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Biomedical subjects

B L Allen

Publications and source records attributed to B L Allen.

At least 55 records · Page 3Linked to original sources
PubMed1985

A biomechanical study of thoracolumbar spine fractures with bone in the canal. Part III. Mechanical properties of the dura and its tethering ligaments.

Experiments were performed to determine some mechanical properties of the spinal cord-meningeal (SCM) complex and its tethering elements with reference to factors contributing to contact pressure of an anterior mass on the SCM complex with spinal fracture and the development of some means to relieve the pressure. Measurements were made using a combined microload cell and displacement transducer that was passed posteriorly through a hole drilled in vertebra T12 through the interpedicular space and contacted the cord. Loss of nerve roots and anterior ligaments as dural tethers in the lumbar region permitted the SCM complex to fall out of the lordosis of the canal and fail to resist transverse loading. Head and neck flexion increased contact force for a given depth of penetration, particularly in the cervical region. This was consistent with measurements of strain along the dura that was greatest in the cervical region. The dura was found to be elastic, having a failure strain averaging 34% but was uniform in thickness, stiffness, and elastic modulus along its length. The study did not delineate any surgical manipulation other than removal of the anterior mass that would be beneficial when there is anterior compression of the spinal cord.

Biomechanical Phenomena↗
PubMed1984

Determination of dissociation constants for enzyme-reactant complexes for NAD-malic enzyme by modulation of the thiol inactivation rate.

Incubation of NAD-malic enzyme from Ascaris suum with the sulfhydryl reagents N-ethylmaleimide (NEM), 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), or 4,4'-dithiodipyridine (4-PDS) results in rapid and complete loss of malate oxidative decarboxylase and pyruvate reductive carboxylase activities. With DTNB, this loss of activity occurs concomitantly with the modification of about 1 thiol group per subunit. The majority of the activity is lost when 0.5 thiol per subunit is modified, indicative of possible half-site reactivity with DTNB. Complete restoration of activity follows addition of dithiothreitol to enzyme inactivated by DTNB and 4-PDS but not with NEM. With the DTNB-inactivated enzyme, replacement of the thionitrobenzoate moiety with cyanide restores activity. The presence of a divalent metal ion (Mg2+ or Mn2+) results in enhancement of the inactivation rate with all sulfhydryl reagents. However, malate alone or competitors of malate provide protection which is more effective in the presence of Mg2+, while NAD provides only about 25% protection. Thus, the Ascaris suum NAD-malic enzyme has a thiol group probably located in or near the malate binding site, which is not essential for enzyme activity. The changes in the rate of inactivation in the presence of reactants were used to determine the dissociation constants for enzyme-reactant complexes. These data suggest that all three possible binary and all three possible ternary complexes form. The binding of malate to free enzyme exhibits negative cooperativity, which is eliminated by the presence of either NAD or Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

A mechanistic classification of thoracolumbar spine fractures.

Thoracolumbar spinal injuries are classified on the basis of the mechanical mode of failure of the vertebral bodies. The fractures are presented in seven categories. Emphasis is placed on the injury component causing the fracture patterns. The choice of instrumentation for surgery is based on the surgeon's understanding of these injury patterns.

Fracture Fixation, Internal↗
PubMed1983

Purification and characterization of phosphorylase B from Ascaris suum.

Glycogen phosphorylase b (EC 2.4.1.1) has been purified from the muscle of the roundworm, Ascaris suum. The 223-fold purified enzyme was shown to be homogenous by high performance liquid chromatography (HPLC), gel filtration column chromatography and sodium dodecyl sulfate (SDS) gel electrophoresis. The apparent native molecular weight of the enzyme determined by size exclusion chromatography by HPLC and gel filtration corresponded to 200 000 and 199 000, respectively. The subunit molecular weight of the enzyme was determined to be 100 000 by electrophoresis in the presence of SDS. Therefore, the enzyme appears to be a dimer with identical or near identical subunits. The enzyme contained 1 mol of pyridoxal 5'-phosphate per mol subunit and exhibited an absorbance index E1% 280 of 13.8. The apparent isoelectric point of the enzyme is 5.53. The enzyme, inactive in the absence of AMP, can be converted to the active form by rabbit muscle phosphorylase kinase and MgATP. The molecular weight of the activated form of the enzyme is 200 000. Kinetic studies showed apparent Km values of 0.17% for glycogen, 36 mM for Pi and 52 mM for glucose-1-P. The apparent Ka for AMP was 0.22 mM.

Animals↗
PubMed1983

Staged correction of neuromuscular scoliosis.

Anterior release and fusion, combined with tong gravity traction and second stage L-rod instrumentation, establishes correctability and accomplishes circumferential arthrodesis of the spine in neuromuscular scoliosis. From March 1979 through April 1982, nine patients with neuromuscular scoliosis, with an average age of 16.4 years, underwent this two-stage surgical procedure. The parameters investigated included correction of scoliotic deformity, correction of pelvic decompensation, and spinal arthrodesis. The preoperative scoliotic curvature measured 81 degrees and the postoperative curve measured 29.3 degrees, an average correction of 63.8%. Pelvic obliquity was significant in five of nine patients, averaging 36.2 degrees preoperatively. Postoperatively the pelvic obliquity averaged 11.8 degrees, an average correction of 67.4%. One of two pelvic fixation rods rotated out of the pelvis of one patient; roentgenographically he appears to have fused without loss of correction. A second patient has a poor fusion mass by roentgenographic criteria, although she has lost no correction and has had no pain. This technique offers results comparable to other series reporting arthrodesis for neuromuscular scoliosis. It has the advantages of requiring no anterior instrumentation and no postoperative immobilization.

