Comparative in vitro biomechanical analysis of a novel posterior cervical fixation technique versus conventional posterior-based constructs.

STUDY DESIGN: Comparative in vitro, cadaveric biomechanical study. OBJECTIVE: To compare the kinematic response of a new posterior cervical midline surgical technique versus that of conventional fixation techniques. SUMMARY OF BACKGROUND DATA: A new method was designed using alternating bilateral intralaminar screws connected with a single midline rod. This technique provides the theoretical benefits of less operative dissection and reduced implant cost, but the acute flexibility properties remain unknown. Using an in vitro cadaveric model, the study objective was to define the operative level(s) changes in multidirectional flexibility after posterior destabilization/reconstruction from C3 to C6. METHODS: A 6 degree of freedom spine stimulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral bending, and axial rotation were tested in the intact condition, followed by destabilization by a simulated posterior column injury from C3 to C6. Specimens were then reconstructed from C3 to C6 and tested in the following sequence: sublaminar hook rod (SH), lateral mass screw rod (LMR), midline laminectomy from C3 to C6 with LMR (MLR), and midline posterior fixation from C3 to C6 (SMF). Range of motion (ROM) and neutral zone were quantified and analyzed. RESULTS: Significant increases in ROM and neutral zone at C3 to C6 were found under all loading conditions for the destabilized condition and intact spine versus all other treatments (P<0.05). The conventional treatments: SH, LMR, and MLR resulted in significantly less ROM than the proposed SMF in flexion-extension and lateral bending (P<0.05). Axial rotation provided similar results; however, no differences were observed between the SH and SMF (P>0.05). Notably, LMR and MLR provided significantly more stability than SH in axial rotation (P<0.05). CONCLUSIONS: Data produced suggest that the new, midline rod fixation approach provides less biomechanical stability than conventional posterior cervical reconstruction techniques. In addition, the high incidence of laminar fracture during screw placement and close proximity of the screw trajectory and polyaxial heads to the dura suggest a practical limitation as well.

Surgical anatomy of the diaphragm in the anterolateral approach to the spine: a cadaveric study.

STUDY DESIGN: Laboratory cadaveric study. OBJECTIVE: To delineate the pertinent surgical anatomy of the diaphragm during access to the anterolateral thoracolumbar junction. SUMMARY OF BACKGROUND DATA: The general anatomy of the thoracic diaphragm is well described. The specific surgical anatomy as it pertains to the lateral and thoracoabdominal approaches to the thoracolumbar junction is not well described. METHODS: Dissections were performed on adult fresh cadaveric specimens. Special attention was paid to the diaphragmatic attachments to the lower rib cage and to the spinal thoracolumbar junction. RESULTS: The pertinent diaphragmatic attachments to the rib cage are at the 11th and 12th ribs. Whether the diaphragm is incised or mobilized ventrally, the pertinent spinal attachments are the lateral and medial arcuate ligaments. Identifying and sectioning these structures allows for direct access to the thoracolumbar junction, particularly the L1 vertebral body. CONCLUSIONS: An understanding of the diaphragmatic-costal and diaphragmatic-spinal attachments is key for the safe and effective implementation of diaphragm mobilization during the lateral and thoracoabdominal approaches to the spine.

Neuronavigation in minimally invasive spine surgery.

OBJECT: Parallel advancements in image guidance technology and minimal access techniques continue to push the frontiers of minimally invasive spine surgery (MISS). While traditional intraoperative imaging remains widely used, newer platforms, such as 3D-fluoroscopy, cone-beam CT, and intraoperative CT/MRI, have enabled safer, more accurate instrumentation placement with less radiation exposure to the surgeon. The goal of this work is to provide a review of the current uses of advanced image guidance in MISS. METHODS: The authors searched PubMed for relevant articles concerning MISS, with particular attention to the use of image-guidance platforms. Pertinent studies published in English were further compiled and characterized into relevant analyses of MISS of the cervical, thoracic, and lumbosacral regions. RESULTS: Fifty-two studies were included for review. These describe the use of the iso-C system for 3D navigation during C1-2 transarticular screw placement, the use of endoscopic techniques in the cervical spine, and the role of navigation guidance at the occipital-cervical junction. The authors discuss the evolving literature concerning neuronavigation during pedicle screw placement in the thoracic and lumbar spine in the setting of infection, trauma, and deformity surgery and review the use of image guidance in transsacral approaches. CONCLUSIONS: Refinements in image-guidance technologies and minimal access techniques have converged on spinal pathology, affording patients the ability to undergo safe, accurate operations without the associated morbidities of conventional approaches. While percutaneous transpedicular screw placement is among the most common procedures to benefit from navigation, other areas of spine surgery can benefit from advances in neuronavigation and further growth in the field of image-guided MISS is anticipated.

