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Biomedical subjects

L H Riley

Publications and source records attributed to L H Riley.

At least 19 recordsLinked to original sources
PubMed1998

Higher electrical stimulus intensities are required to activate chronically compressed nerve roots. Implications for intraoperative electromyographic pedicle screw testing.

STUDY DESIGN: A comparison of the electrical thresholds required to evoke myogenic responses from direct stimulation of normal and chronically compressed nerve roots. OBJECTIVE: To determine whether intraoperative electromyographic testing to confirm the integrity of instrumented pedicles should be performed at higher stimulus intensities in cases where there is preoperative lumbosacral radiculopathy. SUMMARY OF BACKGROUND DATA: Postoperative neurologic deficits may occur as a result of pedicle screw misplacement during spinal instrumentation. The failure to evoke myogenic responses from stimulation of pedicle holes and screws at intensities of 6-8 mA is commonly used to exclude bony pedicular wall perforation. METHODS: Direct nerve root stimulation was used to compare the stimulus thresholds of normal and compressed nerve roots in six patients with limb weakness from chronic lumbosacral radiculopathy. RESULTS: The stimulus thresholds of chronically compressed nerve roots significantly exceeded those of normal nerve roots, indicating partial axonal loss (axonotmesis). In most cases, the direct stimulus thresholds of compressed nerve roots exceeded 10 mA. CONCLUSIONS: When instrumentation is placed at spinal levels where there is preexisting chronic lumbosacral radiculopathy, holes and screws may need to be stimulated at higher intensities to exclude pedicular perforation and prevent further iatrogenic nerve root injury.

Action Potentials↗
PubMed1998

Prophylactic antibiotics for spine surgery: description of a regimen and its rationale.

Cefazolin, an antibiotic commonly used for surgical prophylaxis, may not adequately penetrate the intervertebral disk or cerebrospinal fluid. The combination of gentamicin and cefuroxime has been found to penetrate both structures in adequate levels and was used in 40 consecutive elective spine cases without a postoperative infection or antibiotic-related complications.

Adult↗
PubMed1997

Effect of molecular weight on the diffusion of contrast media into cartilage.

STUDY DESIGN: A comparison of contrast enhancement in the intervertebral disc from two magnetic resonance imaging contrast media in experimental animals. OBJECTIVES: To test the effect of molecular weight on the diffusion of ionic contrast media into the intervertebral disc. SUMMARY OF BACKGROUND DATA: Intravenously administered gadopentetate diffuses similarly into the fibrocartilage of intervertebral discs and herniated disc fragments. Differentiation between recurrent disc fragments and scar tissue via magnetic resonance imaging is optimized by using contrast media, which result in different contrast enhancement of these two tissues. Contrast media of higher molecular weight diffuse more slowly into cartilage; hypothetically, therefore, such media will produce better contrast between scar tissue and recurrent disc fragments. METHODS: Gadopentetate (molecular weight 546) or gadolinium-polylysine (molecular weight 40,000) was injected intravenously into rabbits. The signal intensities of intervertebral disc and muscle tissue were recorded by magnetic resonance imaging at baseline and at pre-determined intervals for 2 hours after injection of the contrast medium. Contrast enhancement in these tissues was calculated in each animal for each contrast medium, and differences in enhancement were tested for significance by a growth-curve model. RESULTS: Contrast enhancement in the intervertebral disc was significantly less with gadolinium-polylysine than with gadopentetate. In muscle, no significant difference between the two media was observed. CONCLUSIONS: Molecular weight affects the diffusion of paramagnetic contrast media into the intervertebral disc. Contrast media of a high molecular weight may produce better contrast between recurrent herniated disc fragments and scar tissue than contrast media of lower molecular weight. This possibility should be rested in further studies.

Animals↗
PubMed1997

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.

Animals↗
PubMed1996

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.

Aged↗
PubMed1996

In vitro load measurement using an instrumented spinal fixation device.

An AO spinal fixateur interne was modified to study the effects of a corpectomy on implant performance. A hermetically sealed cartridge containing strain gauges and an inductively powered telemetry unit was integrated into the threaded portion of the original implant. Five cadaveric spines were instrumented with the modified implant spanning a single lumbar vertebra. The spines were tested in axial compression, torsion, flexion, extension and lateral bending. Measurements of the three forces and moments within the implant were performed in the intact spine and repeated following a corpectomy and corpectomy plus complete posterior ligamentous injury. The bending moment, increased following corpectomy in all testing modes. The largest increase was in the flexion bending moment, which increased from 155 Nmm to 3328 Nmm following corpectomy.

Aged↗
PubMed1996

Ionic versus nonionic paramagnetic contrast media in differentiating between scar and herniated disk.

