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Biomedical subjects

A A White

Publications and source records attributed to A A White.

At least 19 recordsLinked to original sources
PubMed1998

Role of IL-6 and TNF in thermoregulation and survival during sepsis in mice.

Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) have been implicated as key mediators in inflammation, morbidity, and mortality associated with sepsis. We examined the role of IL-6 and TNF-alpha signaling on hypothermia, fever, cachexia, anorexia, and survival during sepsis induced by cecal ligation and puncture (CLP) in male and female gene knockout mice. Male wild-type mice developed an initial hypothermia and subsequent fever during sepsis. Male IL-6 knockout mice did not develop fever; rather, they maintained a profound hypothermia during sepsis. Male TNF p55/p75 receptor (TNFR) knockout mice had attenuated hypothermia, but developed a virtually identical fever as wild-type mice. Cachexia did not differ between male wild-type and IL-6 or TNFR knockout mice, whereas anorexia was prolonged in IL-6 knockout mice. Due to the rapid lethality of sepsis in female mice, survival was the only variable we were able to statistically compare among female genotypes. Female wild-type mice had significantly decreased survival compared with male wild-type mice. Survival was significantly enhanced in male and female TNFR knockout mice compared with their wild-type controls. Lack of IL-6 did not affect male or female lethality. These data support the hypothesis that IL-6 is a key mediator of fever and food intake, whereas TNF is responsible for the initial hypothermia and lethality of sepsis in both sexes of mice. The enhanced lethality of CLP-treated female mice supports a role for sex steroids during sepsis.

Animals↗
PubMed1997

Outcomes of surgeons who have undergone spine surgery.

The objective of this study was to examine the prevalence, characteristics, and outcomes of spine surgery among a membership of American orthopaedic surgeons with a particular interest in spine care [North American Spine Society (NASS)] and a general membership of Canadian orthopaedic surgeons [Canadian Orthopaedic Association (COA)]. A 25-item multiple choice questionnaire was developed and mailed to both memberships. The COA response rate was 45.9%; the NASS response rate was 45.8%. Of those who replied, 17.2% had undergone spinal surgery, and the results differed significantly between the COA at 12.9% and NASS at 21.9%. As a percentage of the total mailing, 7.7% had undergone spinal surgery. These results differed significantly between the COA at 5.9% and NASS at 9.7%. Although the surgery rate for NASS respondents was more than 1.5 times that of COA respondents, they had strikingly similar outcomes. They are a highly motivated, self-employed group who missed little work before and after having surgery.

Back Pain↗
PubMed1996

The anatomy of the human lumbar ligamentum flavum. New observations and their surgical importance.

STUDY DESIGN: An anatomic study was performed to investigate the ligamentum flavum of the human lumbar spine. OBJECTIVES: To describe accurately the interlaminar portion of ligamentum flavum, and to determine if there is an insertion onto the anterosuperior surface of the caudal lamina. SUMMARY OF BACKGROUND DATA: The insertions of the ligamentum flavum onto its adjacent laminas were classically described by Naffzinger. His description has been recounted by others. It has been the authors' observation that there is a slip of inferior ligamentum flavum that inserts onto the anterosuperior surface of the caudal lamina. Review of the literature revealed only anecdotal observations that support the authors' finding. A clear anatomic description of this structure is important to the surgeon who frequently enters the spinal canal at this anatomic site. METHODS: Thirty human lumbar ligamenta flava from six fresh frozen lumbar spines were studied macroscopically, with particular attention paid to the insertions onto the adjacent laminas. RESULTS: The ligamentum flavum consists of a superficial and a deep component. It is continuous in the midline. The superficial ligamentum flavum inserts onto the superior edge and posterosuperior surface of the caudal lamina. The deep ligamentum flavum inserts for a variable distance onto the anterosuperior surface of the caudal lamina. CONCLUSIONS: There is an inferoventral slip of the ligamentum flavum that attaches to the anterosuperior surface of the caudal lamina. This slip is the inferior portion of the deep ligamentum flavum. When the ligamentum flavum's superficial layer is selectively released, the inferoventral slip of the ligamentum flavum's deep layer remains attached to the anterosuperior surface of the caudal lamina and remains between the surgeon and the dura.

