Comparative evaluation of single-level closing-wedge vertebral osteotomies for the correction of fixed kyphotic deformity of the lumbar spine: a cadaveric study.

STUDY DESIGN: Anatomic study. OBJECTIVES: To compare spinal osteotomies with respect to obtainable correction and change in anterior height and distance of the spinal column and to describe a modification of the decancellation closing-wedge osteotomy to obtain further correction. SUMMARY OF BACKGROUND DATA: Fixed kyphotic deformity of the lumbar spine can cause difficulty with sitting, lying flat, and pain and can pose a risk to adjacent spinal cord and nerves as well as impair respiratory and abdominal function. Various corrective osteotomies have been described. Osteotomies involving decancellation and a closing wedge of the apical vertebra theoretically decrease the risk to anterior vascular structures. METHODS: Single-level vertebral osteotomies were performed on three groups of fresh-frozen human cadaveric lumbar spines. Group 1 underwent a conventional anterior opening-wedge/posterior closing-wedge osteotomy, Group 2 underwent a conventional decancellation posterior closing-wedge osteotomy, and Group 3 underwent our modified decancellation posterior closing-wedge osteotomy. Sagittal plane angulation as well as anterior height and distance of the spinal column were measured before and after osteotomy. RESULTS: The mean correction was 38 degrees for Group 1, 36 degrees for Group 2, and 49 degrees for Group 3. The mean change in anterior height and distance was 20 and 30 mm, respectively, for Group 1. For Groups 2 and 3 it was only 2-4 mm. CONCLUSIONS: The authors recommend single-level posterior decancellation procedures for correction of fixed kyphotic deformities of the thoracolumbar spine to decrease the risk to anterior neurovascular structures. An additional 10-13 degrees of correction can be obtained with the authors' modification.

Peak stresses observed in the posterior lateral anulus.

STUDY DESIGN: The stress distributions within cadaveric lumbar intervertebral discs were measured for a range of loading conditions. OBJECTIVES: To examine the distribution of stress across the area of the intervertebral disc and to compare regional variations in peak stress during compression loading with various flexion angles. SUMMARY OF BACKGROUND DATA: The rate of disc degeneration and the occurrence of low back disorders increase with higher mechanical loading of the spine. The largest peak stresses occur in the anulus. METHODS: Human lumbar L2--L3 and L4--L5 cadaver functional spinal units were obtained and tested. The distribution of disc stress was measured using a pressure probe with loads applied, pure compression and compression with 5 degrees of either flexion or extension. RESULTS: Stress profiles were recorded across the intervertebral disc at a compressive force of 1000 N and each of the three flexion-extension angles. The highest values (2.99 +/- 1.31 MPa) were measured during extension-compression lateral to the midline of the disc in the posterior anulus. The pressure in the nucleus was relatively unchanged by flexion angle remaining about 1.00 MPa for a 1000-N compression. CONCLUSIONS: Pressure measurements of the cadaveric nucleus have been used to validate models of lumbar spine loading and to evaluate the risk of low back injury and disc herniation. Previous observations limited to midsagittal measurements of the nucleus did not identify the regions of highest stress. The highest values observed here within the posterolateral anulus correspond to common sites of disc degeneration and herniation.

New technologies in spine: kyphoplasty and vertebroplasty for the treatment of painful osteoporotic compression fractures.