Strategies to avoid wrong-site surgery during spinal procedures.

Wrong-site surgery (WSS) is a rare occurrence that can have devastating consequences for patient care. There are several factors inherent to spine surgery that increase the risk of WSS compared with other types of surgery. Not only can a surgeon potentially operate on the wrong side of the spine or the wrong level, but there are unique issues related to spinal localization that can be challenging for even the most experienced clinicians. The following review discusses important issues that can help prevent WSS during spinal procedures.

Improving proton MR spectroscopy of brain tissue for noninvasive diagnostics.

PURPOSE: To examine preprocessing methods affecting the potential use of Magnetic Resonance Spectroscopy (MRS) as a noninvasive modality for detection and characterization of brain lesions and for directing therapy progress. MATERIALS AND METHODS: Two reference point re-calibration with linear interpolation (to compensate for magnetic field nonhomogeneity), weighting of spectra (to emphasize consistent peaks and depress chemical noise), and modeling based on chemical shift locations of 97 biomarkers were investigated. Results for 139 categorized scans were assessed by comparing Leave-One-Out (LOO) cross-validation and external validation. RESULTS: For distinction of nine brain tissue categories, use of re-calibration, variance weighting, and biomarker modeling improved LOO classification of MRS spectra from 31% to 95%. External validation of the two best nine-category models on 47 unknown samples gave 96% or 100% accuracy, respectively, compared with pathological diagnosis. CONCLUSION: Preprocessing of MRS spectra can significantly improve their diagnostic utility for automated consultation of pattern recognition models. Use of several techniques in combination greatly increases available proton MRS information content. Accurate assignment of unknowns among nine tissue classes represents a significant improvement, for a much more demanding task, than has been previously reported.

Laminar screw fixation of the axis.

OBJECT: Laminar fixation of the axis with crossing bilateral screws has been shown to provide rigid fixation with a theoretically decreased risk of vertebral artery damage compared with C1-2 transarticular screw fixation and C-2 pedicle screw fixation. Some studies, however, have shown restricted rigidity of such screws compared with C-2 pedicle screws, and others note that anatomical variability exists within the posterior elements of the axis that may have an impact on successful placement. To elucidate the clinical impact of such screws, the authors report their experience in placing C-2 laminar screws in adult patients over a 2-year period, with emphasis on clinical outcome and technical placement. METHODS: Sixteen adult patients with cervical instability underwent posterior cervical and cervicothoracic fusion procedures at our institution with constructs involving C-2 laminar screws. Eleven patients were men and 5 were women, and they ranged in age from 28 to 84 years (mean 57 years). The reasons for fusion were degenerative disease (9 patients) and treatment of trauma (7 patients). In 14 patients (87.5%) standard translaminar screws were placed, and in 2 (12.5%) an ipsilateral trajectory was used. All patients underwent preoperative radiological evaluation of the cervical spine, including computed tomography scanning with multiplanar reconstruction to assess the posterior anatomy of C-2. Anatomical restrictions for placement of standard translaminar screws included a deeply furrowed spinous process and/or an underdeveloped midline posterior ring of the axis. In these cases, screws were placed into the corresponding lamina from the ipsilateral side, allowing bilateral screws to be oriented in a more parallel, as opposed to perpendicular, plane. All patients were followed for >2 years to record rates of fusion, instrumentation failure, and other complications. RESULTS: Thirty-two screws were placed without neurological or vascular complications. The mean follow-up duration was 27.3 months. Complications included 2 revisions, one for pseudarthrosis and the other for screw pullout, and 3 postoperative infections. CONCLUSIONS: Placement of laminar screws into the axis from the standard crossing approach or via an ipsilateral trajectory may allow a safe, effective, and durable means of including the axis in posterior cervical and cervicothoracic fusion procedures.

