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Biomedical subjects

N Schachar

Publications and source records attributed to N Schachar.

11 recordsLinked to original sources
PubMed2004

Groin soft tissue tumors--a challenge for local control and reconstruction: a prospective cohort analysis.

BACKGROUND AND OBJECTIVES: Groin soft tissue tumors are associated with high local recurrence rates of 16-48% and postoperative complications in 40-68%. Neoadjuvant chemoradiation and aggressive reconstructive techniques were utilized to improve local control and complication rates in this challenging area. METHODS: Nine patients in this prospective series were treated with neoadjuvant chemoradiation (30 mg IV doxorubicin x 3d followed by 300 cGy/d x 10d) followed by surgery and two patients received radiation (5,000 cGy with tissue spacer) followed by surgery for tumors with a pelvic/retroperitoneal component. Surgery included resection plus reconstruction of the abdominal wall, myocutaneous flaps for large defects, and vascular reconstruction as necessary. RESULTS: The 11 consecutive patients presented with Stage I (30%), II (40%), or III (30%) disease. Four patients (36%) were operated on for possible incarcerated hernia prior to referral and two (18%) presented with recurrent tumors. Pathology included 10 sarcomas and 1 desmoid tumor; tumor grade was low (30%), moderate (40%), or high (30%). Local control (mean follow-up 55 months; minimum follow-up 36 months) and limb salvage rate was 100%. Minor wound complications not requiring re-operation occurred in three patients, lymphedema in two, and there were no postoperative hernias. CONCLUSIONS: Preoperative therapy provides excellent local control of groin soft tissue tumors. Current surgical techniques allow extensive resection with limb salvage, dependable primary wound healing and long-term integrity of the abdominal wall.

Abdominal Wall↗
PubMed1998

Mechanical integrity of subchondral bone in osteochondral autografts and allografts.

OBJECTIVE: To assess the influence of osteochondral graft preservation techniques on post-transplant biomechanics of graft and host subchondral bone in the knee joint. DESIGN: An experimental animal model (sheep), specifically the weight-bearing articular surface of the medial femoral condyle of the knee joints. INTERVENTION: Each sheep received, in the ipsilateral knee, an allograft that was (a) frozen without dimethyl sulfoxide (DMSO), (b) snap-frozen in liquid nitrogen or (c) frozen with DMSO. The contralateral knee received an autograft that was (a) snap-frozen, (b) treated with DMSO or (c) left untreated (fresh). MAIN OUTCOME MEASURES: Mechanical and material properties of bone, including maximal compression stress, modulus of elasticity and bone cores (from the graft centre and surrounding host bone). RESULTS: No significant differences were found in the mechanical properties of the subchondral bone under the graft, but there were significant changes in surrounding bone. Bone surrounding the grafts that were snap-frozen or frozen without DMSO was significantly stronger than the normal control bone. However, bone surrounding fresh autografts and cryoprotected allografts was not significantly different from normal control bone. CONCLUSIONS; The changes in the mechanical behaviour of the host bone may be associated with graft cell viability. The great stiffness of the subchondral host bone may have consequences for long-term graft integrity and for the development of degenerative osteoarthritis.

Animals↗
PubMed1994

Localization of freezing injury in articular cartilage.

In order to improve techniques for cryopreservation of articular cartilage, a study has been carried out to assess localization of cryoinjury in intact articular cartilage. Osteochondral dowels taken from the femoral condyles of sheep were subjected to graded freezing in the presence and absence of a cryoprotectant (10% DMSO). The graded freezing technique involves slow cooling (1 degree C/min) to various subzero temperatures before either rapid warming or rapid cooling by plunging in liquid nitrogen. This protocol allows assessment of the separate effects of rapid and slow freezing which damage cells in different ways, and the effects of cryoprotectants on the different types of damage. To assay damage, thin slices of cartilage were cut with a vibratome, which allows viable cells within the matrix to be observed microscopically. Injury was assessed by staining with fluorescent dyes to indicate damage to the plasma membrane. In general, tissue response was similar to that of cell suspensions, showing at least two mechanisms of injury acting on the cells: one at slow cooling rates and another at rapid cooling rates. The primary effect of DMSO was to reduce injury due to slow cooling. When the location of injury within the tissue was examined, it was found that chondrocytes of the intermediate layer were injured more extensively than those of either the deep or superficial layers.