STUDY DESIGN: Literature review. OBJECTIVES: To describe new treatments for painful osteoporotic compression fractures in light of available scientific literature and clinical experience. SUMMARY OF BACKGROUND DATA: Painful vertebral osteoporotic compression fractures lead to significant morbidity and mortality. This relates to pulmonary dysfunction, eating disorders (nutritional deficits), pain, loss of independence, and mental status change (related to pain and medications). Medications to treat osteoporosis (primarily antiresorptive) do not effectively treat the pain or the fracture, and require over 1 year to reduce the degree of osteoporosis. Kyphoplasty and vertebroplasty are new techniques that help decrease the pain and improve function in fractured vertebrae. METHODS: This is a descriptive review of the background leading to vertebroplasty and kyphoplasty, a description of the techniques, a review of the literature, as well as current ongoing studies evaluating kyphoplasty. RESULTS: Both techniques have had a very high acceptance and use rate. There is 95% improvement in pain and significant improvement in function following treatment by either of these percutaneous techniques. Kyphoplasty improves height of the fractured vertebra, and improves kyphosis by over 50%, if performed within 3 months from the onset of the fracture (onset of pain). There is some height improvement, though not as marked, along with 95% clinical improvement, if the procedure is performed after 3 months. Complications occur with both and relate to cement leakage in both, and cement emboli with vertebroplasty. CONCLUSION: Kyphoplasty and vertebroplasty are safe and effective, and have a useful role in the treatment of painful osteoporotic vertebral compression fractures that do not respond to conventional treatments. Kyphoplasty offers the additional advantage of realigning the spinal column and regaining height of the fractured vertebra, which may help decrease the pulmonary, GI, and early morbidity consequences related to these fractures. Both procedures are technically demanding.

Use of a guide device to place pedicle screws in the thoracic spine: a cadaveric study. Technical note.

In this cadaveric study, the safety and accuracy of a specially designed guide device for the placement of thoracic pedicle screws was investigated in a normal anatomical situation. Five embalmed human cadaveric thoracic spines (T1-12) were used for the study of transpedicular screw placement in the thoracic spine. Overall 120 screws were placed at all thoracic levels. The screws were inserted bilaterally in the thoracic pedicles by using a specially designed guide device. No radiographs or other imaging studies were obtained. Following screw placement, computerized tomography scans were performed to evaluate the accuracy of the pedicle screw positioning. Seven (5.8%) of the screws penetrated the pedicle wall or the vertebral body (VB) cortex. Two screws (1.7%) penetrated the medial wall of the pedicle. Two screws (1.7%) penetrated the lateral wall of the pedicle, and one screw (0.8%) penetrated the lateral wall of the pedicle and the anterior VB cortex simultaneously. Two screws (1.7%) penetrated the anterior VB cortex. Compared with the results of other studies, the findings here indicate that using this device to guide the placement of thoracic pedicle screws can significantly reduce the incidence of pedicle penetration, particularly in the medial wall.

Quantitative changes in spinal canal dimensions using interbody distraction for spondylolisthesis.

STUDY DESIGN: An experimental study was performed using cadaveric lumbar spines to evaluate the effect of anteriorly or laterally placed interbody distraction implants on the alteration of spinal canal and neuroforaminal dimensions. OBJECTIVES: To quantify changes in the spinal canal and neuroforaminal dimensions using interbody fusion devices inserted at various configurations in cadaveric lumbar spines exhibiting degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: Although several clinical studies have demonstrated successful treatment of degenerative spondylolisthesis with anterior interbody fusion, no study has shown the role of interbody distraction in improving lumbar spinal canal and foraminal stenosis. METHODS: Five fresh cadaver lumbar spines exhibiting a degenerative spondylolisthesis or retrospondylolisthesis were used for the study. Computed tomography scans of each specimen and a silicon mold of the left intervertebral foramens were repeated in a consistent manner after pure compressive load (150 lb) was applied to simulate physiologic load (intact case), after two BAK (Sulzer SpineTech Inc., Minneapolis, MN) distraction plugs were anteriorly inserted into the intervertebral disc space (anterior distraction cases), and after one long BAK cage was laterally inserted from the left side (lateral distraction case). The cross-sectional area of the spinal canal was measured from computed tomography images using National Institutes of Health image software (Bethesda, MD). The spinal canal volume was calculated using the cross-sectional area and total scan thickness. Left intervertebral foraminal volumes were calculated from the weight of the silicon mold injected into the foramen. Descriptive statistics and a Student's t test were used to detect statistical differences in the spinal canal and neuroforaminal volumes before and after interbody distraction. RESULTS: The cross-sectional canal area was significantly increased after anterior distraction (35.11%) and lateral distraction (33.14%). The spinal canal volume was markedly increased with anterior distraction (19.92%) and lateral distraction (21.96%). Left foraminal volume was also enhanced by 40.25% for anterior distraction and 41.03% for lateral distraction. CONCLUSIONS: Interbody distraction either by anteriorly inserted plugs or laterally inserted threaded cagescan immediately improve the narrowed canal area and increase spinal canal, as well as foraminal volume for lumbar degenerative spondylolisthesis or retro- spondylolisthesis.

