Pedicle screw-rod instrumentation has become the

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1 spine case report J Neurosurg Spine 22: , 2015 Spine fusion cross-link causing delayed dural erosion and CSF leak: case report Gazanfar Rahmathulla, MD, and H. Gordon Deen, MD Department of Neurosurgery, Mayo Clinic, Jacksonville, Florida The past 2 decades have seen a considerable increase in the number of lumbar spinal fusion surgeries. To enhance spinal stabilization and fusion, make the construct resistant to or stiffer for axial stress loading, lateral bending, and torsional stresses, cross-links and connectors were designed and included in a rod-screw construct. The authors present the case of a 49-year-old woman who presented 11 years after undergoing an L4 5 decompression and fusion in which a pedicle screw-rod construct with an integrated cross-link was designed to attach onto the pedicle screws. The patient s response at the time to the initial surgery was excellent; however, at the time of presentation 11 years later, she had significant postural headaches, severe neurogenic claudication, and radiculopathy. Imaging revealed canal compression across the instrumented levels and a possible thickened adherent filum terminale. Reexploration of the level revealed a large erosive dural defect with a CSF leak, spinal canal compression, and a thickened filum at the level of the cross-link. To the author s knowledge, such complications have not been reported in literature. The authors discuss this rare complication of spinal fusion and the need to avoid dural compression when cross-links are used. Key Words spinal fusion; instrumentation; cross-link; CSF leak; dural erosion Pedicle screw-rod instrumentation has become the standard of care for spinal stabilization and fusion because of its rigid 3-column fixation of the spinal elements. The success of pedicle screw-rod systems in achieving durable fusion has resulted in a proliferation of various designs and types of constructs. Although transpedicular fixation significantly increases sagittal plane stiffness, this effect does not necessarily translate to an increase in lateral bending and torsional loading stresses. To augment construct stiffness in the lateral and torsional axes, transverse cross-link connectors were devised to augment the bilateral transpedicular systems. Various studies have evaluated cross-link design, number of cross-links used, the utility of cross-links in spinal deformity surgery, and fusion constructs of varying length. 17 We are not aware of any reports in which a low- (inverted-) profile cross-link for single-level fusions caused dural erosion, CSF leakage, and terminal filum thickening with neurogenic claudication. We discuss the present case, complicated by such construct design, and review literature on the necessity of cross-links in spinal fusions. Case Report A 49-year-old right-handed woman underwent a lumbar L4 5 discectomy and fusion with instrumentation at an outside hospital in She recovered well from her initial surgery and returned to her vigorous lifestyle that included activities such as walking and riding her bicycle. She presented in 2013, 11 years after her initial surgery, with progressively worsening low-back pain, which shot down her left lower-extremity, neurogenic claudication, and extremely limited mobility. Her pain scores on a visual analog scale (VAS) were 7/10 at baseline and 10/10 with activity. In addition, she complained of ill-defined headaches that were postural and would worsen on moving from the recumbent position to standing up. Her gait and activities were limited by the pain, and she denied having genitourinary symptoms. Conservative treatment included yoga, massage therapy, and more than 6 months of physical therapy. She had a poor response to local pain interventions that included blocks and epidural steroid injections and was taking daily opioid medication. On examination, Abbreviation VAS = visual analog scale. submitted March 8, accepted September 19, include when citing Published online January 30, 2015; DOI: / SPINE Disclosure The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. AANS,

G. Rahmathulla and H. G. Deen she had a body mass index of 34. Neurologically she had Grade 5/5 power in her lower extremities, normal reflexes, and no sensory deficits.

