featured applied radiology article - diagnostic imaging of spinal fusion and complications

14 ! APPLIED RADIOLOGY© www.appliedradiology.com July–August 2009

Back pain is the most commoncause of limited activity in peo-ple younger than 45 years in the

United States. It is the second most fre-quent reason for visits to a physicianand ranks fifth as the reason for hospitaladmission.1 It is estimated that 18% ofthe U.S. population experience low-back pain each year. Fortunately, inmost cases, the underlying pathology isbenign and the pain is self-limited.Noninvasive methods of treatment suchas physical therapy and pharmacother-apy typically resolve such pain.

Treatment of back pain is the thirdmost common indication for surgicalprocedures in the nation. Decompres-sion and occasional arthrodesis with fre-quent instrumentation are the mainsurgical procedures performed in theU.S.2 It is a common belief that immobi-lization and/or removal of the painfulsegment decreases pain. Failed backsurgery syndrome (FBSS) is defined asfailure to relieve lower back pain symp-toms following surgery. In the best of all

situations, this syndrome occurs after aminimum of 20% of spine fusion surg-eries. The syndrome can result from:mistaken diagnoses, technique error,poor application, inappropriate indica-tion, pseudarthrosis or continued naturalprogression of disease. This syndromecan be prevented to a large extent bymeticulous pre- and intraoperative radi-ologic examination.3,4 Since the initialdescription of spinal instrumentation byHarda in 1889 and subsequent spinalfusion surgery by Fred Albee and RusselHibbs in treatment of spinal tuberculosisin 19115–7 there have been a great manyadvances in surgical methods and instru-mentation, as well as many more indica-tions for fusion. Among current in-dications are scoliosis, spondylolisthe-sis, congenital deformities, spinal insta-bility in trauma or by iatrogenic causes(e.g. extensive laminectomy), infectionand neoplasm. The current indication forspinal arthrodesis is broad and it in-cludes the category of degenerative discdiseases.3

Postoperative imaging is used toassess disease progression, positioningof instrumentation, possible complica-tions and the extent of bone-graft fusion.Knowledge of the advantages and limi-tations of different imaging modalities isnecessary for optimal evaluation ofpatients with spinal instrumentation.Radiologists should also be familiarwith different surgical methods used in

spinal fusion, types of instrumentationand potential complications to properlyappraise postoperative images.

Stability is described as resistance ofthe spine to deformation under physio-logic stress. Mulholland8 in a recentreview of instability and low-back painhypothesized that the cause of low-backpain could be due to abnormal disc load-ing. Currently, the most widely acceptedcause of low-back pain and the underly-ing concept promoting the use of spinalfusion is nonphysiologic movement ofthe degenerated segment. Most appli-ances are placed to provide stability dur-ing bone fusion, and their function iscomplete when this has occurred. Be-cause of the morbidity associated withrepeated surgery, intact implants are gen-erally left in place for life. Fractured anddislodged implants are often removedbecause of the need for revision and thepotential for migration of the compo-nents, leading to substantial soft-tissue orneural injury.

Spinal instrumentationSurgical implants in spinal surgeries

are used to stabilize the spine, replace thedefective parts and maintain anatomicreduction. Internal spinal instrumentationhas undergone considerable advancesduring the last century. Radiologistsshould be able to identify the devices mostcommonly used and understand theirbiomedical principles and specifications.

Diagnostic imaging of spinal fusionand complications

Mohammad Reza Hayeri, MD, and Jamshid Tehranzadeh, MD

Dr. Hayeri is a former Research Fellow,Division of MSK Imaging at Universityof California, Irvine Medical Center,Orange, CA, and Dr. Tehranzadeh isChief of Radiology at Long Beach VAand Professor Emeritus and Vice Chairof Radiology, Department of Radiologi-cal Sciences, University of California,Irvine Medical Center, Orange, CA.

www.appliedradiology.com APPLIED RADIOLOGY© ! 15July–August 2009

SPINAL FUSION IMAGING

Common devicesRods, plates and rectangles

Rods can extend to single or multi-ple spine segments. They can be singleor double, straight, L-shaped or can becut and fashioned as required. They areattached to the spine by hooks, pediclescrews or sublaminar or interspinouswires or cables. Rods are usually pre-ferred over plates for multisegmentfusion because of their ability to span along segment. The Hartshill rectangleis seldom used today. It is a stainless-steel rectangle that attaches to the spineby sublaminar wires and occasionallyinterspinous wires. Various shapes ofplates in different sizes have beendeveloped for anterior or posterior

spine fusion.9–11 Some of the commonlyused instruments and systems, andtheir specifications, are summarized inTable 1.

