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Biomedical subjects

D L Wheeler

Publications and source records attributed to D L Wheeler.

At least 37 records · Page 2Linked to original sources
PubMed1999

GenBank.

The GenBank (Registered Trademark symbol) sequence database incorporates DNA sequences from all available public sources, primarily through the direct submission of sequence data from individual laboratories and from large-scale sequencing projects. Most submitters use the BankIt (Web) or Sequin programs to format and send sequence data. Data exchange with the EMBL Data Library and the DNA Data Bank of Japan helps ensure comprehensive worldwide coverage. GenBank data is accessible through NCBI's integrated retrieval system, Entrez, which integrates data from the major DNA and protein sequence databases along with taxonomy, genome and protein structure information. MEDLINE (Registered Trademark symbol) s from published articles describing the sequences are included as an additional source of biological annotation through the PubMed search system. Sequence similarity searching is offered through the BLAST series of database search programs. In addition to FTP, Email, and server/client versions of Entrez and BLAST, NCBI offers a wide range of World Wide Web retrieval and analysis services based on GenBank data. The GenBank database and related resources are freely accessible via the URL: http://www.ncbi.nlm.nih.gov

Amino Acid Sequence↗
PubMed1998

Effect of bioactive glass particle size on osseous regeneration of cancellous defects.

The bioactive glass known as Bioglass or Perioglass (USB) (US Biomaterials, Alachua, FL) has proven to be an effective graft material owing to the apatite layer which forms on the surface of the glass, promoting bone formation. USB particles range in size from 90 to 710 microns in diameter, as determined by optical microscopy. A similar bioactive material, BioGran (OV) (Orthovita, Malvern, PA), was developed to limit the particle size of 4555 to the range between 300 and 360 microns, as determined by sieving. The objective of this study was to histologically and biomechanically compare the 4555 bioactive glass, produced by US Biomaterials, in a wide particle range (USB) to the narrower particle range glass produced by Orthovita (OV) The grafted defects will then be compared to normal cancellous bone (NORM) of the distal femur in rabbits. Histologically, more bone was quantified at both 4 and 12 weeks within the defects filled with USB and NORM when compared to the limbs filled with OV (p < 0.05). The OV particles had greater particle axes and larger particle areas on average than the USB particles (p < 0.05). However, the particle axis and area of the two materials decreased with time at a similar rate. Biomechanically, the USB- and OV-grafted defects had comparable peak compressive load, compressive stiffness, and compressive modulus which were equivalent to normal bone.

Animals↗
PubMed1998

Radiomorphometry and biomechanical assessment of recombinant human bone morphogenetic protein 2 and polymer in rabbit radius ostectomy model.

The study objective was to determine the mechanical integrity and radiopacity of regenerated bone within critical-sized defects (CSDs) in radii of rabbits using recombinant human bone morphogenetic protein 2 (rhBMP-2) with a porous, biodegradable poly(D,L-lactic acid) (PDLLA) carrier (designated PLA). Twenty millimeter, unilateral radial ostectomies were created in 96 skeletally mature New Zealand white rabbits. The rabbits were randomly assigned to six treatment groups with two euthanasia periods. Treatment groups included unfilled defect (n = 8), segmental autograft (n = 8), PLA + 0 microg rhBMP-2 (n = 8), PLA + 17 microg rhBMP-2 (n = 8), PLA + 35 microg rhBMP-2 (n = 8), and PLA + 70 microg rhBMP-2 (n = 8). The radiopacity was significantly greater for the 35- and 70-microg rhBMP-2 groups at 4 weeks compared to unfilled controls, PLA only, and 17-microg rhBMP-2 groups and equivalent to the autograft. At 8 weeks all groups receiving rhBMP-2 were equivalent to the autograft and significantly greater than unfilled defects and PLA alone. Similarly, the biomechanical analysis indicated significantly greater torque at failure for the 35-microg rhBMP-2 group compared to all other groups at 4 weeks. By 8 weeks all groups receiving rhBMP-2 and autograft had significantly greater torque than unfilled controls and PLA alone. These radiomorphometric and biomechanical results indicate PLA may be a suitable carrier for rhBMP-2 used for skeletal regeneration.

