Great Vessel Excursion: Prone Versus Supine Position.

BACKGROUND: It is theorized that pedicle screws could be placed into the anterior vertebral cortex to increase biomechanical strength by 20% to 25%. Although stereotactic navigational tools allow for accurate docking of spinal implants, no data exist regarding operative positioning as it relates to great vessel alignment. Our hypothesis is that the great vessels fall anteriorly, with prone positioning providing a safer margin for implantation of screws from a posterior approach. METHODS: Volunteers underwent magnetic resonance imaging of the spine. Twenty healthy volunteers, affiliated with the academic medical center performing the study, underwent magnetic resonance imaging in both the supine and prone positions. Measurements were taken of the distance (mm) from the projected tip of a pedicle screw to the neighboring great vessels.Measurements were made at every other vertebral level from T3 to L5 by bisecting the pedicle in the transverse and sagittal planes and projecting the trajectory of a screw to the anterior cortex. We then evaluated great vessel position in relationship to the tip of the projected pedicle screw at the anterior cortex in the supine and prone orientations. RESULTS: The vessels were found to lie in a range of 2 to 10 mm from the anterior cortex. The comparison between the supine and prone positions showed that the great vessels in the lumbar region are held securely by the surrounding soft tissue. However, in the thoracic spine, anterior excursion does occur, just not as we expected. The aorta moves anteriorly while prone by 1.4 to 5 mm; however, its movement causes it to slide forward along the vertebra, shortening the distance to the anterior cortex. As a result, the screw trajectory is in a riskier geographic location. In the thoracolumbar area, the inferior vena cava translates 1.7 to 2.9 mm. CONCLUSIONS: These data suggest that the risks of vascular injury from anterior cortical fixation of the vertebra using pedicle screws placed posteriorly in the prone position are apparent. In the lumbar region, the upper thoracic region around the aortic arch, and the thoracolumbar junction the great vessels remain close to the vertebra. While in the mid-thoracic region, the aorta moves closer to the area of screw penetration anteriorly when the subject is prone. CLINICAL RELEVANCE: Spine surgeons commonly attempt pedicle screw placement into the anterior cortex of the vertebral body. Our study helps elucidate the inherent risks of this technique due to vessel positioning when prone.

Computer Assisted Cobb Angle Measurements: A novel algorithm.

BACKGROUND: The standard for evaluating scoliosis is PA radiographs using Cobb angle to measure curve magnitude. Newer PACS systems allow easier Cobb angle calculations, but have not improved inter/intra observer precision of measurement. Cobb angle and its progression are important to determine treatment; therefore, angle variability is not optimal. This study seeks to demonstrate that a performance equivalent to that achieved in the manual method is possible using a novel computer algorithm with limited user input. The authors compared Cobb angles from predetermined spinal levels in the average attending score versus the computer assisted approach. METHODS: Retrospective analysis of PA radiographs from 58 patients previously evaluated for scoliosis was collected. Predesignated spinal levels (e.g., T2-T10) were assigned for different curves and calculated by Cobb method. Four spine surgeons evaluated these Cobb angles. Their average scores were measured and compared to formulated values using the novel computer-based algorithm. Literature reports inter-observer reliability is 6.3-7.2degrees. Limits of accuracy were set at 5 degrees of average orthopedic surgeons' score. RESULTS: The computer-based algorithm calculated Cobb angles within 5 degrees of orthopedic surgeons' average with a standard deviation of 3.2 degrees. This result was based on a 95% confidence interval with p values <0.001. The computer algorithm was plotted against average angle determined by the surgeons, with individual determinations and linear regression (r2 =0.90). The average difference between surgeons' measures and computer algorithm was 0.4 degrees(SD= 3.2degrees, n=79). There was a tendency for the computer algorithm program to overestimate the angle at larger angles, but difference was small with r2 = 0.09. CONCLUSIONS: Our study showed the novel computer based algorithm was an efficient and reliable method to assess scoliotic curvature in the coronal plane with the possibility of expediting clinic visits, ensuring reliability of calculation and decreasing patient exposure to radiation. Level of Evidence: III.

Fifteen to twenty-five year functional outcomes of twenty-two patients treated with posterior Cotrel-Dubousset type instrumentation: a limited but detailed review of outcomes.