Translaminar or facet screwsThese devices can be used when

posterior spinal elements are intact.They attach the lamina of 2 adjacentvertebrae.

Interbody spacersInterbody spacers could be solid

(ramp) or hollow (cages). Cages arefilled with bone-graft material and in-serted into the intervertebral space orreplace a vertebra after its removal (i.e.corpectomy). Cages are usually made of

Table 1: Specifications of spinal fusion instruments and systemsPosterior instrumentation SpecificationLuque system Single or double, straight or L-shaped rod(s)

attached to spine with sublaminar wires.Hartshill rectangle Stainless steel rectangle with bends at upper

and lower ends, attached to spine with sub-laminar wires.

Harrington system Smooth compression or distraction rod withcollar at one end and ratchets at the other,attached to spine by hooks.

Wisconsin system Like Harrington system but the rod is attachedto the spine by interspinous wires.

Knodt rods Two threaded distraction rods with a fixedcentral nut attached to lumbosacral spine by hooks.

Cortel Dubousset rod Two serrated rods connected together by (CD rod) cross links. Set screws attach the pedicle

screws or laminar hooks to the rods. Texas Scottish Rite system Rough surface rod with hooks and pedicle(TSRH) screws attached to the rod with eyebolts

and nuts.Isola system Similar to Texas Scottish Rite system with

rods, hooks, plates and cross links.

Anterior instrumentation SpecificationDwyer Staples are embedded into the vertebral body

and a cable is attached to the vertebral bodyby threaded screws.

Zielke A modified Dwyer system. The cable isreplaced with solid stainless steel.

Kaneda Consists of 2 rods attached to vertebral bodyvia staples and screws.

FIGURE 1. Fracture of pedicular screw. Thisis a 67-year-old man with extensive thora-columbar spinal fusion with CD rods andpedicular screws. Lateral in-flexion radi-ograph shows fracture of the pedicularscrew at L5 level.

FIGURE 2. Spinal fusion with fracture ofanterior titanium plate. This is a 43-year-oldwoman with anterior and posterior spinalfusion. AP radiograph shows anterior fusionat C6 to C7 and posterior fusion at C5through C7. There is a fracture of the anteriortitanium plate. (Reprinted from Seminars inUltrasound, CT and MR, Vol 26, Tehran-zadeh J. et al., Advances in spinal fusion,Pages 103-113, Copyright 2005, with per-mission from Elsevier.)



FIGURE 3. Broken pedicular screw of the lumbosacral fusion. This is a 60-year-old womanwith posterior spinal fusion. A (AP) and B (lateral) radiographs of lumbosacral spine show theposterior fusion of L4 through S1 levels with fracture of pedicular screws on the left and rightsides at the S1 level (arrowhead), which is noted best on the lateral view. (Reprinted fromSeminars in Ultrasound, CT and MR, Vol 26, Tehranzadeh J. et al., Advances in spinal fusion,Pages 103-113, Copyright 2005, with permission from Elsevier.)

FIGURE 4. Failed spinal fusion due to broken Harrington rod. This is a 42-year-old womanwith scoliosis who underwent spinal fusion with Harrington rod fixation extending from the T5through L3 levels. A (AP) and B (lateral) radiographs of the thoracolumbar spine show fractureof the Harrington rod at the T7 to T8 level. (Reprinted from Seminars in Ultrasound, CT andMR, Vol 26, Tehranzadeh J. et al., Advances in spinal fusion, Pages 103-113, Copyright 2005,with permission from Elsevier.)

A B

A B

FIGURE 5. Nonunion of Bagby and Kuslich(BAK) cages due to loosening following lum-bar interbody fusion. This is a 47-year-oldman who underwent interbody fusion withtitanium cages filled with iliac bone graft anddeveloped nonunion. A (reformatted coro-nal) and B (sagittal) CT radiographs showbone resorption around the titanium cage,indicating loosening and nonunion. Thecause of nonunion is due to the lack ofimmobilization at the posterior elements ofthe spine. (Reprinted from Seminars inUltrasound, CT and MR, Vol 26, Tehran-zadeh J. et al., Advances in spinal fusion,Pages 103-113, Copyright 2005, with per-mission from Elsevier.)

A

B



titanium carbon fibers, polyetheretherketan (PEEK) or of cortical bone graft.Most cages contain 2 radiopaque mark-ers to identify their position in radi-ographs and to enable their assessment.They are made in different shapes basedon the method of approach to the inter-vertebral disc.

