Proceedings of the NASS 20th Annual Meeting / The Spine Journal 5 (2005) 1S–189S 143S

the Flexicore group postoperatively was 5 degrees. Lateral bending averaged4 degrees preoperatively and 3 degrees after Flexicore disc replacement.CONCLUSIONS: These initial results demonstrate the Flexicore artificialdisc to compare very favorable to circumferential fusion for the treatmentof lumbar degenerative disc disease unresponsive to nonoperative treatment.DISCLOSURES: FDA device/drug: flexicore lumbar artificial disc. Status:Investigational/not approved.FDA device/drug: allograft bone. Status: Approved for this indication. FDAdevice/drug: pedicle screws.Status: Approved for this indicationCONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2005.05.284

P70. Dural tear and rootlet entrapment in the lumbar burstfractures associated with the laminar fractureJae Chul Lee, MD, Yon-Il Kim, MD, Byung-Joon Shin, MD;Soonchunhyang University Hospital, Seoul, South Korea

BACKGROUND CONTEXT: Lumbar burst fracture associated with ver-tical laminar fracture may have dural tears, and sometimes extruded nerverootlets may be caught between the fractured lamina. It is important tonotice a possibility of rootlet entrapment preoperatively to salvage theendangered neural elements.PURPOSE: To identify and predict dural tear and rootlet entrapment inpatients who had a burst fracture associated with laminar fracture andmoderate to severe canal encroachment.STUDY DESIGN/SETTING: A retrospective study; review of medicalrecords, operation records, and radiographs. The authors explored the duraand nerve roots condition intraoperatively.PATIENT SAMPLE: Seventeen laminectomies were performed for pa-tients who had a lumbar burst fracture and also had vertical laminar fractureassociated with moderate to severe canal encroachment (�60%).OUTCOME MEASURES: Patients were followed up with ASIA motorscore of the lower extremities and ability of bowel and bladder control.METHODS: A vertical osteotomy of the lamina contralateral to the frac-tured side was performed, and it was elevated like open-book laminoplasty toavoid a further injury. Extruded rootlets were reduced into the dural sac, andthe tear was repaired. The patients were divided into three groups by theoperative finding. Group I had no dural injury, group II had dural tear withrootlet extrusion, and group III had dural tear and entrapment of rootletsbetween the laminar fracture. No patient has a dural tear without rootletextrusion. To identify the predictive factors, the following were also evalu-ated: fracture level, preoperative motor scores, ability of bowel and bladdercontrol, and radiologic findings in the axial images of CT or MRI suchas contour of dural sac, deviation of epidural fat, and gap between thecleavage fracture of vertebral body.RESULTS: There were 5 patients in group I, 4 in II, and 8 in III. Threepatients had the fracture at L2, 10 at L3, 3 at L4, and 1 at L5. Average ofthe preoperative motor score was paradoxically higher in the more severeinjury; 21.8 in group I, 34.5 in II, and 43.0 in III. An autodecompressioneffect of the dural tear might play a role. Motor score recovery of groupsII and III was satisfactory after laminectomy and dural repair. Averagescore of group II (49.6) and III (49.5) at follow-up was not lower than thatof group I (49.1). Altered bowel and bladder function was common (14 of17 patients). Recovery of function was also fairly good after the operation:Fourteen of 17 patients showed normal, but 3 showed partial loss. On theradiologic study, a “tail sign” (sharp triangular elevation of the posterocen-tral portion of dural sac) was found frequently in the patients with rootletentrapment (Fig. 1); 7 of 8 in group III. Deviation of epidural fat wasfound 3 in group II, and 4 in III. Wide separation of cleavage fracture (�5mm) was usually associated with dural tear (Fig. 2): all in group II or III.CONCLUSIONS: Dural tear associated with rootlet entrapment in thelaminar fracture should be suspected when the patient had loss of bowelor bladder control but relatively preserved motor function despite severecanal encroachment. A careful evaluation of radiologic studies was helpful

Fig. 1.

