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J Aronson

Publications and source records attributed to J Aronson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Sustained proliferation accompanies distraction osteogenesis in the rat.

These studies were conducted to compare the local cellular proliferation patterns in the rat tibia during distraction osteogenesis with those during nondistracted fracture healing. Bone specimens from distraction osteogenesis and nondistracted fracture groups were analyzed 2, 10, and 20 days after surgery. Proliferation was determined by metabolic labeling with [3H]thymidine and by immunocytochemistry with an antibody to proliferating cell nuclear antigen. Videomicroscopy was used to count the cells staining positively within specified regions. The number of cells incorporating [3H]thymidine was positively correlated (r2 = 0.78) with the number of proliferating cell nuclear antigen positive cells on alternating serial slides. At day 2, the latter cells were largely confined to the bone marrow and periosteum in both groups, and the cell numbers per mm2 were also equivalent. At days 10 and 20, the proliferating cell nuclear antigen positive cells predominated in both the proximal and distal primary matrix front zones in the distraction osteogenesis group. In contrast, the proliferating cell nuclear antigen positive cells in the nondistracted fracture group were scattered throughout the healing area. Significantly more of these cells were in the primary matrix front zones than in any location within the nondistracted fracture-healing area. The number of these cells in the bone marrow adjacent to the surgical area declined from day 2 to day 10 in both groups. The results suggest that (a) proliferating cell nuclear antigen immunostaining is a reliable indicator of cycling cells; (b) by day 10, distraction osteogenesis is characterized by a zone-specific pattern of proliferating cells; and (c) distraction osteogenesis prolongs the stimulation of proliferation within the gap after fracture.

Animals↗
PubMed1997

Working conditions in home care: negotiating race and class boundaries in gendered work.

Home care work in metropolitan areas is a source of employment for immigrant women of color. Service work of this type intertwines domestic and caring labor in ways that reinforce the historically gendered and racialized nature of the work. Such macro level economic and political issues are played out at the micro level of daily service provided within elderly clients' homes. A study of these processes in home care work was carried out in urban southern Ontario in two nonprofit home care agencies. In-depth interviews and focus groups held with visible minority home care workers suggested that workers deal daily with racist attitudes and behaviors from clients and their families; agencies recognize these oppressive processes but usually handle them on a case-by-case basis through supervisors; and home care workers handle racism on the job as they do in their off-work hours-by avoidance, situating incidents within an analysis of the circumstances of elderly clients, setting boundaries on discussions, and occasionally, confrontation.

Adult↗
PubMed1996

Role of portal region lysine residues in electrostatic interactions between heart fatty acid binding protein and phospholipid membranes.

The structure of heart fatty acid binding protein (HFABP) is a flattened beta-barrel comprising 10 antiparallel beta-sheets capped by two alpha-helical segments. The helical cap region is hypothesized to behave as a portal "lid" for the entry and release of ligand from the binding pocket. The transfer of fatty acid from HFABP is thought to occur via effective collisional interactions with membranes, and these interactions are enhanced when transfer is to membranes of net negative charge, thus implying that specific basic residues on the surface of HFABP may govern the transfer process [Wootan, M. G., & Storch, J. (1994) J. Biol. Chem. 269, 10517-10523]. To directly examine the role of charged lysine residues on the HFABP surface in specific interactions with membranes, chemical modification and selective mutagenesis of HFABP were used. All surface lysine residues were neutralized by acetylation of recombinant HFABP with acetic anhydride. In addition, seven mutant HFABPs were generated that resulted in charge alterations in five distinct sites of HFABP. Modification of the protein did not significantly alter the structural or ligand binding properties of HFABP, as assessed by circular dichroism, fluorescence quantum yield, and ligand binding analyses. By using a resonance energy transfer assay, transfer of 2-(9-anthroyloxy)palmitate (2AP) from acetylated HFABP to membranes was significantly slower than transfer from native HFABP. In addition, in distinct contrast to transfer from native protein, the 2AP transfer rate from acetylated HFABP was not increased to acceptor membranes of increased negative charge. Transfer of 2AP from HFABP mutants involving K22, located on alpha-helix I (alpha-I) of the helical cap region, was 3-fold slower than transfer from wild-type protein, whereas rates from a mutant involving the K59 residue, located on the beta 2-turn of the barrel near the helical cap, were 2-fold faster than those of wild type. A double mutant involving K22 and K59 resulted in transfer rates identical to those of wild type, indicating that at least two domains are involved in determining the overall rate of ligand transfer. In addition, 2AP transfer rates from HFABP mutated at position 22 were totally unaffected by the charge characteristics of acceptor membranes, in marked contrast to wild type and other members of the mutant series. Further, by introducing a positive charge to alpha-helix II (alpha-II) of the helical cap region, 2AP transfer rates increased by 4-fold and properties of HFABP transfer began to approach those seen for AFABP, another member of the FABP family thought to transfer ligand via collisional interactions with membranes, which has a lysine residue in the alpha-II helix. These studies demonstrate that the helical cap region of HFABP may play an important role in governing ionic interactions between binding protein and membranes.

