Finite element modelling of stapled colorectal end-to-end anastomosis: advantages of variable height stapler design.

The impact of surgical staplers on tissues has been studied mostly in an empirical manner. In this paper, finite element method was used to clarify the mechanics of tissue stapling and associated phenomena. Various stapling modalities and several designs of circular staplers were investigated to evaluate the impact of the device on tissues and mechanical performance of the end-to-end colorectal anastomosis. Numerical simulations demonstrated that a single row of staples is not adequate to resist leakage due to non-linear buckling and opening of the tissue layers between two adjacent staples. Compared to the single staple row configuration, significant increase in stress experienced by the tissue at the inner staple rows was observed in two and three rows designs. On the other hand, adding second and/or third staple row had no effect on strain in the tissue inside the staples. Variable height design with higher staples in outer rows significantly reduced the stresses and strains in outer rows when compared to the same configuration with flat cartridge.

Interspinous process segmental spinal instrumentation for scoliosis in cerebral palsy.

Interspinous process segmental instrumentation (ISSI) was used in 34 patients with scoliosis due to severe cerebral palsy. Average age was 17 years, and average curve was 82 degrees. Anterior fusion was performed in 21 patients before ISSI. Mean correction was 50.5%, and progression averaged 5 degrees at the 22-month follow-up. Posterior fusion alone gave good results in smaller curves. A brace was needed only for severe movement disorders. Gross functional level improved in fewer than one-third of patients. Minor gains were made by 74%. ISSI is effective in severe cerebral palsy. It may be used alone in the smaller (less than 80 degrees), more supple curves.

Application of 24-hour burst TENS in a back school.

The Back School program consists of exercises and education designed to reduce back pain. Sixty-six percent of the patients had too much back pain to participate. The purpose of this clinical report is to describe how 24-hour burst transcutaneous electrical nerve stimulation (TENS) treatment enabled these patients with severe back pain to participate in the Back School. Patients recovering from a laminectomy, chemonucleolysis, or scoliosis surgery were used to determine that 24-hour burst TENS was the most effective TENS protocol for reducing pain. Twenty-four-hour burst TENS was then prescribed for 129 patients with severe back pain to enable them to complete the Back School program. Eighty percent of these patients returned to their usual activities within 12 months. The Back School program has been shown to be an effective and safe treatment for back pain, and 24-hour burst TENS treatment allows patients with severe back pain to participate in it.

The treatment of severe scoliosis in osteogenesis imperfecta. Case report.

Surgical stabilization of the scoliotic spine in osteogenesis imperfecta (OI) is technically difficult owing to the mechanical weakness of the bone. Brittle bone makes instrumentation of the spine a procedure all too often associated with complications. Combining the instrumentation of the OI spine, both anteriorly and posteriorly, with the use of methylmethacrylate to augment the fixation may prove valuable as a surgical technique. This usage of methylmethacrylate in correcting severe scoliosis in OI has not been previously reported.

Plasma glucose concentrations and the development of blood emboli and hemolysis.

Plasma glucose concentrations were measured in heparinized dog blood as the blood was sheared in polycarbonate coni-cylindrical test cells. The glucose depletion rate during the 4 hr tests increased with increasing shear rate (480 to 2100 sec-1) but was independent of the surface/volume ratio (7.0 and 12.7 cm-1). These results suggest that the glucose metabolism in red cells (the dominant consumer of blood glucose) increases more from shear-induced stretching or tearing of red cells that adhere to the wall than from cell-boundary collisions. (Changes in platelet and leukocyte glucose metabolism would not have been detected in our measurements of whole blood glucose concentrations.) The rate of glucose depletion was also independent of the extent and rate of hemolysis and the extent of microemboli formation (as measured by SFP). When insulin-induced hypoglycemic blood was used to fill the test cells, the resulting hemolysis and SFPs were not significantly different from hemolysis and SFPs produced in normoglycemic blood from the same donors. Thus red cells (which have negligible glycogen stores) do not depend significantly on plasma glucose to resist hemolysis, and platelets may rely on their substantial glycogen storage to form microemboli during hypoglycemia.