Animals↗
PubMed1998

Biomechanical assessment of compression screws.

A series of mechanical tests on anatomic specimen cancellous bone and cancellous bonelike foam were conducted to evaluate and compare an Acutrak compression screw with an AO 4-mm cancellous screw and the Herbert screw. The Acutrak and AO screws produced similar fragment compression in foam and bone; Acutrak and AO compression were significantly greater than that of the Herbert screw. However, Acutrak was able to maintain compression after cyclic loading significantly better than were the AO and Herbert screws. The pushout force of Acutrak and AO screws were significantly greater than that of the Herbert screw in foam and bone. The torque required to break fragment contact was significantly greater for the Acutrak than for the AO or Herbert screws, but that for the AO was greater than that for the Herbert screw. The results of this analysis show the Acutrak screw is capable of producing and maintaining compression between bone fracture fragments. In addition, the Acutrak screw was shown to have superior mechanical characteristics than did Herbert screw in every mode tested. The Acutrak screw did not surpass the fragment compression achieved by the AO screw in foam, but it did not overtighten or experience degradation of compression after 500 cycles of simulated physiologic loading.

Biomechanical Phenomena↗
PubMed1997

Histological and biomechanical evaluation of calcium phosphate coatings applied through surface-induced mineralization to porous titanium implants.

The purpose of this pilot study was to evaluate surface-induced mineralization (SIM) as a potential technique to apply ceramic coatings to metal orthopaedic implants. Cylindrical titanium porous-coated implants were either coated by SIM or plasma-spray (PLS) techniques with calcium phosphate, or left uncoated (CTL). The implants were bilaterally implanted into the intramedullary canal of the proximal femur of 24 adult New Zealand white rabbits segregated into the following groups: PLS/CTL, SIM/CTL, and SIM/PLS. After 6 weeks in vivo, biomechanical and histologic evaluations were completed. Biomechanically, SIM had consistently greater mechanical interlock than PLS implants. However, CTL implants had greater mechanical interlock than both PLS and SIM. The small sample size prevented statistical evaluation and definitive biomechanical conclusions. Histologically, SIM and PLS had significantly greater ingrowth than CTL implants (p < 0.05). The SIM coating technique produced similar ingrowth characteristics as standard PLS coatings, yet may prevent osteolysis by providing a stronger, more reliable, covalent bond between the ceramic and metal.

Alloys↗
PubMed1997

Evaluation of particulate Bioglass in a rabbit radius ostectomy model.

Osseous defects and fractures may require supplimentation to support and promote healing. Bioglass (BG) may be a useful therapeutic for these conditions. Therefore, we executed a study to determine whether particulate BG could promote healing of 20-mm unilateral ostectomies in the radius of rabbits. Ostectomies were either treated with BG or remained untreated in the control (CTL) group. At 4 and 8 weeks post-treatment, ostectomies were assessed histomorphometrically and biomechanically. New bone formation was more intense contiguous to the host bone for both BG and CTL than centrally, yet BG animals displayed active mineralization throughout the ostectomy. The amount of bone within BG-filled defects was greater than CTLs at 4 weeks, whereas, at 8 weeks there was no difference. Biomechanically, the BG-treated limbs required more torque to break than did CTL limbs at 4 weeks; however differences were not significantly different. By 8 weeks, the BG-treated and CTLs, had comparable strength. Bioglass may be a useful therapy to produce the early phase of osseous repair. However, improvements in handling properties of the particles will be needed to enhance efficacy.

Animals↗
PubMed1997

Comparison of reconstruction nails for high subtrochanteric femur fracture fixation.