Acetylation↗
PubMed1996

The impact of total enteral nutrition on distraction osteogenesis in a rat model.

Limb lengthening by gradual mechanical distraction, termed distraction osteogenesis (DO), results in new bone formation. We have developed a rat tibial model for DO and have proceeded to study the effects of nutrition on this process. We have combined the intragastric diet delivery system of total enteral nutrition (TEN) with DO in the rat model. The first study was designed to address the weight loss associated with DO in dogs and patients. Rats in the chow + DO group lost 10% body weight over the 20-day distraction period but gradually gained weight back to the preoperative level by the end of the 5th week of the bone consolidation period. In contrast, in the TEN + DO group, a weight gain was recorded during the 20-day distraction phase. A second study was conducted to determine the effects of TEN on the rate and histology of regenerate bone formation. The weight changes replicated those seen in the first study. Standardized radiographs, taken on day 20, revealed increases (p < 0.003) in regenerate bone formation in the TEN group when compared with the chow group. Increased numbers of osteoclasts in the TEN group may indicate an accelerated entry into the remodeling phase of consolidation. Serum IGF-I values, taken at day 20, did not differ between the groups. These results demonstrate that the nutritional support dramatically increased the mineralized bone formed over the 20-day distraction period.

Animals↗
PubMed1996

The torsional basis for slipped capital femoral epiphysis.

Fifteen moderate to severe acute slipped capital femoral epiphyses were manipulated in 15 patients to correct significant deformities; in each case, torsion played a critical role in the reduction. Nine of 15 patients with acute slips underwent controlled, open reduction from the anterolateral approach, stabilizing the epiphysis while the metaphysis was internally rotated, flexed, and abducted; none had osteonecrosis or chondrolysis. The other 6 acute slips were treated with traction using internal rotation to achieve closed reduction; 2 of these 6 closed reductions progressed to osteonecrosis, and both were reduced in an uncontrolled situation. Of the 15 acute slips, 6 involved torsion as the primary force. Based on the importance of torsion in all the reductions and the prevalence of torsion as an etiologic factor in the initial slips, it is postulated that torsion is an important contributing component in the etiology of slipped capital femoral epiphysis. Despite 2 cases of osteonecrosis in unstable hips, these 15 manipulative reductions were 87% successful. If the 2 inadvertent closed reductions are eliminated, then the success rate is 100%.

Child↗
PubMed1995

Stereotype threat and the intellectual test performance of African Americans.

Stereotype threat is being at risk of confirming, as self-characteristic, a negative stereotype about one's group. Studies 1 and 2 varied the stereotype vulnerability of Black participants taking a difficult verbal test by varying whether or not their performance was ostensibly diagnostic of ability, and thus, whether or not they were at risk of fulfilling the racial stereotype about their intellectual ability. Reflecting the pressure of this vulnerability, Blacks underperformed in relation to Whites in the ability-diagnostic condition but not in the nondiagnostic condition (with Scholastic Aptitude Tests controlled). Study 3 validated that ability-diagnosticity cognitively activated the racial stereotype in these participants and motivated them not to conform to it, or to be judged by it. Study 4 showed that mere salience of the stereotype could impair Blacks' performance even when the test was not ability diagnostic. The role of stereotype vulnerability in the standardized test performance of ability-stigmatized groups is discussed.

