Faculty Bibliography

BACKGROUND:High-grade gliomas of the spinal cord are poorly understood tumors that are very commonly associated with bad outcomes. The transforming effects of platelet-derived growth factor (PDGF) on spinal cord glial progenitor cells may play an important role in the development of these tumors. OBJECTIVE:To investigate the possible tumor-initiating effects of PDGF overexpression in the spinal cord, we delivered a PDGF retrovirus directly into the substance of the spinal cord. METHODS:The spinal cords of wild-type adult rats were surgically exposed and injected with 10⁶ colony-forming units of a green fluorescent protein-tagged, PDGF-expressing retrovirus. A control virus was injected to assess the cell types that become infected during retroviral delivery to the spinal cord. RESULTS:It was observed that PDGF overexpression in the spinal cord causes morbidity from high-grade intramedullary glioma formation between 27 and 49 days after PDGF retrovirus injection. Retroviral transduction was highly efficient with 100% of injected animals displaying the tumor phenotype. The tumors produced were highly proliferative, were locally invasive, and displayed the immunophenotype of virus-targeted glial progenitor cells (Olig2+PDGFR+NG2+GFAP-). CONCLUSION/CONCLUSIONS:PDGF is capable of driving glial progenitor cells within the adult spinal cord to form high-grade gliomas. Further investigation of PDGF signaling in the spinal cord is needed to better understand and treat these devastating tumors.

STUDY DESIGN/METHODS:Retrospective review of consecutive case series. OBJECTIVE:To assess the safety and efficacy of the microendoscopic approach for treatment of recurrent lumbar disc herniation. SUMMARY OF BACKGROUND DATA/BACKGROUND:The standard surgical approach for the treatment of recurrent disc herniation uses an open technique with a wide exposure. Many would consider a minimally invasive approach such as microendoscopic discectomy (MED) to be contraindicated in the setting of recurrent disc herniation. METHODS:Sixteen consecutive patients with recurrent lumbar disc herniation who failed conservative management underwent MED. Before surgery and at follow-up, patients completed the Oswestry Disability Index, SF-36, and assessment of leg pain using the Visual Analog Scale. Outcome was also assessed using modified McNab criteria. RESULTS:No case required conversion to an open procedure. Mean operative time was 108 minutes, and mean estimated blood loss was 32 mL. The only surgical complications were 2 durotomies that were treated with dural sealant without sequelae. Mean hospital stay was 23 hours, and mean follow-up was 14.7 months. Approximately 80% of patients had good or excellent outcomes based on modified McNab criteria. The remaining 3 patients had fair outcomes, and no patient had a poor outcome. All standardized measures improved significantly, including mean Visual Analog Scale for leg pain (8.2 to 2.2, P<0.001), mean Oswestry Disability Index (59.3 to 26.7, P<0.001), SF-36 Physical Component Summary score (28.3 to 42.4, P<0.001), and SF-36 Mental Component Summary score (38.2 to 48.3, P<0.001). As of last follow-up no patient has showed recurrence of herniation or evidence of delayed instability. CONCLUSIONS:MED is a safe and effective surgical approach for the treatment of recurrent lumbar disc herniation. Standardized measures of outcome show that MED for recurrent herniation produces improvement in pain, disability, and functional health that is at least comparable with outcomes reported for conventional open microdiscectomy.

OBJECTIVE:This report illustrates the adequacy of minimally invasive exposure for the resection of an intramedullary ependymoma. CLINICAL PRESENTATION/METHODS:The patient presented with a history of upper back pain, but a lesion was found during a workup for increased back pain after a motor vehicle accident. INTERVENTION/METHODS:The intramedullary ependymoma was approached using a muscle-splitting retractor and extended hemilaminar exposure. The tumor was removed using conventional techniques. CONCLUSION/CONCLUSIONS:This minimally invasive exposure is adequate for selected intramedullary lesions and may be especially useful in patients with a high risk of postlaminectomy deformity.

