Eric M. Horn

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

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.

Proposed Classification for the Transbasal Approach and Its Modifications

The transbasal approach offers extradural exposure of the anterior midline skull base transcranially. It can be used to treat a variety of conditions, including trauma, craniofacial deformity, and tumors. This approach has been modified to enhance basal access. This article reviews the principle differences among modifications to the transbasal approach and introduces a new classification scheme. The rationale is to offer a uniform nomenclature to facilitate discussion of these approaches, their indications, and related issues.

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.

Transfacet screw placement for posterior fixation of C-7 : Technical note

OBJECT Lateral mass screws are traditionally used to fixate the subaxial cervical spine, while pedicle screws are used in the thoracic spine. Lateral mass fixation at C-7 is challenging due to thin facets, and placing pedicle screws is difficult due to the narrow pedicles. The authors describe their clinical experience with a novel technique for transfacet screw placement for fixation at C-7. METHODS A retrospective chart review was undertaken in all patients who underwent transfacet screw placement at C-7. The technique of screw insertion was the same for each patient. Polyaxial screws between 8- and 10-mm-long were used in each case and placed through the facet from a perpendicular orientation. Postoperative radiography and clinical follow-up were analyzed for aberrant screw placement or construct failure. RESULTS Ten patients underwent C-7 transfacet screw placement between June 2006 and March 2007. In all but 1 patient screws were placed bilaterally, and the construct lengths ranged from C-3 to T-5. One patient with a unilateral screw had a prior facet fracture that precluded bilateral screw placement. There were no intraoperative complications or screw failures in these patients. After an average of 6 months of follow-up there were no hardware failures, and all patients showed excellent alignment. CONCLUSIONS The authors present the first clinical demonstration of a novel technique of posterior transfacet screw placement at C-7. These results provide evidence that this technique is safe to perform and adds stability to cervicothoracic fixation.

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.

Biomechanics of C-7 transfacet screw fixation: Laboratory investigation

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.

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.

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.

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.

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.