PURPOSE: To compare the MR contrast enhancement produced by ionic and nonionic paramagnetic contrast media in herniated disk fragments with that in epidural scar tissue. METHODS: A recurrent herniated disk was modeled in canines by using laminectomy to place a fragment of disk cartilage in the epidural space. The dogs were studied 88 and 90 days after laminectomy with MR imaging enhanced with an ionic or a nonionic paramagnetic contrast medium. Contrast enhancement of the epidural scar tissue and the epidural disk fragment was measured at 2, 22, and 45 minutes after the injection. RESULTS: Contrast enhancement was consistently and significantly higher in scar tissue than in disk fragments, although the difference decreased between 2 and 45 minutes after administration of contrast medium. Enhancement of disk fragments was less with the ionic than with the nonionic contrast medium. Contrast between the disk fragments and scar was also greater with the ionic than with the nonionic medium. CONCLUSIONS: The contrast between recurrent disk fragments and scar tissue is affected by the timing of the scan and the choice of contrast medium. Scans obtained immediately after the injection of contrast medium show more contrast between disk fragment and scar than do delayed scans. Recurrent herniated disk fragments are more effectively shown by ionic than by nonionic media.

Animals↗
PubMed1996

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.

Adult↗
PubMed1995

The thoracolumbar spine in Marfan syndrome.

We analyzed the prevalence, inheritance, progression, and functional implications of spinal deformity in Marfan syndrome using four different groups of patients. We studied 113 patients who had Marfan syndrome, eighty-two of whom were skeletally immature, in order to characterize the alignment and function of the spine. The patients were selected from a clinic that provides total care with no bias toward the presence of orthopaedic conditions. Scoliosis was identified in fifty-two of the eighty-two patients, and the prevalences for the sexes were equal. The thoracic portion of the curve was convex to the right in all but two patients. The mean kyphosis was greater than that in the general population. Five distinct sagittal profiles were identified on the basis of whether the thoracic kyphosis was within, greater than, or less than normal limits and whether the transition between the kyphosis and lordosis occurred at or caudad to the normal level or whether the curves were reversed. Spondylolisthesis was present in five patients (6 per cent), with a mean slip of 30 per cent. Fourteen pedigrees were studied in depth. There was no familial pattern of the scoliosis. A separate group of fifty-six patients with scoliosis, for whom serial follow-up radiographs were available, was studied for progression. Patients who had a curve of more than 30 degrees had mild progression, and those who had a curve of more than 50 degrees had marked progression (mean, 3 +/- 4 degrees per year). Pain and function of the back were studied in thirty patients who were thirty-five to forty-five years old; these patients were found to be more impaired than matched controls. The presence of scoliosis was associated with pain in the region of the curve in these patients.

Adolescent↗
PubMed1994

Tissue distribution of antibiotics in the intervertebral disc.

STUDY DESIGN: This study analyzed the distribution of antibiotics within the intervertebral disc of rabbits. Specimens were tested with specific antibodies against antibiotics using an immunofluorescent technique. OBJECTIVES: The results were correlated to provide a rationale for perioperative prophylaxis of infection. SUMMARY OF BACKGROUND DATA: Several groups of investigators and the recent data from our laboratory showed quantitative changes in penetration of antibiotics into intervertebral disc. No previous study has assessed antibiotic distribution in anulus fibrosus and nucleus pulposus. METHODS: Discs were obtained from rabbits after intravenous injection of penicillin or gentamicin. Antibiotics were localized in tissue sections using specific antibodies with a immunofluorescent method. RESULTS: Penicillin (negatively charged) and gentamicin (positively charged) penetrated the neutrally charged anulus fibrosus, but penicillin had less ability than gentamicin to penetrate into the negatively charged nucleus pulposus. CONCLUSION: Our data suggest that penetration and distribution of antibiotics into avascular intervertebral disc is significantly influenced by the charge of antibiotics.

Animals↗
PubMed1989

Considerations in the comparison of cemented and cementless total hip prostheses.

Based on conservative models of the revision rates for cemented and uncemented hip arthroplasties, the required number of patients for a study to show significant uncemented superiority was determined using standard statistical techniques. A review of the literature was done to ascertain the revision rates for cemented total hip arthroplasties. Patients with osteoarthritis who were older than 50 years had an average revision rate of 1% per year, while those younger than 50 years had revision rates in excess of 2% per year. Specific conditions of the hip were also associated with increased failure rates, most notably the implantation of a revision arthroplasty for a previously failed total hip arthroplasty. Assuming that the uncemented hip had a long-term revision rate of 0.5% per year and an early lack of biologic fixation in 1% of patients, it was found that a 5-year study would have to include at least 2,800 patients (1,400 in each group) if the study population had a cemented failure rate of 1% per year and a total of 230 patients in those having a cemented failure rate of 2% per year. The patients needed for a 10-year evaluation would be 700 and less than 100, respectively. Altering the long- or short-term revision rate for uncemented total hip arthroplasty had relatively little effect on the study size. This analysis indicates that a comparison study would be best done in patients who have high failure rates with cemented total hip arthroplasties. Multicenter trials involving younger patients or those undergoing revision surgery are ideally suited for such an investigation.

