The stiffness of lumbar spinal motion segments with a high-intensity zone in the anulus fibrosus

STUDY DESIGN

Biomechanical and anatomic study of human cadaveric spinal motion segments.

OBJECTIVES

To measure the stiffness of spinal motion segments by disc type and by load type (flexion, extension, axial rotation, or lateral bending). To compare stiffness in motion segments with and without a high-intensity zone or radial tear in the anulus fibrosus.

SUMMARY OF BACKGROUND DATA

The high-intensity zone, that is a linear zone of high-intensity on T2-weighted magnetic resonance images corresponding to a radial tear in the anulus fibrosus, is a marker for a painful disc at discography. The high-intensity zone is hypothetically associated with diminished stiffness of the motion segment.

METHODS

Human cadaveric lumbar spinal motion segments with normal disc morphology or a high-intensity zone of the anulus fibrosus were selected on the basis of magnetic resonance imaging. The motion segments were subjected to incremental flexion, extension, rotation, and lateral bending torques. Rotation was measured with a kinematic system. Torque-rotation curves and stiffness were calculated for each motion segment and for each torque. The motion segments were sectioned on a cryomicrotome to verify the disc morphology as normal or as that of a radial tear.

RESULTS

In four motion segments with normal discs, stiffness was greater in axial rotation (8.4 Nm/degree) than in lateral bending (2.3 Nm/degree), flexion (1.8 Nm/degree), or extension (2.6 Nm/degree). In 16 motion segments with a high-intensity zone, stiffness was 2.4 Nm/degree in axial rotation, and less severely reduced in lateral bending, flexion, and extension. Stiffness in motion segments with a high-intensity zone was significantly less with smaller than with larger axial rotation loads.

CONCLUSIONS

The presence of a high-intensity zone in the intervertebral disc is associated with reduced stiffness of motion segments. The reduction is greater in axial rotation than in other torques. The reduction is more in smaller than in larger axial torques.

Cross cultural adaptation and validation of the Chinese Health Assessment Questionnaire for use in rheumatoid arthritis

OBJECTIVE

The Health Assessment Questionnaire - Disability Index (HAQ), used as a disability and outcome measurement in rheumatoid arthritis (RA), has been validated in several languages, but not in Chinese. Our aim was to validate the Chinese version of HAQ (Chinese-HAQ) to suit the needs of Chinese speaking patients with RA in an Asian setting.

METHODS

The original HAQ was modified in the context of Chinese culture and translated into Chinese by 2 translators aware of the objective of the questionnaire. The Chinese HAQ was self-administered by 42 patients with RA during their routine followup visit and one week later.

RESULTS

The test-retest reliability assessed using Spearman's correlation coefficient was 0.84. Between dimensions measured in the HAQ, the highest test-retest reliability was observed for walking (Spearman correlation coefficient rs=0.80) and the lowest was for eating (rs=0.54). The internal consistency of the scale using Cronbach's alpha was high at 0.86. In terms of criterion validity, the Chinese-HAQ score was found to correlate well with American College of Rheumatology functional status (rs=0.501, p=0.01). The Chinese-HAQ scores also correlated well with markers of disease activity such as patient's perception of pain measured on a visual analog scale (rs=0.55, p < 0.001), grip strength in mm Hg (rs=-0.55. p < 0.001 ), and physician's assessment of disease activity (rs=0.59, p < 0.001).

CONCLUSION

The Chinese HAQ is a reliable and valid instrument for studies measuring disability of patients with RA in Singapore.

Mediastinal teratoma: CT differentiation of ruptured and unruptured tumors

OBJECTIVE

The purpose of this study was to differentiate ruptured from unruptured mediastinal teratomas using CT. MATERIALS AND METHODS; CT findings in 17 cases of surgically resected mediastinal teratomas were reviewed retrospectively. Preoperative rupture was found in seven patients during surgery. We compared the clinical symptoms and CT findings of ruptured tumors with those of unruptured tumors. On CT, we evaluated size, wall thickness, location of the mass, presence or absence of internal septation, homogeneity of the internal components of each compartment, calcification or fat within the mass, and ancillary findings in adjacent structures.

RESULTS

Severe symptoms (chest pain or hemoptysis) were more commonly found in ruptured (71%) than in unruptured tumors. All ruptured mediastinal teratomas had a tendency to display inhomogeneity of the internal components, whereas 90% of unruptured masses showed homogeneous densities of internal components in each compartment of the mass. Ancillary CT findings in ruptured tumors included fat-containing masses in adjacent lung parenchyma in two patients, consolidation or atelectasis in the adjacent lung in three patients, pericardial effusion in one patient, and pleural effusion in four patients.

CONCLUSION

In cases of mediastinal teratoma, CT findings of inhomogeneity of the internal components and changes in the adjacent lung parenchyma, pleura, or pericardium can be used as signs of tumor rupture.

Oblique MRI as a useful adjunct in evaluation of cervical foraminal impingement

Magnetic resonance (MR) imaging is considered the gold standard for soft-tissue disease. The traditional MR imaging series uses axial and sagittal views. The purpose of this study was to demonstrate that oblique MR imaging provides valuable information about the cervical foramen not available from the conventional MR imaging technique. Ten asymptomatic individuals volunteered for MR imaging. Measurements were taken of height, width, and area for the nerves and foramen at the entrance and mid zones. Nerves were graded as normal, contacted, or deformed. Normal foraminal morphology in asymptomatic individuals and characteristics that compromise the space available for the nerve root were identified. Nerves with minimal or no contact had significantly greater foraminal widths than nerves with significant contact. Although there was a correlation between nerve contact and foraminal width, regression analysis did not demonstrate a correlation between disc height and foraminal size.

Usual interstitial pneumonia: relationship between disease activity and the progression of honeycombing at thin-section computed tomography

The authors estimate the relationship between the progression of honeycombing and disease activity of usual interstitial pneumonia (UIP) by open lung biopsy specimen and ground-glass opacity on thin-section computed tomography (CT). Open lung biopsy specimens and the initial and follow-up thin-section CT of 29 patients with proven UIP are reviewed. Follow-up thin-section CTs were performed from 2 to 61 months (mean, 15.3 months) after biopsy. The interval between the initial CT and open lung biopsy was from 2 to 30 days (mean, 10.0 days). Areas of ground-glass opacity and honeycombing were quantified respectively on each CT slice by using a 0%-100% scale with 10% increments. Each open lung biopsy specimen was scored semiquantitatively for alveolar desquamation, alveolar septal inflammation, inflammatory airway narrowing, obstructive pneumonitis, and lymphoid nodules. Patients were classified into either a mild or severe activity group according to the median value of the pathologic score and the median value of the area of ground-glass opacity. The authors compared the progression of honeycombing on follow-up thin-section CT between the groups. The progression of honeycombing in UIP was significantly faster in the severe activity group than in the mild group according to the pathologic score (p = 0.003) and the area of ground-glass opacity (p = 0.0024). In patients with UIP, more active inflammation of the pulmonary interstitium results in faster progression of honeycombing in long-term follow-up.

Biomechanical and histologic alteration of facial recipient bone after reconstruction with autogenous bone grafts and alloplastic implants: a 1-year study

Potential alteration of the underlying recipient bone resulting from a graft or implant has significant clinical relevance. The present study was designed to evaluate the biomechanical and histologic alteration of facial recipient bone with autogenous bone graft and alloplastic implants over a 1-year period. The bilateral arches of 15 rabbits were randomized between four groups: (1) control (n = 6), subperiosteal exposure of the zygomatic arch was made; (2) onlay (n = 12), bone graft was placed as an onlay to the zygomatic arch; (3) inlay (n = 6), bone graft was placed as an inlay within the zygomatic arch; (4) implant (n = 6), a stainless steel plate was placed as an onlay to the zygomatic arch. Animals were killed 1 year after grafting. In the onlay groups, all steel implants and half of the onlay bone grafts (n = 6) were separated from the zygomatic arch; the remaining onlay bone grafts (n = 6) were left on the zygomatic arch. Three-point breaking strength was measured through the center of the graft/implant site on the zygomatic arch, followed by histologic evaluation and histometric assessment of residual bone density. The findings demonstrated no difference in the breaking strength per unit bone area between the control zygomatic arch group and the onlay group in which the bone graft was left in place. Breaking strength of the zygomatic arch in the former two groups was significantly greater than that in either group in which the onlay bone graft or implant had been removed, and was also greater than the breaking strength in that group in which inlay bone had been placed (p < 0.05). Histologic assessment showed full-thickness conversion in architecture of the zygomatic arch from compact to woven bone beneath onlays of either autogenous bone graft or steel implant; histometric assessment demonstrated an accompanying decrease in bone density in the latter groups relative to the control zygoma (p < 0.05). We conclude that onlay autogenous bone graft and alloplastic implants to the facial skeleton induce transformation of both graft and recipient bone from compact to woven architecture, accompanied by a reduction in bone density. The biomechanical strength of recipient facial bone is significantly weakened if an onlay bone graft or implant is removed. Weakening occurs per unit area of remaining bone, and is therefore independent of any thinning that may occur within the recipient bone because of graft/implant placement. These findings may impact upon decisions to augment stress-bearing regions of the facial skeleton with bone graft or implants, particularly if the graft/implant may eventually require removal.