BACKGROUND: Long-term outcomes of patients undergoing extensive fusions for adolescent idiopathic scoliosis (AIS) have conflicting results. Moskowitz found uninstrumented scoliosis fusion patients had similar back pain as a normal age matched population. Recently, long-term outcomes of patients with Harrington rod instrumentation were reviewed and found similar functional outcome scores to non-scoliosis patients, with trending toward worse outcomes when fusions extended to L4. Our study examined long-term functional outcomes of patients treated with Cotrel-Dubousset (CD) instrumentation and determined whether distal level of instrumented fusion (L4 and L5) correlate with increased back pain or lower functional level. METHODS: Retrospective review of AIS surgeries from 1986 to 1996 was undertaken. Patient demographics and surgical data were collected via case-note audit. Patients were contacted and asked to complete a series of functional outcome questionnaires including visual analog scales (VAS) for pain, Short-Form 36 (SF-36), Scoliosis Research Society 22 (SRS-22) and Oswestry Disability Index (ODI) for function. ANOVA technique categorically compared outcome scores to most distal levels of fusion. Linear regression compared patient reported outcomes to time elapsed since surgery. Statistical significance was p < 0.05. RESULTS: One hundred twelve patients were identified, 50 patients were contacted, and 22 agreed to participation and completed a full assessment. Follow-up time since surgery ranged from 15 to 26 years and age ranged from 30 to 43 years. Six patients reported daily VAS back pain of ≥5; with a mean of 2.5. Back pain was not associated with level of distal fusion (p = 0.92). ODI was 15.36, with six patients' ODI >20. No relationship was shown between ODI and distal level of fusion (p = 0.72). SF-36 and SRS 22 values were also not related to distal level of instrumentation. Patient reported VAS back pain scores (r(2) = 0.18, p = 0.05), ODI (r(2) = 0.09, p = 0.17), and SF-36 and SRS-22 were not worse in patients with longer follow-up over time. Back pain and certain functional score subcategories of the SF-36 and SRS-22 trended toward improved results over time. CONCLUSIONS: Most patients who underwent multi-segment spinal fixation appeared to do well long-term, with minimal back pain. Lowest instrumented segment did not appear to be associated with increased back pain after 15 to 25 years follow-up.

Spinal cord compression in pseudohypoparathyroidism.

BACKGROUND CONTEXT: Spinal cord compression associated with pseudohypoparathyroidism (PHP) is an increasingly reported sequelae of the underlying metabolic syndrome. The association of neurologic dysfunction with PHP is not well appreciated. We believe this to be secondary to a combination of underlying congenital stenosis, manifest by short pedicles secondary to premature physeal closure, and hypertrophic ossification of the vertebral bony and ligamentous complexes. PURPOSE: The purpose of this case report is to review the case of spinal stenosis in a child with PHP Type Ia. We are aware of only eight published reports of patients with PHP Type Ia and spinal stenosis-there are only two previously known cases of pediatric spinal stenosis secondary to PHP. STUDY DESIGN/SETTING: This is a case report detailing the symptoms, diagnosis, interventions, complications, and ultimate outcomes of a pediatric patient undergoing spinal decompression and fusion for symptomatic stenosis secondary to PHP Type Ia. Literature search was reviewed regarding the reports of spinal stenosis and PHP, and the results are culminated and discussed. PATIENT SAMPLE: We report on a 14-year-old obese male with PHP and progressive lower extremity weakness secondary to congenital spinal stenosis. Examination revealed functional upper extremities with spastic paraplegia of bilateral lower extremities. The patient's neurologic function was cautiously monitored, but he deteriorated to a bed-bound state, preoperatively. METHODS: The patient's chart was reviewed, summarized, and presented. Literature was searched using cross-reference of PHP and the terms "spinal stenosis," "myelopathy", "myelopathic," and "spinal cord compression." All relevant case reports were reviewed, and the results are discussed herein. RESULTS: The patient underwent decompression and instrumented fusion of T2-T11. He improved significantly with regard to lower extremity function, achieving unassisted ambulation function after extensive rehabilitation. Results from surgical decompression in previously reported cases are mixed, ranging from full recovery to iatrogenic paraplegia. CONCLUSIONS: The association of neurologic dysfunction with PHP is not well appreciated. It is important to highlight this rare association. Surgical decompression in patients with PHP yields mixed results but may be of greatest efficacy in younger patients who receive early intervention.

