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Biomedical subjects

J C Leong

Publications and source records attributed to J C Leong.

At least 19 recordsLinked to original sources
PubMed2006

Preliminary studies of sperm cryopreservation in the mushroom coral, Fungia scutaria.

Coral species throughout the world are facing severe environmental pressures. Because of this, we began cryobiological studies on the sperm of the mushroom coral, Fungia scutaria. We determined that F. scutaria sperm had a mean length of 56 microm and head diameter of 2.5 microm, and a mean spontaneous ice nucleation temperature of -37.2 +/- 1.7 degrees C. When the sperm were exposed to the cryoprotectant glycerol for 5 or 20 min (at 10% v/v), no fertilized larvae were produced. However, when sperm were exposed for 20 min to propylene glycol (10% v/v), fertilizations were produced at the same rate as untreated control eggs and sperm (P > 0.05), but slightly less for dimethyl sulfoxide (10% v/v) (P < 0.05). Regardless, dimethyl sulfoxide caused less osmotic damage to the sperm membrane than did propylene glycol. Therefore, we used the dimethyl sulfoxide (10% v/v) to develop cryopreservation protocols that yielded good post-thaw morphology and motility (>95%) for coral sperm.

Animals↗
PubMed2005

Coral larvae conservation: physiology and reproduction.

Coral species throughout the world's oceans are facing severe environmental pressures. We are interested in conserving coral larvae by means of cryopreservation, but little is known about their cellular physiology or cryobiology. These experiments examined cryoprotectant toxicity, dry weight, water and cryoprotectant permeability using cold and radiolabeled glycerol, spontaneous ice nucleation temperatures, chilling sensitivity, and settlement of coral larvae. Our two test species of coral larvae, Pocillopora damicornis (lace coral), and Fungia scutaria (mushroom coral) demonstrated a wide tolerance to cryoprotectants. Computer-aided morphometry determined that F. scutaria larvae were smaller than P. damicornis larvae. The average dry weight for P. damicornis was 24.5%, while that for F. scutaria was 17%, yielding osmotically inactive volumes (V(b)) of 0.22 and 0.15, respectively. The larvae from both species demonstrated radiolabeled glycerol uptake over time, suggesting they were permeable to the glycerol. Parameter fitting of the F. scutaria larvae data yielded a water permeability 2 microm/min/atm and a cryoprotectant permeability = 2.3 x 10(-4) cm/min while modeling indicated that glycerol reached 90% of final concentration in the larvae within 25 min. The spontaneous ice nucleation temperature for F. scutaria larvae in filtered seawater was -37.8+/-1.4 degrees C. However, when F. scutaria larvae were chilled from room temperature to -11 degrees C at various rates, they exhibited 100% mortality. When instantly cooled from room temperature to test temperatures, they showed damage below 10 degrees C. These data suggest that they are sensitive to both the rate of chilling and the absolute temperature, and indicate that vitrification may be the only means to successfully cryopreserve these organisms. Without prior cryopreservation, both species of coral settled under laboratory conditions.

Animals↗
PubMed2005

Inhibition of infectious haematopoietic necrosis virus in cell cultures with peptide-conjugated morpholino oligomers.

Delivery of phosphorodiamidate morpholino oligomers (PMO) into fish cells in vitro and tissues in vivo was examined. Uptake was evaluated by fluorescence microscopy and flow cytometry after treating cultured cells or live rainbow trout with 3' fluorescein-tagged PMO. Arginine-rich peptide conjugated to the 5' end of the PMO markedly enhanced cellular uptake in culture by 8- to 20-fold compared with non-peptide-conjugated PMO as determined by flow cytometry. Enhanced uptake of PMO conjugated to peptide was also observed in tissues of fish treated by immersion. The efficacy of PMO as inhibitors of infectious haematopoietic necrosis virus (IHNV) replication was determined in vitro. Peptide-conjugated PMOs targeting sequences within the IHNV genomic RNA (negative polarity) or antigenomic RNA (positive polarity) significantly inhibited replication in a dose-dependent and sequence-specific manner. A PMO complementary to sequence near the 5' end of IHNV genomic RNA was the most effective, diminishing titre by 97%, as measured by plaque assay and Western blot. These data demonstrate that replication of a negative-stranded non-segmented RNA virus can be inhibited by antisense compounds that target positive polarity viral RNA, or by a compound that targets negative polarity viral RNA.