Subtrochanteric osteotomies were created in 18 matched pairs of embalmed cadaveric femora. The femora were stabilized with a Synthes, Zimmer, or Richards second generation femoral reconstruction nail with retrograde blade or screws. The femoral pairs were randomly assigned to groups based on nails used: Synthes versus Zimmer, Synthes versus Richards, and Zimmer versus Richards. The reconstructions were cyclically loaded in bending for 2000 cycles and then loaded to failure. The mean stiffness of the Synthes, Zimmer, and Richards reconstructions was 17%, 40%, and 40% of the intact femora, respectively. The Richards construct was the strongest, and predominately failed by fracture at the distal interlocking screw hole. The Zimmer construct failed by bending of the nail at the osteotomy site and fracture of the proximal femoral shaft. The Synthes construct was the most flexible and least strong and failed by bending of the spiral, retrograde blade with concomitant fracture of the femoral neck. This study indicates that fixation of subtrochanteric femur fractures with a Synthes spiral blade or Richards or Zimmer reconstruction nails provides stable fixation for postoperative loading conditions. However, the Richards and Zimmer nails were able to withstand higher loads than was the Synthes nail before failure.

Adult↗
PubMed1997

Biomechanical comparison of intramedullary and percutaneous pin fixation for proximal humeral fracture fixation.

OBJECTIVES: The purpose of this study was to investigate the mechanical strength and durability of intramedullary nailing (IM) and percutaneous pinning (PP) for fixation of three-part proximal humeral fractures using a cadaveric model. DESIGN: Three-part surgical neck fractures were created in paired embalmed cadaveric humeri. Fractures were fixed with IM and PP fixation. The fixation stiffness and durability was assessed under cyclic rotational loading (infraspinatus) ramping from 0.1 to 1.25 Newton-meters for 10,000 cycles. The specimen were then torsionally loaded to failure. SETTING: Mechanical testing was performed using a servohydraulic test system (MTS, Minneapolis, MN, U.S.A.). INTERVENTION: PP fixations were accomplished using standard multiplane techniques. IM fixation was attained using an 11.0-millimeter-diameter curved rod interlocked proximally with three splayed 5.0-millimeter cancellous screws and distally with three 3.5-millimeter cortical screws. MAIN OUTCOME MEASUREMENTS: During cyclic loading the reconstruction stiffness, angular migration, and angular displacement per cycle were measured and compared between fixation methods. The ultimate torque at failure, absolute angular migration, and reconstruction stiffness during failure were recorded and compared between fixation methods during destructive testing. RESULTS: The intramedullary device had greater stiffness and less angular displacement of fragments during cyclic loading. When loading the reconstructions to failure, the intramedullary device proved to have greater failure torques, stiffness, energy absorbed, and angular displacement before failure. CONCLUSIONS: This biomechanical study showed that the IM device provided a stronger, more stable, and durable fixation option than did PP fixation for large-fragment multipart proximal humeral fractures with minimal comminution.

Biomechanical Phenomena↗
PubMed1995

Computer simulation of the directional displacement of rod-shaped, arc-shaped, and circular objects in an array of obstacles, representing a simple model for the gel electrophoresis of small DNA.

The gel electrophoresis of DNA of identical length but various static conformations was simulated using a two-dimensional model of the movement of rod-shaped, arc-shaped, and circular objects through random arrays of disk-shaped obstacles. At low obstacle density, the displacement rate of these objects decreases from the rod-shaped to the circular to the arc-shaped objects. At high obstacle densities, the displacement rate of circular objects approaches zero. The alignment of the arc-shaped objects along the axis of the directional movement of the objects were retarded in their movement by collisions with the obstacles; the number of collisions of the former, in view of their greater ability to align, was less than that of the latter. Circular objects were exclusively retarded by collisions, while the arc-shaped objects exhibited an additional retarding mechanism, viz. the suspension ("hanging") on the obstacles. When the rigid objects were made flexible, their displacement increased. The increase was most pronounced with the circular objects, allowing them to penetrate at obstacle densities from which the rigid objects were excluded.

Computer Simulation↗
PubMed1995

The short- and long-term effects of methotrexate on the rat skeleton.