Black or African American↗
PubMed1994

Fractures in children.

The literature published in the past year on fractures in children has helped us to increase our understanding of the natural history of fracture healing in children and introduced new techniques for fracture treatment. There is an impetus for operative fixation of femur fractures in children. The possibility is raised of growth derangement as a result of intramedullary nailing. Supracondylar fractures of the elbow continue to be a frequent topic for discussion. The benefits of adequate reduction and internal fixation have been reinforced. The incidence of nerve palsy, especially that of the anterior interosseous nerve, has been emphasized. New radiographic parameters for determining intraoperative reduction have been described. The management of radial neck fracture has been improved with percutaneous reduction proposed as an alternative to complication-fraught open reduction. New information has been brought to the forefront regarding knee injuries, in particular the implications of hemarthrosis and tibial eminence fractures. Biodegradable implants have become important as they prove to be useful in children's fracture management. Such implants have been shown to be useful in fractures that do not require rigid fixation. However, biodegradable devices may be associated with foreign body reactions.

Child↗
PubMed1994

Skeletal infections in children.

Bacteremia is an almost daily occurrence in childhood. Fortunately, infections in children are usually easily controlled and seldom produce serious sequelae. The prompt diagnosis and treatment of osteomyelitis is especially important to prevent catastrophic complications. Recent articles have pointed out that fine-needle aspiration may be diagnostic in only about 60% of children with acute hematogenous osteomyelitis and have suggested that other diagnostic modalities, such as white-cell scintigraphy, ultrasound, and computed tomography, may be more sensitive. Recent recommendations about treatment of osteomyelitis included a comparison of antibiotic agents, a discussion of follow-up evaluation modalities, and a warning that the clinical effects of osteomyelitis may not be apparent until years after the infection has been successfully treated. Two articles noted the increase in the incidence of septic arthritis in children who are HIV-positive and another described a chlamydial-associated syndrome of arthritis and eye involvement. The increased incidence of HIV infections also was cited by three studies as a factor in the increased incidence of tuberculosis infections in children and in the increased risk of extrapulmonary involvement.

Adolescent↗
PubMed1994

Experimental and clinical experience with distraction osteogenesis.

G.A. Ilizarov's clinical insights and experimental biology have developed into what is known today as distraction osteogenesis. Initially used for the treatment of fractures and nonunions, his methods have proven successful for limb lengthening and bone transportation. A brief history of the development of distraction osteogenesis, definition of terms, methods, and monitoring techniques are described. The primary mechanism, intramembranous ossification, is direct bone formation in uniform gradients of mineralization from a central fibrous interzone. New bone is produced from the local host surfaces and quickly remodels to the equivalent macro and microstructure. Blood supply at the focus of distraction, dependency on a latency period, different rates, and rhythms of distraction are all tested and discussed. Data from experimental tibial lengthening in more than 125 animals (dogs, rabbits, and rats) show that distraction osteogenesis provides unlimited new bone formation that remodels at daily rates ranging from 200 to 400 microns. In over 100 clinical cases, patients ranging in age from 18 months to 49 years have regenerated bone at an average rate of 213 microns in adults and 385 microns in children. Approximately 10% of these cases required supplemental bone grafts. The article proposes that distraction osteogenesis might be successfully applied in craniofacial surgery.

Adolescent↗
PubMed1994

Temporal and spatial increases in blood flow during distraction osteogenesis.

Ten adult mongrel dogs underwent left tibial lengthening at the proximal metaphysis. They were divided into three groups on the basis of distraction period: 14, 28, and 56 days. Quantitative technetium scintigraphy was used to measure regional blood flow within the tibiae during distraction, and periodically during consolidation, up to 17 weeks after operation. Blood flow was measured from regions of interest during the flow phase of the scan and expressed as a ratio of lengthened side to control side. At the distraction site, the flow increased to nearly ten times control, peaked at two weeks postoperatively, then decreased to four to five times the control for the remainder of the distraction period. During the consolidation period, significantly increased flow persisted at levels of two to three times control. The distal tibiae, away from the distraction gap, showed similar amplitude and temporal patterns of increased flow. No significant differences were found between the groups tested or when compared with similar fracture models. These findings lend credence to Ilizarov's hypothesis that distraction osteogenesis may contribute to healing of chronic osteomyelitis or hypovascular nonunions at distant sites by inducing a prolonged hypervascular state. Whether distraction osteogenesis transforms the normal reparative response of bone injury to a regenerative response remains conjectural.