Animals↗
PubMed2001

Bioactive bone cement as a principal fixture for spinal burst fracture: an in vitro biomechanical and morphologic study.

STUDY DESIGN: An in vitro biomechanical and radiographic study to evaluate the properties of a newly developed bioactive bone cement for stabilization of the fractured spine, suitable for minimally invasive application. OBJECTIVES: To determine the mechanical stability of the fractured spine after injection of the newly developed bioactive bone cement under quasi-static and cyclic loading regimens. SUMMARY OF BACKGROUND DATA: Bone cement injection has been reported as a potentially useful, minimally invasive technique for treating vertebral body fracture or stabilizing osteoporosis. However, potential problems associated with the use of polymethylmethacrylate (PMMA) have prompted the search for alternative solutions. The use of bioactive bone cement as a potential replacement for PMMA has been reported. METHODS: Biomechanical and radiographic analyses were used to test the mechanical stability of the fractured spine. The cement used was formed from hydroxyapatite powder containing strontium and bisphenol A diglycidylether dimethacrylate (D-GMA) resin. Twenty-six fresh porcine spine specimens (T10-L1) were divided into three groups: pilot, intact, and cemented. Spinal stiffness and failure strength were recorded in the intact group with the specimens flexed at 10 degrees. Uniform injuries were created in all specimens of the cemented group, and compressive loading was applied with 10 degrees of flexion until a fracture occurred. The bone cement was injected into the fractured spine, and stiffness was evaluated after 1 hour. Failure strength was also recorded after 3000 and 20,000 fatigue load cycles. Morphology of the specimens was observed and evaluated. RESULTS: Results from a cell biocompatibility test indicated that the new bioactive bone cement was favorable for cell growth. Spinal stiffness significantly decreased after fracture (47.5% of intact condition). Instant stiffness of the spine recovered to 107.8% of the intact condition after bone cement injection. After 3000 and 20,000 cycles of fatigue loading, stiffness of the cemented spine was found to be 93.5% and 94.4% of intact stiffness, respectively (P < 0.05). Average failure strength of the spine was 5056 N (after 3000 cycles) and 5301 N (after 20,000 cycles) after bone cement injection and fatigue loading. Radiographs and cross-sectional observations indicated a good cement-bone bonding and fracture fill. CONCLUSIONS: A new bioactive bone cement without cytotoxic effect has been developed. Results show that minimally invasive techniques to apply this cement to porcine spines results in augmentation of mild burst fractures such that the original stiffness and strength of the vertebra are recovered. This new cement therefore shows potential as an augmentation to traditional instrumentation in the surgical management of vertebral fractures. The potential for further clinical applications is currently under investigation.

Animals↗
PubMed2001

Comparison of time-frequency distribution techniques for analysis of spinal somatosensory evoked potential.

Spinal somatosensory evoked potential (SSEP) has been employed to monitor the integrity of the spinal cord during surgery. To detect both temporal and spectral changes in SSEP waveforms, an investigation of the application of time-frequency analysis (TFA) techniques was conducted. SSEP signals from 30 scoliosis patients were analysed using different techniques; short time Fourier transform (STFT), Wigner-Ville distribution (WVD), Choi-Williams distribution (CWD), cone-shaped distribution (CSD) and adaptive spectrogram (ADS). The time-frequency distributions (TFD) computed using these methods were assessed and compared with each other. WVD, ADS, CSD and CWD showed better resolution than STFT. Comparing normalised peak widths, CSD showed the sharpest peak width (0.13+/-0.1) in the frequency dimension, and a mean peak width of 0.70+/-0.12 in the time dimension. Both WVD and CWD produced cross-term interference, distorting the TFA distribution, but this was not seen with CSD and ADS. CSD appeared to give a lower mean peak power bias (10.3%+/-6.2%) than ADS (41.8%+/-19.6%). Application of the CSD algorithm showed both good resolution and accurate spectrograms, and is therefore recommended as the most appropriate TFA technique for the analysis of SSEP signals.