Personal recollections of Walter E. Dandy and his brain team.

Walter Edward Dandy (1886-1946) began his surgical training at the Johns Hopkins Hospital in 1910 and joined the faculty in 1918. During the next 28 years at Johns Hopkins, Dandy established a neurosurgery residency training program that was initially part of the revolutionary surgical training system established by William S. Halsted but eventually became a separate entity. Dandy's residents were part of his "Brain Team," a highly efficient organization that allowed Dandy to perform over 1000 operations per year, not counting ventriculograms. This team also provided rigorous training in the Halsted mold for the neurosurgical residents. Although exacting and demanding, Dandy was universally admired by his residents and staff. This article describes Dandy's neurosurgical residency program at Johns Hopkins, and provides personal recollections of training under Walter Dandy.

Lysis of intracerebral hematoma with stereotactically implanted tissue plasminogen activator polymers in a rabbit model.

OBJECT: Currently no adequate surgical treatment exists for spontaneous intracerebral hemorrhage (ICH). Implantable polymers can be used effectively to deliver therapeutic agents to the local site of the pathological process, thus reducing adverse systemic effects. The authors report the use of stereotactically implanted polymers loaded with tissue plasminogen activator (tPA) to induce lysis of ICH in a rabbit model. METHODS: Ethylene vinyl acetate (EVAc) polymers were loaded with bovine serum albumin (BSA) only or with BSA plus tPA. In vitro pharmacokinetic (three polymers) and thrombolysis (12 polymers) studies were performed. For the in vivo study, 12 rabbits were fixed in a stereotactic frame, and 0.2 ml of clotted autologous blood was injected into the right frontal lobe parenchyma. After 20 minutes, control BSA polymers were stereotactically implanted at the hemorrhage site in six rabbits, and experimental BSA plus tPA polymers were implanted in six rabbits. Animals were killed at 3 days, and blood clot volume was assessed. The pharmacokinetic study showed release of 146 ng of tPA over 3 days. The tPA activity correlated with in vitro thrombolysis. In the in vivo study, the six animals treated with tPA polymers had a mean (+/- standard error of the mean [SEM]) thrombus volume of 1.43 +/- 0.29 mm3 at 3 days, whereas the six animals treated with blank (BSA-only) polymers had a mean (+/- SEM) thrombus volume of 19.99 +/- 3.74 mm3 (p < 0.001). CONCLUSIONS: Ethylene vinyl acetate polymers release tPA over the course of 3 days. Stereotactic implantation of tPA-loaded EVAc polymers significantly reduced ICH volume. Polymers loaded with tPA may be useful clinically for lysis of ICH without the side effects of systemic administration of tPA.

Translaminar screw fixation in the upper thoracic spine.

OBJECT: The use of pedicle screws (PSs) for instrument-assisted fusion in the cervical and thoracic spine has increased in recent years, allowing smaller constructs with improved biomechanical stability and repositioning possibilities. In the smaller pedicles of the upper thoracic spine, the placement of PSs can be challenging and may increase the risk of damage to neural structures. As an alternative to PSs, translaminar screws can provide spinal stability, and they may be used when pedicular anatomy precludes successful placement of PSs. The authors describe the technique of translaminar screw placement in the T-1 and T-2 vertebrae. METHODS: Seven patients underwent cervicothoracic fusion to treat trauma, neoplasm, or degenerative disease. Nineteen translaminar screws were placed, 13 at T-1 and six at T-2. A single asymptomatic T-2 screw violated the ventral laminar cortex and was removed. The mean clinical and radiographic follow up exceeded 14 months, at which time there were no cases of screw pullout, screw fracture, or progressive kyphotic deformity. CONCLUSIONS: Rigid fixation with translaminar screws offers an attractive alternative to PS fixation, allowing the creation of sound spinal constructs and minimizing potential neurological morbidity. Their use requires intact posterior elements, and care should be taken to avoid violation of the ventral laminar wall.

A Clinical Perspective and Definition of Spinal Cord Injury.