Fig. 2.

to recognize these conditions. If these injuries are suspected, reductionof the rootlets and repair of the dural tear after laminectomy should beconsidered to obtain maximal neurologic recovery.DISCLOSURES: No disclosures.CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2005.05.285

P71. The biomechanics of posterior motion preservation systemsTimothy Wright, PhD1, Michael Tauber, MD2, Kate Meyers, MS1,Yuri Sudin3, Shai Fleischer3, Uri Arnin3, Federico Girardi, MD4;1Cornell University Medical College, New York, NY, USA; 2Disc-O-TechMedical Technologies, Tel-Aviv, Israel; 3Impliant, Ltd, Ramat Poleg,Israel; 4Hospital for Special Surgery, New York, NY, USA

BACKGROUND CONTEXT: Non-fusion alternatives for the treatmentof lumbar degenerative conditions include the use of pedicle screw-baseddynamic devices to stabilize the affected lumbar region. Adequate kinematicconstraint must be balanced with appropriate load sharing to insure long-term fixation at the screw-bone interface.PURPOSE: To investigate the influence of design, two systems with differ-ent approaches to constraining motion were compared.STUDY DESIGN/SETTING: The systems were: the Dynesys (Zimmer,Inc), which uses semi-flexible materials and the TOPS (Impliant, Ltd),which uses a titanium-elastomer construct with articulation members. TheDynesis has two bilateral connections at adjacent vertebrae while the TOPS

Proceedings of the NASS 20th Annual Meeting / The Spine Journal 5 (2005) 1S–189S144S

height, comparisons between two groups were made by unpaired two-tailedStudents’s t test.RESULTS: Follow-up radiographs were available in 36 patients, constitut-ing 49 ACDF levels. 16 patients received cortical allograft in 22 ACDFlevels, while 20 patients received resorbable (Bioplex) implants in 27ACDF levels. The group demographics were well-matched with five males,11 females and average age of 45.3�11.9 years (range: 32 to 76 yrs.) inthe allograft group versus seven males, 13 females and average age of47.9�7.6 years (range: 32 to 61yrs.) in the resorbable implant group.Follow-up radiographs were taken at an average of 3.1�1.8 months (range:1 to 9 mos.) in all patients. Patients who received fibular allograft implantshad an average subsidence of 1.01mm�.81mm (range: .06 to 2.78 mm)per level. Patients who received resorbable graft implants had an averagesubsidence of 1.58�1.08 mm (range: .03 to 4.81 mm) per level. Thisdifference was found to be statistically significant (p�.05). Furthermore,three of the 27 resorbable graft levels had greater than 3mm of subsi-dence, while none of the fibular allograft levels had greater than 3mmof subsidence.CONCLUSIONS: There is a statistically significant increase in subsidencewith use of Bioplex resorbable implant graft compared with fibular allograftin ACDF. An ideal implant graft will have greater surface area and favorableelasticity in order to minimize subsidence. The increase in subsidence withBioplex graft may be a function of these two principles.DISCLOSURES: FDA device/drug: Bioplex cervical graft implant. Status:Approved for this indication.FDA device/drug: Fibular allograft cervical implant. Status: Approved forthis indication.CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2005.05.287

P73. Comparison of occurrence of sacroiliac joint pain followingmultilevel lumbar fusion to S1 vs. to L5 or above levelEdward D. Simmons, MD1, Cameron B. Huckell, MD2, Yinggang Zheng,

has rigid crossbars connecting two screws of the same vertebrae at adja-cent segments.PATIENT SAMPLE: L3-S1 cadaver specimens (n�5; age: 49 to 79 yrs;L4 T-score: 0.9 to �4.4) were used.OUTCOME MEASURES: Outcome measures were range of motion(ROM) and the moments (strains) measured in the pedicle screws.METHODS: Specimens were mounted in a six-degree of freedom appara-tus for application of 10 Nm flexion-extension and lateral bending momentsin combination with compressive axial loads of 210 and 630 N. Eachspecimen was tested intact to determine ROM. Next, four pedicle screwswere used to attach a Dynesys adaptor at L4-L5. The screws were instru-mented with strain gages circumferentially; each screw was calibrated byapplying known moments. The specimen was retested, collecting ROM andstrain data. The Dynesys was then removed, a laminectomy and facetectomywere performed to allow the TOPS system to be secured to the same screws,and the specimen was retested.RESULTS: With the Dynesys, ROM decreased two to five degrees inflexion-extension and lateral bending compared with intact; the larger de-creases occurred at the higher compressive load. With the TOPS, ROMwas restored to within a degree of the intact value in flexion-extension,but increased two to four degrees in lateral bending; smaller increasesoccurred at the higher compressive load. The decreased ROM in theDynesys was accompanied by maximum moments in the screws as muchas 45% higher in flexion and 300% higher in lateral bending than withthe TOPS.CONCLUSIONS: While the clinical relevance of these increases is un-known, these results suggest that load sharing between spinal implants ismarkedly influenced by device design.DISCLOSURES: FDA device/drug: Dynesys. Status: Investigational/notapproved. FDA device/drug: TOPS. Status: Investigational/ Not approved.CONFLICT OF INTEREST: Authors (TW, KM) Other: Financial supportprovided by Impliant, Ltd.