Anatomy, Cross-Sectional↗
PubMed1995

Radiographic appearance of the odontoid lateral mass interspace in the occipitoatlantoaxial complex.

STUDY DESIGN: This is an anatomic study in which the odontoid lateral mass interspace is evaluated radiographically in various positions of upper cervical spine rotation. OBJECTIVES: The objectives are to determine whether odontoid lateral mass interspace asymmetry exists in the ligamentously intact cervical spine and to define odontoid lateral mass interspace behavior during atlantoaxial rotation. SUMMARY OF BACKGROUND DATA: Controversy exists regarding the behavior of the odontoid lateral mass interspace during atlantoaxial rotation. The meaning of interspace asymmetry varies depending on the author and the method of study. Atlas fractures account for 7% of cervical spine fractures and are frequently associated with other cervical fractures, so an understanding of the radiographic anatomy is crucial to the evaluation of these patients. METHODS: Ten human cadaveric cervical spines were dissected of all but ligamentous soft tissue and were mounted and prepared for radiographic study in neutral position and in varying degrees of right and left rotation. Radiographs were evaluated for odontoid lateral mass interspace asymmetry in neutral and in rotated positions, and data were analyzed. RESULTS: Measurable asymmetry could be shown when comparing neutral positions and when comparing rotated with neutral positions. A statistically significant difference could not be proven in this asymmetry, although clinical significance is suggested by the analysis of the data. CONCLUSION: Measurable asymmetry can be present in the neutrally positioned, ligamentously intact atlanto-axial complex and is not necessarily indicative of instability. This agrees with the concept of the "neutral zone" as described by White and Panjabi in Clinical Biomechanics of the Spine. There is a trend for increasing odontoid lateral mass interspace on the side to which the head is rotated, and this odontoid lateral mass interspace is measurably different from the contralateral odontoid lateral mass interspace, indicating that odontoid lateral mass interspace asymmetry is not a good indicator for cervical instability in the otherwise asymptomatic individual.

Adult↗
PubMed1995

Optimization technique for the calculation of in vitro three-dimensional vertebral motion.

A method for the calculation of translations and Eulerian rotations of an orthogonal axis system with respect to a fixed reference is described with application to the measurement of position in a vertebral motion segment. Kinematic equations were derived to compute the three-dimensional motion of a moving vertebra relative to an adjacent fixed body, without the requirement of a direct physical link between the two bodies. For this calculation, the quadratic error of the lengths of six position vectors was minimized to obtain a mathematically optimal estimate of the translations and rotations. Tests with a rigid model resulted in mean maximum overall system errors of 2.8 percent for the measurement of translation (translations less than 3.5 mm) and 6.1 percent for the measurement of rotations (rotations less than 10 deg) limited by transducer accuracy. The mathematical techniques presented for the quantitative description of rigid body motion, based on the measurement of three reference vectors, may be extended to a broad range of kinematic problems.

Biomechanical Phenomena↗
PubMed1994

The discectomy membrane (nerve root fibrovascular membrane): its anatomic description and its surgical importance.

The positive identification and protection of the nerve root is crucial prior to addressing the disc during lumbar discectomy. We report here our observation that there exists a membrane which lies immediately posterior to the annulus fibrosus at the level of the disc and connects to the dura of the nerve root at that level. This is a constant anatomic finding during the approach to the disc, and we refer to it as the "discectomy membrane". We found this tissue present at all lumbar levels of five fresh frozen cadaver spines. Its consistency varied from thin wisps of nearly transparent tissue to tissue strong enough to tether the nerve root laterally.

Aged↗
PubMed1994

A comparison of the effects of automated percutaneous diskectomy and conventional diskectomy on intradiscal pressure, disk geometry, and stiffness.