Spinal cord injury (SCI) can be complete or incomplete. The level of injury in SCI is defined as the most caudal segment with motor function rated at greater than or equal to 3/5, with pain and temperature preserved. The standard neurological classification of SCI provided by the American Spinal Injury Association (ASIA) assigns grades from ASIA A (complete SCI) through ASIA E (normal sensory/motor), with B, C, and D representing varying degrees of injury between these extremes. The most common causes of SCI include trauma (motor vehicle accidents, sports, violence, falls), degenerative spinal disease, vascular injury (anterior spinal artery syndrome, epidural hematoma), tumor, infection (epidural abscess), and demyelinating processes (). (SDC Figure 1, http://links.lww.com/BRS/B91)(Figure is included in full-text article.).

A Comparative Biomechanical Analysis of Stand Alone Versus Facet Screw and Pedicle Screw Augmented Lateral Interbody Arthrodesis: An In Vitro Human Cadaveric Model.

STUDY DESIGN: Cadaveric biomechanical study. OBJECTIVE: To investigate the kinematic response of a stand-alone lateral lumbar interbody cage compared with supplemental posterior fixation with either facet or pedicle screws after lateral discectomy. SUMMARY OF BACKGROUND DATA: Lateral interbody fusion is a promising minimally invasive fixation technique for lumbar interbody arthrodesis. The biomechanical stability of stand-alone cage placement compared with supplemental posterior fixation with either facet or bilateral pedicle screws remains unclear. METHODS: A 6-degree of freedom spine simulator was used to test flexibility in 7 human cadaveric specimens. Flexion-extension, lateral-bending, and axial-rotation were tested in the intact condition, followed by destabilization through a lateral discectomy at L2-L3 and L4-L5. Specimens were then reconstructed at both operative segments in the following sequence: (1) lateral interbody cage placement; (2) either Discovery facet screws or the Viper F2 system using a transfacet-pedicular trajectory randomized to L2-L3 or L4-L5; and (3) removal of facet screw fixation followed by placement of bilateral pedicle screw instrumentation. Acute range of motion (ROM) was quantified and analyzed. RESULTS: All 4 reconstruction groups, including stand-alone interbody cage placement, bilateral Discovery facet screws, the Viper F2 system, and bilateral pedicle screw-rod stabilization, resulted in a significant decrease in acute ROM in all loading modes tested (P<0.05). There were no significant differences observed between the 4 instrumentation groups (P>0.05). Although not statistically significant, the Viper F2 system resulted in greatest reduction of acute ROM in both flexion-extension and axial rotation versus all other treatments (P>0.05). CONCLUSIONS: Stand-alone interbody cage placement results in a significant reduction in acute ROM at the operative segment in the absence of posterior supplemental fixation. If added fixation is desired, facet screw placement, including the Viper F2 facet screw system using an integrated compression washer and transfacet-pedicular trajectory, provides similar acute stability to the spinal segment compared with traditional bilateral pedicle screw fixation in the setting of lateral interbody cage deployment.

Hypertrophic neuropathy of the cauda equina: case report.

OBJECTIVE AND IMPORTANCE: Hypertrophic neuropathy of the cauda equina (HNCE) is a rare form of peripheral neuropathy. The diagnosis is complicated by an insidious clinical presentation and complex radiographic images. We present a case of HNCE caused by chronic inflammatory demyelinating polyneuropathy with symptomatic improvement after decompressive lumbar laminectomy and dural expansion. CLINICAL PRESENTATION: A 54-year-old woman with a history of back pain since she was in her 20s presented with low back and radicular pain that had increased during a period of 6 months, bilateral lower-extremity weakness, and sensory loss in the right thigh. Magnetic resonance imaging of the lumbosacral spine revealed multiple, poorly enhancing mass lesions and apparent intrathecal nerve root thickening from L1 to L5. INTERVENTION: An L1-L5 decompressive laminectomy, performed with continuous somatosensory evoked potential and electromyographic monitoring, revealed multiple segmentally enlarged nerve roots. One nerve root that did not respond to high levels of stimulation was identified. This root was resected and submitted for pathological analysis. The dura was expanded with an 11-cm-long dural patch. The pathological examination revealed hypertrophic neuropathy, with extensive S-100-positive "onion bulb" formation. The patient's symptoms improved postoperatively. CONCLUSION: HNCE is a rare disorder that can cause radicular pain and lower-extremity weakness, sensory loss, and hyporeflexia. One possible cause is demyelinating polyneuropathy. Although medical management is typically effective in the treatment of demyelinating polyneuropathy, it has little effect on compressive symptoms caused by intradural nerve root enlargement. As this case demonstrates, surgical management of symptomatic radiculopathy by lumbar laminectomy is a reasonable and effective approach to the treatment of HNCE.