Hemangioblastomas occur in 2% to 15% of reported series of intramedullary spinal cord tumors. They are benign, highly vascular tumors that can be cured with surgical resection. Complete removal of these tumors with low morbidity is possible with current microneurosurgical techniques and a thorough understanding of the typical relationship of the tumor to adjacent neural structures. We describe our experience with 16 intramedullary and 2 lumbosacral nerve root hemangioblastomas and review the relevant published literature. A detailed discussion of the operative technique is provided along with an operative video. Three illustrative cases are used to demonstrate clinical considerations that can arise with these tumors, including surgery during pregnancy, symptoms related to syrinx or syringomyelia, and postoperative consequences of neurological deficits.

STUDY DESIGN/METHODS:A cadaver study comparing 3 different minimally invasive approaches to the anterior thoracic spine. OBJECTIVE:To assess the feasibility of minimally invasive thoracic corpectomy from a posterolateral approach and to compare surgical results from 3 approaches. SUMMARY OF BACKGROUND DATA/BACKGROUND:Traditional posterolateral approaches to the thoracic spine are effective but are associated with a high rate of operative morbidity. METHODS:Thoracic corpectomies were performed using a modified tubular retractor starting at 3, 6, and 9 cm off of midline. Postoperative computed tomography scans were performed and analyzed to assess the extent of corpectomy and ventral decompression. RESULTS:From 3 to 6 to 9 cm, a significant difference in extent of corpectomy (65.8%, 81.5%, and 82.6%, P=0.02) and ventral decompression (83.6%, 90.4%, 94.6%, P=0.05) was noted between 3 cm and the more lateral approaches. The 9 cm approach required more rib resection and average working distances of 8.4 to 11.3 cm, which made the procedure more difficult technically and less suited to the length of standard instruments. CONCLUSIONS:Minimally invasive thoracic corpectomy is feasible and a 6 cm approach off of midline appears optimal.

OBJECTIVE:To demonstrate the feasibility of and initial clinical experience with a novel minimally invasive posterolateral thoracic corpectomy technique. METHODS:Seven procedures were performed on 6 cadavers to determine the feasibility of thoracic corpectomy using a minimally invasive approach. The posterolateral thoracic corpectomies were performed with expandable 22 mm diameter tubular retractor paramedian incisions. The posterolateral aspects of the vertebral bodies were accessed extrapleurally, and complete corpectomies were performed. Intraprocedural fluoroscopy and postoperative computed tomography were used to assess the degree of decompression. In addition, 2 clinical cases of T6 burst fracture, 1 T4-T5 plasmacytoma, and 1 T12 colon cancer metastasis were treated using this minimally invasive approach. RESULTS:In the cadaveric study, an average of 93% of the ventral canal and 80% of the corresponding vertebral body were removed. The pleura and intrathoracic contents were not violated. Adequate exposure was obtained to allow interbody grafting between the adjacent vertebral bodies. The procedures were successfully performed in the 4 clinical cases using a minimally invasive technique, and the patients demonstrated good outcomes. CONCLUSION/CONCLUSIONS:Based on this study, minimally invasive posterolateral thoracic corpectomy safely and successfully allows complete spinal canal decompression without the tissue disruption associated with open thoracotomy. This approach may improve the complication rates that accompany open or even thoracoscopic approaches for thoracic corpectomy and may even allow surgical intervention in patients with significant comorbidities.

BACKGROUND:Minimally invasive approaches to intradural pathology have evolved in part in an effort to reduce approach related destabilization of the spine. No biomechanical data exist however evaluating the effects of traditional and minimally invasive exposures. METHODS:A finite element model of the lumbar spine was generated, and a simulated open laminectomy and a modified hemilaminectomy at L4 were performed. Forces were applied to assess changes in flexion, extension, axial rotation, and lateral bending. FINDINGS/RESULTS:Open laminectomy produced much greater changes in extension, flexion, and axial rotation than the modified hemilaminectomy from the intact. Lateral bending was similarly unaffected for both exposures. INTERPRETATION/CONCLUSIONS:The results suggest that a minimally invasive hemilaminar exposure preserves the structural integrity of the lumbar spine and minimizes alterations to segmental motion postoperatively.