Animals↗
PubMed1994

Experimental healing of distraction osteogenesis comparing metaphyseal with diaphyseal sites.

Distraction osteogenesis was performed on 32 adult dogs to compare bone healing at metaphyseal and diaphyseal sites. Sixteen dogs underwent proximal metaphyseal corticotomy and 16 dogs underwent middiaphyseal corticotomy of the left tibiae for gradual lengthening. Each major group was then divided into four subgroups of four dogs each on the basis of zero-, seven-, 14- and 21-day latency periods. The standard radiograph, quantitative computer tomography density, and bone-healing index were used to evaluate new bone formation and consolidation. A distraction rate of 1 mm per day for four weeks created an average elongation of 23.9 +/- 3.7 mm in the metaphyseal groups and 23.8 +/- 2.0 mm in the diaphyseal groups, excluding nine premature consolidations. In the 16 metaphyseal lengthenings, there were six premature consolidations (37.5%): four with a 21-day latency, two with a 14-day latency, and one nonunion (6.2%). In the 16 diaphyseal lengthenings, three fused prematurely (18.7%), two with a 21-day latency and one incomplete corticotomy with a seven-day latency. Three lengthenings of the diaphyseal group resulted in nonunion (18.7%). All animals, metaphyseal and diaphyseal, successfully bridged the distraction gap after a zero-day latency. The bone-healing index showed that new bone consolidation was best with a zero-day latency in metaphyseal (22 +/- 7.6 days/cm) and diaphyseal lengthening (26.5 +/- 6.5 days/cm). Comparing the minimum quantitative computer tomography density ratio of the experimental side with the contralateral side indicated a significant difference at the end of distraction (p = 0.001), at fixator removal (p = 0.001), and when the dogs were killed (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Noninvasive determination of bone stiffness for distraction osteogenesis by quantitative computed tomography scans.

Apparent density of canine tibial specimens was correlated to measured quantitative computed tomography (QCT) numbers, and a conversion equation was derived. Finite element analysis models of canine tibiae were constructed using spatial coordinates of converted QCT data. Two QCT-derived finite elemental analysis models were constructed for a pair of matched tibiae: one lengthened 15% by distraction osteogenesis and one contralateral control. Two equations relating the modulus of elasticity to apparent density were used. These models were then verified mechanically by measuring strains of the two specimens under applied load. Equation I correlated best with measured strains in the less-dense regenerate bone of the distracted tibia (R2 = 0.914, p = 0.0028, n = 6); Equation II performed best in the denser control tibia (R2 = 0.820, p = 0.0129, n = 6). These results demonstrate that the stiffness of tubular bones, including cortical and heterogenous cancellous structure, can be accurately predicted by a noninvasive QCT scan.

Animals↗
PubMed1994

Mechanical forces as predictors of healing during tibial lengthening by distraction osteogenesis.

Direct axial loads were measured weekly during a 15% left tibial lengthening in 21 skeletally mature dogs using three in-line load cells mounted between the rings of an Ilizarov external fixator. The loads increased linearly over time to a maximum at the end of distraction (Week 4). The metaphyseal lengthening sites (mean, 155 N) generated significantly higher loads than diaphyseal sites (mean, 111 N). Stress was calculated by dividing measured load by the computed tomographic-measured cross-sectional area of each distraction osteogenesis site; the metaphyseal and diaphyseal groups demonstrated equal stress at each time point with a maximum of 47 N/cm2 at the end of distraction. Six premature consolidations occurred that demonstrated loads significantly greater than 200 N by Week 2 of distraction. Three nonunions occurred that had significantly lower loads measured by Week 3 of distraction (mean, 60 N or 26 N/cm2).

Animals↗