Structural features and thickness of the vertebral cortex in the thoracolumbar spine.

STUDY DESIGN: The thickness and structure of the vertebral body cortex were examined from sections of human cadaveric vertebrae. OBJECTIVES: The objectives were to identify the principal structural features of the cortex, to directly measure the minimum and maximum thicknesses of the cortex in the thoracolumbar spine, and to compare regional variations in the structure of the cortex. SUMMARY OF BACKGROUND DATA: The thickness of the vertebral cortical shell contributes to the compressive strength of the vertebral body. There is little consensus concerning the thickness and morphology of vertebral shell and endplate along the spine in existing data. METHODS: Human T1, T5, T9, L1, and L5 vertebral bodies (mean age 70.4 years) from 20 cadaveric spines were sectioned and photographed. The minimum and maximum cortical thickness of the shells and endplates in the midsagittal plane were measured from magnified images. RESULTS: The anterior shell thickness was significantly greater than the posterior shell and both endplates. Endplate thickness was greatest in the lower lumbar vertebrae. There was a significant decrease in cortex thickness over the central portion of endplates and shells, with a mean minimum thickness of 0.40 mm and a mean maximum thickness of 0.86 mm, with an overall mean of 0.64 +/- 0.41 mm. Increased porosity was also observed along the central regions of the cortical shells. In the lower thoracic and lumbar spine, a double-layered endplate structure was observed. CONCLUSIONS: Invasive techniques provide the only means to directly resolve the thickness and distribution of bone in the vertebral cortex. The cortex thickness and structure varies along the endplates and the anterior and posterior surfaces of the vertebral body. The implications of the so called double-layered endplate structure are unknown, but indicate the need for further study.

Posterior lumbar interbody fusion using posterolateral placement of a single cylindrical threaded cage.

STUDY DESIGN: An in vitro biomechanical study of posterior lumbar interbody fusion (PLIF) with threaded cages was performed on 18 bovine lumbar functional spinal units. OBJECTIVES: To compare the segmental stiffness among PLIF with a single long posterolateral cage, PLIF with a single long posterolateral cage and simultaneous facet joint fixation, and PLIF with two posterior cages. SUMMARY OF BACKGROUND DATA: In most cases, PLIF with threaded cage techniques needs bilateral facetectomy, extensive exposure, and retraction of the cauda equina. Posterior element deficiency is detrimental to postoperative segmental stiffness. METHODS: All specimens were tested intact and with cage insertion. Group 1 (n = 12) had a long threaded cage (15 x 36 mm) inserted posterolaterally and oriented counter anterolaterally on the left side by posterior approach with left unilateral facetectomy. Group 2 (n = 6) had two regular-length cages (15 x 24 mm) inserted posteriorly with bilateral facetectomy. Six specimens from Group 1 were then retested after unilateral facet joint screw fixation in neutral (Group 3). Similarly, the other six specimens from Group 1 were retested after fixation with a facet joint screw in an extended position (Group 4). Nondestructive tests were performed in pure compression, flexion, extension, lateral bending, and torsion. RESULTS: The PLIF procedure involving a single cage (Group 1) had a significantly higher stiffness than PLIF with two cages (Group 2) in left and right torsion (P < 0.05). Group 1 had higher stiffness values than Group 2 in pure compression, flexion, and left and right bending, but differences were not significant. Group 3 had a significant increase in stiffness in comparison with Group 1 for pure compression, extension, left bending, and right torsion (P < 0.05). For Group 4, the stiffness significantly increased in comparison with Group 1 for extension, flexion, and right torsion (P < 0.05). Although there was no significant difference between Groups 3 and 4, Group 4 had increased stiffness in extension, flexion, right bending, and torsion. CONCLUSIONS: Posterior lumbar interbody fusion with a single posterolateral long threaded cage with unilateral facetectomy enabled sufficient decompression while maintaining most of the posterior elements. In combination with a facet joint screw, adequate postoperative stability was achieved.