Inhibitory effect of Asparagus cochinchinensis on tumor necrosis factor-alpha secretion from astrocytes

We investigated whether an aqueous extract of Asparagus cochinchinensis Merrill (Liliaceae) roots (ACAE) inhibits secretion of tumor necrosis factor-alpha (TNF-alpha) from primary cultures of mouse astrocytes. ACAE dose-dependently inhibited the TNF-alpha secretion by astrocytes stimulated with substance P (SP) and lipopolysaccharide (LPS). IL-1 has been shown to elevate TNF-alpha secretion from LPS-stimulated astrocytes while having no effect on astrocytes in the absence of LPS. We therefore investigated whether IL-1 mediated inhibition of TNF-alpha secretion from astrocytes by ACAE. Treatment of ACAE to astrocytes stimulated with both LPS and SP decreased IL-1 secretion. Moreover, incubation of astrocytes with IL-1 antibody abolished the synergistic cooperative effect of LPS and SP. These results suggest that ACAE may inhibit TNF-alpha secretion by inhibiting IL-1 secretion and that ACAE has a antiinflammatory activity in the central nervous system.

Clinical and echocardiographic outcomes of aortic intramural hemorrhage compared with acute aortic dissection

Aortic intramural hemorrhage (IMH), which presents clinical manifestations identical to those of acute aortic dissection, is different from aortic dissection in terms of the absence of intimal tear and communication of blood flow between the true and false lumen. This study was conducted for the purpose of diagnosing IMH by transesophageal echocardiography (TEE) prospectively and comparing the clinical and echocardiographic outcome of IMH with aortic dissection. Between August 1991 and November 1996, 27 IMHs and 73 acute aortic dissections were diagnosed using TEE in 202 consecutive patients with suspected aortic dissections. The TEE diagnoses of IMH and aortic dissection were initially compared with computed tomography and magnetic resonance imaging and later confirmed by operative findings (n = 37) or follow-up changes (n = 12). In the 49 patients whose diagnosis was confirmed by operation or follow-up changes, the sensitivity and specificity of TEE for the diagnosis of IMH were 27 of 27 (100%) and 20 of 22 (91%), respectively. There were 11 deaths in 73 patients (15%) from acute aortic dissection and 1 death in 27 patients (4%) from IMH during a follow-up of 1.7+/-1.5 years (p = NS). Stanford classification and types of treatment were not related to death in both groups. Complications developed less often in patients with IMH (3 of 27) than in those with acute aortic dissection (24 of 73), and no death occurred in patients with uncomplicated IMH who were medically treated. A follow-up imaging study of 12 IMH patients showed complete resolution in 8, regression in 3, and progression in 1 patient. TEE is accurate in the diagnosis of IMH and IMH has a lower incidence of complications than aortic dissection because of the absence of intimal tear and communication of blood flow in the false lumen.

Novel application of breath-hold turbo spin-echo T2 MRI for detection of acute myocardial infarction

To assess the clinical utility of the breath-hold turbo spin-echo T2-weighted MRI in patients with acute myocardial infarction, the results of MRI were compared with those of electrocardiography, coronary angiography, and thallium-201 single photon emission tomography (SPECT) in 23 patients and 5 healthy volunteers. To compare MRI and thallium-SPECT, the left ventricle was divided into five segments, and the presence of myocardial infarction was determined in each segment. MRI demonstrated an abnormally bright signal in 49 of 140 segments (five segments each from 23 patients and 5 volunteers); thallium-SPECT showed a fixed perfusion defect in 52 segments, for an 85% diagnostic concordance rate. The size of the myocardial infarction measured on MRI corresponded well to that measured on thallium-SPECT (r = .70, P < .01). Breath-hold turbo spin-echo T2 MRI can be used for detection of acute myocardial infarction in conjunction with thallium-SPECT, especially when accurate localization of lesion, increased spatial resolution, and anatomic landmarks are needed.

Ophthalmic manifestations in human immunodeficiency virus infection in Singapore

The paper retrospectively reviews the spectrum of ophthalmic manifestations in human immunodeficiency virus (HIV) infection in Singapore between May 1995 and October 1996. One hundred and eighteen patients were examined for ocular abnormalities. Criteria for examination were 1) visual complaints, 2) absolute CD4 count of less than 50 cells/ul, 3) patients with acquired immunodeficiency syndrome-defining illness or 4) any relevant systemic illnesses which may have ocular involvement. Only 25 patients (21.2%) had visual symptoms. Eighteen patients (15.3%) had abnormalities associated with microvasculature. Forty-four patients (37.3%) had opportunistic infection involving the eye of which 37 were that of cytomegalovirus retinitis (CMVR). Seven patients (5.9%) had neuro-ophthalmic disorders. One patient presented with proptosis due to orbital lymphoma. Four patients (3.4%) had episcleritis and 3 patients (2.5%) had symptomatic dry eyes. It is still not known if episcleritis and dry eyes are associated with HIV infection or are coincidental. Fifty-one patients (43.2%) had no ocular pathology and remained so throughout the period of study. Nine patients (7.6%) had more than one pathology. The major cause of visual loss was due to ocular infections, with CMVR being most prevalent. Recognising the ophthalmic signs in HIV patients will facilitate early diagnosis. Prompt treatment of eye involvement can prevent or delay blindness, which is psychologically and functionally important to these patients.

A noninvasive, three-dimensional spinal motion analysis method

STUDY DESIGN

A three-dimensional, noninvasive motion analysis method was developed by monitoring the orientation of the principal axes of each vertebra.

OBJECTIVES

To develop a method of performing three-dimensional, noninvasive motion analysis of the spine using computed tomography data.

SUMMARY OF BACKGROUND DATA

The concept of using principal axes of the moment of inertia tensor to measure the orientation and position of a rigid body has been applied to the wrist and subtalar joints, but has not yet been applied to the spine.

METHODS

Scans were taken of two isolated vertebrae in various known positions. Centroids, area, moments, and product of inertia of each scan were determined using a commercial program. Custom software combined data using the parallel axis theorem to give three-dimensional data for each vertebra. Changes in the centroid and principal axes were used to calculate translation and rotation, respectively.

RESULTS

The system accuracy was within 1.0 degree in rotation and 1.0 mm in translation. Some errors occurred in minor motions when a smaller number of scans were used. System resolution was 0.43 mm.

CONCLUSIONS

A system has been developed capable of calculating three-dimensional spinal motion based on measurements of a series of computed tomography images. The system has an accuracy similar to that of current motion analysis methods, but future studies will be necessary to apply this system in vivo.

Penetrating keratoplasty in the Singapore National Eye Centre and donor cornea acquisition in the Singapore Eye Bank

We analyzed all penetrating keratoplasties performed in the Singapore National Eye Centre from 1 January 1991 to 31 December 1995, using records of the Singapore Eye Bank Registry, evaluating the indications, complications, causes of graft failure, visual outcome and graft survival rate. We also looked into donor cornea acquisition in the Singapore Eye Bank and its influence on the development of corneal transplantation in the Singapore National Eye Centre. A total of 327 penetrating keratoplasties were performed during the 5-year period. Bullous keratopathy was an indication in 26.3% of cases. Of these, aphakic bullous keratopathy accounted for 11.6% of all cases, while pseudophakic bullous keratopathy accounted for 11.3%. Other indications were regrafts (11.9%), corneal dystrophies (10.4%), traumatic corneal scarring (10.1%) and keratoconus (9.8%). Graft rejection was a complication in 20% of all cases. Of these, 40.9% led to graft failure. Other major complications were raised intraocular pressure (18%), epithelium-related problems (7.3%), wound dehiscence (4.3%), cataract (3.3%) and microbial keratitis (3.1%). The main causes of graft failure were graft rejection (8.2%), endothelial failure (2.4%), infection (2.4%) and glaucoma (2.1%). Of the 327 grafts, 40.3% achieved best corrected visual acuity of 6/12 or better; 70.8% achieved vision of 6/24 or better. The overall graft survival rate was 82.3% after a mean follow-up period of 2 years. Donor corneas for the penetrating keratoplasties were obtained from foreign eye banks as well as locally, with the local donation rate steadily increasing from 1991 to 1996, with the establishment of proper eye banking facilities and the Singapore Eye Bank. These results show that the indications and outcome of penetrating keratoplasty in the Singapore National Eye Centre are similar and comparable to that of other centres with established corneal grafting programmes. The establishment of the Singapore Eye Bank has ensured the proper co-ordination of acquisition of donor material which has been vital to the development of corneal transplantation in the Singapore National Eye Centre.