Evoked Potentials, Somatosensory↗
PubMed2001

Back muscle contraction patterns of patients with low back pain before and after rehabilitation treatment: an electromyographic evaluation.

The aims of this study were to conduct a comparative investigation of muscle function between patients with low back pain (LBP) and healthy persons, and to determine whether intensive rehabilitation can change back muscle contraction synergy. Twenty healthy persons and 20 patients with chronic LBP were asked to perform symmetrical and asymmetric tasks. The patients with LBP were tested in the weeks immediately before and after 12 weeks of LBP rehabilitation. Tasks include "carrying" weights up and down and with a 45 degrees left rotation. Eight-channel surface electromyographic electrodes were placed on the surface of paraspinal muscles over the lumbar region. Correlations between the right and left corresponding muscles and between values before and after treatment were determined. Lifting capacity for patients with LBP were also measured before and after treatment. Results from electromyographic profiles showed that the muscle activity strategies varied between healthy persons and patients with LBP. The correlation coefficients for spinal muscles have shown very reproducible intrasubject muscle contraction synergies. Unbalanced electromyographic patterns found in patients with LBP given symmetrical tasks were not affected by rehabilitation treatment.

Adult↗
PubMed2001

Effect of stimulation parameters on intraoperative spinal cord evoked potential monitoring.

The purpose of this study was to investigate the effects of the stimulus parameters on spinal cord evoked potential (SCEP) and to recommend a practical epidural stimulation protocol for intraoperative spinal cord monitoring. This prospective study compared the latencies and amplitudes of SCEP obtained on epidural stimulation of 30 patients with scoliosis under anesthesia using different stimulus pulse duration and stimulation rates. SCEP was found to be undetectable with shorter stimulus duration (<0.05 ms). The SCEP latencies did not show any significant difference among different stimulation parameters. However, the SCEP amplitude showed significant changes with differing stimulus durations. The SCEP amplitudes were found to significantly decrease when the pulse durations become shorter than 0.2 ms. Stimulus parameters showed significant effects on SCEP amplitude but not latency. Stimulus rates in the range of 21 to 61 Hz are equivalent for quick and reliable detection of SCEP. Considering the short latency of SCEP, a pulse duration of 0.2 ms is recommended for SCEP using epidural stimulation.

Adolescent↗
PubMed2001

Prevention of spinal cord injury with time-frequency analysis of evoked potentials: an experimental study.

OBJECTIVES: To verify the applicability and validity of time-frequency analysis (TFA) of evoked potential (EP) signals in detecting the integrity of spinal cord function and preventing spinal cord injury. METHODS: The spinal cord was simulated during surgery in 20 mature rats by mechanically damaging the spinal cord. Cortical somatosensory evoked potential (CSEP), spinal somatosensory evoked potential (SSEP), cortical motor evoked potential (CMEP), and spinal cord evoked potential (SCEP) were used to monitor spinal cord function. Short time Fourier transform (STFT) was applied to the CSEP signal, and cone shaped distribution (CSD) was used as the TFA algorithm for SSEP, CMEP, and SCEP signals. The changes in the latency and amplitude of EP signals were measured in the time domain, and peak time, peak frequency, and peak power were measured in the time-frequency distribution (TFD). RESULTS: The TFDs of EPs were found to concentrate in a certain location under normal conditions. When injury occurred, the energy decreased in peak power, and there was a greater dispersion of energy across the time-frequency range. Strong relations were found between latency and peak time, and amplitude and peak power. However, the change in peak power after injury was significantly larger than the corresponding change in amplitude (p<0.001 by ANOVA). CONCLUSIONS: It was found that TFA of EPs provided an earlier and more sensitive indication of injury than time domain monitoring alone. It is suggested that TFA of EP signals should therefore be useful in preventing spinal cord injury during surgery.

Algorithms↗
PubMed2001

Talectomy in patients with recurrent deformity in club foot. A long-term follow-up study.

