Thursday, October 31, 2002 3:16–3:46 pm Select Poster Presentations

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Proceedings of the NASS 17th Annual Meeting / The Spine Journal 2 (2002) 47S–128S

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-

Proceedings of the NASS 17th Annual Meeting / The Spine Journal 2 (2002) 47S–128S ity of the thoracic aorta (TA) to the screw tips and the possibility of vessel was erosion over time. This preoperative and postoperative computed tomograpy (CT) study attempts to define the relative position of the TA, and other vital structures in deformity patients, to the spine (preoperatively), as well as to the projected instrumentation (postoperatively) by level and curve magnitude. Methods used: Twenty consecutive patients (17 female, 3 male) with an average age of 14.5 years (range, 12.4 to 15.5 years) with AIS and a right main thoracic/Lenke 1 curve, average 55.2 degrees (range, 50 to 66 degrees; average apex T8), underwent preoperative and postoperative CT scans as part of their planned ASF. All images were analyzed for proximity (distance from the mid-vertebral body) and position to (as defined relative to the center of the vertebral body in the axial plane) the spine preoperatively and the projecting screw tip postoperatively. These were compared with 10 age-matched nondeformity thoracic CT scans to assess the relative position of the thoracic aorta to the vertebral bodies by level. Preoperative and postoperative plain radiographs were also analyzed for curve magnitude, correction and fusion levels to assess the possible effect of these variables on thoracic aorta proximity. Summary of findings: Postoperative curve magnitude averaged 26.9 degrees (range, 17 to 40 degrees; 51% correction) with an average follow-up of 4.1 years (range, 3.2 to 7.0 years) analyzing 151 screws (7.5 levels/patient). The trachea/main bronchi, esophagus and pleura were not found to be at risk. Screw to spinal canal distance averaged 5.3 mm (range, 3.5 to 8.2 mm), and 4.5 degrees (range, 11 to 15 degrees) from the coronal axis. Screw tip extrusion (distance beyond far cortex) averaged 2.8 mm (0 to 5 mm). Spine/screw tip to aorta distances are shown in Table 1. Table 1

Proximal (n20) Periapical (n40) Distal (n51)

Control

55 preop

55 postop

55 preop

55 postop

5.9 mm 5.1 mm 3.8 mm

5.1 mm 4.8 mm 5.0 mm

3.6 mm 2.0 mm1 2.4 mm1

4.1 mm 5.2 mm 3.8 mm

3.5 mm 1.6 mm1 2.2 mm1

denotes p  0.05

1

Additionally, 23 of 151 screws (15%) were thought to be adjacent to the TA with 4 of 60 proximal screws (7%) judged to be juxtaposed to the aorta, whereas 6 of 40 periapical screws (15%) and 13 of 51 distal screws (26%) were juxtaposed (p.05). There were no screws compressing (indenting) the aorta and no complications. Relationship between findings and existing knowledge: The course of the thoracic aorta may vary in individuals and in deformity. However, it generally moves from a relatively anterolateral position proximally, to posteromedial position at the apex, and then to a more anterior position distally. Consequently, the aorta moves closer to the screw tips both at the apex and distally, whereas the distal screws are more frequently juxtaposed to the descending aorta. Overall significance of findings: Because of the course of the thoracic aorta and the tethering effect of the diaphragm hiatus, the distal screws are frequently juxtaposed to the descending aorta in anterior spinal fusion. Disclosures: No disclosures. Conflict of interest: Lawrence Lenke, grant research support; consultant; and other support. PII: S1529-9430(02)00212-7

Occult intraspinal anomalies in association with an isolated congenital hemivertebra Phillip Belmont, Jr., MD1, Kenneth Taylor, MD1, Timothy Kuklo, MD1, Joh Prahinski, MD1, Richard Kruse, DO2; 1Walter Reed Hospital Army Medical Center, Washington, DC, USA; 2DuPont Hospital for Children, Wilmington, DE, USA