doi: 10.1016/j.spinee.2005.05.286

P72. Graft subsidence with use of cortical allograft vs. resorbableimplant in anterior cervical fusionMichael Musacchio, Jr., MD*, Tibor Boco, MD, Sepehr Sani, MD,John Ratliff, MD, Harel Deutsch, MD; Rush University Medical Center,Chicago, IL, USA

BACKGROUND CONTEXT: Resorbable cervical graft implantation hasbecome increasingly popular in anterior cervical discectomy and fusion(ACDF). Resorbable grafts are designed to match the strength of autograftsand allograft, but have the added benefit of resorbing once fusion is achieved.To date, there have been no studies that have evaluated subsidence withuse of these resorbable grafts.PURPOSE: The purpose of this study is to evaluate subsidence observedwith use of resorbable graft implants versus fibular allograft implants inACDF procedures.STUDY DESIGN/SETTING: Retrospective review and data analysis.PATIENT SAMPLE: A retrospective review was performed with 59patients who underwent a total of 75 single, double, or triple level ACDFprocedures by two spine surgeons at a single institution between 2003and 2004.OUTCOME MEASURES: The outcome measure in this study is thecomparison of subsidence between resorbable interbody graft implants tofibular allograft implants in ACDF procedures, using a standardized methodof measuring postoperative and follow-up radiographs.METHODS: Follow-up radiographs were available in 36 patients. Compar-isons were made between patients who received fibular allograft implantsversus those who received Bioplex resorbable implant grafts. Subsidencewas evaluated on immediate postoperative lateral radiographs in comparisonto follow-up lateral radiographs by determining the change in verticaldistance between screw tips in relation to the known screw length. Assuminghomoscedasticity and normal distribution of measured changes in graft

MD1; 1University at Buffalo, Buffalo, NY, USA; 2State University ofNew York at Buffalo, Buffalo, NY, USA

BACKGROUND CONTEXT: There is an increased interest in the man-agement of sacroiliac joint (SIJ) pain in recent years. Controversy existsregarding the etiology of SIJ pain and few clinical studies reported theoccurrence of this disorder in patients after lumbar or lumbaosacral fusion.PURPOSE: A retrospective study of occurrence of SIJ pain in patientswith lumbar fusion to S1 versus to L5 or above level was conducted todetermine if lumbosacral fusion has an impact on the development ofsacroiliac joint pain.STUDY DESIGN/SETTING: A computerized database was used to iden-tify two groups of patients who underwent multi-level lumbar fusion toS1 (Group A) versus to L5 or above level (Group B) between January1997 and August 2001 and who developed new SIJ pain during postopera-tive follow-up.PATIENT SAMPLE: Patients who developed SIJ pain after lumbar orlumbosacral fusion were included for this study.OUTCOME MEASURES: The inclusion criteria of SIJ pain were: noprevious SIJ pain; having lumbar or lumbosacral fusion; developed new SIJpain and responded to SIJ injection; with or without accordant degenerativechanges on radiograph or CT of SIJ.METHODS: Patients’ history, physical examination, radiographic findings,diagnosis and treatment were reviewed by an independent physician whowas not involved in the patient care. The occurrence of SIJ pain in thesetwo groups was statistically compared.RESULTS: A total of 129 patients underwent lumbar/lumbosacral fusion;50 men and 79 women. The mean age was 62 years and the mean numberof fused level was 2.7. The mean follow-up time was 6 years. There were90 (69.8%) patients in the Group A and 39 (30.2%) patients in the GroupB. 33 (36.7%) patients of Group A developed SIJ pain and 7 (18%) ofGroup B had SIJ pain, showing Group A with significantly higher occur-rence of SIJ pain (p�.05).