In vitro evaluation of shoulder external rotation after a Bankart reconstruction

The Bankart procedure is a commonly performed anterior shoulder reconstruction that may shorten the anterior capsule. In this study, biomechanical testing was performed to evaluate the effect of the classic Bankart reconstruction on external rotation of the shoulder. The procedure was performed on six fresh-frozen cadaveric specimens that were free of intraarticular pathologic changes. With the arm in 0 degrees of abduction, resisting torques about the vertical axis were measured while the humerus was externally rotated. The intact specimens demonstrated a nonlinear load displacement behavior in which little resisting torque was measured until a moderate amount of external rotation was applied. Shortening the capsule by 2 mm resulted in a 40% decrease in the low-tension zone of external rotation, and shortening the capsule an additional 5 mm resulted in a 67% decrease in the low-tension zone. This study demonstrates that the normal shoulder capsule is quite sensitive to anterior capsular shortening and suggests that care must be exercised when performing a Bankart reconstruction to avoid overtightening this structure.

Laparoscopic assisted fusion of the lumbosacral spine. A biomechanical and histologic analysis of the open versus laparoscopic technique in an animal model

STUDY DESIGN

An animal model for laparoscopic lumbosacral fusion.

OBJECTIVES

To compare the biomechanical and histologic results of open to laparoscopic lumbosacral discectomy and fusion in an animal model.

BACKGROUND DATA

Early clinical reports of laparoscopic lumbosacral fusions are encouraging, but animal experiments have not been reported.

METHODS

Ten pigs (50-80 kg) were divided into two groups. Group 1 underwent an open anterior lumbosacral discectomy and fusion at L7-S1 using autologous bone graft and a titanium MOSS (DePuy Motech) cage. Group 2 was identical to Group 1 except that a laparoscopic technique was used. The animals were killed at 3 months, and the lumbosacral spines were harvested for biomechanical and histologic testing.

RESULTS

Estimated blood loss and average length of operation, respectively, for the two groups were: Group 1, 50 mL, 2 hours 50 minutes; and Group 2, 40 mL, 3 hours 40 minutes. There were no perioperative or postoperative complications in either group. Motion analysis results showed less motion in lateral bending, flexion, and extension than in the intact specimen in both groups. Tensile testing showed that the stiffness was significantly greater in the open group than in the laparoscopic group (P < 0.004). Histologic examination showed a less extensive discectomy and less bone growth in the implant in the laparoscopic group. Inadequate decortication of end-plates occurred in two animals who underwent laparoscopy.

CONCLUSIONS

Although lumbosacral discectomy and implant insertion can be performed using the laparoscopic technique, the construct may not have the same biomechanical strength as that attained with the open procedure. Laparoscopic-assisted lumbosacral fusion surgery requires additional investigation before it is widely used in clinical situations.

Gas Chromatographic Determination of Acephate in Technical Material and Soluble Powder Formulations: Collaborative Study

A gas chromatographic (GC) method was developed for quantitation of acephate (Orthene) in technical material and soluble powder formulations. Acephate is an organophosphate with broad spectrum contact and systemic insecticidal properties. Fourteen collaborators from 8 countries participated in a collaborative study of the method. Collaborators were provided with the method; samples of technical acephate and formulated soluble powder containing 95-99% and 71-75% acephate, respectively; an acephate reference standard; and internal standard. Samples were weighed, diluted to volume with internal standard, and quantitated by using GC peak area ratios. Relative standard deviation values for reproducibility (RSDR) were 1.03-2.55 for 95-99% technical acephate and 1.36-2.73 for formulated soluble powder containing 71-75% acephate. The GC method for determination of acephate in technical material and soluble powder formulations has been adopted by AOAC INTERNATIONAL

Changing indications for penetrating keratoplasty: a newly developed country's experience

PURPOSE

To study the changing indications for penetrating keratoplasty in Singapore and compare local indications with developed countries with established corneal graft programs.

METHODS

A descriptive study of all penetrating keratoplasty cases performed in the Singapore National Eye Center over a 5 year period, from 1 January 1991 to 31 December 1995 using records of the Singapore Eye Bank registry.

RESULTS

A total of 327 penetrating keratoplasties were performed. Bullous keratopathy was the indication in more than a quarter of all cases (26.3%). Aphakic bullous keratopathy (11.6%) and pseudophakic bullous keratopathy (11.3%) accounted for the majority of the bullous keratopathy cases. The other leading indications were regrafts (11.9%), corneal dystrophies (10.4%), traumatic scarring (10.1%) and keratoconus (9.8%). A higher proportion of aphakic and pseudophakic bullous keratopathy as well as regrafts was noted in this series compared to a previous report on corneal transplantation in the 1980s. A rising indication rate of pseudophakic bullous keratopathy, in conjunction with a declining indication rate of herpetic keratitis was observed over the 5 year study period.

CONCLUSIONS

The indications for penetrating keratoplasty in Singapore appear to follow the trend seen in developed Western countries over the past few decades.

Pseudomyopia in a patient with blocked ventriculo-peritoneal shunt--a case report

Accommodative spasm usually encompasses a classical triad of pseudomyopia, esodeviation and pupillary constriction. Accommodative spasm is most often psychogenic in nature; however, it may be associated with other organic diseases of which a rare cause is that of intracranial catheter complications. We report a case of dorsal midbrain syndrome with pseudomyopia in a patient with a blocked ventriculo-peritoneal shunt inserted for aqueductal stenosis. Clinical presentation was unusual in this patient as pseudomyopia occurred with exodeviation and without pupillary constriction.

Biomechanical evaluation of anterior and posterior fixations in an unstable calf spine model

STUDY DESIGN

Fresh calf lumbar spines were used to perform flexibility tests in multiple loading directions to compare the stabilizing effects of anterior and posterior rigid instrumentations.

OBJECTIVE

To compare the biomechanical flexibility of anterior and posterior instrumentation constructs using an unstable calf spine model.

SUMMARY OF BACKGROUND DATA

Unstable burst fractures of the thoracolumbar spine can be managed anteriorly or posteriorly. Controversy persists, however, on the merit of anterior fixation versus that of posterior fixation in terms of how much stability can be achieved.

METHODS

Fifteen fresh calf spines (L2-L5) were loaded with pure unconstrained moments in flexion, extension, axial rotation, and lateral bending directions. After removal of L3-L4 disc and endplates to create an 1.5-cm anterior and middle column defect, testing was performed on five specimens after anterior Kaneda rod fixation, anterior University Plate fixation, or posterior ISOLA pedicle screw fixation (AcroMed, Cleveland, OH). Testing was repeated after inserting a polymethylmethacrylate block to stimulate an interbody anterior graft with instrumentation.

RESULTS

All fixation devices provided a significant stabilizing effect in flexion and lateral bending. In extension, all constructs except ISOLA (AcroMed) without graft were stiffer than the intact specimen. In axial rotation with no graft, only the Kaneda device significantly reduced the flexibility from that of the intact specimen. The interbody graft provided additional rigidity to the ISOLA (AcroMed) instrumentation construct in flexion and extension and to the Kaneda construct in lateral bending. There was no significant effect of grafting in axial rotation.

CONCLUSIONS

A short, transpedicular instrumentation, such as ISOLA (AcroMed), provided less rigid fixation in flexion and extension without the anterior structural graft. The Kaneda rod and University plate with grafting provided a significant stabilizing effect in all directions compared with the intact specimen. When no graft was inserted, the Kaneda device was more effective in preventing axial rotation than the other devices. In lateral bending, the University plate provided more rigid fixation than the Kaneda device without grafting.

