A theoretical and experimental investigation of the nonlinear acoustic response of acoustic insertion elements.

In a previous paper, a model was developed for the nonlinear acoustic resistance for compact insertion elements. Within the model, two loss coefficients are used to tune the model for each type of element, and data were used to empirically determine these coefficients for an area contraction. This paper extends the nonlinear model, developing expressions based on physical principles for the forward and reverse loss coefficients for both an area contraction and orifice. In addition, experimental data for the acoustic resistance of both elements was taken using an impedance tube. Utilizing the expressions developed, the model compares favorably with the experimental data.

Use of an intraoperative sodium oxychlorosene-based infection prevention protocol to safely decrease postoperative wound infections after spine surgery.

OBJECTIVE: Postoperative infection remains prevalent after spinal surgical procedures. Institutional protocols for infection prevention have improved rates of infection after spine surgery. However, prior studies have focused on only elective surgical patients. The aim of this study was to determine the efficacy of a multiinstitutional intraoperative sodium oxychlorosene-based infection prevention protocol for decreasing rate of infection after instrumented spinal surgery. METHODS: A retrospective analysis was performed at two tertiary care institutions with level I trauma programs, and patients who underwent posterior instrumented spinal fusion between January 1, 2011, and May 31, 2019, were included. Postoperative deep wound infection rates were captured before and after implementation of a multiinstitutional infection prevention protocol. Possible adverse outcomes related to infection prevention techniques were also examined. In addition, consecutive patients treated from January 1, 2018, to May 31, 2019, were prospectively included in a database to collect preoperative and postoperative spine-specific quality of life measures and to assess the impact of postoperative infection on quality of life. RESULTS: A total of 5047 patients fit the inclusion criteria. Of these, 1043 patients underwent surgery prior to protocol implementation. The infection rate of this cohort (3.5%) decreased significantly after protocol implementation (1.2%, p < 0.001). Postoperative sterile seroma rates did not differ between the preprotocol and postprotocol groups (0.7% vs 0.7%, p = 0.5). In the 1031 patients who underwent surgery between January 2018 and May 2019, the fusion rate was 89.2%. Quality of life outcomes between patients with infection and those without infection were similar, although statistical power was limited owing to the low rate of infection. Notably, 2 of 10 patients who developed deep wound infection died of infection-related complications. CONCLUSIONS: An intraoperative sodium oxychlorosene-based infection prevention protocol helped to significantly decrease the rate of infection after spine surgery without negatively impacting other postoperative procedure-related metrics. Postoperative wound infection may be associated with higher-than-expected rate of postoperative mortality.

Minimally invasive lateral transpsoas approach for spinal discitis and osteomyelitis.

We present a series of patients with discitis and osteomyelitis who were surgically treated via a minimally invasive lateral transpsoas approach to the lumbar spine. Surgical treatment for spinal discitis and osteomyelitis presents challenges because of comorbidities that are common in patients undergoing this procedure. A retrospective review found six patients who met strict operative criteria including instability, intractable pain, neurological deficit, and disease progression. All patients were non-ambulatory before surgery because of intractable back pain. The patients underwent standard lateral minimally invasive surgery using either the extreme lateral interbody fusion (NuVasive, San Diego, CA, USA) or direct lateral interbody fusion (Medtronic Sofamor Danek, Memphis, TN, USA) system. The patients underwent debridement with a discectomy and partial or complete corpectomy, with polyetheretherketone or titanium cage placement. Two patients had additional posterior fixation with percutaneous pedicle screws, and none had immediate perioperative complications. The postoperative CT scans demonstrated satisfactory debridement and hardware placement. All patients experienced significant pain improvement and could ambulate within a few days of surgery. So far, the 1 year follow-up data have demonstrated stable hardware with solid fusion and continued pain improvements. One patient demonstrated hardware failure secondary to refractory infection, 2 months postoperatively, and required additional posterior decompression and debridement with pedicle screw fixation. The lateral transpsoas approach permits debridement and fixation coupled with percutaneous pedicle screw fixation to further stabilize the spine in a minimally invasive fashion. Due to the significant comorbidities in this patient population, a minimally invasive approach is a suitable surgical technique. A close follow-up period is necessary to detect early hardware failure which may necessitate more extensive treatment.

Subacute posttraumatic ascending myelopathy in a 15-year-old boy.