2 G. Rahmathulla and H. G. Deen she had a body mass index of 34. Neurologically she had Grade 5/5 power in her lower extremities, normal reflexes, and no sensory deficits. Her straight leg raising test was restricted on the left side, and there were no other evident neurological deficits. She was evaluated with lumbar radiography and a CT myelography. The radiographs revealed pedicle screw-rod construct with a pseudarthrosis at L4 5. In addition there was a Grade 1 spondylolisthesis and loss of lumbar lordosis (Fig. 1). The terminal filum appeared to be thickened and tethered to the cross-link along with adhesive arachnoiditis in the L4 5 region, seen by clumping of the nerve roots in the region (Fig. 2). Intraoperatively we observed a pedicle screw-rod construct with an integrated low-lying transverse cross-link curving inwards into the spinal canal. There was a pseudarthrosis at the level of the L4 5 fusion. The cross-link was embedded in the spinal canal, causing significant dural compression, as predicted by the preoperative imaging studies (Fig. 3A). We noted a significant CSF leak as soon as we started to dissect and expose soft tissue around the construct, and a large dural rent was evident at the site where the cross-link was embedded (Fig. 3B). The underlying filum and nerve roots appeared to be impinged by the cross-link, when visualized through this dural defect (Fig. 3C). The construct was revised: We placed larger-diameter pedicle screws, and the thickened adherent filum was sectioned and released (Fig. 3D). Following the release of the filum, a duraplasty was performed using paraspinal muscle fascia to close the defect, suturing the fascial graft onto the adjacent dura (Fig. 3E). Postoperatively the patient s low-back pain and radiculopathy significantly improved and no new postoperative neurological deficits occurred. She remained asymptomatic and without any evidence of a CSF leak at the 3-month follow-up. Her VAS score at baseline was 4 of 10 in the absence of any opioid medication, and she was able to gradually return to all her activities of daily living. At clinical evaluation at 11 months postoperatively her VAS score at baseline was 0 1 of 10 and, with activity, it varied from 1 3 of 10 without the use of any pain medication. Clinically she had no neurological deficits, had returned to work, and was near her preoperative activity levels. MRI was performed to evaluate any residual or persistent CSF leakage or filum tethering. T2-weighted imaging (Fig. 4A) 10 months following surgery did not reveal any evidence of filum tethering or a pseudomeningocele, although there was a small residual fluid collection in the dead space adjacent to the fusion mass. To assess the completeness of arthrodesis across the L4 5 level, we performed CT scanning of the lumbar spine 11 months following her surgery. The CT scan (Fig. 4B) revealed a good bone fusion across the L4 5 levels. Discussion Procedure-related complications following placement of pedicle screw-rod constructs have been widely reported on in literature and include those related to the implanted hardware/device such as screw backout, screws breakage, and construct collapse. 16 Other reported complications include incidental durotomies with CSF leaks, wound infections, hematomas, and possible neural injury with deficits. However, our case remains unique in the type of instrument-related complication. Pseudarthrosis and adjacent- Fig. 1. A: Axial CT scan of the pedicle screw-rod construct showing the transverse cross-link that caused spinal canal indentation. The adjacent filum is seen as a thickened gray dot in the midline adjacent to the cross-link. B: Image negative of that shown in A, made using Microsoft image inverter, delineating the bony margins of the vertebra and instrumentation. The filum appears to be abutting/in contact with the transverse cross-link in the midline. C and D: Midsagittal CT and MR images of the lumbar spine revealing a spondylolisthesis Grade 1 at L4 5. Evidence of prior posterior decompressive surgery at L4 5 with artifact from transverse cross-link evident and prior intradiscal implants at L2 3, L3 4, and L5 S1. 440

Complications of a spinal cross-link Fig. 2. A: Sagittal CT scan of the lumbar spine revealing absence of bony fusion on the right posterolateral side.