Diskectomy, chemonucleolysis, percutaneous diskectomy, and laser ablation are used to treat patients with sciatica. The effects of percutaneous diskectomy on the intradiscal pressure of the human disk are not known. Our aims were to determine (a) whether removal of nucleus through automated percutaneous diskectomy significantly reduces intradiscal pressure without altering the disk geometry and stiffness, and if so, how much nucleus removal is required to achieve these goals; and (b) whether the effects of conventional diskectomy on these same parameters are equivalent to removal of nucleus through automated percutaneous diskectomy. Cyclic compressive loads of 20-900 N were applied to lumbar disks. Conventional diskectomy or automated percutaneous diskectomy (performed for 40 min with biomechanical measurements made four times at 10-min intervals) was then performed under zero load and the specimens retested under the same cyclic compressive loading. There were significant (p < 0.01) decreases in intradiscal pressure (by 7% under 900 N) after 10 min of automated percutaneous lumbar diskectomy. There were no further significant decreases in pressure during the next 30 min of percutaneous diskectomy. There were also significant decreases in pressure due to a puncture hole made with the Nucleotome trephine alone, without removal of disk material, and there was no difference in pressure after trephining alone and after percutaneous diskectomy. Decreases in disk height were significant, ranging from 5% at 10 min to 7% at 40 min of treatment. There were equivalent decreases in intradiscal pressure and disk height due to removal of similar amounts of nucleus during conventional diskectomy and during 40 min of percutaneous diskectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Cryogenic solvents inhibit the binding of the Escherichia coli heat-stable enterotoxin to intestinal brush border membranes.

The cryogenic solvents ethylene glycol, glycerol, dimethyl sulfoxide (Me2SO) and dimethylformamide (Me2FM), with increasing potency, produced concentration-dependent inhibition of the binding of the Escherichia coli heat-stable enterotoxin (STa) to pig intestinal brush border membranes. Inhibition increased with time, and both Me2SO and Me2FM appeared to decrease both the affinity of the STa receptor and the effective receptor number. Both solvents stimulated the release of previously bound 125I-STa (Me2FM > Me2SO), 3 M Me2FM inducing 93% release by 120 min. These effects were reversible, and preincubation of membranes with up to 3 M Me2SO or Me2FM at 37 degrees C for 30 min, followed by washing, did not alter subsequent 125I-STa binding. Also, 125I-STa released from membranes by 3 M Me2FM was shown to rebind to the membranes after 10-fold dilution of Me2FM. Since pretreating membranes with the thiol reagent p-chloromercuribenzenesulfonate had no effect on the release of bound 125I-STa by Me2SO or Me2FM, and since neither of these can reduce disulfide bonds, the formation of mixed disulfides between STa and receptor is unlikely. Me2SO inhibition of 125I-STa binding was greater with membranes than with a partially purified receptor preparation, which may result from the substitution of detergent for the phospholipid normally associated with the receptor(s).

4-Chloromercuribenzenesulfonate↗
PubMed1993

Biomechanics of pin and screw fixation of femoral neck fractures.

Using an in vitro cadaveric femoral neck osteotomy model and a paired experimental design, we compared fixation stiffness and yield load for three- and four-pin configurations for both Knowles pins and Asnis screws and for three Asnis screws versus an AO-ASIF sliding hip screw. Repeat measure analyses of variance indicated a significant increase in stiffness (p < 0.05) with the use of three versus four pins; the yield load did not depend significantly on the number of pins. Fixation was significantly stiffer (p < 0.01) and stronger (p = 0.02) for Knowles pins if the osteotomy was oblique rather than transverse to the femoral neck; the opposite was found for Asnis screws. Femoral fixed with hip screws were significantly stiffer (p < 0.01) than the contralateral side fixed with three Asnis screws. No significant difference in yield load was observed, however. Clinically, it appears from these findings that the use of three Asnis screws or three Knowles pins provides modest increases (averaging 4%) in fixation stiffness with no degradation in strength when compared with four screws or pins. Parallel placement of Asnis screws also provides advantages over nonparallel Knowles pins by allowing controlled impaction of the femoral head. While three Asnis screws provide fixation stiffness approximately 40% less than that found with a sliding hip screw, there is no compromise in fixation strength.