Secondary injury following initial spinal cord trauma is uncommon and frequently attributed to mismanagement of an unprotected cord in the acute time period after injury. Subacute posttraumatic ascending myelopathy (SPAM) is a rare occurrence in the days to weeks following an initial spinal cord injury that is unrelated to manipulation of an unprotected cord and involves 4 or more vertebral levels above the original injury. The authors present a case of SPAM occurring in a 15-year-old boy who sustained a T3-4 fracture-dislocation resulting in a complete spinal cord injury, and they highlight the imaging findings and optimum treatment for this rare event.

Percutaneous pedicle screw placement with computer-navigated mapping in place of Kirschner wires: clinical article.

OBJECT: Percutaneous pedicle screw insertion techniques are commonly used to treat a variety of spinal disorders. Typically, Kirschner (K)-wires are used to guide the insertion of taps and screws during placement since the normal anatomical landmarks are not visualized. The use of K-wires adds risks, such as vascular and nerve injuries as well as increased radiation exposure given the use of fluoroscopy. The authors describe a series of patients who had percutaneous pedicle screws placed using a new computer-assisted navigation technique without the need for K-wires. METHODS: Minimally invasive percutaneous pedicle screw placement in the thoracic and lumbar spine was performed in a consecutive series of 15 patients for a variety of spinal pathologies. Intraoperative 3D CT images were obtained and used with a computer-assisted navigation system to insert an awl-tap into each pedicle. The tap location in the pedicle was marked with the navigation software, and the awl-tap was then removed. The navigation system was used to identify each landmark to insert the pedicle screw. Connecting rods were then inserted percutaneously under fluoroscopic guidance. Postoperative CT scans were obtained in each patient to evaluate screw placement. RESULTS: On postprocedure scanning, only 1 screw had a minor lateral and superior breach that was asymptomatic. To date, there have been no hardware failures. CONCLUSIONS: Percutaneous pedicle screws can be placed effectively and safely without the use of K-wires.

Thoracic phosphaturic mesenchymal tumors causing oncogenic osteomalacia.

Oncogenic osteomalacia is a rare paraneoplastic syndrome induced by mesenchymal tumors. Just over 100 cases have been reported for this rare disorder, and only seven instances were caused by phosphaturic mesenchymal tumors of the spine. The authors present an illustrative case of a 61-year-old woman with oncogenic osteomalacia induced by a tumor of the spine, and review the literature describing the clinical presentation, surgical treatment, and follow-up of this syndrome.

Outcomes of spinal fusion following autologous stem cell transplantation.

Patients who have undergone myeloablative chemotherapy followed by autologous hematopoietic stem cell transplantation (HSCT) for conditions such as multiple myeloma, Hodgkin's disease, and primary amyloidosis may be at higher risk for failure of spinal fusion. As HSCT care and outcomes continue to improve, it is increasingly likely that neurosurgeons will encounter patients post-HSCT who require spinal procedures. To our knowledge there are no published data on fusion outcomes in this unique patient population. We report three patients who underwent spinal fusion following an autologous HSCT. Spinal surgery was performed, on average, 4.5 years after autologous HSCT. No patients were on immunosuppressant chemotherapy at the time of the procedure, although one patient was being treated with rituximab for disease progression peri-operatively. Average radiographic confirmation of fusion was 37 months and all patients ultimately demonstrated fusion, although not without incident. Our results suggest that spinal fusion can occur in patients who have previously undergone myeloablative chemotherapy followed by autologous HSCT.

Treatment strategy for chondromyxoid fibroma of the sacrum.

We present a 59-year-old woman with a rare sacral chondromyxoid fibroma discovered incidentally and treated with curettage, bone grafting, and lumbopelvic fixation. At 1 year following surgery she remains symptom-free, has successfully fused her lumbopelvic construct and has no signs of tumor progression. The known literature contains only six previous reports of sacral chondromyxoid fibroma and discussion is presented on the diagnosis and treatment of this rare lesion.

Absence of MRI soft tissue abnormalities in severe spinal cord injury in children: case-based update.

INTRODUCTION: Occult spinal cord injury should be suspected based not only on the mechanism of trauma but also on the age of the patient. The pediatric spine has unique biomechanical and anatomical properties that must be considered carefully when evaluating spinal cord trauma. For instance, the hypermobility and elasticity of the spinal column in children often lead to self-reducing injuries that can mask spinal cord injury. CASE ILLUSTRATION: We present the case of a 22-month-old male patient who was found to have ligamentous injury detected by magnetic resonance imaging (MRI) in the upper cervical spine but missed by MRI in the lower thoracic spine. Furthermore, there was no spinal cord injury in the upper cervical spine, but indeed a serious insult in the thoracic region. Since the advent of MRI, spinal cord injury without radiographic abnormality (SCIWORA) has become increasingly rare but not altogether extinct. CONCLUSIONS: We present a noteworthy example of the inadequacy of MRI in revealing SCIWORA, a term that is antiquated as we combine the latest imaging techniques with a better understanding of the biomechanics of trauma and spine injury. Based on the literature and our case illustration, we believe that the biomechanics of the pediatric spine must be considered when children who may have sustained a SCIWORA are examined.