Effects of Bufo marinus skin toxins on human fetal extracorporeal blood vessels

The effects of extracts of Bufo marinus toad skin toxin on human isolated umbilical arterial rings and the fetal vessels of perfused placentae were examined and compared with those of ouabain, an inhibitor of Na+/K(+)-ATPase. Umbilical artery rings and fetal vessels of the perfused placenta responded to extracts, or ouabain, with constriction which persisted after the removal of each agent. Extraction of the skin, using various solvents, revealed that the umbilical artery constriction was due mainly to the effects of water-soluble, polar compounds. Fractionation of a water extract and bioassay on the rat isolated aorta revealed maximum vasoconstrictor activity in a low mol. wt fraction. During Na+/K(+)-ATPase inactivation in the fetal circulation of the human placenta, by perfusion with K(+)-free Kreb's solution, reactivation of the enzyme by K+ infusion caused vasodilatation. This effect was inhibited both by water extracts of load skin and by ouabain. Thus, properties of some of the endogenous compounds in B. marinus skin resemble those of ouabain, by causing persistent constriction of human fetal blood vessels. A component of the vasoconstrictor response probably results from inhibition of vascular smooth muscle Na+/K(+)-ATPase, but it is likely that a contribution is also made by additional vasoconstrictor substances contained in B. marinus toxin.

Seasonal variation in the secretion of mammotrophic hormones in normal women and women with previous breast cancer

Hormones such as melatonin whose serum concentrations vary seasonally have been previously implicated in the growth of breast cancer. The present study was undertaken to identify possible seasonal variation in a range of mammotrophic hormones which could exert a chronobiologic influence in women with breast tumours. Fifteen premenopausal women with a history of previous breast cancer (BC subjects) and 10 control women underwent 2-hourly serum sampling for 24 h at both summer and winter solstice for measurement of melatonin, growth hormone (GH), insulin-like growth factor-I (IGF-I), cortisol, prolactin and thyrotrophin (TSH). Hormone secretion at the different seasons was compared by measuring the area under the 24 h serum hormone concentration x time curves and by time series analysis of summer-to-winter differences in hormone concentration. Control women had significantly higher GH and IGF-I levels in summer compared to winter and significantly higher cortisol secretion in winter than summer. In contrast, BC women had no significant seasonal difference in IGF-I concentrations and had a reversal of the normal seasonal pattern of melatonin secretion, although seasonal changes in GH production were similar to controls. Prolactin and TSH showed no significant summer/winter variation in either group. Thus, seasonal variations in hormone secretion seen in normal women were, with exception of GH, absent or reversed in women with a previous history of breast cancer. As a result these individuals may be exposed to an asynchronous hormonal stimulus which could influence tumour growth. These changes could reflect a constitutional abnormality in BC women or may have been induced by the previous breast tumour.

Dosimetry for occupational exposure to cosmic radiation

In the course of their work, aircraft crew and frequent flyers are exposed to elevated levels of cosmic radiation of galactic and solar origin and secondary radiation produced in the atmosphere, aircraft structure, etc. This has been recognised for some time and estimates of the exposure of aircraft crew have been made previously and included in, for example, UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) publications. The recent increased interest has been brought about by several factors--the consideration that the relative biological effectiveness of the neutron component as being underestimated; the trend towards higher cruising altitudes for subsonic commercial aircraft and business jet aircraft; and, most importantly, the recommendations of the International Commission on Radiological Protection (ICRP) in Publication 60, and the revision of the Euratom Basic Safety Standards Directive (BSS). In 1992, the European Dosimetry Group (EURADOS) established a Working Group to consider the exposure to cosmic radiation of aircraft crew, and the scientific and technical problems associated with radiation protection dosimetry for this occupational group. The Working Group was composed of fifteen scientists (plus a corresponding member) involved in this field of study and with knowledge of radiation measurement at aviation altitudes. This paper is based on the findings of this Working Group. Where arrangements are made to take account of the exposure of aircraft crew to cosmic radiation, dose estimation procedures will not be necessary for persons for whom total annual doses are not liable to exceed 1 mSv, and therefore, in general, for crew on aircraft not routinely flying above 8 km. Where estimates of effective dose and, in the case of female staff who are pregnant, equivalent dose to the embryo or fetus, are required (for regulatory or other purposes), it was concluded that the preferred procedure was to determine route doses and fold these with data on staff rostering.

Testicular aspiration of sperm for intracytoplasmic sperm injection: an alternative treatment to electro-emission: case report

The quantity and quality of spermatozoa produced by electro- or vibro-ejaculation in spinal cord injury patients is often poor, thus advanced reproductive techniques are required if pregnancy is to be achieved. On other occasions no spermatozoa are obtained. We present a successful case of pregnancy achieved using spermatozoa aspirated directly from the testicle combined with intracytoplasmic sperm injection in an in vitro fertilization cycle. We propose this as an alternative to electroejaculation in selected patients.

Anatomic changes of the spinal canal and intervertebral foramen associated with flexion-extension movement

STUDY DESIGN

A cadaveric study was done to analyze the dimensional changes in the spinal canal and intervertebral foramen of the lumber spine with flexion and extension movements.

OBJECTIVES

To investigate the relationship between flexion and extension movements and morphologic changes in the spinal canal and the intervertebral foramen.

SUMMARY OF BACKGROUND DATA

Previous studies have reported that the dimensions of the spinal canal and the intervertebral foramen may change significantly with motion. The purpose of this study was to assess the quantitative changes in the spinal canal and the intervertebral foramen with segmental flexion-extension movements.

METHODS

Nineteen fresh cadaveric spines yielding 25 motion segments were used. The lumbar motion segments were frozen and then imaged in axial and sagittal projections by a computed tomography scanner. They were thawed then, and the motion segments were loaded to 5.7 Nm in flexion (13 motion segments) and in extension (12 motion segments) specimens. While in flexion or extension, the specimens again were frozen and imaged by computed tomography scan. The frozen specimens than were sliced using a cryomicrotome in the sagittal plane to study the dimensions of the intervertebral foramen. Eighteen other fresh cadaveric spines were sliced sagittally for study in the neutral position.

RESULTS

The axial computed tomography scans showed that extension significantly decreased the canal area, midsagittal diameter, and subarticular sagittal diameter, whereas flexion had the opposite effects. The sagittal computed tomography scans showed that extension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. The translational changes were associated with the bulging of the disc and the presence of traction spurs. The cryomicrotome sections showed the cross-sectional area of the foramen to be 12% greater for the flexion group and 15% smaller for the extension group than the cross-sectional area of the neutral group. Nerve root compression in the foramen was found to be 21.0% in neutral, 15.4% in flexion, and 33.3% in extension groups.

CONCLUSIONS

The study supports the concept of dynamic spinal stenosis. In addition to static anatomic changes, careful dynamic studies may be required to evaluate better the central canal and the foramen.

Biomechanics of transfixation in pedicle screw instrumentation

STUDY DESIGN

The biomechanical role of transfixation in pedicle screw instrumentation was investigated using flexibility tests and finite element analyses.

OBJECTIVE

To assess the stabilizing effect of use and position of transfixators.

SUMMARY OF BACKGROUND DATA

Transfixation is common in pedicle screw instrumentation, however, its biomechanical role and optimal position are not completely understood.

METHODS

Specimens underwent nondestructive flexibility tests using a three-dimensional motion analysis system. Tests compared the intact spine with instrumentation with and without transfixators Rotational angles of the superior vertebra, resulting from the maximum moment of 6.4 Nm, were compared. Three-dimensional finite element models investigated transfixator position. Rotations of the superior vertebra were compared for cases with and without transfixators to determine the position providing the greatest stability.

RESULTS

Biomechanical test showed that only axial rotational stability significantly improved with transfixators compared with instrumentation alone. Pimte element models predicted improvement in lateral bending and axial rotation with transfixators compared with the case with no transfixator. With one transfixator, the greatest improvement in axial rotation stability occurred with the transfixator at the proximal 1/4 position of the rods. When two transfixators were used, the optimal locations were with one transfixator in the middle and the second at the proximal 1/8 position.

CONCLUSIONS

Transfixators improved the stabilizing effects of pedicle screw instrumentation. The greatest axial rotation stability was obtained with two transfixators; one in the middle and the other at the proximal 1/8 position of the longitudinal rods.