In anterior interbody fusion (AIF),cages are more round in shape, while inposterior interbody fusion (PIF) theyare more rectangular. Transforaminalinterbody fusion (TIF) cages are morecrescent-shaped. Expandable cylindri-cal or mesh cages are used in vertebral-body replacement procedures.

Cages are usually supported by addi-tional posterior, anterior or lateral instru-mentation (i.e. screw with plates or rods)to increase stability. For a standaloneinterbody fusion cage, the interbodyspacer is fixed to the adjacent vertebralbody with screws to eliminate the needfor additional instrumentation support.Retropulsion of the cage is a possiblecomplication, but is more common inPIF.12 A distance of !2 mm between thecage’s posterior marker and the posteriormargin of the vertebra should exist toprovide reassurance that the cage is notinvading the spinal canal.11 Cage subsi-dence (defined as migration of >3 mminto the adjacent vertebra) and lateral dis-placement is a disadvantage of usingmesh and standalone cages.13–15 The inci-dence of subsidence is reported from18% to !62.5% in patients who undergospinal procedures with standalone cervi-cal cages. Expandable cages havebroader surface area and duller edges atboth ends, which minimize their subsi-dence and also allow immediate loadbearing and stability after corpectomy.16

MiscellaneousDynamic stabilization devices are a

new category of instruments that are invarious stages of development. They canbe used alone or in conjunction with otherinstrumentation. They act by controllingthe abnormal motion and uneven load insegments adjacent to the level of fusion inorder to minimize progressive degenera-tion. Artificial ligaments (e.g. Dynamic

FIGURE 6. Nonunion of anterior interbody fusion at C6 to C7. This is a 47-year-old man withanterior fusion of C5 through C7 with interbody cadaveric bone graft. Although C5 to C6 fusedvery well, C6 to C7 had nonunion. A (flexion) and B (extension) lateral views of the cervicalspine show lucency at the intervertebral disc bone graft site at C6 to C7. Note the posteriorcompartment showing motion and interspinous-process space changes during flexion andextension. The cause of nonunion is due to the lack of immobilization at the posterior elementsof the spine. C (Sagittal reformatted CT myelogram) shows resorption of the cadaveric graft atC6 to C7 disc space. D is a flexion lateral view radiograph of the cervical spine following poste-rior wiring and fusion of C6 to C7. The patient proceeded to have good fusion later on, even atthe C6 to C7 level, without further intervention. However, he developed facet arthritis abovethe fusion at the C4 to C5 level as shown by vaccum phenomenon and sclerosis at the facetjoint at this level. Later on, the C4 level had to be incorporated in the fusion to relieve the paincaused by facet arthritis.(Reprinted from Seminars in Ultrasound, CT and MR, Vol 26, Tehran-zadeh J. et al., Advances in spinal fusion, Pages 103-113, Copyright 2005, with permissionfrom Elsevier.)

A B

C D



Stabilization System [Dynesys], ZimmerInc., Warsaw, IN), interspinous decom-pression systems (e.g. X-STOP Spacer,Medtronic Spine, Memphis, TN; and theWallis Dynamic Posterior StabilizationSystem, Zimmer Inc., Bordeaux, France),and posterior element replacement systems (e.g. Total Facet Arthroplasty

System, Archus Orthopedics, Redmond,WA) are examples of such devices.11

Surgical methodsSurgical techniques can be divided

on the basis of perceived patient mor-bidity into minimally invasive or tradi-tional-open procedures performed via

either an anterior or posterior approach.In interbody fusion, the intervertebraldisc or a complete vertebra is removedand replaced with bone graft. Interbodyfusion of the spine can be approachedanteriorly or posteriorly.

Anterior interbody fusion (AIF) hasthe advantage of a broader access to thedisc space. However, it is limited bypotential injury to major vessels andsympathetic nerve chain.17 Oskouianand Johnson reported a 5.8% incidence(12 of 207 patients) of vascular compli-cations in patients who underwent ante-rior thoracolumbar spine reconstructionprocedures.18

Extreme lateral interbody fusion(XLIF) is a newer surgical approach tofuse L1 to L5 and to minimize disad-vantages of AIF. Extreme lateral inter-body fusion approaches the anteriorspine from the flank.