Artificial disc technology.

After approximately 40 years of research and development, artificial disc technology may finally be coming of age. A number of devices are either at the late stage of preclinical study or in the early stage of clinical trial, and the results are promising so far. Due to the multicomponent structure of the disc, surgeons performing disc arthroplasty have the option of replacing either the entire disc or a portion of it. The decision will be largely dependent on the pathological entity addressed, the condition of the patient's spinal disc and surrounding tissues, and the cost and potential risk of the procedure. Driven by demand, almost all the emphasis in artificial disc development has been placed on the lumbar disc, with a smaller effort directed toward the cervical disc. No attempt has been made to develop an artificial thoracic disc. However, by examining the differences and similarities in structure, anatomy, function, mechanism of degeneration, pathology, surgical technique, and complications between the lumbar and thoracic disc, the authors believe it is feasible to apply artificial disc technology in the treatment of thoracic disc disease. Nonetheless, due to the rarity of thoracic disc disease and the more stable structure of this spinal component, the demand for artificial disc or artificial nucleus technology for the thoracic disc probably will be smaller than that for lumbar disc technology.

Gelfoam as a barrier to prevent polymethylmethacrylate-induced thermal injury of the spinal cord: in vitro and in vivo studies in pigs.

Gelatin sponge (Gelfoam; Upjohn, Kalamazoo, MI, U.S.A.) is commonly used as an interpositional barrier to shield the spinal cord from thermal injury during vertebral reconstruction with polymethylmethacrylate bone cement. The aim of this study was to record epidural and intradural temperatures during polymethylmethacrylate reconstruction of vertebral corpectomy defects. Three surgical techniques (subtotal corpectomy, total corpectomy with insertion of a Gelfoam barrier, and total corpectomy with no barrier) were compared in vivo and in vitro in a porcine model. As expected, total corpectomy defects cemented without a Gelfoam barrier produced the highest epidural temperatures in vivo (52.8 degrees C) and in vitro (58 +/- 2 degrees C). The Gelfoam barrier provided some protection against heat transfer, but peak temperatures and absolute temperature increases were significantly higher than in defects with an intact posterior cortex (p < 0.05). These results indicate that an intact posterior cortex provides the best protection against heat transfer, whereas the use of a Gelfoam barrier appears to provide only partial protection against thermal injury.

Cervical spine injuries in football players.

Cervical spine injuries have been estimated to occur in 10% to 15% of football players, most commonly in linemen, defensive ends, and linebackers. The overwhelming majority of such injuries are self-limited, and full recovery can be expected. However, the presenting symptoms of serious cervical spine injuries may closely resemble those of minor injuries. The orthopaedic surgeon frequently must make a judgment, on the field or later in the office, about the advisability of returning the athlete to the game. These decisions can have an enormous impact on the player and his family. Most severe cervical spine injuries share the common mechanism of application of an axial load to the straightened spine. Avoiding techniques that employ head-down "spear" tackling and wearing properly fitted equipment markedly reduce the risk of serious injury.

Video-assisted thoracic diskectomy and anterior release: a biomechanical analysis of an endoscopic technique.