Both clinical and laboratory studies have shown that the chemotherapy drug, Methotrexate (MTX), has adverse short-term effects on bone. There are no studies that demonstrate the long-term response of bone to MTX. The purpose of this study was to determine the short- and long-term effects of MTX on bone volume, turnover, mineralization and strength. Three-month-old Sprague-Dawley rats were randomly assigned to a control (CTL) or MTX group and were given either daily MTX or saline injections for two separate 5-day courses (5 on/9 off/5 on). Fluorochrome compounds were injected prior to killing to label actively mineralizing bone surfaces. One CTL and MTX group were killed at 30, 80 and 170 days after treatment. Both femurs and tibiae were harvested for cancellous and cortical bone histomorphometry and biomechanical testing (torsion). Standard cancellous and cortical histomorphometric parameters were measured from undecalcified, methyl-methacrylate-embedded sections from the right proximal tibia and tibial and femoral diaphyses. The contralateral femur and tibia were torsionally loaded to failure and standard mechanical parameters were measured. All bone responses were statistically analyzed using a two-way ANOVA followed by Duncan's multiple comparison procedure (significance: p = 0.05). Cancellous bone volume was significantly lower in the MTX-treated group at 80 and 170 days. Cancellous mineralizing surface and longitudinal bone growth were significantly depressed at all time points yet mineral apposition rate was only depressed at the 170-day point. Cancellous osteoclast surface was increased at all time points for the MTX-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1995

Effects of running on the torsional strength, morphometry, and bone mass of the rat skeleton.

Intensity and duration effects of weight-bearing exercise on the rat skeleton were investigated. Eighty-four 3-month-old female Sprague-Dawley rats were assigned to control and nine exercise groups. Exercised rats were run on a treadmill for either 30, 60, or 90 min.d-1 at low (Vo2max approximately 55%), medium (VO2max approximately 65%), or high (VO2max approximately 75%) intensity 4 d.wk-1 for 10 wk. Rat femurs, tibias, and vertebrae were harvested for torsional mechanical tests, bone density assessment, and morphometry. Our results indicate exercise has a significant effect (P < 0.05) on the femoral mechanical response (energy absorbed and twist angle), tibial morphometry (cortical bone area and thickness), and tibial and vertebral bone density measurements but had no effect (P > 0.05) on bone strength when compared with control values. Higher intensity exercise decreased tibial and femoral torque (P < 0.05). Long duration exercise increased tibial and femoral stiffness and decreased twist angle and energy absorbed (P < 0.05). These results indicate bone adapts to its loading environment by increasing bone mineral density, increasing cortical bone area, increasing stiffness, decreasing energy absorbed, and decreasing twist angle. High-intensity exercise decreased the maximum force the bone could withstand, whereas long duration exercise made the bone more brittle.

Absorptiometry, Photon↗
PubMed1994

Functional assessment for prediction of lifting capacity.

OBJECTIVE: This study investigated the ability to predict maximal functional lifting capacity from peak isometric lumbar extension torque and submaximal lifting mechanics. METHODS: Peak isometric lumbar extension torques were measured on 26 healthy men and women, ages 18 to 39 years. In addition, their lifting mechanics were evaluated while they lifted a submaximal load. Each subject's maximal lifting capacity (kg) then was predicted from the peak torque and submaximal kinetic analysis using a linear regression model. RESULTS: Mean values for the predicted and actual maximum weight the subjects lifted were not significantly different (50.3 +/- 15.6 kg and 48.5 +/- 17.0 kg, respectively, P > or = 0.05). The correlation between predicted and criterion values was high (r = 0.96), and the total error of the prediction was 5.1 kg, which represented 10.5% of the actual maximum value. CONCLUSIONS: This multi-faceted functional assessment model involving biomechanical analysis of a submaximal lift and maximal isometric lumbar extension strength accurately predicted a subject's maximum functional lifting capacity.

Adult↗
PubMed1994

A computer simulation accounting for dissimilar electrophoretic behavior between two similarly curved DNA fragments due to a difference in arc-length.

Arc-shaped bent DNA fragments of the same predicted planar curvature but differing in length by 20% were compared in regard to their mobilities in 3 to 10% polyacrylamide. The longer (155 bp) fragment is retarded far more severely than the shorter (124 bp) fragment. The effect of gel concentration in promoting the retardation is far more pronounced for the 155 bp than for the 124 bp fragment. Moreover, a temperature change from 25 degrees C to 4 degrees C does not substantially affect the gel concentration dependent mobility of the 124 bp fragment while it increases the retardation of the 155 bp fragment greatly. The strong increase in retardation brought about by a mere 20% increase in the length of the arc was accounted for by a simple computer simulation of gel electrophoresis which considered the rate of passage of arc-shaped objects through a two-dimensional array of disc-shaped obstacles. Since the simulation relies exclusively on geometric factors, its success in predicting the behavior of the 124 and 155 bp DNA fragments suggests that geometric factors are largely responsible for their electrophoretic properties. The simulation can account for the strong temperature effect on the retardation of a model of the 155 bp DNA in polyacrylamide gels by showing that a decreased degree of random motion has a profound effect on the modeled 155 bp particle, but not on the modeled 124 bp DNA.