The ideal amount of lumbar foraminal distraction for pedicle screw instrumentation

STUDY DESIGN

A cadaveric study was performed to analyze the changes of foraminal dimensions of the lumbar spine and also to estimate the amount of foraminal distraction, achieved with pedicle screw instrumentation, that will create the greatest improvement in foraminal dimensions.

OBJECTIVES

To establish the ideal amount of lumbar foraminal distraction using pedicle screw instrumentation and to investigate the changes of adjacent segments and lumbar lordosis with distraction maneuvers.

SUMMARY OF BACKGROUND DATA

In patients undergoing fusions and instrumentation for foraminal stenosis, distraction of the lumbar spine may improve the dimensions of the intervertebral foramen. Results of previous studies have shown that anterior interbody distraction of the lumbar spine significantly increased the space in the lumbar foramen. No previous study has assessed the ideal amount of distraction, changes in the adjacent segments, or the effect on lumbar lordosis using posterior pedicle screw instrumentation.

METHODS

Six fresh frozen human cadaveric spines from 15 to the sacrum were used. The ISOLA instrumentation system (Acromed Inc., Cleveland, OH) was applied using pedicle screws at L4, L5, and S1, L4-L5 and L5-S1 rods were contoured to the same degree of lumbar lordosis as in the specimen. The spine was potted in the upright position with the sacrum secured in the mold, and an axial load of 40 pounds was applied to the specimen. Radiographs were used to measure the posterior disc height, foraminal height, foraminal area, and lumbar lordosis. Two mm, 4 mm, 6 mm, 8 mm, and 10 mm of single level distraction were added to L4-L5 and L5-S1. The dimensions of the specimen were digitized and calculated after each distraction.

RESULTS

The posterior disc height, foraminal height and foraminal area increased with distraction. The greatest incremental change in the foraminal area was noted at 6 mm of distraction. The L4-L5 foraminal area increased 22.6% at 6 mm of L4-L5 distraction, and the L5-S1 foraminal area increased 39.2% at 6 mm of L5-S1 distraction. With distraction above 6 mm, the foraminal change plateaued. The greatest decrease in lumbar lordosis was only 4.6 degrees and occurred at 10 mm of distraction. There was no significant effect of distraction on the foramina of adjacent levels.

CONCLUSION

Posterior distraction using pedicle screws increased foraminal dimensions. The ideal amount of distraction on the rod, or the minimal amount of distraction necessary for improving foraminal dimensions, may be 6 mm using pedicle screw instrumentation.

Occult lumbar lateral spinal stenosis in neural foramina subjected to physiologic loading

PURPOSE

To measure the effect of extension, flexion, lateral bending, and axial rotation loads applied to the spine on the anatomic relationship of the spinal nerves in the neural foramen to the ligamentum flavum and the intervertebral disk, anc to determine the effect of disk degeneration on the response to loading.

METHODS

Cadaveric lumbar motion segments were examined with CT and MR imaging, loaded with pure moment forces, frozen in situ, reexamined with CT, and sectioned with a cryomicrotome. The morphology of the intervertebral disks was classified on the basis of the appearance of the cryomicrotome sections. The neural foramina were classified as having no evident stenosis, as being stenotic, as having occult stenosis, or as showing resolved stenosis on the basis of the images and sections before and after loading. The stenotic and nonstenotic foramina were stratified by disk level, intervertebral disk classification, and type of loading applied. The effect of spinal level, disk type, and load type on the prevalence of stenosis was studied.

RESULTS

On average, extension, flexion, lateral bending, and axial rotation resulted in the ligamentum flavum or intervertebral disk contacting or compressing the spinal nerve in 18% of the neural foramina. Extension loading produced the most cases of nerve root contact, and lateral bending produced the fewest cases. Each of the loading types resulted also in diminished contact between the spinal nerve and the intervertebral disk or ligamentum flavum in some cases. Disk degeneration significantly increased the prevalence of spinal stenosis. All foramina associated with advanced disk degeneration and half of the foramina associated with disks having radial tears of the annulus fibrosus either developed occult stenosis or were stenotic before loading.

CONCLUSIONS

The study supports the concept of dynamic spinal stenosis; that is, intermittent stenosis of the neural foramina. Flexion, extension, lateral bending, and axial rotation significantly changed the anatomic relationships of the ligamentum flavum and intervertebral disk to the spinal nerve roots.

Sub-Tenon's versus retrobulbar anesthesia for cataract surgery

BACKGROUND AND OBJECTIVE

A prospective, randomized, double-blind study was conducted to compare sub-Tenon's anesthesia with retrobulbar anesthesia.

PATIENTS AND METHODS

One hundred six patients undergoing cataract extraction received either sub-Tenon's anesthesia (55 patients) or retrobulbar anesthesia (51 patients). The number of injections required, time until adequate akinesia was achieved, degree of pain experienced, and complications of the anesthetic injection were compared. The depth of the akinesia after sub-Tenon's injection was graded.

RESULTS

There was no significant difference between the two study groups with respect to time of onset of adequate akinesia, the need for a second top-up injection, and the effectiveness of the akinesia. The sub-Tenon's injection group reported less pain during the anesthetic injection, as well as during the postoperative injection of subconjunctival gentamicin.

CONCLUSION

Sub-Tenon's anesthesia is a safe technique that is comparable to retrobulbar anesthesia.

31P nuclear magnetic resonance evidence of skeletal muscle metabolic abnormalities in mitral stenosis

We used in vivo 31P nuclear magnetic resonance spectroscopy to follow phosphorylated metabolites of dominant forearm flexor muscles during exercise in patients with mitral stenosis. The results showed that skeletal muscle metabolism during exercise is abnormal.

Prediction of fatigue screw loosening in anterior spinal fixation using dual energy x-ray absorptiometry

STUDY DESIGN

A biomechanical study was performed to investigate a relation between the bone mineral density of the vertebral body and the number of loading cycles to induce fatigue loosening of an anterior vertebral screw.

OBJECTIVES

The objective of this study was to investigate the potential usefulness of dual energy x-ray absorptiometry of measuring bone mineral density of the vertebral body in predicting the fatigue loosening of th anterior vertebral screw.

SUMMARY OF BACKGROUND DATA

Loosening of the vertebral body screw is a well know failure in spinal instrumentation, and more commonly observed than pullout failure. The relation between bone mineral density and pullout strength of the screw has been investigated previously, but no studies are available on the fatigue loosening in anterior spinal fixation.

METHODS

Bone mineral density was measured using dual energy x-ray absorptiometry and the screw loosening was produce by a cyclic loading in the cephalad-caudal direction. Screw loosening was defined as 1 mm displacement of the screw relative to bone, and the number of loading cycles to induce the screw loosening was obtained and statistically correlated with bone mineral density.

RESULTS

There was a positive correlation between the number of loading cycles to induce screw loosening and bone mineral density (R = 0.8, P < 0.01). The average number of loading cycles to induce screw loosening was significantly less for specimens with bone mineral density < 0.45 g/cm2 compared to those with bone mineral density > or = g/cm2.

CONCLUSIONS

These findings suggest that bone mineral density may be a good predictor of anterior vertebral screw loosening. Bone mineral density < 0.45 g/cm2 may be critical value of loosening of the anterior vertebral body screw. However, further biomechanical and clinical studies are required before using threshold value clinically.

Evaluation of porous biphasic calcium phosphate ceramics for anterior cervical interbody fusion in a caprine model

STUDY DESIGN

This study compared the efficacy of characterized 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics of 30%, 50%, and 70% porosity and autograft to promote interbody spinal fusion at C2-C3 and C5-C6 in 24 goats: 12 at 3 months and 12 at 6 months.

OBJECTIVES

Radiographs, histology, dual energy x-ray absorptiometry analysis, and biomechanical testing were used to evaluate the ability of the 30%, 50%, and 70% porous 50/50 hydroxyapatite/beta-tricalcium phosphate ceramics and autograft to promote cervical interbody fusion.

SUMMARY OF BACKGROUND DATA

The conundrum in the use of calcium phosphates for interbody fusion is what porosity is most effective to promote ingrowth yet strong enough to resist compressive stresses found in the spine? It is known that the ability for bone ingrowth increases and the compressive strength decreases as porosity of the ceramic is increased. Dense ceramics remain intact but may be surrounded by fibrous tissue. Porous ceramics have good ingrowth but may fracture.