Spinal surgery following organ transplantation.

OBJECT: Organ transplantation for renal, liver, cardiac, and pulmonary failure has become more common in recent years, and patients are living longer as a result of improved organ preservation methods, immunosuppressive regimens, and general posttransplant care. Some of these patients undergo spine fusion surgery following organ transplantation, and there is little available information concerning outcomes. The authors report on their experience with and the outcomes of spine fusion in this rare and unique immunosuppressed patient group. METHODS: Using the Current Procedural Terminology and ICD-9 codes for solid organ transplants, bone marrow transplantations (BMTs), and spine fusion surgeries, the authors searched their patient database between 1997 and 2008. Data points of interest included primary diagnosis, type of organ transplant, immunosuppressant drug therapy, complications from spine surgery, and radiographic analysis of spine fusion. Spine fusion was assessed with CT or radiography at the latest follow-up. RESULTS: The database search results revealed 5999 patients who underwent heart, lung, liver, kidney, pancreas, intestine, or bone marrow transplant between 1997 and 2008. Eighteen of the 5999 patients underwent a spine fusion surgery while receiving immunosuppressive therapy. Organ transplants included kidney, liver, heart, pancreas, and allogenic BMT. There were 3 deaths unrelated to spine fusion within 1 year of the surgery and 1 death immediately after spine surgery. Graft-versus-host disease developed in 1 patient when prednisone was stopped prior to the spine surgery. Thirteen patients underwent follow-up radiographic imaging at an average of 25 months after spine surgery; 12 demonstrated radiographic fusion. CONCLUSIONS: The results suggest that spine fusion rates are adequate despite immunosuppressive therapy in patients undergoing spinal fusion after transplant procedures. The data also illustrate the high morbidity and mortality rates found in the organ transplant patient population.

Multi-level corpectomies and reconstruction via a single posterolateral approach.

The surgical treatment of ventral spinal canal compression has traditionally required either an anterior or combined anterior-posterior decompression and stabilization. These types of approaches carry a significant morbidity and may not be appropriate for all patients. We report our experience with multi-level corpectomies and reconstruction performed via a single, posterolateral approach. A retrospective review was performed of six consecutive patients at a single institution who were treated for ventral multi-level spinal cord compression via a single posterolateral approach. All six patients underwent reconstruction and stabilization with an expandable cage and posterior fixation. Five patients had metastatic cancer with spinal cord compression and one patient had osteomyelitis with a ventral epidural abscess and vertebral body collapse. All patients underwent 2-level corpectomies. Pre-operative and post-operative neurologic function and stabilization construct integrity were analyzed. All patients had successful decompression and stabilization and there were no hardware complications. Three peri-operative complications were encountered: post-operative pleural effusion needing thoracostomy drainage, transient leg paresis that resolved at 2months and a post-operative wound infection needing operative debridement. At last follow-up all patients had improvement or stabilization of their neurological function. Long-term follow-up was limited by the progression of metastatic disease and death in all the patients with cancer. This study demonstrates that symptomatic improvement can be achieved in select patients requiring multi-level corpectomies when using a single posterolateral approach with expandable cage reconstruction and posterior stabilization.

Sacral fractures following stand-alone L5-S1 anterior lumbar interbody fusion for isthmic spondylolisthesis.

Recent studies have demonstrated excellent results in treating isthmic spondylolisthesis via an anterior lumbar interbody fusion (ALIF). The authors describe 3 patients with isthmic spondylolisthesis at L5-S1 who experienced sacral fractures after insertion of a unique, stand-alone anterior interbody fixation device. Three consecutive patients at a single institution were treated for Grade I spondylolisthesis at L5-S1 via a standalone ALIF with insertion of a novel biomechanical interbody device. This device is made of polyetheretherketone and has an integrated system for internal fixation into the vertebral bodies. In each patient a bone morphogenetic protein-soaked sponge was placed for the fusion. The indications for treatment in each patient were back and radicular pain that had been unsuccessfully treated with conservative measures. All 3 patients had reduction of their spondylolisthesis and resolution of their unilateral radiculopathies immediately postoperatively. Within 1 month of surgery, all 3 patients had failure of the device and recurrence of their symptoms. In each case the failure was due to fracture of the anterior portion of the S-1 body. Each patient underwent reduction and pedicle screw fixation at L5-S1. In all cases, there was successful reduction in their recurrent spondylolisthesis and resolution of their radiculopathies. Treatment of Grade I isthmic spondylolisthesis at L5-S1 with stand-alone ALIF and fixation can lead to sacral fracture from high stress loads at that level in the spine, and consideration should be made either for supplemental pedicle screw fixation or a completely posterior approach.

