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ABSTRACT: : Intraoperative neuromonitoring of thoracic-level pedicle screw implantation for detecting breaches in the pedicle cortex has adopted methods originally developed in the early 1990s for stainless steel (SS) alloy screws used at lumbosacral levels. In our recent attempts to monitor thoracic-level pedicle screw placement, we were surprised to find that these widely used stimulation parameters were largely ineffectual when stimulating directly through titanium alloy (Ti-alloy) pedicle screws. The objectives of this study, then, were twofold: (1) to report the number of episodes in which intraoperative neuromonitoring of thoracic screw position failed to detect a medially directed breach (or malplacement) in a previously described and limited sample set; and (2) to compare the frequency-specific impedance of a sample of Ti-alloy pedicle screws to comparably sized screws made of SS alloys. We predicted that Ti-alloy screws would demonstrate impairment in conduction properties that could help explain the difficulties we, and others, have recently experienced with neuromonitoring of thoracic pedicle screw placement.
: Based on threshold values for train-of-four stimulation of spinal motor pathways, we quantified the incidence of medial breaches of thoracic-level pedicles in a small cohort of subjects. We also evaluated the conductive properties of Ti-alloy pedicle screws and compared these with SS screws. Eleven pedicle screws were examined using energy-dispersive x-ray spectroscopy to identify their alloys, after which DC resistance and AC impedance for each screw was measured. Furthermore, a subset of five screws was used to investigate the current delivery under dynamic testing conditions.
: Postoperative computed tomography of 6 subjects revealed 10 instances of significant medial screw malpositioning, out of a total of 88 screws placed. In each of these 10 instances, direct stimulation of thoracic pedicle screws at intensities considered in the literature to be clinically significant (i.e., ≤11 mA) failed to predict these medial pedicle breaches, yet each breach was reliably identified with low-intensity stimulation applied via a ball-tipped probe. For in vitro studies, most screws made of titanium alloys had higher resistance and impedance at tested frequencies compared with their SS counterparts. Moreover, there was widespread variability in conduction properties between Ti-alloy screws, whereas SS screws behaved in a more homogeneous manner.
: When compared with screws made of SS, most Ti-alloy pedicle screws behaved more like semiconductors, showing conduction properties that were highly frequency dependent. These properties likely contributed to the difficulties we encountered in interpreting thoracic screw placements based on stimulus-evoked electromyography from direct screw stimulation.
Journal of clinical neurophysiology: official publication of the American Electroencephalographic Society 12/2012; 29(6):502-8. · 1.47 Impact Factor
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JAAPA: official journal of the American Academy of Physician Assistants 06/2008; 21(5):29, 31-3.
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ABSTRACT: Thoracic pedicle screw location and the current needed to stimulate adjacent neural tissue was evaluated using brief, high-frequency pulse trains and monitoring electromyography (EMG) from muscles in the lower limbs.
To establish a safe and reliable method for detecting medial malpositioning of pedicle screws placed in the thoracic spine during instrumentation and fusion.
Neurophysiologic studies for testing thoracic pedicle screw placement used single-pulse stimulation and monitored EMG from thoracic-innervated muscles. We propose that with this approach, stimulation fails to activate lower motor neurons innervated by spinal cord axons, such that medial malplacement of screws will go largely undetected.
EMG was monitored from multiple lower-limb muscles. Pedicle tracks were created free-hand, using a curved pedicle finder. A ball-tipped probe-insulated along its shaft-was used to palpate the walls of the pedicle tracks. During probing, constant-current, high-frequency 4-pulse stimulus trains were delivered through the ball tip, and the minimum current (i.e., threshold) needed to evoke EMG was determined for each pedicle track. The threshold current for stimulation through each screw was also determined. Postoperative serial computed tomography scans of all implanted thoracic and L1 screws were rated with respect to screw position and the pedicle wall.
A total of 116 screws were implanted in 7 subjects. Two pedicle tracks were redirected during surgery because of particularly low thresholds to stimulation. Definite medial defects were found in 19 screws, 18 of which were detected by the experimental technique. For these screws, the average threshold to probe stimulation of their associated pedicle tracks was 7.9 +/- 4.6 mA, much lower than current thresholds for less medially placed pedicle tracks. Stimulation of these screws resulted in high thresholds (19.8 +/- 5.3 mA) when a response was evoked at all; stimulating 8 of these 19 medially malpositioned screws failed to elicit any lower-limb EMG at considerably higher (25 or 30 mA) stimulus intensities.