METHODS

Radiographs were evaluated for fusion and fracture or collapse of the ceramics or autograft. Dual energy x-ray absorptiometry was used to evaluate the fusion mass. Treated motion segments underwent biomechanical testing to quantify the flexibility of the segment. Undecalcified and decalcified histologic analysis were performed to evaluate the presence or absence of a bony union.

RESULTS

Thirty percent, 50%, and 70% porous ceramics had better radiographic fusion scores than the autograft at 3 and 6 months. Incidence of ceramic fracture did not increase with porosity and was equivalent to the collapse of autograft, although ceramics maintained disc height when fracture occurred. No statistically significant differences were found between autograft and the porous ceramics with biomechanical testing and peri-implant bone mineral density values as measured by dual energy x-ray absorptiometry. At 3 months, histologic analysis showed a union rate of 0% for autograft and 30% porous ceramic, 67% for 50% porous ceramic, and 83% for 70% porous ceramic. At 6 months, the union rate was 67% for the 30%, 50%, and 70% porous ceramics and 50% for autograft.

CONCLUSIONS

Thirty percent, 50%, and 70% porous ceramics performed equal to or better than autogenous bone after 3 and 6 months. There may be promise for the use of 50/50 hydroxyapatite/beta-tricalcium phosphate in spine surgery as the need to harvest autograft from the iliac crest is obviated, and complications and cost associated with the harvest are avoided.

Biomechanical evaluation of anterior thoracolumbar spinal instrumentation

STUDY DESIGN

A biomechanical study was designed to assess relative construct stabilities of modern anterior thoracolumbar instrumentations in a calf spine model with an anterior and middle column defect.

OBJECTIVES

The purpose is to compare the biomechanical stability of various anterior fixation devices in an unstable calf spine model.

SUMMARY OF BACKGROUND DATA

Modern types of anterior thoracolumbar instrumentations evolved to either rods or plates. Biomechanical properties and comparative studies of these instrumentations are lacking.

METHODS

Twenty fresh calf spines (L2-L5) were used for the biomechanical tests. L2 and L5 vertebrae were used to attach the loading and base frames, respectively. Specimens underwent nondestructive biomechanical tests performed using a three-dimensional motion measuring system. In each specimen, three different cases were tested: intact spine, anterior fixation with an interbody graft after total discectomy and endplate excision of L3-L4 disc, anterior fixation only without the graft. Four anterior fixators, University Anterior Plating System, the Kaneda device, the Z-plate, and Texas Scottish Rite Hospital system were used. Each device was tested on five specimens. A polymethylmethacrylate block was inserted into the disc space to simulate the interbody grafting, and a fixation device was implanted with axial compression. Rotational angles of the L3-L4 segment stabilized by a fixation device and graft were normalized by the corresponding angles of the intact specimen to study the overall stabilizing effects.

RESULTS

With the interbody graft and fixation devices, all showed significant stabilizing effects in flexion, extension, and lateral bending. All devices restored axial rotation stability to intact specimen, but only the Kaneda device restored the torsional stability beyond the intact specimen. No statistical differences in stabilizing effects in axial rotation were found between any of the tested devices. When the graft was removed, the Kaneda device significantly decreased the motions in all directions compared with the intact motion, whereas the University plate decreased the motions in flexion, extension, and lateral bending. The Texas Scottish Rite Hospital system was found to reduce the flexion and lateral bending motions significantly, and Z-plate decreased lateral bending motions only. Stabilizing effects of the interbody graft were significant in lateral bendings for all devices. Additionally, the significant stabilizing role of the graft was noted in flexion and extension in Z-plate only. The graft did not significantly reduce the axial rotation motion in any instrumentations.

CONCLUSIONS

Modern anterior instrumentations for the thoracolumbar spine, such as the Kaneda device, Texas Scottish Rite Hospital system, Z-plate, and University plate, restored the stability in all motions when an interbody graft was inserted. The stability of fixation devices revealed that the Kaneda device is the best, particularly in restoring the torsional stability. The information on the relative stability provided by different instrumentations should help the spine surgeon in choosing the appropriate instrumentation for the particular circumstance.

Comparison of two fixation methods of oblique lesser metatarsal osteotomies: a biomechanical study

Two methods of internal fixation of oblique lesser metatarsal osteotomies were compared biomechanically using fresh-frozen human cadaver bones. Osteotomies were made obliquely through the metatarsal shafts and fixed with either crossed Kirschner wires or a single AO screw using the lag technique. The specimens were then fixed at their proximal end and loaded to failure using an axial torsion material testing system (MTS, Minneapolis, MN). Load displacement curves were obtained and the stiffness of the constructs were determined. Single-screw fixation was found to be significantly stiffer than the crossed wire configuration (P < .01). Single-screw fixation resulted in a stiffness of 211.2 +/- 111.7 N/cm (mean +/- SD), while stiffness of the crossed wire configuration averaged 56.9 +/- 25.1 N/cm.

The pharmacodynamic interaction of propofol and alfentanil during lower abdominal surgery in women

BACKGROUND

Propofol and alfentanil are frequently combined to provide general anesthesia. The purpose of this study was to characterize the pharmacodynamic interaction between propofol and alfentanil for several clinically relevant end points.

METHODS

Twenty-one women, aged 20-55 yr, scheduled for lower abdominal surgery, were randomly assigned in a double-blind manner to one of three groups to receive a computer-controlled infusion of propofol with target concentrations of 2, 4, or 6 micrograms/ml. In addition, all patients received computer-controlled infusion of alfentanil (initial target concentration 50 ng/ml). While the target concentration of propofol was maintained constant, the target concentration of alfentanil was varied in steps of 10-50 ng/ml according to the presence or absence of patient responses to perioperative stimuli. Arterial blood samples for alfentanil and propofol determination were taken at clinically relevant stimuli. Alfentanil-propofol interactions for laryngoscopy, intubation, skin incision, the opening of the peritoneum, and awakening were determined by logistic regression over the three groups (n = 21). The alfentanil concentrations associated with a 50% probability (EC50s) of suppression of responses to intraabdominal surgical stimuli, as determined by logistic regression in the individual patients, were related to corresponding mean blood propofol concentrations by nonlinear regression analysis.

RESULTS

With blood propofol concentrations increasing from 2 to 10 micrograms/ml, the EC50 of alfentanil decreased from 170 to 25 ng/ml for laryngoscopy, from 280 to 23 ng/ml for intubation, from 259 to 9 ng/ml for the opening of the peritoneum, and from 209 to 16 ng/ml for the intraabdominal surgical stimuli. With plasma alfentanil concentrations increasing from 10 to 150 ng/ml, the EC50 of propofol for the regaining of consciousness decreased from 3.8 to 0.8 microgram/ml.

DISCUSSION

We defined the pharmacodynamic interaction between propofol and alfentanil for suppression of responses to perioperative stimuli during lower abdominal surgery. We conclude that propofol reduces alfentanil requirements for all studied clinical end points. In addition, alfentanil decreases propofol concentrations at which patients regain consciousness.

Significance of magnetic resonance signal enhancement in evaluation of myocardial infarction in cats

RATIONALE AND OBJECTIVES

To correlate magnetic resonance (MR) signal enhancement with pathophysiologic changes occurring during ischemia and reperfusion in evaluation of myocardial infarction in cats.

METHODS

Seven cats were subjected to 150 minutes of occlusion of the left anterior descending coronary artery followed by 90 minutes of reperfusion. Gadolinium (Gd) diethylenetriaminepentaacetic acid-polylysine (molecular weight [mw] = 40 to 50 kd, DP230) contrast-enhanced MR images were acquired with coinjection of poly-L-lysine-fluorescein isothiocyanate (mW = 40 to 50 kd, DP219) as a fluorescent tracer molecule of the contrast agent. Signal intensities on the MR images and fluorescence activities on the resected cardiac specimens were measured. Pathologic examinations by electron and light microscopes and 2,3,5-triphenyltetrazolium chloride histochemical staining were performed on the specimens.

RESULTS

Magnetic resonance signal intensity was lower in the center (3.49 +/- 0.36) than in the periphery (4.71 +/- 0.89) of the enhanced area. Fluorescence activities were absent in the normal myocardium; they were scant as nonspecific discrete dots in the center and numerous as specific interstitial distribution in the periphery of the ischemic myocardium. Electron and light microscopic examinations showed severely damaged ultrastructures of the center and moderately distorted ultrastructures of the periphery.