In posterior interbody fusion (PIF)bilateral laminectomies are performedand bone-graft material is inserted intothe disc space after the disc is removed.Posterior interbody fusion has the dis-advantage of potential injury to nerveroots. Retrograde migration of the graftor cage is also more common with theposterior approach.19

Transforminal interbody fusion (TIF)is a modified PIF that uses a more lateralapproach and thus leaves the midlinebone structures intact. Min et al. showedboth AIF and PIF can produce good out-comes in treating lumbar spondylolis-thesis, but AIF is more advantageous inpreventing the development of adjacentsegment degeneration.20

Overall, Lemcke et al. reported that,with regard to the indications and con-traindications, AIF and PIF are unques-tionably accepted as up-to-date methods.21

The decision to use AIF or PIF is mainlybased on the patient’s presenting pathol-ogy, spine anatomy, the surgeon’s experi-ence, history of previous surgery andother conditions that may favor oneapproach over another (e.g. AIF is diffi-cult in the presence of marked vascularcalcification).11,22 Laparoscopic interbodyfusion can also be performed; however,compared with open surgery, the overall

FIGURE 7. Loosening of screw. (A) Lateral radiograph of lumbar spine in a 49-year-old manwho underwent posterior spinal fusion of L4-S1 levels with pedicular screws and posterior barsand bone graft. The 2 radiopaque markers of intradiscal PEEK spacer are noted at the L5 toS1 level (thin arrows). (B) Lateral flexion view of lumbar spine shows loosening of the L4 screw(thick arrow) with spondylolysis (arrowhead) and subluxation of L5 over S1 level which indi-cates instability.

FIGURE 8. Infection and pseudarthrosis following spinal fusion: (A) Coronal CT reformattedimage of a 74-year-old woman with spinal fusion and bone graft shows erosions around thetitanium cage indicating loosening due to infection. (B) Sagittal CT reformatted image of thesame patient shows loosening around the titanium cage due to infection and pseudarthrosis.

A B

A B



complication rate is higher (19% vs. 14%,respectively).

Posterolateral fusion is an alternativefor interbody fusion. In posterolateralfusion, adjacent vertebrae are fusedtogether by placing the bone-graft mate-rial between the transverse processes. Incomparison, interbody fusion providesa greater surface area of bone contactand produces a more favorable fusioncompared to the posterolateralmethod.23 Addition of instrumentationto interbody fusion increases success

rates to nearly 100%. Using cages ininterbody fusions provides more imme-diate stability during bone graft incor-poration.23–25

Imaging of postoperative spine fusion

Postoperative imaging plays animportant role in the assessment offusion and bone formation. It is alsohelpful to detect instrument failure andother suspected complications. It is nec-essary to compare current images with

FIGURE 9. Infection and abscess formation. (A) Lateral radiograph of lumbar spine in a 57-year-old man shows erosion around base of proximal screw (arrows). (B) Sagittal spin echoT1-weighted image of lumbar spine shows low signal areas in posterior spine following spinalfusion (stars). (C) Sagittal T2-weighted fat saturated image shows focal areas of increasedsignal in posterior spine due to infection and abscess formation (arrowheads). (D) Axial T1-weighted fat saturated image shows contrast enhancement in the margin of abscesses in theposterior spine (arrows) with soft tissue inflammation.

A B

C D

FIGURE 10. Collapsd vertebral endplate fol-lowing spinal fusion. (A) Lateral radiographof lumbar spine in a 61-year-old man withposterior spinal fusion of L2 to L5 levels withpediclular screws, posterior bars and bonegraft. (B) Lateral radiograph of lumbar spine3 months later shows spinal fusion with col-lapse of superior endplate of L2 and inferiorendplate of L1 vertebrae.

A

B



previous studies to identify any subtlechanges and disease progression.

Evaluation of the postoperative spineusually begins with conventional radi-ographs in AP and lateral projections. Itusually takes 6 to 9 months for a solidbone fusion to be established radi-ographically. Conventional radiographsare capable of detecting instrument fail-ure, infection and other causes of failedfusion (Figures 1 through 7). Addi-tional views in lateral flexion andextension are sometimes used to evalu-ate the presence of motion and theintegrity of the fusion.17 Ray defined 6criteria to radiographically verify asolid fusion:

(1) no motion or <3 degrees of inter-segment position change on lat-eral flexion and extension views,