Small intestinal submucosa for anular defect closure: long-term response in an in vivo sheep model.

STUDY DESIGN: After undergoing anulotomy, lumbar intervertebral discs from sheep were treated with small intestinal submucosa (SIS) and assessed functionally at 24 weeks after surgery. OBJECTIVE: To determine the efficacy of an SIS-based patch and plug scaffold to facilitate anular defect closure and anular functional recovery after anulotomy and partial discectomy. SUMMARY OF BACKGROUND DATA: The incidence of reherniation following discectomy remains high and mechanical means of anular closure have met with limited success. SIS is a naturally occurring collagen-based material, which acts as a resorbable scaffold in vivo that promotes soft tissue regeneration. METHODS: Twelve sheep underwent retroperitoneal exposure of the lumbar spine. Three levels were assigned to either: no additional procedure, box anulotomy alone, or box anulotomy followed by placement of an SIS "patch and plug" anchored by titanium bone screws. At 26 weeks after surgery, 18 motion segments underwent pressure-volume testing to assess the competency of the anulus. High resolution MRI images were taken of the remaining 18 segments. Undecalcified histology was conducted on all specimens. RESULTS: Radiographs, MRI images, and histology indicate that there was an exuberant tissue response at SIS-treated levels. New tissue formation in SIS-treated specimens was integrated well with the native anulus, but did not resemble the organization of native anulus. The extent of anular closure was substantial enough to allow the disc a functional recovery to a mean 66% of its capacity to develop internal pressure. MRI images indicate that SIS-treated levels did not maintain signal intensity comparable to exposure-only (intact) levels, but SIS-treated discs were statistically significantly higher than anulotomy-only levels. CONCLUSION: SIS-treated discs were better able to maintain hydration and resulted in a functional recovery relative to anulotomy alone levels. The SIS patch and plug reduced the cascade of functional degeneration that an intervertebral disc undergoes following anulotomy.

Epidural granuloma arising from epidural catheter placement.

Indwelling epidural catheter placement for prolonged drug delivery or is commonplace. Epidural catheter placement leading to a subsequent epidural mass is infrequently symptomatic and thus not often sought after or uncovered. Such masses can mimic lesions causing tumor, infection, and inflammation, and when found, the etiology of granuloma formation is unclear. This article describes a case of a benign epidural granuloma masquerading as an epidural tumor thought to be caused by epidural catheter placement for postoperative total hip replacement pain control. After symptoms of mechanical and radiculopathic pain arose, the patient underwent an open biopsy, spinal decompression, and intradural exploration as an MRI evaluation identified a mass in the spinal canal. Pathologic examination identified a benign fibrous granuloma. At 36-month follow-up, there was no evidence of symptom or tumor recurrence.

Pregnancy after anterior spinal surgery: fertility, cesarean-section rate, and the use of neuraxial anesthesia.

BACKGROUND CONTEXT: Previous publications have reported results with respect to functional outcome and sexual function in young women after traumatic injuries to the pelvis. It is well known that anterior spinal surgery has the possibility of causing reproductive dysfunction in men. Little has been described concerning deleterious effects of anterior spinal surgery in women of childbearing age. PURPOSE: The purpose of the study was to determine the fertility, cesarean section rate, and the use of neuraxial anesthesia in a population of women of childbearing age who have undergone anterior spinal surgery. STUDY DESIGN/SETTING: This was a retrospective chart review combined with a telephone questionnaire of the patients who had undergone anterior spinal surgery by a single orthopedic surgeon. METHODS: Demographic data were collected from hospital and office records. Patients were asked if they had tried to become pregnant, if their pregnancy had come to term, the use of spinal or epidural anesthesia for that labor and delivery, and the type of delivery. RESULTS: Seventy-nine potential subjects were identified and 67 patients were contacted to determine their fertility status. Ninteen patients had tried to become pregnant after their anterior spinal surgery. All patients who reported that they tried to become pregnant were successful at having a child. Seven of the 19 women had children who were born by cesarean section (37%). Only two patients received an epidural as analgesia for their delivery. CONCLUSIONS: Although the cesarean-section rate appears high, it is consistent with the current obstetrical trends. Anesthesiologists appear less inclined to offer neuraxial anesthesia to a population which has undergone anterior spinal surgery.

