Effect of vertebroplasty on the compressive strength of vertebral bodies

Proceedings of the NASS 17th Annual Meeting / The Spine Journal 2 (2002) 47S–128S Relationship between findings and existing knowledge: The formation of the dense, fibrous laminectomy membrane after lumbar surgery may be a strong indicator of persistent pain, morbidity, slow recovery and poor outcomes. Because this membrane is adherent to the dura and overlying muscles, it increases the technical difficulty of dissection in subsequent surgical procedures. Several antifibrotic agents as well as barrier materials have been investigated as techniques for the inhibition or neutralization of postlaminectomy fibrous scar tissue formation. Overall significance of findings: Sites treated separately with Adcon-L or fat exhibited the least amount of scar. Fibrous tissue was decreased in both these sites when compared with surgery alone. The greatest amount of scar was typically observed in sites treated with ACS or for untreated laminectomy sites. The findings from this pilot study indicate potential use of antifibrotics or fat independently in the reduction of postlaminectomy scar tissue formation and warrant consideration for future studies. Disclosures: Device or drug: Preclude. Status: approved. Device or drug: Adcon-L. Status: approved. Device or drug: absorbable collagen sponge. Status: approved. Conflict of interest: No conflicts. PII: S1529-9430(02)00218-8

Autologous activated macrophage therapy shows potential as a treatment for acute complete spinal cord injury Nachshon Knoller 1, Moshe Hadani 1, J. Brotchi 2, Zvi Rappaport 3, Gabi Zelig 1, Josef Attias 3, Balenti Fulga 4; 1Sheba Medical Center, TelHashomer, Israel; 2Erasme Hospital, Brussels, Belgium; 3Rabin Medical Center, Petah-Tikva, Israel; 4Proneuron Biotechnologies, Rehovot, Israel Purpose of study: Complete spinal cord injury is a devastating and, until now, almost untreatable condition. Experiments showing central nervous system regeneration and partial functional recovery in rats [1] served as proof of principle. Safety and efficacy have been demonstrated in extensive preclinical experiments that continue to produce promising results. Methods used: A phase 1 clinical trial is underway, involving eight patients with acute complete spinal cord injury (ASIA A). The treatment consists of activating autologous macrophages derived from the patient’s peripheral blood and administering them into the parenchyma of the spinal cord within 14 days of injury. The follow-up consists of neurological, electrophysiological, rehabilitation and quality-of-life assessments. The patient outcomes are compared with historical controls. Summary of findings: Eight patients have been followed for up to 30 months, depending on the date of treatment. In none of them short- or long-term side effects that could be linked to the experimental treatment were detected. Of these eight patients, the three patients who have been followed for more than 6 months exhibit partial recovery of sensory and motor function and have upgraded their ASIA classification from ASIA A to ASIA C. These clinical findings are also supported by elctrophysiological examinations. Relationship between findings and existing knowledge: This phase 1 also proves that the results in rats (as described by Rapalino et al. [1]) can be mimicked in human. Overall significance of findings: Based on the interim results of this small sample, it is proposed that autologous activated macrophage therapy can be an effective treatment for complete spinal cord injury. Disclosures: Device or drug: activated macrophage. Status: investigational. Conflict of interest: Nachshon Knoller, grant research support for study initiation: and consultant. Reference [1] Rapalino et al. Nat Med 1998;4:814–21. PII: S1529-9430(02)00217-6

Attenuation of CNTF in ASCI treated with intravenous methylprednisolone A. Merola1, Haher, MD1, M. O’Brien, MD1, A. Lamba1, Castro, MD1, F. Vigna, MD1, S. Mathur, MD1, M. Brkaric, MD1, D. Smith, MD1,

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G. Chejfec1, J. Eule1, N.J. Espat1; 1Saint Vincents Medical Centers of NY, New York, NY, USA Purpose of study: The effect(s) of steroid administration on secondpathway mediators associated with inflammation and repair after spinal cord injury have not been well characterized. CNTF, an interlekin-6 superfamily protein associated with neuronal repair and regeneration is one such mediator. We hypothesized that methylprednisolone (MP) administration is a standard model of ASCI would inhibit CNTF expression at the site of injury. Methods used: Sprague-Dawley rats (n24) were randomly divided into MP-treated and control groups. Paraplegia after lower thoracic laminectomy was achieved using a standardized weight drop technique. MP rats were treated with a human dose equivalent MP continuous infusion for 23 hours. Spinal cords were harvested at variable timed intervals from both groups and prepared for histologic/immunohistochemical evaluation. Summary of findings: Representative stained spinal cord sections prepared with a specific CNTF antibody (24 hours post ASCI); MP-treated and CTNF  neurons are not observed; control section demonstrates significant CNTF staining. At both 0 and 8 hours after injury, the MP-treated group and the control group demonstrated negative CNTF staining. At 24 and 48 hours, respectively, a consistent staining trend was appreciated. The control group exhibited a positive CNTF reaction, whereas the MP group did not. Relationship between findings and existing knowledge: In the present experiment, MP treatment in a model of ASCI led to histologically evident inhibition of CNTF in spinal cord tissue by immunohistochemistry 24 to 48 hours after injury. Overall significance of findings: The known role of CNTF as a neuronal repair and regenerative cytokine supports future studies to evaluate MP dosing regimens that inhibit spinal cord edema while optimizing CNTF expression. Disclosures: No disclosures. Conflict of interest: No conflicts.