Aged↗
PubMed1993

Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength.

This study investigated (1) the effect of screw diameter and insertion technique in lumbar vertebrae, and insertion site in the sacrum, on the axial pullout force and transverse bending stiffness of pedicle screws, and (2) the effect of bone cement augmentation using polymethylmethacrylate (PMMA) and the biodegradable composite, poly(propylene glycol-fumarate) on axial pullout force and transverse bending stiffness of pedicle screws inserted into lumbar vertebrae. The axial pullout force and transverse bending stiffness of a 6.25-mm Steffee screw and a 6-mm Kluger screw did not differ significantly in vertebral bodies of similar equivalent bone mineral density. The axial pullout force of Schanz screws was significantly increased with a 1-mm increase in screw diameter. However, there was no significant increase in transverse bending stiffness. In the sacrum, an approach through the S1 facet produced significantly higher axial pullout forces and transverse bending stiffness than the approach described by Harrington and Dickson. PMMA and a biodegradable composite bone cement poly(propylene glycol-fumarate) both increased the axial pullout force. PMMA also increased the transverse bending stiffness.

Biomechanical Phenomena↗
PubMed1993

Rehabilitation of athletes following spine injury.

We feel that the described system for staging cervical and lumbar spine injuries in the high-performance athlete affords a basic framework for the rehabilitation of those individuals. With spine injuries, one has to exercise care to rule out those injuries and additional pathologies presenting as neck or back pain that could result in catastrophic sequelae. We stress due diligence in the initial and continued follow-up of these patients with careful evaluation to rule out associated fractures, dislocations, and attendant disc pathology. The treatment of the "stinger" or "burner" is controversial. We suggest a conservative approach, although the orthopedic and neurologic literature reports that these individuals have been returned to full contact sports activity without documented subsequent neurologic sequelae. The final decision remains at the discretion of the treating physician. This program provides a rational approach to the rehabilitation of the spine-injured high-performance athlete that will provide for the return of him or her to preinjury activity level in an expeditious manner with the minimal period of interruption in training.

Athletic Injuries↗
PubMed1993

Magnetic resonance imaging analysis of percutaneous discectomy. A preliminary report.

Twenty-one consecutive patients (27 lumbar discs) were treated by percutaneous discectomy for lumbar herniated disc disease from July 1988 through March 1989. Twenty-six discs in 20 patients were evaluated with preoperative and postoperative magnetic resonance images graded by a neuroradiologist blinded to the clinical and prior imaging results. Fifteen patients were treated by one-level percutaneous discectomy and six patients by two-level percutaneous discectomy. The disc herniations were graded with respect to size, type, location, and hydration status on the magnetic resonance image scans. The postoperative magnetic resonance images were obtained 2-6 months after percutaneous discectomy. Early clinical outcomes after percutaneous discectomy were compared with the various magnetic resonance imaging parameters. Overall, treatment for thirteen patients (62%) was considered clinically successful (decrease or elimination of pain) after percutaneous discectomy, whereas treatment for eight (38%) patients was considered to clinically fail (persistence of pain) with follow-up ranging from 1 to 6 months postoperatively. Three of the patients in whom treatment failed have been subsequently treated successfully by laminotomy and discectomy. On the average, there is a small absolute decrease (5% of the anteroposterior diameter of the spinal canal) in the size of disc herniations when treated by percutaneous discectomy. Although this study is limited by a small sample size and lacks statistical significance, it appears that an early clinical success after percutaneous discectomy may be related to a few magnetic resonance imaging parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Strength reductions from trabecular destruction within thoracic vertebrae.