We reviewed 24 feet in 15 patients who had undergone talectomy for recurrent equinovarus deformity; 21 were associated with arthrogryposis multiplex congenita, two with myelomeningocele and one with idiopathic congenital talipes equinovarus. The mean follow-up was 20 years. Good results were achieved in eight feet (33%) in which further surgery was not needed and walking was painless; a fair result was obtained in ten feet (42%) in which further surgery for recurrence of a hindfoot deformity had been necessary but walking was painless; the remaining six feet (25%) were poor, with pain on walking. All patients wore normal shoes and could walk independently, except one who was wheelchair-bound because of other joint problems. Recurrent deformity, the development of tibiocalcaneal arthritis and spontaneous fusion of the tibia to the calcaneum were all seen in these patients.

Child↗
PubMed2001

Necrotising fasciitis of a limb.

Between January 1992 and December 1998, we treated 24 patients with necrotising fasciitis of a limb. There were 15 men and nine women with a mean age of 59.8 years (5 to 86). The infection was usually confused with cellulitis. Exquisite pain and early systemic toxicity were the most consistent clinical features. Diabetes mellitus and hepatic cirrhosis were the most commonly associated medical diseases. One third of the patients died. Those with involvement of the limbs above the knee or elbow on admission had a significantly higher rate of mortality than those with distal lesions (Fisher's exact test, p = 0.027). There was no correlation between mortality and advanced age (Student's t-test, p = 0.22) or between amputation and survival (Fisher's exact test, p = 0.39).

Adolescent↗
PubMed2000

The effects of cyclic loading on pull-out strength of sacral screw fixation: an in vitro biomechanical study.

STUDY DESIGN: The pull-out strength of sacral screw fixation after cyclic loading was tested using young human cadaveric specimens. OBJECTIVES: To evaluate the effects of fatigue loading on the pull-out strength of medial and lateral unicortical and bicortical sacral screws and to correlate the pull-out strength with sacral bone density and the screw insertion torque. SUMMARY OF BACKGROUND DATA: The immediate biomechanical effects of depth of penetration, screw orientation, and bone density on sacral screw fixation have been studied in aged cadaveric specimens. The effect of cyclic loading on the pull-out strength of sacral screw fixation is unknown, however, and data from young specimens is rare. METHODS: Eleven fresh specimens of human sacrum were used in this study. Bone mineral density at the vertebral body and the ala were determined by peripheral quantitative computed tomography. Seven-millimeter compact Cotrel-Dubousset sacral screws were inserted into the sacrum anteromedially and anterolaterally, both unicortically and bicortically, and the insertion torque for each screw was measured. Cyclic loading from 40 to 400 N was applied to each screw at a frequency of 2 Hz up to 20,000 cycles. Pull-out tests were conducted after completion of the fatigue tests. RESULTS: The average bone density was 0.38 +/- 0.08 g/mL at the S1 body and 0.24 +/- 0.05 g/mL at the S1 ala. The insertion torque and average pull-out force after cyclic loading were significantly higher for bicortical fixation than for unicortical fixation for a particular screw alignment. The pull-out strength and insertion torque of medially oriented fixation was always higher than that for lateral fixation, however, regardless of whether the insertion was unicortical or bicortical. The pull-out force of unicortical and bicortical medial screw fixations after cyclic loading showed significant linear correlations with both the insertion torque and the bone mineral density of the S1 body. CONCLUSIONS: In a young population, screw orientation (anterolateral or anteromedial) was more important in determining pull-out strength than screw depth (unicortical or bicortical) after fatigue loading, anteromedially directed screws being significantly stronger than laterallyplaced screws. Bone mineral density of the S1 body andinsertion torque were good preoperative and intraoperative indicators of screw pull-out strength.

Adult↗
PubMed2000

Mx mRNA expression and RFLP analysis of rainbow trout Oncorhynchus mykiss genetic crosses selected for susceptibility or resistance to IHNV.

Three interferon-inducible Mx genes have been identified in rainbow trout Oncorhynchus mykiss and their roles in virus resistance have yet to be determined. In mice, expression of the Mx1 protein is associated with resistance to influenza virus. We report a study to determine whether there was a correlation between the expression of Mx in rainbow trout and resistance to a fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV). A comparison of Mx mRNA expression was made between different families of cultured rainbow trout selected for resistance or for susceptibility to IHNV. A trout-specific Mx cDNA gene probe was used to determine whether there was a correlation between Mx mRNA expression and resistance to the lethal effects of IHNV infection. Approximately 99% of trout injected with a highly virulent strain of the fish rhabdovirus, IHNV, were able to express full length Mx mRNA at 48 h post infection. This is markedly different from the expression of truncated, non-functional Mx mRNA found in most laboratory strains of mice, and the ability of only 25% of wild mice to express functional Mx protein. A restriction fragment length polymorphism (RFLP) assay was developed to compare the Mx locus between individual fish and between rainbow trout genetic crosses bred for IHNV resistance or susceptibility. The assay was able to discriminate 7 distinct RFLP patterns in the rainbow trout crosses. One cross was identified that showed a correlation between homozygosity at the Mx locus and greater susceptibility to IHN-caused mortality.