This preliminary study supports the hypothesis that high-frequency stimulus pulse trains areeffective at detecting defects in the medial wall of pedicles in the thoracic spine during instrumentation, thereby improving on techniques using single-pulse stimulus protocols.
Spine 06/2008; 33(12):E378-85. · 2.08 Impact Factor
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ABSTRACT: Single institution retrospective review.
To report a series of pyogenic spinal infections treated with single-stage debridement and reconstruction with titanium mesh cages.
Various studies have reported surgical results of pyogenic spinal osteomyelitis with anterior debridement, strut grafting and fusion, including delayed posterior spinal instrumentation. Additionally, various authors have recommended against the use of instrumentation because of the concern about glycocalyx formation on the metal and chronic infection. At our institution, we routinely treat chronic vertebral osteomyelitis with single-stage debridement, reconstruction with a titanium mesh cage filled with allograft chips and demineralized bone matrix, and posterior pedicle screw instrumentation. To our knowledge, this is the largest single series reporting single-stage debridement and instrumentation of pyogenic spinal infection with titanium mesh cages and posterior instrumentation.
We retrospectively reviewed the patient records and radiographs of 21 consecutive patients (average age 49.3 years, range 23 to 80 years) with pyogenic vertebral osteomyelitis, all treated with titanium mesh cages. Average follow-up was 44 months (range, 25 to 70 months). Spinal levels included 6 thoracic, 4 thoracolumbar, 9 lumbar, and 2 lumbosacral (L5-S1) lesions. All patients had preoperative serum evaluation, which usually included blood cultures, complete blood count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), in addition to plain radiographs and magnetic resonance imaging. A positive needle biopsy was available in only 2/7 patients (29%), and overall, preoperative pathogen identification was available in only 7/21 patients (33%). All patients were treated postoperatively with a minimum of 6 weeks of intravenous antibiotics, with a specific antibiotic regimen directed toward the postoperative pathogen when identified (17/21 cases). Extensive radiographic evaluation was also performed.
ESR and CRP were routinely elevated (18/20 and 11/17 cases respectively), whereas the white blood count was elevated in only 8 out of 21 cases (38%). The average duration of symptoms to diagnosis was approximately 13.6 weeks (range 3 weeks to 10 months). The indications for surgery included neurologic compromise, significant vertebral body destruction with loss of sagittal alignment, failure of medical treatment, and/or epidural abscess. All patients had resolution of infection, as noted by normalization of the ESR and CRP. Further, 16 out of 21 patients also had a significant reduction of pain. There were no deaths or new postoperative neurologic compromise. The most common pathogen was Staphylococcus aureus. Two patients required a second surgery (posterior irrigation and debridement) during the same admission for persistent wound drainage. Radiographically, the average segmental kyphosis (or loss of lordosis) was 11.5 degrees (range, 0 to 24 degrees) preoperatively, and +0.8 degrees (range, -3 to +5 degrees) at latest postoperative follow-up. There was an average of 2.2 mm cage settling (range, 0 to 5 mm) on latest follow-up. There were no instrumentation failures, signs of chronic infection, or rejection.
Titanium mesh cages present a viable option for single-stage anterior surgical debridement and reconstruction of vertebral osteomyelitis, without evidence of chronic infection or rejection. When used in conjunction with pedicle screw instrumentation, there is minimal cage settling without loss of sagittal alignment.
Journal of Spinal Disorders & Techniques 08/2006; 19(5):376-82. · 1.50 Impact Factor
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ABSTRACT: Burr hole craniotomy for posttraumatic intracranial hematoma is rarely performed since the advent of computerized tomography revolutionized the treatment of these patients. It is still necessary in unique circumstances although, and the clinical urgency may require surgery by a non-neurosurgeon. This occurs rarely in rural or overseas locations in peacetime, but more commonly in combat health support operations where computed tomography and neurosurgeons are not widely available. Recent experiences in the Global War on Terrorism have prompted a detailed review of this procedure. The nonoperative care, localization of intracranial hematoma, and surgical technique are outlined here in detail, and results from the literature are reviewed. This review emphasizes that burr holes should not be performed at random on head-injured patients and should be performed only by general surgeons or other physicians who have undergone formal instruction by experienced neurosurgeons, and every reasonable attempt to contact a neurosurgeon should be made first.