STUDY DESIGN/METHODS:A validated finite element model of the intact lumbar spine (L1-S1) was modified to study the biomechanical changes as a result of surgical alteration for treatment of stenosis at L3-L4 and L4-L5 using 2 established techniques and 1 new minimally invasive technique. OBJECTIVE:To investigate the impact of graded posterior element removal associated with new surgical techniques on postoperative segmental motion and loading in the annulus. SUMMARY OF BACKGROUND DATA/BACKGROUND:Several studies have shown that laminectomy increases and produces segmental instability unless fusion is performed. However, no data exist comparing the biomechanical impact of completely preserving the contralateral anatomy and what effect this has compared to traditional approaches. METHODS:The effect of graded removal of posterior elements because of iatrogenic change associated with the 3 approaches was investigated using an 800 N compressive preload using the follower load technique and application of 8 Nm flexion, 6 Nm extension, 4 Nm torsion, and 6 Nm lateral bending moments. RESULTS:This study shows that removal of posterior elements for treatment of stenosis at L3-L4 and L4-L5 results in increased flexion-extension and axial rotation at the surgical site. This study also shows that the segmental motion following a traditional laminectomy is greater than the minimally invasive approach in flexion, extension, left and right axial rotation. Moderate preservation of the posterior elements which occurs in the intralaminar approach generates greater segmental motion that the minimally invasive approach in extension, left and right axial rotation. CONCLUSION/CONCLUSIONS:Minimization of bone and ligament removal associated with minimally invasive procedures results in greater preservation of the normal motion of the lumbar spine after surgery. This study suggests that preservation of the posterior spinal elements associated with minimally invasive surgery could minimize the risk of developing de novo postoperative changes in spinal alignment and/or acceleration of facet and disc degeneration.

OBJECTIVE:Many patients undergoing lumbar spine fusion are overweight or obese. The relationship between body habitus and outcome after lumbar spine fusion surgery is not well defined. METHODS:We analyzed a prospectively maintained database of self-reported pain and quality of life measures, including Visual Analog Scale pain score, Short Form 36, and Oswestry Disability Index. We selected patients undergoing minimally invasive transforaminal lumbar interbody fusion between September 2002 and June 2006 at a single institution. We used linear regression models and mixed-effects linear models to examine the relationships between body habitus and self-reported outcomes. RESULTS:The analysis identified 110 patients meeting the study criteria, with a median follow-up period of 14.8 months. The mean age was 56 years, mean height was 169 cm, and mean weight was 82.2 kg. The mean body mass index (BMI) was 28.7 kg/m2; 31% of patients were overweight (BMI, 25-29.9), and 32% of patients were obese (BMI, >30). Linear regression analysis did not identify a correlation between weight or BMI and pre- and postsurgery changes in any of the outcome measures. The significant findings observed in the mixed-effects linear models were that the changing patterns of Short Form 36 Body Pain subscale and Short Form 36 Vitality subscale varied significantly by category of BMI (P = 0.01 and P = 0.002, respectively), but not significantly if continuous BMI was used (P = 0.53 and P = 0.46, respectively). BMI correlated marginally with estimated blood loss (P = 0.08), but not operative time, length of hospital stay, or complications. CONCLUSION/CONCLUSIONS:Among this cohort of minimally invasive lumbar fusion patients, body habitus measured by BMI, weight, or height did not have a significant relationship with most self-reported outcome measures, operative time, length of hospital stay, or complications. Obesity should not be considered a contraindication to minimally invasive lumbar spinal fusion surgery.