CONCLUSIONS

The center of the MR signal-enhanced area is the infarct center with severe ultrastructural damages, which also might be an area of little or absent of blood reflow. Conversely, the peripheral-enhanced area is the infarct periphery with moderate myocardial damages.

Strength of anterior vertebral screw fixation in relationship to bone mineral density

A biomechanical study was performed to investigate the relationship among the pullout strength of anterior vertebral screw fixation, bone mineral density (BMD) of the vertebral body, screw insertion torque, and width of the vertebral body. BMD was measured using a dual energy x-ray absorptiometry unit. Screw insertion torque and width of the lumbar vertebrae were also measured before the pullout test. Pullout strength was significantly correlated with BMD (r = 0.85) and screw insertion torque (r = 0.47), but not with width of the vertebral body. Multiple regression analyses demonstrated better correlation between pullout strength and the other parameters (r = 0.886). A stepwise regression analysis showed that BMD is the most significant predictor of the pullout strength followed by width of the vertebral body, whereas screw insertion torque is not a significant predictor. Furthermore, the mean pullout strength of the grade I osteoporosis group was significantly greater than that of grade II or III osteoporosis group.

Prediction of bone graft strength using dual-energy radiographic absorptiometry

STUDY DESIGN

A biomechanical study of anterior iliac crest bone was done to investigate a relationship between the compressive strength of tricortical iliac crest grafts and bone mineral density (BMD) of the iliac crest measured by dual-energy x-ray absorptiometry (DEXA).

OBJECTIVES

This study investigated the potential usefulness of DEXA for measuring BMD of the iliac crest and documented bone graft strength predictability by BMD measurements.

SUMMARY OF BACKGROUND DATA

The corticocancellous iliac bone is frequently used as an interbody graft for anterior spine fusion. The decreased compressive strength of bone graft may lead to collapse, pseudarthrosis and recurrence of symptoms, particularly in the osteoporotic patient. The DEXA accurately determines BMD of the spine and the hip, but no previous studies are available on the pelvis.

METHODS

The BMDs were measured on the intact pelvis of the elderly and the corresponding tricortical grafts, using DEXA. The strut and Smith-Robinson type grafts were placed under axial loading using Material Testing System. Load to failure and compressive strength were obtained and statistically correlated to BMDs.

RESULTS

There was a high correlation between the BMDs of the intact pelvis and each graft (R = 0.8, P < 0.001). The ultimate load to failure and compressive stress were linearly correlated to the BMD of the intact pelvis (R = 0.82, P < 0.001, R = 0.78, P < 0.001, respectively) as well as to the BMD of the graft (R = 0.77, P < 0.001, R = 0.75, P < 0.001, respectively).

CONCLUSIONS

These results suggest that the biomechanical strength of the iliac bone graft is very dependent on its BMD, and DEXA has a potential clinical value in predicting iliac bone graft strength for cervical spine fusion.

Stress analysis of a canine spinal motion segment using the finite element technique

Canine models have been frequently employed to investigate the in vivo effects of a surgical procedure. Various studies indicate that canine models can provide a successful in vivo biological model for these studies. Use of canine models for the biomechanical studies of the spine, however, have been questioned because of different loading conditions on the canine and human spines originated from posture differences between canine and human. Similarities between the stress distributions within the canine and human motion segments under physiological loads will strengthen the use of canine models for the studies of spine biomechanics. In the present study, finite element models of the canine intact and stabilized motion segments were developed to investigate these aspects. Comparison of model predicted flexion angle, axial stiffness, and facet contact force for the canine intact L6-L7 motion segment revealed good agreement with the corresponding parameters experimentally measured under the similar loading conditions. Similar stress distributions within the intact canine and human models were found from the predicted results in response to the physiological load. Stabilizing and stress-shielding effects of a pedicle screw-plate-type fixation device [variable spinal plating (VSP)] on the stabilized motion segment were also similar for the canine and human stabilized models. Furthermore, maximum stresses in the pedicle screws were found at the junction between the bone screw and the integrated nut of the inferior screw in both the canine and human stabilized models. This corresponds to the location of pedicle screw breakage reported in the literature. These findings suggest that a canine is a suitable model for the biomechanical studies of the lumbar spine.

Contrast sensitivity in a large adult population

The contrast sensitivity test (using Vistech charts) was performed on a consecutive sample of 1612 eyes of 807 Republic of Singapore Air Force personnel (two diseased eyes excluded), which had no known ophthalmic disorder. This yielded a large sample norm of spatial Contrast Sensitivity Function (CSF) distribution curves, based on the local population. Although all subjects had their refractive errors fully corrected by spectacles, whenever necessary, to visual acuity of 6/6 or better, myopes had lower mean contrast sensitivity, in the higher spatial frequencies, compared to the emmetropic. Postulates were offered to explain this association, including the concept of micro-amblyopia. Pilots and aircrew performed consistently better than the ground crew, suggesting that target acquisition training may improve contrast sensitivity. Interestingly, sex was also shown to be associated with differences in contrast sensitivity: females were found to have lower spatial contrast sensitivity compared to males. Age was associated with poorer contrast sensitivity only at the lower spatial frequencies in this study sample, while race, with that of higher frequencies; Chinese having lower contrast sensitivity than other races (a heterogeneous group consisting of Malays, Indians, Eurasians and Others). The association of contrast sensitivity with race highlights the importance of using normograms based on the local population. All the above associations were statistically significant at P = 0.05, and independent of each other, based on analysis by multiple regression.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro MR imaging of the resected stomach with a 4.7-T superconducting magnet

PURPOSE

To study the effects of formalin fixation, signal intensity characteristics of the stomach-wall layers, and findings suggestive of cancerous invasion to the stomach wall in vitro with magnetic resonance (MR) imaging in humans.

MATERIALS AND METHODS

MR images of nine specimens of stomach cancer and 29 normal specimens were obtained at 4.7 T; 26 of the normal specimens were fixed in 10% formalin for 2 hours to 187 days before imaging. The field gradient was 10 G/cm; the spatial resolution, 0.1 mm.

RESULTS

The mucosal, submucosal, and proper-muscle layers were clearly identifiable. The submucosa of the fresh specimens had the lowest signal intensity of all specimens on both T1- and T2-weighted images (P < .01). No statistical correlation existed between signal intensity and duration of fixation. Tumor invasion was detected in seven of eight specimens with mucosal invasion, all eight specimens with submucosal invasion, and three of six specimens with muscle invasion.

CONCLUSION

In vitro MR imaging enabled differentiation of all three layers of the stomach wall, detection of the cancer, and measurement of the depth of invasion.

A comparison of stress-induced porosity due to conventional and a modified spinal fixation device

A hypothesis that device-related osteopenia can be reduced by decreasing the rigidity of a fixation device was tested through a canine study. Polymer washers were interposed between the integral nut and plate of the variable spinal plating (VSP) system to reduce its rigidity. A solid fusion was observed 6 months postoperatively in all of the animals using VSP or modified systems. The stabilized segment using both systems showed similar load-displacement behaviors immediately after surgery and 6 months postoperatively. Although not significant, 5.6 and 1.8% decreases in volumetric density of mineralized bone were found in the stabilized segments due to VSP and modified systems, respectively. The modified system also increased bone growth around screws. The new concept of using polymer washers, to decrease rigidity of the fixation device over time, may reduce device-related osteopenia.

Occlusive and reperfused myocardial infarction: detection by using MR imaging with gadolinium polylysine enhancement

PURPOSE

To assess the capability of gadolinium polylysine-enhanced cardiac magnetic resonance (MR) imaging in depicting normal and ischemic myocardium during occlusion and reperfusion of the left anterior descending artery.

MATERIALS AND METHODS

Contrast-enhanced MR images were obtained in 18 cats during 90 minutes each of occlusion and reperfusion. The change in signal intensity (SI) was compared among normal myocardium and central and peripheral ischemic zones. Results were compared with those of 2,3,5-triphenyltetrazolium chloride staining.

RESULTS

During occlusion, the ischemic zone lacked enhancement while normal myocardium had gradual enhancement. During reperfusion, the ischemic zone had strong enhancement. In cats with large infarction, the central and peripheral ischemic zones had intermediate and high SI, respectively; in cats with focal or no infarction, the entire ischemic zone had high SI.

CONCLUSION

Occlusive and reperfused myocardial infarction can be detected at gadolinium polylysine-enhanced MR imaging by means of differential SI changes in normal myocardium and central and peripheral ischemic zones.