3 Complications of a spinal cross-link Fig. 2. A: Sagittal CT scan of the lumbar spine revealing absence of bony fusion on the right posterolateral side. B: Sagittal CT scan of the lumbar spine demonstrating a defect in the fusion mass, with an inadequate fusion on the left posterolateral side across L4 5 after 10 years. C: Sagittal CT myelogram revealing a thickened filum that appears adherent to the cross-link, as well as adjacent thickened and clumped nerve roots of the cauda equina suggestive of adhesive arachnoiditis. Figure is available in color online only. segment disease are expected complications over time, but dural erosion with CSF leak and an adherent terminal filum is not. In our case the cross-link remains the direct cause and the literature provides no evidence for the use of crosslinks in short-segment fusions. Cross-links were initially designed to improve and maintain coronal stability in long-segment scoliosis corrections.2 They may also prevent rod migration, improve axial stress loading, prevent lateral bending, and reduce the number of pedicle screws used in long-segment constructs.4,11,18 The factors affecting biomechanical analysis include the design of different cross-links, the biological model used for testing, and length of the construct.5 When cross-links were evaluated in the sagittal plane, no biomechanical difference in stability was identified in flexion-extension5, although variable results were seen in lateral bending.13 There are no clear indications for the use of cross-links in short-segment lumbar spinal fusion surgery, but longer constructs in the thoracic and thoracolumbar segments may benefit by the increase in torsional stiffness that cross-links may provide.2,7 Long-segment constructs also benefit from cross-links as the torsional load through the length of the rod can generate stresses causing loss of correction.17 The cross-links resist lateral displacement and improve pullout strength of long transpedicular constructs, although a number of biomechanical studies evaluating the role of cross-links have reported variable results.3,4,6,12,14,15,17 The use of cross-links in short-segment lumbar fusions, hence, does not appear to be warranted in cases of spinal pathology in which excessive torsional forces across the construct would not be anticipated. Cross-link design may also play an important role in the overall stiffness of the construct. Alizadeh et al.1 identified an X-type cross-link configuration that provided the greatest stability, reducing stress at the adjacent vertebral body and implant under various loading conditions in long-segment constructs; they found no benefit to the cross-link configuration in short-segment constructs. In our patient, the low-profile cross-link design, with the transverse connecting bar of the cross-link curved in toward the spinal canal, may have over time added to the dural erosion and filum scarring. The changes associated with degenerative spondylolisthesis, loss of lumbar lordotic curvature, and pseudarthrosis at L4 5, in conjunction with the inverted cross-link transverse bar, created an ideal environment for the dural erosion. Additionally, the spinal instability at L4 5 due to a pseudarthrosis and micromotion at the instrumented level caused intermittent tethering and inflammation of the filum resulting in its thickening. Along with this an adhesive arachnoiditis secondary to overcrowding of the cauda equina and constant micromotion secondary to the pseudarthrosis may have contributed to the recurrent pain and left lower-extremity radicular symptoms. We postulate a dynamic intermittent spinal stenosis at the L4 5 level with loading of the spine along with the filum tethering and arachnoiditis, resulting in the crosslinks gradually eroding into the spinal dura over a period of many years. The defect was barely sealed off by the overlying soft tissue. In retrospect, possible intermittent CSF leaks when the patient stood erect may have been the cause of her headaches, with low pressure in concert with a possible ball-valve like mechanism playing an important role.8 10 Conclusions A case of delayed dural erosion and CSF leakage sec 441

When this condition is encountered the treatment must include repair of the CSF leakage and more important, neural decompression and solidification of the fusion mass. References Fig. 3.

4 G. Rahmathulla and H. G. Deen ondary to dural compression by a low-profile cross-link is reported. When cross-links are used, care must be taken to ensure the device is situated well away from the dura. There should be a heightened awareness for such rare complications. When this condition is encountered the treatment must include repair of the CSF leakage and more important, neural decompression and solidification of the fusion mass. References Fig. 3. A: Intraoperative image showing the transverse cross-link as low profile and inverted into the spinal canal, ultimately eroding the dura and causing spinal stenosis. The cross-link integrated with pedicle screw has its convexity toward dura. B: Intraoperative image. The asterisk is placed adjacent to location of dural erosion. The cross-link integrated with pedicle screw construct with an inverted contour. Adjacent to this, a dural defect is evident from which a CSF leak was seen. C: Removal of the instrumentation and cross-link revealed an evident dural defect with a thickened filum (beneath the Penfield dissector) and adjacent nerve roots of the cauda equina. D: Low-magnification intraoperative image showing the cross-link removed, a large area of dural erosion, and underlying thickened filum with arachnoid bands. Pedicle screws were replaced with large-diameter and longer screws. The thickened filum was cut after revision of the pedicle screws. E: Revised L4 5 pedicle screwrod construct without the cross-link. The dural defect was repaired by suturing paraspinal fascia graft into the adjacent spinal dural edge. 1. Alizadeh M, Kadir MR, Fadhli MM, Fallahiarezoodar A, Azmi B, Murali MR, et al: The use of X-shaped cross-link in posterior spinal constructs improves stability in thoracolumbar burst fracture: a finite element analysis. J Orthop Res 31: , Asher M, Carson W, Heinig C, Strippgen W, Arendt M, Lark R, et al: A modular spinal rod linkage system to provide rotational stability. Spine (Phila Pa 1976) 13: , Benzel EC: Deformity prevention and correction: component strategies, in Biomechanics of Spine Stablization. Rolling Meadows, IL: AANS Publications, 2001, pp Brodke DS, Bachus KN, Mohr RA, Nguyen BK: Segmental pedicle screw fixation or cross-links in multilevel lumbar constructs. A biomechanical analysis. Spine J 1: , Dhawale AA, Shah SA, Yorgova P, Neiss G, Layer DJ Jr, Rogers KJ, et al: Effectiveness of cross-linking posterior segmental instrumentation in adolescent idiopathic scoliosis: a 2-year follow-up comparative study. Spine J 13: , Dick JC, Jones MP, Zdeblick TA, Kunz DN, Horton WC: A biomechanical comparison evaluating the use of intermediate screws and cross-linkage in lumbar pedicle fixation. J Spinal Disord 7: , Dick JC, Zdeblick TA, Bartel BD, Kunz DN: Mechanical evaluation of cross-link designs in rigid pedicle screw systems. Spine (Phila Pa 1976) 22: , Gardner WJ: Hydrodynamic mechanism of syringomyelia: its relationship to myelocele. J Neurol Neurosurg Psychiatry 28: , Gardner WJ, Angel J: The cause of syringomyelia and its surgical treatment. Cleve Clin Q 25:4 8, Gardner WJ, Angel J: The mechanism of syringomyelia and its surgical correction. Clin Neurosurg 6: , 1958 Fig. 4. A: Postoperative sagittal T2-weighted MR image obtained at 10 months revealing an untethered filum and an expanded L4 5 dural space. B: Postoperative coronal CT scan acquired at 11 months revealing evidence of a good bony fusion across the L4 5 construct. Figure is available in color online only. 442