Dorcas Hager Padget: neuroembryologist and neurosurgical illustrator trained at Johns Hopkins.

Dorcas Hager Padget was a pioneer in the fields of neurosurgical illustration and neuroembryology who practiced during the early 20th century at The Johns Hopkins University. Without a college degree, she trained as a medical illustrator in the Johns Hopkins School of Medicine's Department of Art as Applied to Medicine under Max Brödel. She began her career working for Walter Dandy as his medical artist, gaining worldwide recognition for her neurosurgical illustrations. With Dandy's encouragement, Hager Padget undertook her own scientific research, studying neurodevelopment and aneurysm formation in the circle of Willis by using human embryos from the world-renowned Carnegie Collection. She made lasting contributions to the field of neuroembryology, publishing the first major work on neurodevelopment of the cerebral arterial and venous systems. Following Dandy's death in 1946, Hager Padget began a full-time career as a scientific researcher, first at the Department of Embryology at the Carnegie Institution of Washington in Baltimore and later at the University of Maryland School of Medicine. She continued to make contributions to the field of congenital malformations of the brain and spine, coining the term "neuroschisis" to describe a possible mechanism of neural tube damage leading to the creation of a myelomeningocele. The authors describe Dorcas Hager Padget's contributions to neurosurgical illustration and neuroembryology, as well as her remarkable career.

Cadaver training module for teaching thoracic pedicle screw placement to residents.

Surgical training using simulators has been shown to be highly effective but is not available for some applications and is too expensive for many programs. The authors piloted a cadaver-based module with the goal of objectively measuring and significantly improving orthopedic residents' surgical skills in placing thoracic pedicle screws, an advanced procedure. An experienced spine surgeon placed thoracic pedicle screws in 7 cadavers (T1-T12) to establish the skilled accuracy rate. For this pilot study, 3 orthopedic residents unfamiliar with the procedure were given didactic training for safe thoracic pedicle screw insertion. Each resident instrumented alternating sides of 5 consecutive cadavers (T1-T12). Screw positions were graded by computed tomography in a blinded fashion, with accuracy defined as no shank breach of the pedicle or vertebral body. Results were reviewed with the residents, instruction was repeated, and alternating sides of 5 cadavers were instrumented by the residents. The experienced surgeon accurately placed 67 (82%) of 82 pedicle screws. Residents accurately placed 80 (44%) of 180 pedicle screws in the initial set of specimens and 105 (58%) of 180 pedicle screws in the second set of specimens (P=.01). Accuracy varied significantly among residents before but not after computed tomography review. The study's results show that a cadaver-based training module that resembles the clinical setting can be used to teach complex surgical skills to orthopedic residents.

Ultrasonic BoneScalpel for osteoplastic laminoplasty in the resection of intradural spinal pathology: case series and technical note.

BACKGROUND: Osteoplastic laminoplasty is a well-described technique that may decrease the incidence of progressive kyphosis when used in the setting of intradural spinal cord tumor resection. OBJECTIVE: The BoneScalpel by Aesculap (Central Valley, Pennsylvania) is an ultrasonic osteotome that precisely cuts bone while preserving the underlying soft tissues, potentially reducing the risk of dural laceration during laminoplasty. By producing osteotomies as narrow as 0.5 mm, the device may also facilitate postoperative osteointegration. METHODS: A retrospective analysis was conducted of 40 patients (mean age, 38.0 years; range, 4.0-79.7 years) who underwent osteoplastic laminoplasty using the BoneScalpel for the treatment of intradural spinal pathology at the Johns Hopkins Hospital between January 2009 and December 2011. After lesion resection, titanium plates were used to reconstruct the lamina in all cases. The technical results and procedure-related complications were subsequently noted. RESULTS: Successful laminoplasty was carried out in all 40 patients. Intraoperatively, 1 case of incidental durotomy was noted after use of the device, which was repaired primarily without neurological or clinical sequelae. During the follow-up period (mean, 195 days; median, 144 days), there were 2 complications (1 cerebrospinal fluid leak, 1 seroma) and no cases of immediate postoperative instability. CONCLUSION: The BoneScalpel is a safe and technically feasible device for performing osteoplastic laminoplasty.