Animals↗
PubMed2000

Variation in bone mineral density of the sacrum in young adults and its significance for sacral fixation.

STUDY DESIGN: Bone mineral density variations throughout the sacrum were measured and correlated with sacral screw insertion torque. OBJECTIVE: To quantify bone mineral density variations within the S1 body and ala of young human specimens, especially along the pathways of sacral screws, and to examine the relation between sacral screw fixation and bone mineral density. SUMMARY OF BACKGROUND DATA: Vertebral bone quality is an essential factor in anterior or posterior screw fixation of the spine. Several studies have been conducted regarding bone mineral density variations in the cervical and thoracolumbar spine. However, such variations in bone mineral density in the sacrum have not been well documented. METHODS: The bone mineral density of 13 sacral specimens from young male cadavers (mean age, 31 years) was measured using highly accurate quantitative computed tomography. Variations in bone mineral density were measured in five transverse layers and seven vertical columns within the S1 body, and in four transverse layers and six vertical columns within the ala. The sacral screw insertion torque was measured (unicortical and bicortical), and the correlation with bone mineral density was calculated. RESULTS: The mean bone mineral density of the S1 body was 381.9 +/- 59 mg/cm3, which was 31.9% higher than that of the sacral ala (mean, 296.9 +/- 86 mg/cm3) (P < 0.05). Bone mineral density of the superior sacral endplate was higher than that of any other transverse layer. Columns near the lateral posterior and lateral anterior of the S1 body had the highest bone mineral density. In the ala, bone mineral density values of the internal columns (pedicle) were the highest. Screw insertion torque for bicortical purchase along the S1 pedicle correlated well with the bone mineral density of the S1 body (r = 0.67, P < 0.05). CONCLUSION: This study quantified the volumetric bone mineral density variations within the S1 body and ala, and a significant linear correlation between the screw insertion torque and bone mineral density was found. Optimal sacral screw insertion pathways were also outlined based on bone mineral density values.

Adult↗
PubMed2000

A novel injectable bioactive bone cement for spinal surgery: a developmental and preclinical study.

The injection of bone cement by minimally invasive techniques for the treatment of vertebral body fractures or for stabilization of an osteoporotic vertebral body is regarded as promising in spinal surgery. The purpose of this study was to develop a novel injectable bioactive bone cement to address such concerns. The cement was composed mainly of strontium-containing hydroxyapatite (Sr-HA) filler and Bisphenol A Diglycidylether Dimethacrylate (D-GMA) resin. The Sr-HA filler was prepared by precipitation and calcination, then analyzed with Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns. Samples of strontium-containing hydroxyapatite cement (SrHAC) were formed by a combination of powder filler and resin matrix, with the setting time and peak temperature recorded. Cell relative growth rate (RGR), Tetrazolium bromide (MTT), and haemolysis tests were used to detect initial in vitro biocompatibility of the new cement. In vitro spinal biomechanical testing and morphological observation after bone cement injection were performed on pig spines. Results indicate that the setting time and peak temperature of the cement was 15 min and 55 degrees C, respectively. Cytotoxicity of the cement was class 1 (no cytotoxicity) and haemolysis was 1% (no haemolysis). Stiffness after cement injection and fatigue loading were 112% and 95% of the intact bone, respectively, which is similar to that of natural bone. Radiopacity of SrHAC allowed easy radiographic imaging. The use of SrHAC cement is, thus, promising in spinal surgery.

Animals↗
PubMed2000

Loosening of sacral screw fixation under in vitro fatigue loading.