(2) lack of a lucent area around theimplant,

(3) minimal loss of disc height,(4) no fracture of the instrument,

bone graft or vertebrae, and(5) no sclerotic change in the graft or

adjacent vertebrae,(6) visible osseous formation in or

around the cage.26

Sometimes radiographs are nondiag-nostic and, based on clinical suspicionand the type of the applied instrument,additional imaging with other modalitiesmay be applied. Currently, computedtomography (CT) with multiplanarreconstruction (MPR) is considered themodality of choice for imaging bonydetail and assessing osseous formationand hardware position despite artifactformation. CT is also useful in demon-strating the spinal canal and its alignmentand is capable of detecting infection andpseudarthrosis12 (Figure 8). Cook et al.evaluated the extent of bony fusion in ananimal model and reported that CT wascapable of detecting fusion in 83% ofcases, but coincidence of CT imageresults with histological findings waspresent in only 14% of specimens andCT significantly overestimated the extentof fusion.27

In another study, Heithoff et al. com-pared CT images with reoperation find-ings in symptomatic pseudarthrosispatients and reported that CT was notreliable in identifying these patients.28

Artifacts are the primary disadvantageof CT although artifacts are seen less

commonly with titanium implants com-pared with stainless steel because of thelower beam attenuation coefficient oftitanium implants.11

Magnetic resonance imaging (MRI)has been used increasingly in recentyears since introduction of titanium-based implants with reduced artifactcompared to formerly used stainless-steel devices. These artifacts could be decreased even more by changingimaging parameters such as reducingecho time, increasing bandwidth anddecreasing voxel size. Aligning theimplant along the axis of the magneticfield also reduces artifact although it isoften not completely achievable due tothe multidirectional configuration ofmost hardware. Spin echo sequencesare less vulnerable to magnetic suscep-tibility artifact and give better qualityimages compared with gradient echosequences. MRI is useful in detectinginfection (Figure 9) and assessingrecurrent tumor. MRI is the modality ofchoice in assessing intraspinal contents.Myelography (Figure 6) is an alterna-tive when MRI is contraindicated or isnondiagnostic because of artifact.

FIGURE 11. Poor screw placement in thoracic spinal fusion. This is a 61-year-old woman who underwent thoracic spinal fusion. A. (AP) radi-ographs show thoracic spine fusion with rod and pedicular screws with side plate and screw fixation and corpectomy with titanium cageplacement. B (axial) and C (coronal reformatted) CT scans show the screw is protruding through the soft tissue of the posterior mediastinumand lung.

A B C



Radionuclide scans are mainly usedto detect infection.29 Early stages ofpseudarthrosis can also be assessed byincreased radionuclide uptake, althoughthis may appear indistinguishable fromremodeling. Sonography is used todetect fluid collections and abscesses inthe postoperative spinal fusion.17

Spinal fusion instrumentation and complications

Potential complications of spinalsurgery vary based on the site ofsurgery, surgical approach, underlyingdisease, applied instrumentation, sur-geon skill and other clinical factors.

Besides the common complicationsassociated with spinal fusion proce-dures; there are some additional com-plications based on site, procedure andtype of instrumentation.

Hardware fracture (Figures 1 through4) occurs most commonly as a result ofmetal fatigue from the repeated stress inspinal movements. The fractured appli-ance may not be displaced, making itsdetection difficult. A dislodged or frac-tured appliance does not necessarilyindicate instability or clinical failure ofthe fusion but is most frequently associ-ated with motion, instability andpseudarthrosis.30 The prominence of the

instruments can cause chronic tissueirritation leading to pain, bursa forma-tion and even pressure sores with tissuenecrosis. This is an occasional indica-tion for hardware removal.30 There isalso a risk of bone resorption aroundscrews or under the implants that are indirect contact with the bone (Figures 5and 7). This will cause the bones toweaken and predisposes them to frac-ture and it leads to hardware failure. Aloose appliance repeatedly moves andproduces bone resorption or erosion.Fused bones are less mobile, whichmakes the bones vulnerable to fracturesabove or below the implants if sub-jected to trauma (Figure 10). Unsuc-cessful fusion may have other causessuch as development of facet arthritis(Figure 6C) or disc disease above orbelow the fusion level.3 Prematuredegenerative changes at the disc levelsabove and below the fused segment canoccur due to the reduced number ofmobile segments. This complication isreported in 10.2% of patients with pos-terior fusion and instrumentation.31

In the cervical spine, potential com-plications of the posterior approach aremainly neurological and include dural,nerve root or cord injury. The anteriorapproach is associated with risks ofinjuring the main vascular structures(carotid and vertebral arteries, jugular

FIGURE 12. Poor technical fusion and screw insertion of sacroiliac joint. This is a 26-year-old woman who underwent fusion of the right sacroil-iac joint. The posterior screw is violating the sacral neural foramen on the right. A (axial) and B (coronal) views show the screw encroaching onthe first sacral foramen on the right.