Computer Simulation↗
PubMed1994

Reliability of passive wrist flexion and extension goniometric measurements: a multicenter study.

BACKGROUND AND PURPOSE: The purpose of this study was twofold: (1) to determine whether passive wrist flexion and extension goniometric measurements using ulnar alignment, radial alignment, and volar/dorsal alignment were similar or dissimilar and (2) to examine which of these three techniques had the greatest intratester and intertester reliability. SUBJECTS: One hundred forty patients (141 wrists) were measured. The testers were 32 therapists from eight different hand/upper-extremity clinical sites around the United States. METHODS: Randomly paired testers measured passive wrist flexion and extension. The intraclass correlation coefficient (ICC) was used as an estimate of agreement for both intratherapist (model 3.1) and intertherapist (model 2.1) reliability. RESULTS: Six of the eight clinics showed significant differences among the various goniometric techniques. Flexion intratherapist mean ICCs for the radial, ulnar, and dorsal alignment techniques were .86, .87, and .92, respectively. Extension intratherapist mean ICCs were .80, .80, and .84 for the three techniques. Intertherapist flexion mean ICCs were .88, .89, and .93 for the radial, ulnar, and volar alignment techniques, respectively. Extension intertherapist mean ICCs were .80, .80, and .84 for the three techniques. The standard error of measurement was also used to quantify reliability, with the volar/dorsal alignment technique consistently producing less error than the ulnar and radial alignment techniques. The generalizability theory statistical model was utilized to identify the sources of error. The patient contributed to variance the most, although inherent error within the study, diagnostic category, therapeutic approach, and goniometric technique also contributed. CONCLUSION AND DISCUSSION: The overall results indicated there were differences among the three goniometric techniques. The volar/dorsal alignment technique is the goniometric technique of choice, as it consistently had the greatest reliability.

Adolescent↗
PubMed1994

A comparison of the amount of vascularity in pagetic and normal human bone.

The lower extremity of a patient with Paget's disease of the proximal femur was infused with contrast medium after hemipelvectomy. Cross sectional specimens were computer analyzed to compare quantitatively the microvascularity of the proximal femoral pagetic bone to the distal femoral normal bone. The pagetic bone contained nearly six times more contrast per cross sectional area (28%) than the normal bone (5%).

Angiography↗
PubMed1993

An experimental assessment of facilitated communication.

This report presents a quantitative study of facilitated communication. Participants were 12 people living at an institutional autism program and 9 people who provided them with facilitated communication support. These subjects were the 12 most competent producers of facilitated communication in the program. They were shown pictures of familiar objects and asked to type the names of the objects under three conditions: (a) assisted typing with facilitators unaware of the content of the stimulus picture, (b) unassisted typing, and (c) a condition in which the participants and facilitators were each shown pictures at the same time. In this last condition the paired pictures were either the same or different, and the participant's typing was facilitated to label or describe the picture. These participants were unable to succeed in the tasks without facilitator assistance. On trials when the facilitators and participants had different pictures, the only "correct" labels were for pictures shown to the facilitators and not shown to the participants. This finding demonstrates that the facilitators were unknowingly determining what was typed.

Adolescent↗
PubMed1990

Overview of the Department of Energy's Off-Site Radiation Exposure Review Project (ORERP).

The Off-Site Radiation Exposure Review Project (ORERP) was established by the U.S. Department of Energy to (1) collect, preserve, and disseminate historical data related to radioactive fallout and health effects from nuclear testing, and (2) reconstrut, insofar as possible, the exposures to the off-site public from nuclear testing at the Nevada Test Site and doses to individuals resulting from these exposures. The goals, methods, and example results of the ORERP are presented.

Archives↗