5 Complications of a spinal cross-link 11. Hart R, Hettwer W, Liu Q, Prem S: Mechanical stiffness of segmental versus nonsegmental pedicle screw constructs: the effect of cross-links. Spine (Phila Pa 1976) 31:E35 E38, Kuklo TR, Dmitriev AE, Cardoso MJ, Lehman RA Jr, Erickson M, Gill NW: Biomechanical contribution of transverse connectors to segmental stability following long segment instrumentation with thoracic pedicle screws. Spine (Phila Pa 1976) 33:E482 E487, Lim TH, Kim JG, Fujiwara A, Yoon TT, Lee SC, Ha JW, et al: Biomechanical evaluation of diagonal fixation in pedicle screw instrumentation. Spine (Phila Pa 1976) 26: , Lynn G, Mukherjee DP, Kruse RN, Sadasivan KK, Albright JA: Mechanical stability of thoracolumbar pedicle screw fixation. The effect of crosslinks. Spine (Phila Pa 1976) 22: , Pintar FA, Maiman DJ, Yoganandan N, Droese KW, Hollowell JP, Woodard E: Rotational stability of a spinal pedicle screw/rod system. J Spinal Disord 8:49 55, Rivet DJ, Jeck D, Brennan J, Epstein A, Lauryssen C: Clinical outcomes and complications associated with pedicle screw fixation-augmented lumbar interbody fusion. J Neurosurg Spine 1: , Valdevit A, Kambic HE, McLain RF: Torsional stability of cross-link configurations: a biomechanical analysis. Spine J 5: , Wood KB, Wentorf FA, Ogilvie JW, Kim KT: Torsional rigidity of scoliosis constructs. Spine (Phila Pa 1976) 25: , 2000 Author Contributions Conception and design: both authors. Acquisition of data: Rahmathulla. Analysis and interpretation of data: both authors. Drafting the article: Rahmathulla. Critically revising the article: both authors. Reviewed submitted version of manuscript: both authors. Approved the final version of the manuscript on behalf of both authors: Rahmathulla. Administrative/technical/material support: Deen. Correspondence Gazanfar Rahmathulla, Mayo Clinic, 4500 San Pablo Rd., Cannaday 2E, Jacksonville, FL rahmathulla.gazanfar@ mayo.edu. 443

Original Date: October 2015 LUMBAR SPINAL FUSION FOR

National Imaging Associates, Inc. Clinical guidelines Original Date: October 2015 LUMBAR SPINAL FUSION FOR Page 1 of 9 INSTABILITY AND DEGENERATIVE DISC CONDITIONS FOR CMS (MEDICARE) MEMBERS ONLY CPT4