Effect of kyphoplasty on survival after vertebral compression fractures.

BACKGROUND: A growing population of patients with osteoporosis and fragility fractures has developed. Fragility fractures, including vertebral compression fractures, have been associated with increased mortality. Early operative interventions for patients sustaining hip fractures have been found to reduce mortality. PURPOSE: To determine if kyphoplasty improves survival after vertebral compression fractures. STUDY DESIGN: A retrospective chart review of all kyphoplasty procedures performed by the same orthopedic surgeon between June 2000 and June 2004 and a review of patients receiving nonoperative care consisting of oral analgesia and an orthosis during the same time period were conducted. PATIENT SAMPLE: Patients seen by a single surgeon for an osteoporotic vertebral body fracture. OUTCOME MEASURES: The primary outcome measured was patient death within the study time period. METHODS: Data from both groups were tabulated and analyzed for statistical differences by Student t test and chi-squared analysis. Kaplan-Meier curves comparing age, medical comorbidity, and surgical intervention were constructed. Log-rank test was used to analyze the survival curves. RESULTS: Of the 94 patients who elected for kyphoplasty, 38 patients were deceased at the close of the current study which ended in September 2006, whereas 26 of the 90 patients who elected for conservative therapy had died. Student t test revealed a significant age difference between patients treated with kyphoplasty and those who were treated nonoperatively (p=.0002). Chi-squared analysis revealed a significant difference between the two populations with respect to Charlson score (p=.050) but no statistical difference between the two populations with respect to ASA (p=.81) or gender (p=.1207). Kaplan-Meier curves were constructed to independently assess the influence of age, medical comorbidity, and kyphoplasty on survival. A significant relationship was detected by log-rank test for age (p=.0172), ASA (p=.0497), and Charlson score (p=.0015) but not treatment with kyphoplasty (p=.1037). An age-adjusted mortality rate was calculated and was found to be 35.3 per 1,000 patient-years for the conservative treatment population and 40.1 for the surgical population. A multivariate analysis comparing age, comorbidity, and surgical treatment with survival did not detect a statistical relationship. CONCLUSION: Kyphoplasty did not seem to effect the survival of patients with a vertebral compression fracture.

Novel lumbosacral axial fixation techniques.

For patients with low back pain secondary to pathological motion of an unstable lumbar motion segment, interbody fusion may be indicated. Numerous open and minimally invasive techniques have been traditionally used, but all suffer from shortcomings related to biomechanics or inherent iatrogenic destabilization. A novel transaxial approach to the lumbosacral junction has recently been described which appears to obviate many of the limitations of previous techniques. Preliminary results of the transaxial approach to lumbosacral fixation appear promising.

Ganglioneuroma with scoliosis of the thoracic spine: a case report.

BACKGROUND CONTEXT: Ganglioneuroma is a benign tumor of neural crest origin that may provoke a scoliosis as well as neurological symptoms. Treatment includes resection with possible spinal fusion for instability and close follow-up for many years. PURPOSE: The purpose is to report an invasive ganglioneuroma that was successfully treated by resection without spinal fusion. STUDY DESIGN/SETTING: Case report. PATIENT SAMPLE: A 15-year-old white female. OUTCOME MEASURES: Resolution of the patient's back pain with radiographic and clinical follow-up for recurrence of the tumor. METHODS: Not applicable. RESULTS: The patient experienced resolution of her back pain without recurrence of the tumor. CONCLUSIONS: This is a rare benign tumor that was effectively treated with surgical resection and without spinal fusion.

Biomechanical evaluation of a novel lumbosacral axial fixation device.