Adolescent↗
PubMed1983

The technique of scoliosis revision surgery utilizing L-rod instrumentation.

Operative treatment of failed scoliosis surgery requires an instrumentation that is readily adaptable to the multiple causes and sequelae of failed spinal surgery. A "modified L-rod" technique is described for segmental spinal instrumentation to treat failed scoliosis surgery. Nine patients underwent 10 scoliosis revision operations, with an average follow-up of 37.1 months. Three neuromuscular, five idiopathic, and one congenital scoliosis were revised. The average blood loss for the L-rod instrumentation was 2,960 ml, and the average operative time was 6.2 h. Four patients had attempted correction of their deformities, with 21.2% improvement. Five cases had triangular base-transverse bar pelvic fixation. None of the 10 revisions had pseudarthrosis at follow-up. No postoperative immobilization was used. Complications included one fracture of a fusion mass below the L-rods, penetration of the skin by a prominent wire with subsequent infection, minimal loss of correction in one case, and one broken wire without loss of correction.

Adolescent↗
PubMed1983

Segmental spinal instrumentation with L-rods.

LRI is a relatively new and highly effective technique of spinal fixation. Because the need for a cast or orthosis after the operation is eliminated, it is especially applicable to scoliosis of neuromuscular origin. The early success with segmental fixation has stimulated much laboratory and clinical investigation that seems certain to make operative treatment for most spine deformities more effective. With LRI the assets of secure fixation and adaptability are gained at the expense of more complex surgery, longer operating time, greater blood loss, and probable higher risk of neural injury.

Adult↗
PubMed1982

Phosphofructokinase from Ascaris suum. Purification and properties.

A rapid and efficient procedure has been developed to purify phosphofructokinase from the muscle of the parasitic roundworm, Ascaris suum. The procedure can be accomplished in 1 day with a 420-fold purification and a 60% yield. The enzyme was shown to be homogeneous by two-dimensional electrophoresis, Sepharose 6B column chromatography, and high performance liquid chromatography utilizing a size exclusion column. The subunit molecular weight of the enzyme was found to be 95,000 by electrophoresis in the presence of sodium dodecyl sulfate. In solutions of low ionic strength, the native enzyme aggregated to species of higher molecular weight than did the rabbit muscle phosphofructokinase. In the presence of 0.2 M (NH4)2SO4, the minimum native molecular weight was determined to be 398,000 by high performance liquid chromatography and Sepharose 6B column chromatography. Therefore, the enzyme appears to be a tetramer with identical or near-identical subunits. The apparent isoelectric point of the enzyme was shown to be 7.3 to 7.4 by both column and gel isoelectric focusing. Amino acid analysis revealed a lower number of the aromatic residues Phe, Tyr, and Trp than in the rabbit muscle enzyme and this is in agreement with the lower extinction coefficient of E1%280 nm = 6.5. Analysis of the purified enzyme revealed 7.4 +/- 0.6 mol of phosphate/mol of enzyme.

Amino Acids↗
PubMed1982

L-rod instrumentation for scoliosis in cerebral palsy.

From April 1977 through September 1980 at the University of Texas Medical Branch, 10 cerebral palsied individuals with total body involvement were surgically treated for their scoliosis. Each underwent L-rod instrumentation either as a definitive procedure or as the second surgery in a two-staged correction and arthrodesis. The average age of the group was 15.6 years and the average curve severity 70.8 degrees. An average correction of 59.9% or 41.5 degrees was obtained; two-stage procedures averaged 7.2 degrees correction per segment as contrasted with 5.4 degrees for single stage surgery. Most patients had regained their preoperative level of function within 2 weeks after L-rod instrumentation. At an average follow-up interval of 2.73 years, all have a solid spinal arthrodesis. On the basis of this experience, we feel that L-rod instrumentation is a more effective adjunct in the surgical management of cerebral palsy scoliosis than combined Harrington-Dwyer instrumentations.

Adolescent↗
PubMed1981

Purification of malic enzyme from Ascaris suum using NAD+-agarose.

Malic enzyme has been purified from Ascaris suum by polyethylene glycol precipitation, ion-exchange chromatography, ammonium sulfate precipitation, and NAD-agarose affinity chromatography to a specific activity of 80 units/mg (V/[E]t = 350 s-1). The preparation was shown to be homogeneous by SDS polyacrylamide disc gel electrophoresis. The procedure can be accomplished in a maximum of four days with a 74% yield.

Ascaris↗
PubMed1978

Pelvic displacement osteotomy in young myelodysplastic patients with dislocatable hips.

This prospective study of the role that pelvic displacement osteotomy may have in the management of dislocatable hips in patients with myelomeningocele defines the technical points to be considered and gives preliminary results for ten hips in eight children. The procedure may salvage failed posterior iliopsoas transfers or, in patients not operated on previously, it may limit cephalad displacement of the femoral head. Both control of muscle imbalance and improvement of acetabular contour appear essential to a high rate of success in these patients. Eight of ten hips in this series were stable upon short-term review. All patients were less than 7 years of age.

Acetabulum↗
PubMed1978

Immediate spica cast system for femoral shaft fractures in infants and children.

From August 1973 through August 1976, 55 femoral shaft fractures in children were treated by manipulative reduction and immediate application of a double hip spica cast. All had satisfactory results and none had serious complications. Data from the study support our opinion that the immediate spica system is the treatment of choice for these fractures and that traction methods should probably be abandoned as definitive treatment of a femoral shaft fracture in a child.

Adolescent↗