Advanced cataract in Singapore--its prognosis and complications

A retrospective study of 995 eyes that had undergone cataract surgery between January and March 1990 revealed that one in 20 (50 eyes) were advanced cataracts which, by our definition, included hypermature, Morgagnian and intumescent cataracts. Thirty percent of these cases suffered from cataract-related complications preoperatively: phacomorphic glaucoma (12/50 eyes), phacolytic glaucoma (1/50 eyes), and subluxed cataract without trauma (2/50 eyes). Cataract surgery in these advanced cataracts produced significantly poorer results than the rest. One in four eyes failed to achieve visual acuity of 6/12 or better (best corrected) postoperatively, while one in eight eyes did not improve beyond Hand Movement vision. The main reason for poor visual results was lens-induced glaucoma (80%).

A retrospective study of cataract surgery in the Singapore General Hospital in 1990

Nine hundred and ninety-five consecutive cases of cataract extraction with or without lens implantation performed within the first three months of 1990 in the Singapore General Hospital were examined retrospectively. Of the 995 cases, 874 (87.84%) were deemed to have adequate postoperative evaluation at an average of 12.5 months. Of these cases, 79.52% (695 eyes) obtained a visual acuity of 6/12 or better. When cases with pre-existing causes of poor vision were excluded, 90.25% of cases obtained a visual acuity of 6/12 or better. If potentially treatable causes of postoperative poor vision (such as posterior capsule opacification awaiting Nd:YAG laser capsulotomy and high astigmatism prior to suture removal) were further excluded from analysis, this figure would rise to 93.66%. The incidence of posterior capsule rupture was 1.4%. Factors affecting visual success included patient age, lens hypermaturity and duration of surgery.

Hearts with twisted atrioventricular connections: findings at MR imaging

The "crisscross" heart and the heart with "superoinferior ventricles" are closely related congenital cardiac malformations that are characterized by twisted atrioventricular connections. The authors studied the morphologic characteristics of three hearts with twisted atrioventricular connections as seen on magnetic resonance (MR) images. The most important clue to the diagnosis was the distorted atrioventricular connections that were demonstrated on serial images. The axes of the atrioventricular connections through the atrioventricular valves were not parallel to each other. The presence of unusual recesses in the cardiac chambers, the angulated or curved configuration of the atrial and ventricular septa, and the unexpected great arterial relationship for the given combination of segmental connections supported the findings of twisted atrioventricular connections. MR imaging facilitated the precise morphologic diagnosis of these hearts.

Effect of recombinant human erythropoietin on muscle energy metabolism in patients with end-stage renal disease: a 31P-nuclear magnetic resonance spectroscopic study

To evaluate the effects of recombinant human erythropoietin (r-HuEPO) on muscle energy metabolism in patients with end-stage renal disease (ESRD), 10 patients receiving maintenance hemodialysis were given r-HuEPO (3,000 U three times a week for 8 weeks). Intracellular phosphocreatine to inorganic phosphate ratios and pH were measured with 31P-nuclear magnetic resonance spectroscopy before and after all-out handgrip exercise, before treatment and at 4 and 8 weeks after r-HuEPO treatment. The same measurements, from 14 normal individuals also were studied for comparison. The hematocrit increased significantly with r-HuEPO treatment, although the dose of r-HuEPO did not correct it to the normal level. The exercise capacity improved significantly. Intracellular pH was not different between the ESRD patients and controls or between before and after r-HuEPO treatment. The phosphocreatine to inorganic phosphate ratio at the resting state improved significantly with r-HuEPO treatment, reaching the same level as the normal subjects even before the low hematocrit normalized. The measurements immediately after exercise were the lowest levels obtained (the nadir state) and were not different between groups. In the state of maximum recovery, a pattern was noted that was similar to that found in the resting state. These results showed that r-HuEPO treatment improved the phosphorylation potential during the resting state and the maximum phosphorylation potential during the postexercise recovery phase, and suggest that the treatment improved the rate of oxidative phosphorylation in ESRD patients receiving hemodialysis.

Pharmacodynamics of alfentanil as a supplement to propofol or nitrous oxide for lower abdominal surgery in female patients

BACKGROUND

Although propofol and alfentanil are given in combination in clinical practice, the pharmacodynamic interaction between these drugs has not been described.

METHODS

The pharmacodynamics of alfentanil when given as a supplement to propofol were studied in 10 ASA physical status 1 female patients (group P) undergoing lower abdominal surgery and compared to the pharmacodynamics of alfentanil when given as a supplement to nitrous oxide (group N, n = 10). Anesthesia was induced by either computer-controlled infusion of propofol and alfentanil at target concentrations of 3 micrograms/ml and 100 ng/ml (group P) or computer-controlled infusion of 400 ng/ml alfentanil as a supplement to nitrous oxide and oxygen (ratio 2:1; group N). The target concentration of alfentanil was varied to patient responses, and the nitrous oxide and propofol concentrations were maintained constant. A sigmoid Emax model was fitted to response/no response data versus plasma alfentanil concentrations at intubation, skin incision, and the opening of the peritoneum in both groups and for the intraabdominal part of surgery in the individual patients. In addition, the speed of recovery in both groups was determined by a deletion-of-p's test.

RESULTS

The EC50 (the concentration at which, with a 50% probability, the patients did not respond to the surgical stimuli) of alfentanil during propofol anesthesia was 92 ng/ml for intubation, 55 ng/ml for skin incision, 84 ng/ml for the opening of the peritoneum, and 66 +/- 38 ng/ml (mean +/- SD) for the intraabdominal part of surgery. The corresponding values during nitrous oxide anesthesia were significantly higher: 429 ng/ml for intubation, 101 ng/ml for skin incision, and 206 +/- 65 ng/ml for the intraabdominal part of surgery (P < 0.001). The speed of recovery was similar in both groups.

CONCLUSIONS

The alfentanil requirements in ASA physical status 1 female patients undergoing lower abdominal surgery are less when given as a supplement to propofol (4 micrograms/ml) compared to 66% N2O.

Adult-onset pulmonary tuberculosis: findings on chest radiographs and CT scans

Adult-onset pulmonary tuberculosis refers to primary tuberculous infection occurring initially in adults. The decreasing exposure in childhood, owing to careful public health measures and the advent of antituberculous chemotherapy, has resulted in later initial exposure to tuberculosis and an increased likelihood of susceptibility to tuberculosis during adulthood [1-3]. In addition, chest radiographs typically show a pattern more consistent with primary infection in pulmonary tuberculosis associated with AIDS. In this essay, we illustrate the spectrum of radiographic and CT findings of adult-onset pulmonary tuberculosis in patients without AIDS.

Effectiveness of netilmicin and tobramycin against Pseudomonas aeruginosa in vitro and in an experimental tissue infection in mice

The activity of netilmicin and tobramycin against Pseudomonas aeruginosa was assessed in vitro in the presence of constant and exponentially declining concentrations, and in mice in an experimental thigh infection. The activity in vitro at constant concentrations was expressed as the maximal killing rate (ER) during 3 h of exposure. On the basis of the quantitative relation between E(R) and the drug concentration, the numbers of cfu expected at consecutive times, at constant as well as at declining concentrations, were predicted. The relationship between observed numbers and predicted values of ERt were similar under both conditions for both drugs. On the same basis the numbers of cfu expected in the experimental thigh infection were predicted. There was indeed a significant linear relationship between observed numbers of cfu in homogenized muscle and the values predicted on the basis of the pharmacokinetics of the aminoglycosides, but the slope of this relationship was only 0.22. There was no difference in this respect between the two antibiotics. It is concluded that the efficacy of netilmicin and tobramycin against P. aeruginosa is considerably less in vivo than in vitro, but the relation is about the same for the two drugs; therefore the slightly higher activity of tobramycin in vitro is relevant in the in-vivo situation.

NMR venography using the susceptibility effect produced by deoxyhemoglobin

A new angiography technique using the susceptibility effect is proposed. Blood containing deoxyhemoglobin is more paramagnetic than surrounding tissue and thereby produces a susceptibility effect at blood-tissue interfaces. By use of a specially tailored RF pulse, signals from normal tissues are suppressed while the signals from blood interfaces, where strong susceptibility-induced fields are created, are enhanced. The design and characteristic behavior of the tailored RF pulse are discussed and experimental results obtained using both a phantom and a human volunteer with a 2.0-T whole-body NMR system are also presented.