Stephanus V. Viljoen

Intradural approach to selective stimulation in the spinal cord for treatment of intractable pain: design principles and wireless protocol

We introduce an intradural approach to spinal cord stimulation for the relief of intractable pain, and describe the biophysical rationale that underlies its design and performance requirements. The proposed device relies on wireless, inductive coupling between a pial surface implant and its epidural controller, and we present the results of benchtop experiments that demonstrate the ability to transmit and receive a frequency-modulated 1.6 MHz carrier signal between micro-coil antennae scaled to the ≈ 1 cm dimensions of the implant, at power levels of about 5 mW. Plans for materials selection, microfabrication, and other aspects of future development are presented and discussed.

Traumatic intracranial hemorrhage in patients taking dabigatran: report of 3 cases and review of the literature.

BACKGROUND AND IMPORTANCE Dabigatran is a direct thrombin inhibitor gaining popularity as a stroke prevention agent in patients with atrial fibrillation. In comparison with warfarin, dabigatran showed superiority in stroke prevention, but lower rates of major hemorrhage and intracerebral hemorrhage. Although warfarin has a well-established reversal strategy, there is far less experience reversing dabigatran. CLINICAL PRESENTATION We present our experience with 3 patients who experienced an intracranial hemorrhage either spontaneously or after low-energy cranial trauma and review the available literature describing dabigatran use in patients with traumatic brain injury. CONCLUSION Intracranial hemorrhage in patients taking anticoagulants and/or antiplatelets can have either a benign or malignant clinical course. At this time, there is little experience with dabigatran reversal; however, several strategies for rapid reversal have been proposed. All patients with intracranial hemorrhage taking dabigatran should be admitted for close neurological monitoring and serial imaging.

Biophysical attributes of an in vitro spinal cord surrogate for use in developing an intradural neuromodulation system

We have developed a spinal cord surrogate for use in testing a pial-surface spinal cord stimulator. Our surrogate is of a commercially available silicone mix, has an oval cross-sectional area that matches that of actual human spinal cord at the lower thoracic level, and has measured values of durometer A = (10.96 ± 1.68), durometer O = (14.76 ± 1.48), and durometer OO = (50.24 ± 2.65). These correspond to model-inferred elastic moduli of 0.41 to 0.44 MPa, which match well with the existing low-strain rate measurements of ex vivo human spinal cord. Upcoming applications for this surrogate in developmental studies of the new stimulator system are discussed.

Clinical and radiographic predictors of neurological outcome following posterior fossa decompression for spontaneous cerebellar hemorrhage.

Spontaneous cerebellar hemorrhage often requires surgical suboccipital decompression and clot evacuation. Predictors of postoperative neurological deficits and outcome are not widely addressed in the literature. A retrospective review was conducted on 37 consecutive patients with the diagnosis of cerebellar hemorrhage requiring suboccipital decompression and clot evacuation. Clinical and radiographic variables were analyzed. Outcome measures were postoperative Glasgow Coma Scale (GCS) score, and long-term outcome measured by Rankin score and Glasgow Outcome Scale (GOS) score. A multivariate statistical analysis was conducted. The average age of patients was 71.1 years. There was significant improvement of neurological exam from a mean preoperative GCS score of 8.8 to a mean postoperative GCS score of 13.0. The mortality rate was 37.9%. According to the Rankin scale, 58.6% were functionally independent, 3.4% had a moderate disability, and none had a major disability or was in a vegetative state. Using GOS score, 62.1% had a favorable outcome. The presence of multiple comorbidities was associated with worse postoperative GCS and long-term outcome. A worse preoperative neurological exam, age older than 70 years, and the presence of intraventricular hemorrhage correlated only with a worse postoperative exam but not with the long-term outcome. Patients improve neurologically after posterior fossa decompression for cerebellar hemorrhage and a high percentage attain long-term functional outcome. Only the presence of multiple clinical comorbidities was associated with a worse outcome. Since there are no other preoperative predictors of long-term outcome, we recommend suboccipital decompression, when indicated, for patients with cerebellar hemorrhage regardless of age, hematoma size, or preoperative neurological exam.

Cordectomy for intramedullary spinal cord glioblastoma with a 12-year survival.

Background: Prognosis of patients with spinal cord glioblastoma is poor, with an average survival of 18 months. There are reports in the literature describing cordectomy as a treatment option for patients with spinal cord tumors. Case Description: This is a case report of a patient with spinal cord glioblastoma who, in addition to radiation and chemotherapy, was treated with cordectomy. Outcome of treatment resulted in 12-year survival. Conclusion: Cordectomy in spinal cord glioblastoma can result in prolonged and meaningful survival.

Biomechanical performance of an ovine model of intradural spinal cord stimulation

Abstract The authors are developing a novel type of spinal cord stimulator, designed to be placed directly on the pial surface of the spinal cord, for more selective activation of target tissues within the dorsal columns. For pre-clinical testing of the device components, an ovine model has been implemented which utilizes the agility and flexibility of a sheep’s cervical and upper thoracic regions, thus providing an optimal environment of accelerated stress-cycling on small gauge lead wires implanted along the dorsal spinal columns. The results are presented of representative biomechanical measurements of the angles of rotation and the angular velocities and accelerations associated with the relevant head, neck and upper back motions, and these findings are interpreted in terms of their impact on assessing the robustness of the stimulator implant systems.

Biomechanical analysis of anterior versus posterior instrumentation following a thoracolumbar corpectomy: Laboratory investigation.