An in vitro model of metastatic lesions in thoracic vertebrae was used to determine if the reduction in vertebral cross-sectional area could be used to predict the associated strength reduction. Defects, entirely within the trabecular bone, were created in alternating vertebrae of unembalmed human thoracic spines. The adjacent vertebrae were tested intact and served as controls. Defect size was determined as the cross-sectional area of the defect divided by the nominal cross-sectional area of the vertebral body midplane. Vertebrae were tested to failure using combined axial-flexion loads. For each spine, a linear regression was determined between the cross sectional area of the superior endplate and the load at failure for the intact vertebrae. The intact strength of bodies with defects was estimated from this regression. The normalized strength of thoracic vertebrae with trabecular defects was linearly related to the reduction in cross-sectional area (normalized failure load = 1.0-Ad/Ai, r2 = 0.51; Ad = cross-sectional area of defect; and Ai = intact cross-sectional area at midplane). The data suggest that the strength reduction due to lytic defects within the centrum of thoracic vertebrae is proportional to the cross-sectional area of bone resorbed.

Aged↗
PubMed1993

Cervical injuries under flexion and compression loading.

Cervical spine segmental tests were performed to determine the specific patterns of initial cervical injury in response to loading just beyond the point of structural failure. Well-defined combinations of flexion rotation and compression translation were applied to segments with varying degrees of disc and facet degeneration. Twelve cervical spine specimens (from human cadavers ages 52-91 years), each consisting of three vertebrae (two motion segments) from the middle (C2-C5) or lower (C5-T1) regions, were subjected to pure flexion rotation (seven specimens) or to combined flexion rotation and axial compression translation (five specimens). Specimens were sectioned and dissected to determine the patterns of structural failure. Pure flexion, and combined flexion and compression produced similar patterns of injuries. The disc was the most commonly injured structure, with annular injuries noted in 8 of the 12 specimens, and with anterior herniation of the nucleus occurring in two specimens. Wedge fractures and posterior ligament injuries were noted in both specimen groups and with both modes of loading. We conclude that similar patterns of initial anterior bony compressive failure and posterior ligamentous failure can occur with both flexion and with combined flexion-compression, without axial or lateral rotation, at low rates of loading. Anterior cervical disc herniations were produced in both middle and lower cervical segments.

Aged↗
PubMed1992

Nucleotide regulation of heat-stable enterotoxin receptor binding and of guanylate cyclase activation.

Certain nucleotides were found to regulate the binding of the Escherichia coli heat-stable enterotoxin (STa) to its receptor in pig intestinal brush border membranes. ATP and adenine nucleotide analogues inhibited 125I-STa binding, while guanine nucleotide analogues stimulated binding, with maximal effects at 0.5-1.0 mM. The strongest inhibitors were adenosine 5'-[beta gamma-imido]triphosphate (App[NH]p) (36%) and adenosine 5'-[beta-thio]diphosphate (ADP[S]) (41%). Inhibition did not require Mg2+, and was blocked by p-chloromercuribenzenesulphonate (PCMBS). Stimulation of binding required Mg2+, was not prevented by PCMBS and was maximal with GDP[S] (41%). While App[NH]p and MgGDP[S] appeared to be acting at different sites, they also interfered with each other. These nucleotides exerted only inhibitory effects on STa-stimulated guanylate cyclase activity, in contrast with the stimulatory effects of adenine nucleotides on atrial natriuretic peptide (ANP)-stimulated guanylate cyclase. Inhibition by low concentrations of MgApp[NH]p and MgATP was weaker above 0.1 mM, while MgGDP[S] and magnesium guanosine 5'-[gamma-thio]triphosphate (MgGTP[S]) inhibited in a single phase. Inhibition by MgApp[NH]p, at all concentrations, was competitive with the substrate (MgGTP), as was that by MgGDP[S] and MgGTP[S]. Whereas membrane guanylate cyclases usually show positively co-operative kinetics with respect to the substrate, STa-stimulated activity exhibited Michaelis-Menten kinetics with respect to MgGTP. This changed to positive co-operativity when Lubrol PX was the activator, or when the substrate was MnGTP. These results suggest the presence of both a regulatory and a catalytic nucleotide-binding site, which do not interact co-operatively with STa activation.

4-Chloromercuribenzenesulfonate↗