Operations Desert Shield and Desert Storm: neurosurgical experience and transformative legacy for operational medicine.

Operation Desert Storm (ODS) was an astounding success for combat arms and logistical units of the US Military. In contrast, Department of Defense (DOD) medical units struggled to keep pace with combat operations and were fortunate that casualty estimates for a Cold War-era battle failed to materialize. The medical support plan included a large contingent of active-duty and reserve neurosurgeons in anticipation of care requirements for more than 500,000 deploying service members engaged in a large-scale combat operation. Here, the authors review the clinical experience and operational challenges encountered by neurosurgeons deployed in support of this conflict and discuss legacies of ODS for both surgeons and the military medical system.

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 1. Methods and alarm criteria.

OBJECT: Reports of the accuracy of existing neuromonitoring methods for detecting or preventing medial malpositioning of thoracic pedicle screws have varied widely in their claimed effectiveness. The object of this study was to develop, test, and validate a novel neuromonitoring method for preventing medial malpositioning of pedicle screws in the thoracic spine during surgery. METHODS: This is a prospective, blinded and randomized study using a novel combination of input (4-pulse stimulus trains delivered within the pedicle track) and output (evoked electromyography from leg muscles) to detect pedicle track trajectories that-once implanted with a screw-would cause that screw to breach the pedicle's medial wall and encroach upon the spinal canal. For comparison, the authors also used screw stimulation as an input and evoked electromyogram from intercostal and abdominal muscles as output measures. Intraoperative electrophysiological findings were compared with postoperative CT scans by multiple reviewers blinded to patient identity or intraoperative findings. RESULTS: Data were collected from 71 patients, in whom 802 screws were implanted between the T-1 and L-1 vertebral levels. A total of 32 screws ended up with screw threads encroaching on the spinal canal by at least 2 mm. Pulse-train stimulation within the pedicle track using a ball-tipped probe and electromyography from lower limb muscles correctly predicted all 32 (100%) of these medially malpositioned screws. The combination of pedicle track stimulation and electromyogram response from leg muscles proved to be far more effective in predicting these medially malpositioned screws than was direct screw stimulation and any of the target muscles (intercostal, abdominal, or lower limb muscles) we monitored. Based on receiver operating characteristic analysis, the combination of 10-mA (lower alarm) and 15-mA stimulation intensities proved most effective for detection of pedicle tracks that ultimately gave rise to medially malpositioned screws. Additional results pertaining to the impact of feedback of these test results on surgical decision making are provided in the companion report. CONCLUSIONS: This novel neuromonitoring approach accurately predicts medially malpositioned thoracic screws. The approach could be readily implemented within any surgical program that is already using contemporary neuromonitoring methods that include transcranial stimulation for monitoring motor evoked potentials.

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 2. The role of feedback.

OBJECT: The authors have reported in Part 1 of this study on a novel neuromonitoring test for the prevention of medial malpositioning of thoracic pedicle screws. In the present paper they examine the impact of providing the results of the test as intraoperative feedback to the surgical team. METHODS: This is the second part of a 2-part report of a prospective, blinded and randomized neuromonitoring study designed to lower the incidence of medially malpositioned thoracic pedicle screws. Details of the neuromonitoring technique and data supporting the alarm criteria used are contained in the companion article (Part 1). For the majority of pedicle screw placements, intraoperative test results were withheld from the study team (that is, the team members were blinded to the test results). However, for a limited number of pedicle sites the authors provided one of 2 forms of testing feedback to the surgical team: 1) "break the blind" feedback, if testing suggested that screw placement would result in direct contact between screw and the dura mater; and 2) "planned" feedback, beginning during the later stages of the study and provided for 50% of pedicle sites. Feedback gave the surgeon the opportunity to adjust the trajectory that the screw would ultimately take within the pedicle. The final screw position relative to the pedicle's medial wall for all sites in which feedback was withheld from the surgical team was compared with the screw position for those sites in which either form of feedback ("break the blind" or "planned") was provided to and acted upon by the surgical team. RESULTS: Of the 820 pedicle tracks tested among the 71 surgical cases included in this study, a total of 684 were operated upon without any form of feedback. Planned feedback was provided for an additional 107 pedicle tracks, of which 15 triggered an intraoperative alarm (evoked electromyogram response in leg muscles to stimulus intensity ≤ 10 mA) leading to a warning to the surgical team of a medially biased pedicle track. Finally, the blind was broken 29 times, in each case when testing revealed a particularly low threshold (≤ 4 mA) for evoked responses in leg muscles when stimulating along the pedicle track with the ball-tipped probe. As detailed in the companion paper to this one, there were 32 screws with threads lying at least 2 mm medial to the pedicle wall. In all 32 instances (100%), either these screws were in the "no feedback" category (n = 29) or they were in a feedback category but the surgeon elected to not revise the pedicle-track trajectory. Two patients returned to the operating room for revision of screw placements because the screws were encroaching upon the central canal; the pedicle tracks for these screws had been in the "no feedback" category. CONCLUSIONS: This is the first blinded and randomized study to prove that implementing a novel neuromonitoring strategy during placement of thoracic pedicle screws can significantly reduce the incidence of clinically relevant thoracic pedicle screw medial malpositioning.