PII: S1529-9430(02)00216-4

Effect of vertebroplasty on the compressive strength of vertebral bodies Siros Pheumaticos, MD, PhD1, Nguyen Lyndon, MS1, John Hipp, PhD2, Jason Stein, BS1, Michael Heggeness, MD, PhD1; 1Baylor College of Medicine, Houston, TX, USA; 2Medical Metrics, Inc., Houston, TX, USA Purpose of study: To compare the effect of vertebroplasty on the compressive strength of unfractured vertebral bodies. Methods used: Four cadaveric thoracic spines were used for this experiment, for a total of 40 vertebral bodies. Before testing, each thoracic spine was submitted to bone density testing and a radiographic evaluation to rule out any obvious fractures. Under image intensification, 6 ml of a mixture of polymethylmethacrylate (PMMA) with barium was injected into every other vertebral body of each spine specimen. After vertebroplasty, all soft tissues were dissected from the spine and the vertebral bodies were separated and potted into circular fames to allow for mechanical testing. Testing to failure was performed using a combination of axial compression and anterior flexion movements. Two pneumatic cylinders applied anterior and posterior loads at a distance ratio of 4:3 relative to the anterior vertebral body wall while two additional cylinders applied lateral loads, each at a constant rate of 200 N/second. Summary of findings: Average failure load for nonvertebroplasty specimens was 6,724.023,291.70 N, whereas the specimens injected with PMMA failed at an average compressive force of 5,770.502,133.72 N. No statistically significant difference in failure loads could be found between intact specimens and those that had undergone vertebroplasty. Relationship between findings and existing knowledge: Vertebroplasty is gaining popularity as a treatment for osteoporosis-related problems. We are not aware of any previous biomechanical studies on the effect of PMMA injection on the vertebral compressive strength. Overall significance of findings: We were surprised to note that under these loading conditions, no significant increase in compressive strength of

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the vertebral bodies could be documented. This suggests that some caution be applied to the concept of “prophylactic” vertebroplasty in patients at risk for fracture. Disclosures: No disclosures. Conflict of interest: No conflicts. PII: S1529-9430(02)00215-2

Validity and responsiveness of Short Form 12-item survey in patients with back pain Xuemei Luo, PhD1, Mandy George, BS1, William Richardson, MD1, Lloyd Hey, MD, MS1; Duke University, Durham, NC, USA Purpose of study: There is a growing recognition in the area of back pain research that evaluation of health-related quality of life (HRQL) is important for assessing the treatment effectiveness and for making clinical decisions. Numerous measures have been developed to assess HRQL. Among them, Short Form 12-item survey (SF-12) has become many back pain researchers’ top choice, because this instrument is much shorter than many other HRQL measures and can significantly reduce the burden of respondents and the cost for data collection. Despite its widespread use, the validity and responsiveness of SF-12 in patients with back pain have not been well established. The purpose of this study is to evaluate the validity and responsiveness of SF-12 in patients with back pain. Methods used: Starting from January 1998, patients who consulted the Duke University Spine Center were asked to complete a comprehensive computerized survey questionnaire. The questionnaire included SF-12, Oswestry Back Disability Index and questions concerning patients’ demographic characteristics, psychosocioeconomic status, medical history, present spine symptoms and the severity of back pain. A total of 2,520 patients who indicated in their first surveys that they had back pain were included in the validity study. Of these patients, 506 completed another survey in 3 to 6 months of follow-up and were used for assessing the responsiveness of SF-12. Only construct validity was evaluated, because content validity has been established, and the current lack of the “gold standard” for HRQL measure makes it difficult to determine the criteria validity. Construct validity was evaluated by assessing the correlation between the two summary scales of SF-12 and six other measures theoretically related or unrelated to these scales. Summary of findings: Physical component summary of SF-12 (PSC-12) was significantly correlated with age, back pain, measures of overall well being and Oswestry Back Disability Index. Mental component summary of SF-12 (MCS-12) was significantly correlated with stress, depression, back pain, measures of overall well being and Oswestry Back Disability Index. Both PCS and MCS performed as expected without exception, demonstrating the construct validity of SF-12. The responsiveness of SF-12 was supported by several pieces of evidence. First, the changes in PCS-12 and MCS-12 were significantly correlated with the changes in back pain intensity. Second, for patients whose back pain improved, there was a significant increase in the follow-up PCS-12 and MCS-12 as compared with the baseline. Third, in the group whose back pain became improved or became worse, small to large effect size was obtained for PCS-12 or MCS-12. Relationship between findings and existing knowledge: To our knowledge, the current study is the first to evaluate the validity and responsiveness of SF-12 in patients with back pain. Overall Significance of findings: The current study demonstrated that SF-12 was a valid and responsive instrument for measuring health status or HRQL in patients with back pain. Given its brevity and the current findings, SF-12 may be considered as a useful outcome tool in the future back pain research. Disclosures: No disclosures. Conflict of interest: No conflicts. PII: S1529-9430(02)00214-0