This study evaluates the residual biomechanical stability of the spine following multilevel anterior diskectomies and anterior longitudinal ligament release using video-assisted thoracoscopic surgery (VATS). Eighteen domestic pigs were randomly divided into three groups of six pigs. Group 1 underwent thoracic anterior release from T4-T9 using a left-sided VATS approach, group 2 underwent thoracic anterior release from T4-T9 via a traditional left thoracotomy (open), and group 3 did not undergo surgery and served as a control. After surgery, the animals were euthanized, and the thoracic spinal columns were harvested for biomechanical testing. Nondestructive testing was performed on all specimens in pure compression, flexion, extension, right lateral bending, and torsion. Specimens from group 1 had significantly lower stiffness values (P<.05) than the control group for all five test modes. These data demonstrate that adequate anterior release of the thoracic spine can be obtained with the VATS technique. Further prospective clinical studies on VATS are required before the widespread application of this technique.

A double-blind study of capacitively coupled electrical stimulation as an adjunct to lumbar spinal fusions.

STUDY DESIGN: A randomized double-blind prospective comparison with a placebo control. This report of the results is the first in an ongoing study. OBJECTIVES: To evaluate the effect of noninvasive capacitively coupled electrical stimulation on the success rate of lumbar spine fusion surgery, and to compare active with placebo stimulators as adjuncts to contemporary fusion techniques. SUMMARY OF BACKGROUND DATA: Previous studies have established the effectiveness of direct current and electromagnetic field stimulation as adjuncts for some forms of spinal fusion. None of the previous placebo-controlled studies on external bone stimulation included posterolateral fusion techniques, and most were conducted with prior generations of internal fixation hardware. METHODS: The investigation was conducted by 28 U.S. surgeons. Patients with a primary diagnosis of degenerative disc disease with or without other degenerative changes were selected. The study protocol defined success as a clinical outcome rated as excellent or good and a fusion documented as solid by both the investigator and the blinded independent radiologist. Disagreements on radiographic success were resolved by a second blinded independent reviewer. RESULTS: For the 179 patients who completed treatment and evaluation, the overall protocol success rate (both clinical and radiographic results rated as successes) was 84.7% for the active patients and 64.9% for the placebo patients. This difference is highly significant according to the Yates corrected chi-square test (P = 0.0043). Best improvements in patient outcomes (20% or greater success rate) occurred when active stimulation was used in conjunction with posterolateral fusion (P = 0.006) and when internal fixation also was incorporated (P = 0.013). DISCUSSION: This study was consistent in that active stimulation improved results for each stratification, although some strata had insufficient numbers of patients for the results to have statistical significance. Improved success rates when capacitively coupled stimulation is added to internal fixation are hypothesized to result from overcoming the biochemical effects of stress shielding. CONCLUSIONS: Capacitively coupled stimulation is an effective adjunct to primary spine fusion, especially for patients with posterolateral fusion and those with internal fixation.

Early versus delayed surgery for acute cervical spinal cord injury.

The optimal timing of surgical intervention in cervical spinal cord injuries has not been defined. The goals of the study were to investigate changes in neurologic status, length of hospitalization, and acute complications associated with surgery within 3 days of injury versus surgery more than 3 days after the injury. All patients undergoing surgical treatment for an acute cervical spinal injury with neurologic deficit at two institutions between March 1989 and May 1991 were reviewed retrospectively. Forty-three patients initially were evaluated. At one institution, patients with neurologic spinal injuries had surgical intervention within 72 hours of injury. At the other institution, patients underwent immediate closed reduction with subsequent observation of neurologic status for 10 to 14 days before undergoing surgical stabilization. This study indicates that patients who sustain acute traumatic injuries of the cervical spine with associated neurologic deficit may benefit from surgical decompression and stabilization within 72 hours of injury. Surgery within 72 hours of injury in patients sustaining acute cervical spinal injuries with neurologic involvement is not associated with a higher complication rate. Early surgery may improve neurologic recovery and decrease hospitalization time in patients with cervical spinal cord injuries.

Surgical treatment of internal disc disruption: an outcome study of four fusion techniques.