Minimally invasive resection of an extrapelvic sciatic schwannoma.

Schwannomas associated with the sciatic nerve are relatively rare. Surgical excision of symptomatic sciatic schwannomas traditionally involves a posterior sciatic nerve approach with a large, open exposure and transection of the gluteal muscles. The authors provide a technical report of a minimally invasive approach for the resection of an extrapelvic schwannoma arising from the sciatic nerve. The patient was discharged to home on the same day of surgery and his symptoms of severe sciatica immediately and dramatically improved.

A 61-year-old woman with osteomalacia and a thoracic spine lesion.

Phosphaturic mesenchymal tumor, mixed connective tissue variant (PMT-MCT) is a rare, largely benign, mesenchymal neoplasm almost invariably associated with oncogenic osteomalacia. It is generally found in the soft tissue and bone of the extremities. We report a case of a 61-year-old female with long-standing osteomalacia who was found to have PMT-MCT of the thoracic spine. There have been very few previously reported cases of PMT involving the spinal vertebrae and neuropathologists should be aware of this lesion. Recognition of PMT-MCT is critical for optimal patient care since complete surgical resection without additional therapy is curative.

Spinal accessory nerve cavernous malformation.

We present the first reported case of a spinal accessory nerve cavernous malformation. A 54-year-old Caucasian male presented with a several-year history of progressive, vague bilateral upper and lower extremity paresthesias and pain. MRI of the spine revealed a heterogenously enhancing mass in the dorsal aspect of the spinal canal at the level of the atlas with mild spinal cord compression. The lesion was resected and upon gross and histologic examination it was a cavernous malformation embedded within a branch of the spinal accessory nerve. Post-operatively, the patient had no complications and some improvement in his symptoms. To our knowledge, this is the first report of a patient with a spinal accessory nerve cavernous malformation, and this should be considered in the differential of lesions in the craniocervical region.

Circumferential fixation with craniofacial miniplates for a cervical spine injury in a child.

Unstable pediatric cervical spine injuries present significant challenges in terms of fixation. Given the smaller cervical vertebral bodies in the preschool-aged population, commercially available pediatric cervical fixation instrumentation may be unsuitable because of the inappropriately large size of the screws and plates. The authors describe a 2-year-old girl who sustained an unstable C6-7 distraction injury during a motor vehicle accident. Because of the small size of her vertebral bodies, standard cervical spine instrumentation was not feasible, and posterior wiring alone was believed to be insufficient because of the complete distraction of all 3 spinal columns. The patient was taken to the operating room where craniofacial plates with an inherent locking mechanism were used to circumferentially stabilize the cervical spine. Follow-up examination 6 months postoperatively demonstrated stable cervical spine alignment and fusion with no evidence of the failure of either the anterior or posterior hardware. The use of craniofacial miniplates with an intrinsic locking mechanism represents a superior alternative for both anterior and posterior cervical fixations when spinal instrumentation is needed in the pediatric age group.

Biomechanics of C-7 transfacet screw fixation.

OBJECT: The small diameter of the pedicle can make C-7 pedicle screw insertion dangerous. Although transfacet screws have been studied biomechanically when used in pinning joints, they have not been well studied when used as part of a C7-T1 screw/rod construct. The authors therefore compared C7-T1 fixation using a C-7 transfacet screw/T-1 pedicle screw construct with a construct composed of pedicle screws at both levels. METHODS: Each rigid posterior screw/rod construct was placed in 7 human cadaveric C6-T2 specimens (14 total). Specimens were tested in normal condition, after 2-column instability, and once fixated. Nondestructive, nonconstraining pure moments (maximum 1.5 Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while recording 3D motion optoelectronically. The entire construct was then loaded to failure by dorsal linear force. RESULTS: There was no significant difference in angular range of motion between the 2 instrumented groups during any loading mode (p > 0.11, nonpaired t-tests). Both constructs reduced motion to < 2 degrees in any direction and allowed significantly less motion than in the normal condition. The C-7 facet screw/T-1 pedicle screw construct allowed a small but significantly greater lax zone than the pedicle screw/rod construct during lateral bending, and it failed under significantly less load than the pedicle screw/rod construct (p < 0.001). CONCLUSIONS: When C-7 transfacet screws are connected to T-1 pedicle screws, they provide equivalent stability of constructs formed by pedicle screws at both levels. Although less resistant to failure, the transfacet screw construct should be a viable alternative in patients with healthy bone.