Cervical stability with lateral mass plating: unicortical versus bicortical screw purchase Anthony Muffoletto, MD1, Walt Simmons Ii, II, MD2, Jinping Yang, MD2 Kim Garges, MD2, Mukta Vadhva, MD2, Alexander Hadjipavlou, MD3

1

University of Texas Medical Branch at Galveston, Galveston, TX, USA; University of Texas Medical Branch, Galveston, TX, USA; 3University of Crete, Iraklion, Iraklion, Crete, Greece;

2

Purpose of study: The purpose of this study was to determine if there is a significant difference in stability between cervical spines instrumented with lateral mass plates affixed with unicortical versus bicortical Magerl screws. Methods used: Eleven human, cadaveric, cervical spines were harvested and radiographed, and all soft tissues except for supporting ligamentous structures were removed. Segments C3 through C5 were mounted in polymethylmethacrylate and instrumented segmentally with Axis lateral mass plates (Medtronic Sofamor-Danek) and screws using the Magerl technique. Fixation in the lateral masses was either bicortical (21 mm screws) or unicortical. Bicortical constructs were tested in all 11 spines. Unicortical constructs were subdivided into short screws (10 mm) in six specimens and long screws (up to but not through anterior cortex) in eight specimens. Nondestructive testing, using an MTS Bionix 858 machine, was carried out in flexion, extension, axial rotation and lateral bending at 0.45, 0.9, 1.35 and 1.8 Nm, respectively. Loads were applied sinusoidally, and data were recorded on the third cycle. The tests were then repeated after C3–C5 laminectomy. Analysis of variance was used to determine differences in construct stability. A p value of .05 was considered significant. Summary of findings: There were no significant differences in stability between bicortical and long unicortical constructs in flexion, extension or axial torsion either with or without laminectomy. In lateral bending, bicortical and long unicortical constructs demonstrated a significant difference in stability but only after laminectomy (p.0004). Short unicortical screw constructs demonstrated less stability without laminectomy in lateral bending (p.0001), and with laminectomy in all bending modes: flexion/extension (p.038), torsion (p.005) and lateral bending (p.0004). Bicortical screw constructs yielded equal or greater average stiffness than the unicortical constructs in all modes of testing. Relationship between findings and existing knowledge: Virtually all authors have recommended bicortical lateral mass screw purchase since the technique was first described by Roy-Camille. Bicortical fixation is associated with a small but finite risk of injury to the cervical neurovascular structures. Unicortical screw purchase should decrease or even eliminate these complications. Our results suggest that unicortical purchase using the Magerl technique allows for a biomechanically stable lateral mass plate construct, especially when the unicortical screw length is maximized. Clinical studies are necessary before recommending screw fixation. Overall significance of findings: Cervical lateral mass fixation with long, unicortical Magerl screws (up to but not through the anterior lateral mass cortex) may allow for a biomechanically stable construct while minimizing or even eliminating risk to cervical neurovascular structures. Disclosures: Device or drug: Axis lateral mass plates (Medtronic SofamorDanek). Status: Not approved. Conflict of interest: Anthony Muffoletto, AAS lateral mass instrumentation supplied by Medtronic Sofamor Danek. PII: S1529-9430(02)00213-9

Thursday, October 31, 2002 3:16–3:46 PM Select Poster Presentations Preoperative and postoperative computer tomography evaluation of structures at risk with anterior spinal fusion Timothy Kuklo, MD1, Ronald Lehman, Jr., MD1, Lawrence Lenke, MD2; 1 Walter Reed Army Medical Center, Washington, DC, USA; 2Washington University in St. Louis, Saint Louis, MO, USA Purpose of study: With the increasing popularity of anterior spinal fusion (ASF) for AIS, there has also been an increasing concern over the proxim-