Leg-length discrepancies in monoarticular and pauciarticular juvenile rheumatoid arthritis.

A retrospective study was performed to determine the course of limb-length discrepancies occurring in patients with monoarticular and pauciarticular juvenile rheumatoid arthritis. Data were assessed on thirty-six patients followed to skeletal maturity, on fifteen patients who had not reached skeletal maturity but who had been followed for four years or more, and on forty-nine patients followed for three years or less. In seventy-two of the total of 100 patients the onset of the disease occurred before they were five years old, and ninety patients had involvement of the knee. All patients in whom the disease developed before the age of nine had overgrowth of the involved extremity, but that overgrowth never exceeded 3.0 centimeters. The major discrepancy developed within the first three or four years and either increased very slowly thereafter, remained level, or decreased. Of the thirty-six patients who were followed to skeletal maturity, in twenty-nine a discrepancy of 1.5 centimeters or more developed at some time during the period of assessment. Twelve of the thirty-six patients had diminution of the discrepancy to the extent that epiphyseal arrest was not required. Fifteen eventually had an epiphyseal arrest. Rapid premature closure of the epiphyseal growth plate occurred only in those patients in whom the disease developed after the age of nine years. This led to immediate shortening of the involved side and on occasion to marked limb-length discrepancies.

The effect of thromboresistent surfaces on the development of blood emboli and hemolysis.

Heparinized dog blood was sheared in conicylindrical test cells which had been coated with thrombo-resistant materials. Hemolysis and blood emboli formation in the coated cells were as great or greater than in uncoated polycarbonate cells. These results suggest that materials which resist the buildup of thrombi may still be stimulating emboli formation and red cell damage.

The thrombogenicity of radiation grafted polymers as measured by the vena cava ring test.

Radiation grafted hydrogels on silicone rubber with water contents ranging from 10--90% have been evaluated by the vena cava ring test. All hydrogel grafted materials were found to accumulate less thrombus than ungrafted silicone rubber, and graft level was found to have little effect on thrombus accumulation. Acrylamide grafts demonstrated superior thromboresistance by this test. Poly (2-hydroxyethyl methacrylate-ethyl methacrylate (HEMA/EMA) copolymers were examined along with pure HEMA and EMA grafts. At two weeks implantation, intermediate HEMA/EMA copolymers were found to have the least thrombus accumulation of any of the polymers in this series. EMA grafted rings were highly thrombogenic. The results from these studies indicate that the sensitivity of the vena cava ring test for detecting certain differences in polymer structure is poor. Also, the significance of the vena cava ring test for evaluating materials for use in contact with flowing human blood is questionable, based upon comparisons of results for similar materials tested in other blood compatibility evaluation systems.

The effect of shear, specific surface, and air interface on the development of blood emboli and hemolysis.

Heparinized dog blood was exposed to shear and foreign surfaces in conicylindrical test cells. The cells were injection molded from polycarbonate and were filled using a technique that avoided contact of the blood with air. Particulate-matter formation was measured and was found to be dominated by the surface-to-blood-volume ratio and to be independent of shear rate. Hemolysis was also measured and was found to vary linearly with shear rate and to increase with increasing surface-to-blood volume ratio. Thus, at low shear rates and high specific surface conditions, the degree of hemolysis was found to be minimal while particulate-matter formation was high. The results suggest that the safety of extracoporeal perfusion procedures cannot be inferred from hemolysis measurements alone. In one series of tests, a gas-blood interface was generated at a rate equivalent to the rate of surface renewal in conventional disc oxygenators. The gas-blood interface failed to contribute significantly to the damage indices, which suggests that the apparent superiority of membrane oxygenators may be a result of factors other than the absence of a blood-gas interface.