A B

FIGURE 13: Screw inside the neural foramen. Axial CT of the sacrum in a 59-year-old womanwith spinal tuberculosis shows destruction of sacral vertebra. The sacral screw placed forspinal fusion is in the neural foramen of the sacrum, impinging on the left sacral nerve root.



vein), causing recurrent damage to thelaryngeal nerve or soft tissue, such as theesophagus, trachea or lungs (Figure 11).Postoperative complications includehematoma, pseudomeningocele, infec-tion and instability as a result of lami-nectomy or incorrect hardware place-ment. Wires and cables are used as a pri-mary or supplementary instrument in sta-bilizing the posterior cervical spine(Figure 6). Complications include break-age and slippage of skeletal attachments.Cables (e.g. Songer cable) are muchmore resistant to fatigue fracture and fail-ure. Plates are used for the anterior andposterior cervical spine. They are alsoprone to fracture and failure (Figure 2).Screws may break or dislodge or may bemisplaced and impinge the cord or nerveroot when placed posteriorly.17 In a retro-spective study of 1015 patients whounderwent anterior cervical discectomyfor cervical radiculopathy and/or myelop-athy due to degenerative disc disease and/or cervical spondylosis, Fountas et al. re-ported the most common postoperativecomplications to be dysphagia (9.5%),

FIGURE 14. Pedicular screw encroaching the spinal canal. (A) This is a 51-year-old man withspinal fusion.The CT scan following spinal fusion shows the pedicular screw is encroaching onthe right side of the spinal canal. (B) Sagittal CT reformatting of the same patient as figure Ashows the L2 pedicular screw is crossing the spinal canal on the right side.

A B

FIGURE 15. Poor fusion technique of lumbosacral spine with misplacement of pedicular screw. This is a 67-year-old woman with posteriorspinal fusion at the L5 to S1 level with pedicular screws. A (coronal reformatted) and B (axial) CT scans at L4 and L5 disc space show misplace-ment of the pedicular screws in the right lateral disk space. (Reprinted from Seminars in Ultrasound, CT and MR, Vol 26, Tehranzadeh J. et al.,Advances in spinal fusion, Pages 103-113, Copyright 2005, with permission from Elsevier.)

A B



postoperative hematoma (5.6%) andrecurrent laryngeal nerve palsy (3.1%).32

Screws should approach the oppositecortex but should not breach it. In ante-rior-plate screw fixation, the screws mayback out and impinge soft tissue (e.g.great vessels, trachea and esophagus) oroverpenetrate the posterior cortex andimpinge on the cord. These complicationscan be prevented by using a cervical-spine locking plate with screw caps (e.g.Morscher). This device prevents thescrews from backing out and providesincreased holding power removing theneed for transcortical purchase with therisk of overpenetration.

Immobility of the fused segmentcauses additional stress on adjacentlevels of the vertebral column. Ossifi-cation of anterior longitudinal ligamentand facet disease are common compli-cations of anterior plate and screw fix-ation (Figure 6).9,17

In anterior fusion of the thoracic orlumbosacral spine, the devices shouldbe laterally located in the anterior col-umn. Neurologic deterioration is themost-feared complication of surgeryand may be caused by hardware move-ment or malpositioned screws (Figures12 through 15). Incorrect use and laterdislodgment or fracture of instrumentsmay also contribute to complicationssuch as instability, fusion failure orpain—with possible resultant neuro-logic damage. Postoperative neurologiccomplication due to lumbar instrumen-tation has been reported in 3% to 11%of patients undergoing spinal proce-dures. Postoperative neurologic injuriescan also be due to cord edema orhematoma and are often self-limited.30

Bone graft material can migrate orhypertrophy resulting in impingementon the spinal canal or neural fora-men.17,33,34 Radiographs often show the

failed instrument that may have causedneurologic deterioration. Rare but life-threatening complications such asdelayed aortic rupture due to instrumen-tation have also been reported.35

Infection is reported in 1% to 2.4% ofpatients undergoing lumbar instrumen-tation. Infection leads to bone destruc-tion and resorption around the implant.On imaging, a lucent area around animplant implies a loose appliance andpotential infection (Figures 8 through 9).CT-guided aspiration can be used to iso-late the microorganism. Unlike superfi-cial infections that can even be diag-nosed clinically, deeper infections suchas discitis are sometimes more challeng-ing. Osteomyelitis in adjacent vertebrae,disc collapse and destruction indicatediscitis radiographically. Radionuclide-labeled white blood cell scintigraphyand MRI can be helpful to detect infec-tion in early stages.36

