach is the most serious complication that occurs after a gastric bariatric operation. The experience with 19 leaks that occurred after 791 gastric bariatric operations performed at North Carolina Memorial Hospital from 1975 to 1986 is described. The incidence of leaks was higher (8.3%) after a second than after a first gastric bariatric operation (2.0%). Ten leaks were life threatening and nine were not. There were no deaths. The diagnosis was made on the basis of Gastrografin swallow in seven patients, clinical findings in six, oral dye studies in three, barium study, a sinogram, and operation in one patient each. Thirteen of 16 patients were operated on within 4 hours of the diagnosis of a leak. One patient with a life-threatening leak and two with non-life-threatening leaks were managed without operations. Three patients were discharged after uncomplicated courses and readmitted, and the diagnosis of a leak was established. To minimize morbidity and mortality related to a leak, it is imperative to (1) recognize that a leak can occur after any gastric bariatric operation, (2) perform a Gastrografin swallow when a leak is suspected, and (3) operate on the patient if the Gastrografin swallow is positive or if the clinical findings suggest a leak.

Adult↗
PubMed1987

Electron microscopic analysis of articular cartilage proteoglycan degradation by growth plate enzymes.

To assess the effect of intracellular growth plate chondrocyte enzymes on proteoglycan structure, we examined enzyme-treated articular cartilage proteoglycans and untreated articular cartilage proteoglycans with the electron microscopic monolayer technique. The untreated proteoglycan monomers ranged in length from less than 20 nm to more than 700 nm, with a mean length of 224.5 +/- 101.6 nm in one experiment and 224.6 +/- 95.7 nm in a second experiment. Incubation with growth plate enzymes reduced proteoglycan monomers to fragments with lengths that varied from less than 5 nm to 143 nm, increased the variability in monomer length, and destroyed proteoglycan aggregates. The enzyme treated monomers had an average length of 29.5 +/- 17.9 nm in one experiment and 35.2 +/- 17.0 nm in a second experiment. The smallest common fragments were 15 nm long and would be expected to contain about 15 glycosaminoglycan chains. This experiment demonstrates that enzymes extracted from growth plate chondrocytes can degrade the chondroitin sulfate-rich region of proteoglycan monomer core proteins, produce a range of monomer fragment sizes with less than 2% of the fragments shorter than 5 nm or longer than 100 nm, increase the variability in monomer length, and degrade proteoglycan aggregates.

Animals↗
PubMed1987

Differences in matrix vesicle concentration among growth plate zones.

We studied the proximal tibial growth plates of 15-day-old mice to determine if matrix vesicle concentration varies among growth plate zones or between the pericellular and territorial matrix compartment and the interterritorial matrix compartment. Growth plates were examined by electron microscopy and divided into five zones: reserve zone (RZ), upper proliferative zone (UPZ), lower proliferative zone (LPZ), upper hypertrophic zone (UHZ), and lower hypertrophic zone (LHZ) which included the calcifying zone. We measured the diameter and volume fraction of matrix vesicles and calculated their numerical density and volume per cell and number per cell in the pericellular and territorial matrix and in the interterritorial matrix of each zone. In the pericellular and territorial matrix compartment, the matrix vesicle concentration progressively decreased from the RZ to the LHZ. Changes in matrix vesicle concentration in the interterritorial matrix followed a different pattern. Between the RZ and the UPZ, matrix vesicle numerical density declined slightly and then increased to peak values in the LPZ and UHZ, followed by a decline between the UHZ and the LHZ. These changes in matrix vesicle concentration paralleled previously reported changes in intramitochondrial calcium content, suggesting that matrix vesicle production in growth plate may be related to intracellular calcium concentration. The existence of the maximum concentration of matrix vesicles in the LPZ and UHZ longitudinal septa which do not mineralize followed by a decline in matrix vesicle concentration in the LHZ longitudinal septa which mineralize suggests that a high concentration of matrix vesicles may be needed to prepare the matrix for mineralization or to initiate mineralization and that matrix vesicles are depleted during mineralization.

Animals↗