BACKGROUND: Interbody arthrodesis is employed in the lumbar spine to eliminate painful motion and achieve stability through bony fusion. Bone grafts, metal cages, composite spacers, and growth factors are available and can be placed through traditional open techniques or minimally invasively. Whether placed anteriorly, posteriorly, or laterally, insertion of these implants necessitates compromise of the anulus--an inherently destabilizing procedure. A new axial percutaneous approach to the lumbosacral spine has been described. Using this technique, vertical access to the lumbosacral spine is achieved percutaneously via the presacral space. An implant that can be placed across a motion segment without compromise to the anulus avoids surgical destabilization and may be advantageous for interbody arthrodesis. The purpose of this study was to evaluate the in vitro biomechanical performance of the axial fixation rod, an anulus sparing, centrally placed interbody fusion implant for motion segment stabilization. METHOD OF APPROACH: Twenty-four bovine lumbar motion segments were mechanically tested using an unconstrainedflexibility protocol in sagittal and lateral bending, and torsion. Motion segments were also tested in axial compression. Each specimen was tested in an intact state, then drilled (simulating a transaxial approach to the lumbosacral spine), then with one of two axial fixation rods placed in the spine for stabilization. The range of motion, bending stiffness, and axial compressive stiffness were determined for each test condition. Results were compared to those previously reported for femoral ring allografts, bone dowels, BAK and BAK Proximity cages, Ray TFC, Brantigan ALIF and TLIF implants, the InFix Device, Danek TIBFD, single and double Harms cages, and Kaneda, Isola, and University plating systems. RESULTS: While axial drilling of specimens had little effect on stiffness and range of motion, specimens implanted with the axial fixation rod exhibited significant increases in stiffness and decreases in range of motion relative to intact state. When compared to existing anterior, posterior, and interbody instrumentation, lateral and sagittal bending stiffness of the axial fixation rod exceeded that of all other interbody devices, while stiffness in extension and axial compression were comparable to plate and rod constructs. Torsional stiffness was comparable to other interbody constructs and slightly lower than plate and rod constructs. CONCLUSIONS: For stabilization of the L5-S1 motion segment, axial placement of implants offers potential benefits relative to traditional exposures. The preliminary biomechanical data from this study indicate that the axial fixation rod compares favorably to other devices and may be suitable to reduce pathologic motion at L5-S1, thus promoting bony fusion.

Surgeon perceptions of the complications and value of threaded fusion cages as a spine fusion technique: results of a consensus survey.

BACKGROUND CONTEXT: Threaded cage technology has had a meteoric rise in usage. It has been touted as a procedure with low risk and minimal complications. PURPOSE: To gauge the spine surgical community's general consensus regarding cage usage and its complications. STUDY DESIGN/SETTING: A canvassing questionnaire regarding threaded cage usage and complications was sent to members of the North American Spine Society. PATIENT SAMPLE: A total of 665 doctors reported on their perception of 22,585 cages placed by the second year after pre-market approval from the Food and Drug Administration approval. OUTCOME MEASURES: A nonscientific canvassing questionnaire was thought to give a consensus of surgical outcome perception in a large number of caregivers with hopes of understanding general trends. METHODS: Simple statistical measurements were used to report perceived complications by surgeons involved in performing threaded cage surgical procedures. RESULTS: Sixty-nine percent of doctors reported at least one complication with threaded cages, but the complication incidence was low. Visceral injuries were reported in 0.1%; vascular injuries, 1.0%; cage displacement and dislodgement, 1.4%; temporary and permanent neurologic injuries, 2.25% and 0.56%, respectively; infection 0.34%; retrograde ejaculation 1.2% and revision surgery recorded for 2.7%. Those rating cages as fair to poor (16.5%) were those physicians reporting the longest experience with this technology. CONCLUSIONS: The general consensus is that threaded cages have low complication rates and high satisfaction rates, 83.5%. The data represent a convenience sampling and is not scientific.

A pilot study to evaluate the effectiveness of small intestinal submucosa used to repair spinal ligaments in the goat.