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Failed fusion with the developmentof pseudarthrosis is a common endresult of implant failure or impropersurgical technique (Figures 5 and 6). Itsincidence in lumbar instrumentation isreported in 5% to 32% of patients. CT isthe optimal method for evaluating abone graft. A failed fusion with pseud-arthrosis formation results in continuedstress on the implant, and hardwarefracture is inevitable. Suda et al.described radiological risk factors forpseudarthrosis and/or instrument break-age after PLF with pedicle screws to berelated to preserved disc height and thepresence of segmental kyphosis.37

The risk of pseudarthrosis escalateswith increased patient age and smok-ing. Pseudarthrosis is more commonusing external braces than internal fix-ation. The rate of pseudarthrosis isdecreased with meticulous surgicaltechnique, including careful facet exci-sion and adequate graft placement.Repair is necessary if the patient pre-sents with implant failure or pain. Inasymptomatic patients, interventionmay be deferred and the patient’s con-dition should be followed.38,39

ConclusionRadiologists face new challenges as

the number of, and indications for,spinal surgery grow. Adequate under-standing of various surgical techniquesand instruments, coupled with improvedawareness of the possible complications,are vital when interpreting postoperativestudies. Radiologists should carefullycompare these critical points with base-line studies to develop a targeted assess-ment of grafts and hardware. With morefamiliarity of postoperative spinalimages obtained on various modalitiesand the knowledge of how certain situa-tions (e.g. surgical technique and hard-ware) contirbute to failed back surgerysyndrome, radiologists can quicklyarrive at a precise diagnosis, permittingappropriate treatment and minimizingpatient suffering.

REFERENCES1. Andersson GB. Epidemiological features ofchronic low-back pain. Lancet. 1999;354:581-585.

2. Deyo RA, Gray DT, Kreuter W, et al. UnitedStates trends in lumbar fusion surgery for degener-ative conditions. Spine. 2005;30:1441-1445; dis-cussion 1446-1447.3. Tehranzadeh J, Ton JD, Rosen CD. Advancesin spinal fusion. Semin Ultrasound CT MR.2005;26:103-113.4. Rosales-Olivares LM, Miramontes-Martínez V,Alpízar-Aguirre A, et al. Failed back surgery syn-drome. Cir Cir. 2007;75:37-41.5. Hadra BE. The classic: Wiring of the vertebraeas a means of immobilization in fracture and Pott’sdisease. Berthold E. Hadra. Med Times and Regis-ter. 1891;Vol 22. Clin Orthop Relat Res. 1975;112:4-8.6. Albee FH. The classic: Transplantation of a por-tion of the tibia into spine for Pott’s disease. JAMA.1911;57:885-887.7. Hibbs RA: A report of 59 cases of scoliosistreated by fusion operation. By Russel A. Hibbs,1924. Clin Orthop Relat Res. 1988;229:4-19.8. Mulholland RC. The myth of lumbar instability:The importance of abnormal loading as a cause oflow-back pain. Eur Spine J. 2008;17:619-625.9. Slone RM, MacMillan M, Montgomery WJ.Spinal fixation. Part 1. Principles, basic hardware,and fixation techniques for the cervical spine.Radiographics. 1993;13:341-356.10. Slone RM, MacMillan M, Montgomery WJ,Heare M. Spinal fixation. Part 2. Fixation tech-niques and hardware for the thoracic and lum-bosacral spine. Radiographics. 1993;13:521-543.11. Rutherford EE, Tarplett LJ, Davies EM, et al.Lumbar spine fusion and stabilizaion: Hardware,techniques, and imaging appearances. Radi-ographics. 2007;27:1737-1749.12 Berquist TH. Imaging of the postoperativespine. Radiol Clin North Am. 2006;44:407-418.13. Bartels RH, Donk RD, Feuth T. Subsidence ofstandalone cervical carbon fiber cages. Neuro-surgery. 2006;58:502–508. 14. Gercek E, Arlet V, Delisle J, Marchesi D. Sub-sidence of stand-alone cervical cages in anteriorinterbody fusion: Warning. Eur Spine J. 2003;12:513–516.15. Barsa P, Suchomel P. Factors affecting sagittalmalalignment due to cage subsidence in stand-alone cage assisted anterior cervical fusion. EurSpine J. 2007;16:1395-1400. 16. Riaz S, Fox R, Lavoie MV, Mahood JK. Verte-bral body reconstruction for thoracolumbar spinalmetastasis – a review of techniques. J Ayub MedColl Abbottabad. 2006;18:70-77.17. Slone RM, MacMillan M, Montgomery WJ.Spinal fixation. Part 3. Complications of spinal instru-mentation. Radiographics. 1993;13:797-816.18. Oskouian RJ Jr, Johnson JP. Vascular complica-tions in anterior thoracolumbar spinal reconstruction.J Neurosurg. 2002;96(1 Suppl):1-5.19. McAfee PC. Interbody fusion cages in recon-structive operation on the spine. J Bone Joint Surg[AM].1999;81-A:859-878.20. Min JH, Jang JS, Lee SH. Comparison of ante-rior- and posterior-approach instrumented lumbarinterbody fusion for spondylolisthesis. J NeurosurgSpine. 2007;7:21-26.21. Lemcke J, Klötzer S, Klötzer R, Meier U. PLIFand ALIF for the degenerative spondylolisthesis ofthe lumbar spine. Z Orthop Ihre Grenzgeb. 2007;145:48-54.22. Blumenthal SL, Ohnmeiss DD; NASS. Interver-tebral cages for degenerative spinal diseases. SpineJ. 2003; 3:301-309.