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Purpose of study: Previous studies have reported the high incidence of intraspinal anomalies in congenital scoliosis. However, various authors do not consider the presence of an isolated hemivertebra sufficient to warrant magnetic resonance imaging (MRI). To our knowledge, the incidence of intraspinal anomalies detected by MRI and the need for subsequent neurosurgical intervention comparing patients with a single hemivertebra versus patients with a complex pattern involving with hemivertebra at multiple levels or a hemivertebra coupled with a failure of segmentation is unknown. Methods used: A retrospective review over a10-year period (1988–1998) of physical examination findings and plain radiographs in patients presenting with congenital scoliosis and hemivertebra was conducted to correlate these results with the presence of intraspinal anomalies as detected by MRI and the need for subsequent neurosurgical intervention. Summary of findings: A total of 116 patients with congenital scoliosis and a curve that included at least one hemivertebra were identified, 76 of whom presented after 1988 and had an MRI. These patients were the subject of this study and had a mean age at presentation of 59 months (range, 1 to 198 months) with mean follow-up of 7.1 years (range 1 to 17 years). Twenty-nine had an isolated hemivertebra, and 47 had a complex hemivertebral pattern. Six patients (21%) with isolated hemivertebra compared with 11 patients (23%) with a complex hemivertebral pattern had an MRIdetected intraspinal anomaly (p.99). A positive history or physical examination finding was present in 41% of all patients and was of limited benefit in predicting the presence of intraspinal anomaly in either isolated hemivertebra (sensitivity, 67%; specificity, 43%) or complex hemivertebral patterns (sensitivity, 55%; specificity, 78%). Three patients with an isolated hemivertebra (10%) versus four patients with a complex hemivertebral pattern (9%) underwent neurosurgical intervention (p.88). All seven patients who underwent neurosurgical intervention has an MRI-detected intraspinal anomaly, and five (71%, two complex and three isolated) had either an abnormal history or physical examination finding. Relationship between findings and existing knowledge: Isolated hemivertebra and complex hemivertebral patterns have similar incidences of MRIdetected intraspinal anomalies and subsequent need for neurosurgical intervention. Therefore, we recommend obtaining an MRI for all cases of congenital scoliosis, including isolated hemivertebra. Overall significance of findings: Isolated hemivertebra and complex hemivertebral patterns have similar incidences of MRI-detected intraspinal anomalies and subsequent need for neurosurgical intervention. Therefore, we recommend an MRI even for isolated hemivertebra. Disclosures: No disclosures. Conflict of interest: No conflicts. PII: S1529-9430(02)00211-5

Longitudinal length of the spinal cord after cervical laminoplasty Toru Yokoyama, MD1, Kazumasa Ueyama, MD1, Akihiro Okada, MD1, Takashi Tomita, MD1; 1Department of Orthopedic Surgery, Hirosaki University, Hirosaki, Aomori, Japan Purpose of study: In cases of cervical myelopathy, the relationship between surgical outcome after laminoplasty and the sagittal alignment is controversial. In our cases with OPLL of unexpected poor surgical outcome, we often found a straight, tense spinal cord on postoperative magnetic resonance imaging, (MRI). So we tried to measure a longitudinal length of the cervical spinal cord (LSC) as a new parameter. The purpose of this study is to prove our hypothesis that an increase of LSC after cervical laminoplasty may be a risk factor for poor surgical outcome. Methods used: Thirty-six patients (24 male and 12 female) with cervical myelopathy were operated on at an age of 33 to 76 years (average, 59 years). The follow-up period was 12 to 86 months (average, 39 months). There were 25 patients in the laminoplasty (LP) group (13 cervical spondylotic myelopathy and 12 OPLL) and 11 in the anterior fusion (AT) group as control (8 cervical spondylotic myelopathy and 3 OPLL). There were no significant differences in the age, sex and follow-up period between the two groups. We evaluated surgical outcome with the recovery rate with the scoring system for cervical myelopathy of the Japanese Orthopedic Associ-