Animals↗
PubMed1992

Metabolic and biochemical status of articular cartilage following cryopreservation and transplantation: a rabbit model.

To determine the fate of transplanted cryopreserved articular cartilage, an animal model employing the proximal humerus in the rabbit has been developed. Previous studies have been hindered by problems of postoperative joint instability, secondary injury due to immobilization, and paucity of cartilage for analysis. This experiment demonstrates the survival and function of transplanted cartilage by quantitative assessment of metabolic and biochemical parameters. Forty-five New Zealand white rabbits underwent transplantation of the right proximal humerus. In 29 animals, the proximal half of the humerus was resected and replaced by a cryopreserved osteoarticular allograft. Autograft procedures were carried out in the remaining animals. Following sacrifice at 3, 6, 9, and 12 months postoperatively, articular cartilage was analyzed for gross appearance, collagen synthesis, proteoglycan synthesis, and water, hydroxyproline, hexosamine, and hexuronic acid contents. The results indicate that the cryopreserved osteoarticular allografts retained their metabolic and biochemical integrity and behaved as viable and biologically functional units 1 year postoperatively.

Animals↗
PubMed1989

Cryopreserved articular chondrocytes grow in culture, maintain cartilage phenotype, and synthesize matrix components.

For osteochondral allograft transplantation to be successful, chondrocytes must survive preservation and retain their capacity to produce normal matrix components: proteoglycans and Type II collagen. Clinical success with osteochondral allograft transplantation has created an increased demand for supplies of suitable cartilage-bearing grafts. This demand has stimulated attempts to find successful methods for low temperature storage of cartilage for "banking" and heightened interest in cartilage cryobiology. In order to achieve the maximum viability of cryopreserved articular cartilage, previous comprehensive studies have focused on rates and temperatures of freezing, cryoprotective agents, and methods and influences of thawing. This study presents evidence that cryopreserved articular chondrocytes maintain their ability to grow in tissue culture following thawing and to produce normal matrix components. Chondrocytes isolated from Japanese white rabbits were divided into groups of fresh controls and experimental cryopreserved cells. Cells were incubated in dimethylsulfoxide, frozen at a rate of -1 degrees C/min, stored at -79 degrees C, rapidly thawed, and plated for culture. Growth rates were comparable in all groups. In all groups, typical chondroid characteristics were maintained throughout 14 days of culture. Typical cartilage phenotypic characteristics included maintenance of polygonal and rhomboidal cells, cell aggregation, proteoglycan production, and Type II collagen synthesis. This investigation strongly indicates that articular chondrocyte cryopreservation yields viable, functional cells and although these results cannot be directly extrapolated to intact adult articular cartilage, they do give further support for low temperature banking of cartilage-bearing allografts for transplantation.

Animals↗
PubMed1988

Kinetics of osmotic water movement in chondrocytes isolated from articular cartilage and applications to cryopreservation.

The ability of chondrocytes to survive conditions encountered during cryopreservation depends on the responses of the cells to the physiochemical changes that result when water is removed from the environment of the cells in the form of ice. Cellular responses are therefore closely related to the osmotic permeability properties of the plasma membrane. In order to optimize the conditions for cryopreservation of chondrocytes, osmotic properties of the chondrocyte membrane were determined from the kinetics of volume change in hypertonic solutions at different temperatures. The hydraulic conductivity of the plasma membrane was 0.305 +/- 0.025 micron3/micron2/min/atmosphere at 24 degrees C, with an Arrhenius activation energy of 8.06 kcal/mol. These values are similar to those reported for other cell types, but the osmotically inactive volume of the chondrocytes (0.41 +/- 0.04) was significantly higher than for other cells, implying that chondrocytes have a higher dry weight ratio or that they contain a higher proportion of osmotically inactive or bound water. These results were used to calculate the osmotic responses of chondrocytes at low temperatures and to predict that the least damaging cooling rate for isolated chondrocytes in the absence of cryoprotective compounds is 10 degrees C/min. The ultimate goal of this study is the development of an analytical model applicable to the optimization of techniques for cryopreservation of intact cartilage and other tissues.