OBJECT The objective of this study was to evaluate the biomechanical properties of lateral instrumentation compared with short- and long-segment pedicle screw constructs following an L-1 corpectomy and reconstruction with an expandable cage. METHODS Eight human cadaveric T10-L4 spines underwent an L-1 corpectomy followed by placement of an expandable cage. The spines then underwent placement of lateral instrumentation consisting of 4 monoaxial screws and 2 rods with 2 cross-connectors, short-segment pedicle screw fixation involving 1 level above and below the corpectomy, and long-segment pedicle screw fixation (2 levels above and below). The order of instrumentation was randomized in the 8 specimens. Testing was conducted for each fixation technique. The spines were tested with a pure moment of 6 Nm in all 6 degrees of freedom (flexion, extension, right and left lateral bending, and right and left axial rotation). RESULTS In flexion, extension, and left/right lateral bending, posterior long-segment instrumentation had significantly less motion compared with the intact state. Additionally, posterior long-segment instrumentation was significantly more rigid than short-segment and lateral instrumentation in flexion, extension, and left/right lateral bending. In axial rotation, the posterior long-segment construct as well as lateral instrumentation were not significantly more rigid than the intact state. The posterior long-segment construct was the most rigid in all 6 degrees of freedom. CONCLUSIONS In the setting of highly unstable fractures requiring anterior reconstruction, and involving all 3 columns, long-segment posterior pedicle screw constructs are the most rigid.

Effects of brain derived neurotrophic factor Val66Met polymorphism in patients with cervical spondylotic myelopathy.

Cervical spondylotic myelopathy (CSM) is the leading cause of spinal cord related disability in the elderly. It results from degenerative narrowing of the spinal canal, which causes spinal cord compression. This leads to gait instability, loss of dexterity, weakness, numbness and urinary dysfunction. There has been indirect data that implicates a genetic component to CSM. Such a finding may contribute to the variety in presentation and outcome in this patient population. The Val66Met polymorphism, a mutation in the brain derived neurotrophic factor (BDNF) gene, has been implicated in a number of brain and psychological conditions, and here we investigate its role in CSM. Ten subjects diagnosed with CSM were enrolled in this prospective study. Baseline clinical evaluation using the modified Japanese Orthopaedic Association (mJOA) scale, Nurick and 36-Item Short Form Health Survey (SF-36) were collected. Each subject underwent objective testing with gait kinematics, as well as hand functioning using the Purdue Peg Board. Blood samples were analyzed for the BDNF Val66Met mutation. The prevalence of the Val66Met mutation in this study was 60% amongst CSM patients compared to 32% in the general population. Individuals with abnormal Met allele had worse baseline mJOA and Nurick scores. Moreover, baseline gait kinematics and hand functioning testing were worse compared to their wild type counterpart. BDNF Val66Met mutation has a higher prevalence in CSM compared to the general population. Those with BDNF mutation have a worse clinical presentation compared to the wild type counterpart. These findings suggest implication of the BDNF mutation in the development and severity of CSM.

An ovine model of spinal cord injury.

Objective: To develop a large animal model of spinal cord injury (SCI), for use in translational studies of spinal cord stimulation (SCS) in the treatment of spasticity. We seek to establish thresholds for the SCS parameters associated with reduction of post-SCI spasticity in the pelvic limbs, with implications for patients. Study Design: The weight-drop method was used to create a moderate SCI in adult sheep, leading to mild spasticity in the pelvic limbs. Electrodes for electromyography (EMG) and an epidural spinal cord stimulator were then implanted. Behavioral and electrophysiological data were taken during treadmill ambulation in six animals, and in one animal with and without SCS at 0.1, 0.3, 0.5, and 0.9 V. Setting: All surgical procedures were carried out at the University of Iowa. The gait measurements were made at Iowa State University. Material and Methods: Nine adult female sheep were used in these institutionally approved protocols. Six of them were trained in treadmill ambulation prior to SCI surgeries, and underwent gait analysis pre- and post-SCI. Stretch reflex and H-reflex measurements were also made in conscious animals. Results: Gait analysis revealed repeatable quantitative differences in 20% of the key kinematic parameters of the sheep, pre- and post-SCI. Hock joint angular velocity increased toward the normal pre-injury baseline in the animal with SCS at 0.9 V. Conclusion: The ovine model is workable as a large animal surrogate suitable for translational studies of novel SCS therapies aimed at relieving spasticity in patients with SCI.

A Novel Dural Reconstruction Method Following Spinal Tumor Resection

Objective:This report describes a new method for reducing the risk of postoperative obliteration of the subdural space and spinal cord tethering that frequently occurs following resection of intradural spinal tumors. Methods:A 66-year-old patient underwent resection of a T1 to T2 intradural meningioma. A duraplasty procedure was performed to reconstruct the thecal sac and create a capacious cerebrospinal fluid (CSF)-filled space around the spinal cord. To prevent subsequent inward compression of the thecal sac from dorsally located soft tissue, a titanium strap was fashioned to span the laminectomy defect. Dural tack-up stitches were secured to the titanium strap and the laminoplasty construct was secured in place using standard bone screws. Results:The combined duraplasty-titanium laminoplasty procedure was technically straightforward and there were no complications following surgery. Postoperative MR imaging 6 weeks following surgery demonstrated that the goal of creating a capacious CSF-filled space around the spinal cord, without inward compression of the thecal sac by scar tissue, was achieved. MR images of the spinal cord and dura were not degraded by the presence of the overlying titanium strap. Conclusions:This simple method that combines a duraplasty and titanium laminoplasty procedure seems to be a safe and effective approach to achieving the objective of maintaining a capacious CSF-filled space surrounding the spinal cord following intradural surgery.