Surgical treatment for internal disc disruption remains controversial in terms of efficacy of spinal fusion and optimal fusion method. The present study was carried out in 56 consecutive patients, with the diagnosis confirmed by computed tomographic (CT) discography, who were operated with one of four different lumbar fusion procedures. Outcomes were determined by postoperative pain questionnaires, independent clinical assessment, and radiographic evaluation. Simultaneous anterior interbody fusion using BAK cage and posterior facet fusion provided the highest rate of fusion (88%) and clinical satisfaction (63%). Pain scores were also significantly lower than facet screw augmented posterolateral fusion, and anterior interbody fusion with fibula allograft, but not significantly different from pedicle screw instrumented posterolateral fusion. Patients who achieved successful lumbar fusion had better clinical outcomes and a better chance of work resumption.

Predictive signs of discogenic lumbar pain on magnetic resonance imaging with discography correlation.

STUDY DESIGN: The correlation between discogenic lumbar pain and disc morphology was investigated by using magnetic resonance imaging and discography. OBJECTIVES: To assess the various pathologic parameters seen on magnetic resonance imaging in patients with discogenic lumbar pain and to correlate them with observations on discography. SUMMARY OF BACKGROUND DATA: Although numerous previous studies on the subject have been performed, the correlations between various pathologic findings on magnetic resonance imaging and pain reproduction by provoked discography have not been explained fully. METHODS: One hundred and one lumbar discs in 39 patients were studied with magnetic resonance imaging and pain provocation discography. When pain reproduction under discography was concordant, various pathologic parameters on magnetic resonance imaging were analyzed by three statistical parameters to determine the associated magnetic resonance imaging findings. RESULTS: Radial tears commonly are demonstrated on magnetic resonance imaging in discs with concordant pain on discography. The presence of these tears is not a reliable predictor of a painful disc on discography. Although a high-intensity zone on T2-weighted images is a relatively reliable predictor of pain, the statistical values were lower than those in previous studies. Massive degeneration and severe disc height loss were rare in this population. These findings were good predictors of pain on disc injection. CONCLUSIONS: Although the lumbar intervertebral discs with posterior combined anular tears are likely to produce pain, the validity of these signs for predicting discogenic lumbar pain is limited.

Arthroscopic microdiscectomy: comparison of preoperative and postoperative imaging studies.

Forty-three patients with symptomatic lumbar disc herniations underwent paralumbar arthroscopic disc extraction by a uniportal or biportal approach and postoperative imaging studies. Thirty-one patients were subjected to immediate postoperative computed tomography (CT) at the operative site. The other 12 underwent magnetic resonance imaging (MRI at varying times postoperatively. Images obtained before and after surgery were magnified; the herniation area (H) and the spinal canal area (C) were measured by computerized digitization. The H/C ratio was calculated, and the percentage of canal clearance was obtained in each case. Immediate postoperative CT imaging in 16 of 18 patients with subligamentous and extraligamentous nonmigrated herniation showed a significant change in the external geometry of the annulus and canal clearance (75% to 100% canal clearance). Less compelling change in the postoperative CT images was unexpectedly seen with extraforaminal and foraminal herniations. This result may be attributable to limitations in our study methodology and not to inadequate decompression. Follow-up MRI on these patients within 8 weeks postoperatively did eventually show significant change in two cases that were initially not significant. This study confirms that the arthroscopic microdiscectomy technique effectively extracts herniated disc fragments and alters posterior annular contour, including removal of sequestered pieces.

Food and Drug Administration regulation of spinal implant fixation devices.

The role of the Food and Drug Administration in regulating medical devices generally is not well understood by physicians. The practice of medicine does not fall under Food and Drug Administrations's regulatory purview. Nevertheless, the Food and Drug Administration and its regulation of medical devices can influence physicians' activities. This article provides an overview of the scope of the Food and Drug Administration's authority and the agency's regulatory framework, with particular focus on orthopaedic medical devices as related to spinal implant devices. During the past 10 years, a regulatory dilemma has arisen surrounding the use of bone screws in the pedicles of the spine. Except for recent clearances for a limited treatment indication, the Food and Drug Administration has not cleared these devices to be labeled for pedicle screw fixation and, therefore, has restricted industry supported educational activities pertaining to this type of treatment. In spite of the Food and Drug Administration's regulatory position, physicians have chosen to use pedicle screw fixation in treating patients who have a variety of spinal disorders. This use is now considered an accepted (state of the art) medical practice by many physicians for certain spinal conditions. This article explores this specific Food and Drug Administration regulatory issue, its impact on physicians and manufacturers (especially as it pertains to medical education), and recent actions taken to resolve it.