Endogenous stem cell proliferation induced by intravenous hedgehog agonist administration after contusion in the adult rat spinal cord.

OBJECT: Sonic hedgehog (Shh) is a glycoprotein molecule that upregulates the transcription factor Gli1. The Shh protein plays a critical role in the proliferation of endogenous neural precursor cells when directly injected into the spinal cord after a spinal cord injury in adult rodents. Small-molecule agonists of the hedgehog (Hh) pathway were used in an attempt to reproduce these findings through intravenous administration. METHODS: The expression of Gli1 was measured in rat spinal cord after the intravenous administration of an Hh agonist. Ten adult rats received a moderate contusion and were treated with either an Hh agonist (10 mg/kg, intravenously) or vehicle (5 rodents per group) 1 hour and 4 days after injury. The rats were killed 5 days postinjury. Tissue samples were immediately placed in fixative. Samples were immunohistochemically stained for neural precursor cells, and these cells were counted. RESULTS: Systemic dosing with an Hh agonist significantly upregulated Gli1 expression in the spinal cord (p < 0.005). After spinal contusion, animals treated with the Hh agonist had significantly more nestin-positive neural precursor cells around the rim of the lesion cavity than in vehicle-treated controls (means +/- SDs, 46.9 +/- 12.9 vs 20.9 +/- 8.3 cells/hpf, respectively, p < 0.005). There was no significant difference in the area of white matter injury between the groups. CONCLUSIONS: An intravenous Hh agonist at doses that upregulate spinal cord Gli1 transcription also increases the population of neural precursor cells after spinal cord injury in adult rats. These data support previous findings based on injections of Shh protein directly into the spinal cord.

Primary thoracolumbar Ewing's sarcoma presenting as isolated epidural mass.

BACKGROUND CONTEXT: Ewing's sarcoma is the most common childhood malignancy of bone, but it rarely occurs as a primary extraosseous epidural tumor. PURPOSE: To heighten awareness and treatment options of this rare (epidural) presentation of Ewing's sarcoma. STUDY DESIGN: Case report. METHODS: Retrospective review. RESULTS: We present a 13-year-old boy with progressive low back and bilateral lower extremity pain and normal neurologic examination. Magnetic resonance imaging showed an extradural tumor in the dorsal epidural space from T11 to L1. He underwent a posterior laminoplasty and gross total resection of tumor; histopathological diagnosis was consistent with Ewing's sarcoma. After surgery, the patient underwent adjuvant chemotherapy and irradiation. At 10 months follow-up, the patient is neurologically intact without evidence of residual disease. CONCLUSIONS: Ewing's sarcoma of the epidural space should be considered in the differential diagnosis of epidural mass lesions. Because wide surgical margins cannot be obtained, close follow-up with a low threshold for reoperation is mandatory.

The effects of intrathecal hypotension on tissue perfusion and pathophysiological outcome after acute spinal cord injury.

OBJECT: Venous stasis and intrathecal hypertension are believed to play a significant role in the hypoperfusion present in the spinal cord following injury. Lowering the intrathecal pressure via cerebrospinal fluid (CSF) drainage has been effective in treating spinal cord ischemia during aorta surgery. The purpose of the present study was to determine whether CSF drainage increases spinal cord perfusion and improves outcome after spinal injury in an animal model. METHODS: Anesthetized adult rabbits were subjected to a severe contusion spinal cord injury (SCI). Cerebrospinal fluid was then drained via a catheter to lower the intrathecal pressure by 10 mm Hg. Tissue perfusion was assessed at the site of injury, and values obtained before and after CSF drainage were compared. Two other cohorts of animals were subjected to SCI: 1 group subsequently underwent CSF drainage and the other did not. Results of histological analysis, motor evoked potential and motor function testing were compared between the 2 cohorts at 4 weeks postinjury. RESULTS: Cerebrospinal fluid drainage led to no significant improvement in spinal cord tissue perfusion. Four weeks after injury, the animals that underwent CSF drainage demonstrated significantly smaller areas of tissue damage at the injury site. There were no differences in motor evoked potentials or motor score outcomes at 4 weeks postinjury. CONCLUSIONS: Cerebrospinal fluid drainage effectively lowers intrathecal pressure and decreases the amount of tissue damage in an animal model of spinal cord injury. Further studies are needed to determine whether different draining regimens can improve motor or electrophysiological outcomes.