Is in vivo manual palpation for thoracic pedicle screw instrumentation reliable?

OBJECT: Previous reports on the accuracy of manual palpation for thoracic pedicle screw placement have been restricted to cadaveric studies. Authors of the present novel study assessed the accuracy of manual palpation for the detection of medial and lateral pedicle breaches during thoracic spine surgery in living adult humans. METHODS: Pedicle tracks were created freehand and manually palpated using a ball-tipped probe. Postoperative CT scans of all implanted thoracic and L-1 screws were evaluated with respect to screw position and the pedicle wall. RESULTS: Five hundred twenty-five pedicle track/screw placements were compared. There were 21 pedicles with medial breaches measuring ≥ 2 mm. The surgeon correctly identified only 4 of these pedicle tracks as having a medial breach. The surgeon correctly identified 17 of 128 pedicles with a significant (≥ 2 mm) lateral breach. One hundred two screw placements had no measurable breach in any direction (medial, lateral, or foraminal). The surgeon correctly identified 98% of these ideally placed screws. CONCLUSIONS: In this real-time study of thoracic pedicle screw placement, the accuracy of manual palpation for detecting medial or lateral breaches that were ≥ 2 mm was disturbingly low. These findings are consistent with those in recent cadaveric evaluations of palpation accuracy and point to the critical need for more reliable alternative methods to assess pedicle integrity during the placement of thoracic pedicle screws for spine instrumentation surgery.

Intraoperative neuromonitoring: can the results of direct stimulation of titanium-alloy pedicle screws in the thoracic spine be trusted?

UNLABELLED: OBJECTVIE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Pulse-train stimulation for detecting medial malpositioning of thoracic pedicle screws.

STUDY DESIGN: 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. OBJECTIVE: To establish a safe and reliable method for detecting medial malpositioning of pedicle screws placed in the thoracic spine during instrumentation and fusion. SUMMARY OF BACKGROUND DATA: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Operative techniques for fusion across the cervical-thoracic junction.

BACKGROUND AND SIGNIFICANCE: The cervical-thoracic junction represents a significant challenge for stabilization because of anatomical constraints. PURPOSE: To review the indications, techniques, and results of various stabilization techniques applied to the cervical-thoracic junction. CONCLUSIONS: 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.

Single-stage treatment of pyogenic spinal infection with titanium mesh cages.

STUDY DESIGN: Single institution retrospective review. OBJECTIVES: To report a series of pyogenic spinal infections treated with single-stage debridement and reconstruction with titanium mesh cages. SUMMARY OF BACKGROUND DATA: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Cranial burr holes and emergency craniotomy: review of indications and technique.

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.

Thoracic hemivertebra excision in adults via a posterior-only approach. Report of two cases.

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.

Combined anterior-posterior fusion with laterally placed threaded interbody cages and pedicle screws for Scheuermann kyphosis. Case report and review of the literature.

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.

Socioeconomic issues of United States military neurosurgery.

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."

Weapons of mass destruction: biological.

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.