BACKGROUND CONTEXT: Destabilization of the lumbar spine results from sacrifice of the anterior longitudinal ligament and disc when removed for graft or cage placement. In a similar fashion, transection of the interspinous ligament during surgical approaches to the posterior spine may result in segmental instability. Such instability can cause abnormal motion or implant migration resulting in a higher incidence of pseudarthrosis. Small intestinal submucosa (SIS) is a naturally occurring extracellular collagen-based matrix, which is derived from porcine small intestine. SIS contains cytokines and growth factors and has been shown to act as a resorbable scaffold in vivo that promotes host soft tissue regeneration with little scar tissue formation. SIS can be manufactured in laminated sheets of various sizes and thicknesses for different indications. Successful applications of SIS in animals have included dural substitution, rotator cuff repair, vessel repair, abdominal and bladder wall repair, and others. However, SIS has not been investigated to determine its ability to facilitate regeneration of spinal ligaments. PURPOSE: The purpose of this pilot study was to evaluate the efficacy of SIS as a barrier to prevent interbody device migration, and to act as a scaffold for regeneration of the anterior longitudinal ligament (ALL) and posterior interspinous ligament (PISL) in a goat model. STUDY DESIGN/SETTING: The thoracolumbar spine of the goat was exposed surgically. After resection and removal of the ALL or PISL at alternating levels, either SIS was placed or no treatment was administered. New ligament formation and SIS resorption were monitored over a 12-week period. OUTCOME MEASURES: Plain film radiographs and histomorphometry were used to assess the progress of healing over a 12-week time period. METHODS: Four skeletally mature nubian-alpine crossbred goats were used in this study. Under general anesthesia, each T10 to L5 motion segment was exposed surgically. Both anterolateral and posterior approaches were performed simultaneously at each level. Anteriorly, alternating levels received either 1) anterior discectomy, sacrifice of ALL and placement of SIS (SIS group); 2) anterior discectomy, sacrifice of ALL and no SIS (surgical control group) or 3) no surgical intervention (nonoperative group). A solid interbody spacer was placed into the disc space after discectomy to deter spontaneous anterior interbody fusion. Posteriorly, alternating levels were treated with either 1) sacrifice of the PISL with placement of SIS (SIS group); 2) sacrifice of PISL and no SIS (surgical control group) or 3) no surgical intervention (nonoperative group). The SIS was secured to the adjacent superior and inferior spinous processes to create a tension-band effect. Animals were radiographed immediately postoperatively to confirm placement of interbody spacers and anchors and to serve as a baseline for monitoring interbody spacer positioning. After surgery, all animals were allowed unrestricted motion for 12 weeks. At the end of the 12-week period, animals were radiographed and euthanized. The lumbar spine was harvested en bloc and processed for decalcified histologic evaluation. The dorsal and ventral aspects of each motion segment were analyzed for signs of inflammation and scar tissue formation, residual SIS and regenerated ALL or PISL. RESULTS: All animals tolerated the surgical procedure well, and there were no intraoperative or anesthesia-related complications. Twelve-week radiographs showed some evidence of ventral migration of the interbody spacers in several animals. Fifty percent (two of four) of spacers in surgical control group levels had migrated more than 10 mm (resulting in complete migration out of the disc space), whereas no spacers migrated completely out of levels with SIS placed. Gross analysis at necropsy indicated iatrogenic scar formation at operated levels, the degree of which was not different from surgical control group to SIS levels. Histologic evaluation of areas where the ALL had been removed indicated formation of organized fibrilar collagenous tissue that spanned the disc space at some levels where the SIS was placed. In some cases, the newly formed tissue was approximately the thickness of the ALL at the nonoperative group levels. The newly formed collagenous tissue was accompanied by sparse focal areas of inflammation, with small fragments of residual SIS at some levels. At surgical control group levels, there was a varying degree of connective tissue that ranged from moderately organized to randomly oriented with no significant signs of inflammation. Similarly, histologic analysis of some levels where SIS was placed posteriorly showed formation of organized collagenous tissues where the PISL had been removed. CONCLUSIONS: In this model, the SIS patch was sufficient to prevent acute ventral migration of interbody spacers from the disc space. The extent of long-term healing and new tissue formation in the SIS group indicates that it may be efficacious as a reparative intervention for transected ligaments in the spine. Most SIS specimens showed formation of organized collagenous tissue, indicating a long-term potential for ligament formation. However, in this model, 12 weeks of postoperative healing is insufficient to assess the full potential of SIS as a spinal ligament repair. Further research that follows the healing process to a longer time point postoperatively may be necessary to fully understand the potential of SIS as a resorbable scaffold for tissue replacement.