The rib head as a landmark in the anterolateral approach to the thoracic spine: a computed tomography-based morphometric study.

OBJECT: The rib head is an important landmark in the anterolateral approach to the thoracic spine. Resection of the rib head is typically the first step in gaining access to the underlying pedicle and ultimately the spinal canal. The goal of this work is to quantify the relationship of the rib head to the spinal canal and adjacent aorta at each thoracic level using CT-based morphometric measurements. METHODS: One hundred thoracic spine CT scans (obtained in 50 male and 50 female subjects) were evaluated in this study. The width and depth of each vertebra body were measured from T-1 to T-12. In addition, the distance of each rib head to the spinal canal was determined by drawing a line connecting the rib heads bilaterally and measuring the distance to this line from the most ventral aspect of the spinal canal. Finally, the distance of the left rib head to the thoracic aorta was measured at each thoracic level below the aortic arch. RESULTS: The vertebral body depth progressively increased in a rostral to caudal direction. The vertebral body width was at its minimum at T-4 and progressively increased to T-12. The rib head extended beyond the spinal canal maximally at T-1. This distance incrementally decreased toward the caudal levels, with the tip of the rib head lying approximately even with the ventral canal at T-11 and T-12. The distance between the aorta and the left rib head increased in a rostral to caudal direction as well. CONCLUSIONS: The rib head is an important landmark in the anterolateral approach to the thoracic spine. At more cephalad levels, a larger portion of rib head requires resection to gain access to the spinal canal. At more caudad levels, there is a safer working distance between the rib head and aorta.

Adjacent-level range of motion and intradiscal pressure after posterior cervical decompression and fixation: an in vitro human cadaveric model.

STUDY DESIGN: This in vitro human cadaveric study measured adjacent-level kinematics after posterior cervical decompression and fixation. OBJECTIVE: Quantify adjacent-level changes in range of motion (ROM) and intradiscal pressure after posterior cervical decompression and fixation. SUMMARY OF BACKGROUND DATA: Optimal length of instrumentation after posterior decompression is unclear. Longer posterior cervical fixation constructs may increase the risk of adjacent-segment degeneration. METHODS: Eight cervicothoracic spines were evaluated intact, with C3-C6 laminectomy, C3-C6 laminectomy + C3-C6 fixation, C3-C6 laminectomy + C3-C7 fixation, C3-C7 laminectomy, C3-C7 laminectomy + C3-C7 fixation, C3-C7 laminectomy + C2-C7 fixation, C3-C7 laminectomy + C3-T2 fixation, and C3-C7 laminectomy + C2-T2 fixation. Testing included intact moments (± 2.0 N·m) in flexion/extension, axial rotation, and lateral bending, with quantification of ROM at C2-C3, C6-C7, and C7-T1 normalized to the intact spine. Intradiscal pressures were also measured at each level. RESULTS: For the C3-C6 laminectomy group, there were no differences in adjacent-level flexion/extension ROM or intradiscal pressure based on construct length, except at C6-C7, where ROM was significantly decreased when fixation was extended to C7 (P < 0.05). After C3-C7 laminectomy and reconstruction, the greatest increase in C2-C3 flexion/extension ROM and intradiscal pressure occurred in the C3-T2 fixation subgroup (ROM: 348% [P < 0.05]; intradiscal pressure: 319 ± 243 psi [pounds per square inch] vs. 65 ± 41 psi intact [P < 0.05]). At C7-T1, the greatest increase in flexion/extension ROM and intradiscal pressure occurred after C2-C7 fixation (ROM: 531% [P < 0.05]; intradiscal pressure: 152 ± 83 psi vs. 21 ± 14 psi intact [P < 0.05]). CONCLUSION: For C3-C6 laminectomy, instrumentation to C7 significantly decreased flexion/extension ROM and intradiscal pressure at C6-C7 without significantly increasing either measure at C2-C3 or C7-T1 relative to C3-C6 fixation. In the setting of a C3-C7 laminectomy, when instrumenting to either C2 or T2, consideration should be given to including both levels within these constructs.