Animals↗
PubMed1983

Natural history of healing in the repaired medial collateral ligament.

The purpose of this study was to assess morphologically the healing of repaired medial collateral ligaments (MCLs) in a rabbit model. Healing ligaments were examined grossly and histologically at various intervals, from 3 days to 2 1/2 years after injury, and compared with the appearances of normal age-, sex-, and activity-matched controls. Results show that all ligaments healed by bridging scar formation rather than true ligament regeneration. Increases in cellularity and temporary matrix disorganization along the entire length of the ligaments during healing suggest a combination of diffuse mechanical damage from their failure in tension and regional inflammatory injury (in excess of surgical exposure alone) from the processes of degradation and replacement. Substance that was not injured physically in this model demonstrated complete recovery, while that replaced by scar did not. Healing processes were similar to those of other highly specialized soft tissues (e.g., tendons), with short phases of hemorrhage and inflammation, an intermediate phase of proliferation, and a prolonged phase of remodeling. Failure of repairs to maintain anatomical apposition of torn ends may have contributed to the delay of these healing processes by increasing scar mass. Incomplete scar remodeling at 2 1/2 years, however, suggests much slower MCL healing than previously reported and probably, therefore, a longer period for potential treatment influence.

Animals↗
PubMed1983

Electromagnetic stimulation of ligament healing in rabbits.

To evaluate the effect of a specific noninvasive method of electrical stimulation on ligament healing in rabbits, a solid core electromagnet energized by a square wave unidirectional current was applied to injured and repaired medial collateral ligaments seven hours per day, five days per week for intervals of up to six weeks. Healing was evaluated by gross, histologic, biochemical, and biomechanical parameters. Stimulation was shown to increase histologic maturity relatively, restore stiffness and failure strength earlier, and return collagen content toward normal unoperated values sooner in these healing ligaments. It is uncertain whether the end point of healing is affected by this technique, but at six weeks both histologic and biochemical evidence of acceleration remains. Further investigation into the effect of electromagnetic stimulation by this and other fields on non-osseous tissues and their components is indicated.

Animals↗
PubMed1982

A computerized study of knee-ligament injuries: repair versus removal of the torn anterior cruciate ligament.

A retrospective review of 202 patients with acute injury to knee ligaments was carried out by chart review, scored questionnaire and scored physical examination. Of 62 patients with complete midsubstance injury to the anterior cruciate ligament, repair was attempted in 46, while 16 had complete excision of the ligament without replacement or augmentation. Computer analysis revealed that these groups were similar with respect to mean age of the patients, sex distribution, incidence of meniscectomy and distribution of associated injuries. At 4-year follow-up, there was no advantage of primary repair over excision for these injuries. In fact, repair seemed to be subjectively and objectively worse than excision, being associated with increased pain and decreased range of motion. The high rate of signs and symptoms of deterioration in both groups suggests a need for better alternatives in the acute phase of anterior cruciate ligament injury.

Adolescent↗
PubMed1982

Immobilization hypercalcemia.

Three cases of immobilization hypercalcemia are presented and the incidence, clinical symptoms, laboratory investigation, pathophysiology and treatment of this metabolic abnormality are reviewed. Immobilization hypercalcemia is more common that has previously been suspected. Vague clinical symptoms may not suggest the diagnosis of hypercalcemia. Laboratory investigation of these clinical complaints in the immobilized patient should include determination of the serum calcium and total protein levels and the urinary calcium to creatinine ration. The pathophysiology of this entity is unknown. Treatment is directed towards lowering the serum calcium level using intravenous hydration, furosemide and salmon calcitonin. Definitive treatment consists of mobilizing the patient. Exercises in bed have not been effective in preventing or treating immobilization hypercalcemia.

Adolescent↗