Military medicine 02/2006; 171(1):12-9. · 0.92 Impact Factor
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ABSTRACT: Hemivertebrae are a common cause of congenital scoliosis. Depending on their location and the magnitude of the resultant deformity, they may be asymptomatic or require treatment. In the past, treatment has focused on prevention of deformity progression in growing children. Little has been written about congenital scoliosis presenting in adulthood. Because the aging of the spine is a kyphosing process and hemivertebrae often present with a local segmental kyphotic alignment, this can become symptomatic. Excision of hemivertebrae is well established as a safe and effective procedure when treatment is required. Initially this was conducted via a combined anterior-posterior approach. Recently some authors have indicated that in the lumbar spine hemivertebra resection can safely and effectively be achieved via a single posterior transpedicular approach. The authors report two adult cases in which they performed posterior transpedicular lateral extracavitary excision of a thoracic, fully segmented hemivertebrae. Essentially complete correction of the deformity was achieved. There were no neurological complications. The patients were spared a thoracotomy and no chest tubes were required.
Neurosurgical FOCUS 03/2003; 14(2):e9. · 2.87 Impact Factor
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ABSTRACT: The authors report their preferred method for correcting Scheuermann disease via a combined anterior-posterior approach; their procedure is associated with a lower morbidity rate than the standard approach. Twenty-month followup examination demonstrated excellent maintenance of correction. The results satisfied the requirements to function without restriction in a vigorous military environment.
Neurosurgical FOCUS 02/2003; 14(1):e10. · 2.87 Impact Factor
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ABSTRACT: Although the practice of neurosurgery in the United States (US) Armed Forces is in many ways similar to the civilian practice of neurosurgery, there are many differences as well. The unique challenges, duties, and opportunities US military neurosurgeons are given, both in peacetime and in times of conflict, are discussed, as are pathways for entering into service. The advantages of military service for neurosurgeons include sponsored training, decreased direct exposure to tort actions, little involvement with third-party payers, significant opportunities for travel, and military specific experiences. The most appealing aspect of military practice is serving fellow members of the US Armed Forces. Disadvantages include the extreme gap between the military and civilian pay scales, lack of support personnel, and in some areas low surgery-related case volume. The greatest concern faced by the military neurosurgical community is the failure to retain experienced neurosurgeons after their obligated service time has been completed, for which several possible solutions are described. It is hoped that future changes will make the practice of military neurosurgery attractive enough so that it will be seen as a career in itself and not an obligation to endure before starting practice in the "real world."
Neurosurgical FOCUS 05/2002; 12(4):e6. · 2.87 Impact Factor
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ABSTRACT: Humans are susceptible to microbial infections from many sources. Biological warfare is the use of microbial forms of life to diminish the capabilities, disrupt the organization, and terrorize the noncombatant population of an adversary. This form of warfare has been used throughout history and has gained renewed interest with the current use of asymmetrical warfare. The civilized world has condemned its use by the implementation of treaties specifically against it. This is a brief review of some of the more easily used biological agents such as anthrax, plague, tularemia, Q fever, and smallpox. Each agent's biology, infectious route, and disease course will be discussed. Possible delivery systems and signs of outbreak will also be reviewed. There are few real neurosurgery-related implications in biological warfare. Neurosurgeons, as members and leaders of the healthcare community, must have the ability to recognize and initiate treatment when biological agents have been deployed. If there is widespread use of these inhumane agents, the neurosurgical community will not be able to practice the surgical art for which we have trained. New knowledge must be acquired so that we can best serve our patients and communities during times of extreme need.
Neurosurgical FOCUS 04/2002; 12(3):E2. · 2.87 Impact Factor
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Ross R Moquin
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ABSTRACT: The cervical-thoracic junction represents a significant challenge for stabilization because of anatomical constraints.
To review the indications, techniques, and results of various stabilization techniques applied to the cervical-thoracic junction.
Innovative instrumentation design, improved operative techniques, and detailed knowledge of the regional anatomy and biomechanics have significantly improved the surgeon's ability to address instability at the cervical-thoracic junction.
The Spine Journal 6(6 Suppl):308S-316S. · 3.29 Impact Factor