Sacral screw fixation is frequently used for fusion of the lower lumbar spine, but sacral screws appear to offer less secure fixation than lumbar pedicle screws, and failure due to loosening under fatigue loading is common. The aim of this study was to examine in vitro the stability of medial and lateral bicortical and unicortical sacral screw fixation under a physiologically relevant fatigue-loading pattern. Bone mineral density, screw insertion torque, and screw-fixation stiffness were measured prior to cyclic loading between 40 and 400 N compression at 2 Hz for 20,000 cycles. The screw-fixation stiffness was measured every 500 cycles, and the axial pullout strength of the screws was recorded following loading. All of the lateral insertions loosened under the applied loading, but some of the medial insertions remained stable. Medial insertions proved stiffer and stronger than lateral insertions, and bicortical fixations were stronger than unicortical fixations. Bone mineral density and insertion torque were correlated with screw stiffness and pullout strength, although better correlation was found for insertion torque than bone mineral density. Bone mineral density is a good preoperative indicator of sacral screw-fixation strength, and insertion torque is a good intraoperative indicator. An insertion torque greater than 1.5 Nm is suggested as an indicative value for a stable medial unicortical insertion, whereas an insertion torque greater than 2 Nm suggests a stable medial bicortical insertion. It appears that, apart from the choice of technique (screw orientation and depth), minimizing the load on the screws during the initial part of the fusion process is also critical to maintain stability of the fused section and to obtain a solid fusion mass.

Adult↗
PubMed2000

Neutrophil-independent protective effect of r-metHuG-CSF in ischaemia-reperfusion injury in rat skeletal muscle.

The aim of this study was to investigate the effect of the cytokine, r-metHuG-CSF, in a rat model of ischaemia-reperfusion (IR) injury and the pathophysiological mechanism involved. The administration of r-metHuG-CSF (20 (g/kg, s.c.) 4 h prior to either 100 min or 2 h of tourniquet ischaemia to the upper thigh significantly improved the viability of skeletal muscle after 24 h reperfusion compared with saline-treated rats (P < 0.05). Administration of r-metHuG-CSF earlier (24 h before ischaemia) or later (immediately before ischaemia) had no protective effect. At the dose used, r-metHuG-CSF caused a three-fold increase in the level of circulating blood neutrophils and a modest but significant increase in the neutrophil content of ischaemic muscle after 24 h reperfusion. Reduction of neutrophils to 1.4% of normal levels by cyclophosphamide (150 mg/kg, i.p.) prior to injury had no significant effect on the survival of muscle subjected to 2 h ischaemia and 24 h reperfusion or on the protective effect of r-metHuG-CSF. IR injury to skeletal muscle was accompanied by a time-dependent increase in plasma TNFalpha levels during the first 8 h of reperfusion and the increase was reduced significantly by pretreatment with r-metHuG-CSF. However, a similar time-dependent increase in plasma nitrite/nitrate levels was unaffected by pretreatment with r-metHuG-CSF. These findings suggest that the protective effect of r-metHuG-CSF may be mediated by the attenuated release of TNFalpha and indicate that the level of neutrophils in either blood or injured tissue does not influence significantly the viability of rat muscle after IR injury.

Animals↗
PubMed2000

Bone mineral density variations along the lumbosacral spine.

Vertebral bone quality is essential in vertebral strength and the stability of spinal screw fixation. A major factor of bone quality is the density of bone mineral and its distribution throughout the bone. There have been studies regarding bone mineral density variations in the cervical and thoracolumbar spine, but bone mineral density variations in the lumbosacral spine have not been documented. The purpose of the current study was to quantify bone mineral density variations at different lumbosacral levels and within vertebra, especially along the pathways of lumbar pedicle screws. Bone mineral density variations within the vertebrae along the lumbosacral spine were measured in 13 specimens from young male cadavers using peripheral quantitative computed tomography. Measurements included bone mineral density variations at different lumbosacral levels and in transverse layers and vertical columns within each vertebral body. These original data showed that the bone mineral density increased gradually from lumbar to S1 vertebrae, possibly reflecting a caudally increasing load on different lumbosacral levels. The highest bone mineral density in the lumbosacral spine is found at the pedicles and regions closest to pedicle bases, supporting the use of pedicle screw fixation.

Adult↗