The effect of pulsed electromagnetic fields on instrumented posterolateral spinal fusion and device-related stress shielding.

STUDY DESIGN: This study was designed to examine stress-shielding effects on the spine caused by rigid implants and to investigate the effects of pulsed electromagnetic fields on the instrumented spine. OBJECTIVES: To investigate the effects of pulsed electromagnetic fields on posterolateral spinal fusion, and to determine if osteopenia induced by rigid instrumentation can be diminished by pulsed electromagnetic fields. SUMMARY OF BACKGROUND DATA: Although device-related osteopenia on vertebral bodies is of a great clinical importance, no method for preventing bone mineral loss in vertebrae by stiff spinal implants has been effective. METHODS: Twenty-eight adult beagles underwent L5-L6 destabilization followed by posterolateral spinal fusion. The study was divided into four groups: 1) Group CNTL: without instrumentation, without pulsed electromagnetic fields, 2) Group PEMF: without Steffee, with pulsed electromagnetic fields, 3) Group INST: with Steffee, without pulsed electromagnetic fields, 4) Group PEMF + INST: with Steffee, with pulsed electromagnetic fields. At the end of 24 weeks, the dogs were killed, and L4-L7 segments were tested biomechanically without instrumentation. Radiographs and quantitative computed tomography assessed the condition of the fusion mass. RESULTS: Stress shielding was induced in the anterior vertebral bodies of L6 with the Steffee plates; bone mineral density was increased with the addition of pulsed electromagnetic fields, regardless of the presence or absence of fixation. A decrease in flexion and bending stiffness was observed in the Group INST; pulsed electromagnetic fields did increase the flexion stiffness regardless of the presence or absence of fixation, although this was not statistically significant. CONCLUSIONS: Use of pulsed electromagnetic fields has the potential to minimize device-related vertebral-bone mineral loss.

The artificial disc: theory, design and materials.

Low back pain is one of the most common medical conditions in the Western world. Disc degeneration, an inevitable process of aging, of variable rate and degree, is one of the major causes of low back pain. Currently, there are two major surgical interventions for treating conditions related to the degenerative disc: discectomy and fusion. Although discectomy and fusion produce a relatively good short-term clinical result in relieving pain, both these surgical treatments alter the biomechanics of the spine, possibly leading to further degeneration of the surrounding tissues and the discs at adjacent levels. Over the past 35 years, a tremendous effort has been made to develop an artificial disc to replace the degenerated disc. The goal is the restoration of the natural biomechanics of the segment after disc excision, thus relieving pain and preventing further degeneration at adjacent segments. However, the artificial disc faces a complex biomechanical environment which makes replication of the biomechanics difficult and long-term survival challenging to designs and materials. The purpose of this article is to examine the factors of importance in designing a disc replacement. Topics covered include the structure and function of the natural disc, the changes that occur with disc degeneration and existing methods of treatment for the degenerative spine. The progress in achieving a functional, long-lasting disc replacement is outlined.

Neurosurgical care of spinal epidural, subdural, and intramedullary abscesses and arachnoiditis.

Epidural abscess of the spinal column is a rare but potentially devastating disease. When recognized early and treated appropriately, the outcome can be excellent. Abscesses in the spinal subdural space or in the spinal cord proper are even more unusual but can also lead to complete and irreversible loss of neurologic function if not diagnosed and treated rapidly. Although infection frequently can result in arachnoiditis, there are other more common causes, such as surgery and chemical irritants. It remains a difficult condition to treat, and long-term therapeutic results are mediocre. Newer technology with spinal cord stimulation seems to show improved results but pain relief is incomplete, and the percentage of patients with poor results remains high.