Follow-Up Studies↗
PubMed1989

A method of tack fixation of tibial bone grafts in total knee arthroplasty.

A simple and secure method of bone graft fixation using a tack is described for reconstruction of peripheral tibial defects during cemented and uncemented total knee arthroplasties. In use since 1985, this method facilitates minimization of tibial bone resection and provides an intrinsically stable platform for tibial component seating. This method is technically simple to perform with routine primary total knee arthroplasty equipment and is especially helpful for intermediate-sized grafts, which are too small to be handled conveniently with screws.

Aged↗
PubMed1989

Advanced three-dimensional evaluation of acetabular trauma: volumetric image processing.

Volumetric image processing is a new approach to generating simulated three-dimensional images from transaxial CT data. The major advantages compared to conventional surface-rendering 3D technique include: preservation of every pixel of CT data for increased accuracy of rendered image; tissue layer translucency allowing appreciation of multiple tissue layers on each image; simulation of real-time rotation in varying axes for optimal appreciation of abnormalities; and a high-speed, high-capacity computer setup which generates high-quality images rapidly, giving the system sufficient flexibility for these complicated functions while remaining user friendly and fast.

Accidents, Traffic↗
PubMed1987

Three-dimensional imaging of acetabular trauma.

Computed tomography (CT) scanning is widely used in evaluation of acetabular fractures. Three-dimensional (3D) images of the pelvis can be created from CT scan data. This article reports two studies, each employing one type of 3D imaging in acetabular trauma cases. The first was a study of 21 patients utilizing surface-rendered 3D images, the second, a study of 19 patients using volume-rendered 3D images. Both types of 3D images were clinically helpful and can be used in lieu of conventional plain films as a supplement to CT examination. Advantages of volume-rendered images are described.

Acetabulum↗
PubMed1987

Volumetric rendering techniques: applications for three-dimensional imaging of the hip.

Volumetric rendering is a new approach to three-dimensional (3D) imaging that overcomes many of the drawbacks of currently available surface-rendering systems. Its application on the Pixar Imaging System in two cases of acetabular fracture was assessed to illustrate the features of the technique. The fast-computing architecture and large memory of this system allow rapid generation of a series of high-quality 3D images in each plane of rotation (x or spinal axis, z or somersaulting axis) that can be viewed as independent static images or as an animated real-time video loop. Editing to remove the normal contralateral hemipelvis enhances appreciation of acetabular abnormalities. Every pixel of computed tomographic data is preserved, allowing representation of both soft tissue and bone as translucent overlap. The presentation of data also allows detection of subtle abnormalities and features and minimizes the artifact generation common in surface-rendered images.

Computers↗
PubMed1987

The anterior retropharyngeal approach to the upper part of the cervical spine.

Since 1959, we have used a superior extension of the anterior approach to the cervical spine of Robinson and Smith in a consecutive series of seventeen patients. This approach provided anterior access to the neural elements from the clivus to the body of the third cervical vertebra, without the need for posterior dissection of the carotid sheath or entrance into the hypopharynx or oral cavity. It also provided adequate exposure for the insertion of iliac or fibular strut grafts, which was necessary in thirteen patients. The approach gave excellent exposure for anterior intralesional excision of a tumor in ten patients, marginal excision of an osteochondroma, two corpectomies of the second cervical vertebra combined with removal of the odontoid process, corpectomy of the second cervical vertebra for the treatment of fixed atlanto-axial subluxation, removal of a bullet anterior to the clivus, reduction of a dislocation of the second on the third cervical vertebra secondary to an unstable fracture of the pedicles of the second cervical vertebra, and anterior débridement for treatment of pyogenic vertebral osteomyelitis. In contrast to the reported results of transmucosal approaches to the atlas and axis, there were no infections or iatrogenic neurological deficits of the spine in the present series. Twelve patients who were followed for two years or more had a solid anterior fusion and no subsequent loss of cervical stability. Pain in the neck was relieved in all of the patients who had had a pathological or traumatic fracture.

Adolescent↗
PubMed1987

Pyogenic osteomyelitis of the occiput, the atlas, and the axis. A report of five cases.

Pyogenic osteomyelitis rarely affects the first and second cervical vertebrae, and when it does it can progress to abscess formation, compressing the spinal cord. If the process is unrecognized, it can be fatal. The cases of five patients are reported. Two patients were treated by anterior débridement and posterior cervical-occipital arthrodesis; one, by transoral drainage; one, by posterior cervical-occipital arthrodesis; and the fifth, by posterior atlanto-axial arthrodesis. The causative organism was Staphylococcus aureus in four patients and Pasteurella multocida in one. In all patients, intravenous antibiotics were used, followed by prolonged administration of oral antibiotics. All five patients recovered.

Aged↗