23. Ekman P, Moller H, Tullberg T, et al. Posteriorlumbar interbody fusion versus posterolateral fusionin adult isthmic spondylolisthesis. Spine. 2007;32:2178-2183.24. Weatherley CR, Prickett CF, O'Brien JP. Disco-genic pain persisting despite solid posterior fusion. J Bone Joint Surg Br. 1986;68:142-314.25. Brantigan JW, Steffee AD, Lewis ML, et al.Lumbar interbody fusion using the Brantigan I/Fcage for posterior lumbar interbody fusion and the variable pedicle screw placement system:Two-year results from a Food and Drug Adminis-tration investigational device exemption. Clinicaltrial. Spine. 2000;25:1437-1446.26. Ray CD. Threaded fusion cages for lumbarinter-body fusions: An economic comparison with360 degrees fusions. Spine. 1997;22:681–685.27. Cook SD, Patron LP, Christakis PM, et al.Comparison of methods for determining the pres-ence of anterior lumbar interbody fusion. Spine.2004;29:1118-112328. Heithoff KB, Mullin WJ, Holte D, et al. The fail-ure of radiographic detection of pseudoarthrosis inpatients with titanium lumbar interbody fusioncages. Paper presented at: International Societyfor the Study of the Lumbar Spine; June 1999;Kona, HI.29.Berquist TH, Currier BL, Broderick DF. Thespine. In: Berquist TH, editor. Imaging atlas oforthopedic appliances and prosthesis. New York,NY:Raven Press;1995:109-21530. Heller JG, Whitecloud TS III, Butler JC, et al.Complications of spinal surgery. In: Rothman RR,Simeone FA, eds. The spine. 3rd ed. Philadelphia,PA:Saunders;1992:1817-1898.31. Cho KJ, Suk SI, Park SR, et al. Complica-tions in posterior fusion and instrumentation fordegenerative lumbar scoliosis. Spine. 2007;32:2232-2237.32. Fountas KN, Kapsalaki EZ, Nikolakakos LG,et al. Anterior cervical discectomy and fusionassociated complications. Spine. 2007;32:2310-2317.33. Lowery GL, McDonough RF. The significanceof hardware failure in anterior cervical plate fixa-tion. Patients with 2- to 7-year follow-up. Spine.1998;23:181-186; discussion 186-187.34. Spanu G, Marchionni M, Adinolfi D, KnerichR. Complications following anterior cervical spinesurgery for disc diseases: An analysis of tenyears experience. Chir Organi Mov. 2005;90:229-240. 35. Ohnishi T, Neo M, Matsushita M, et al. Delayedaortic rupture caused by an implanted anteriorspinal device. Case report. J Neurosurg. 2001;95(2 Suppl):253-256. 36. Young PM, Berquist TH, Bancroft LW, Peter-son JJ. Complications of spinal instrumentation.Radiographics. 2007;27:775-789.37. Suda K, Ito M, Abumi K, et al. Radiologicalrisk factors of pseudoarthrosis and/or instrumentbreakage after PLF with the pedicle screw sys-tem in isthmic spondylolisthesis. J Spinal DisordTech. 2006;19:541-546.38. Schlegel J, Yunan HA, Fredricksen B. Ante-rior interbody fixation devices. In: Frymoyer JW,Ducker TB, eds. The adult spine: principles ofpractice. New York, NY: Raven;1991:1947-1959.39. Emami A, Deviren V, Berven S, et al. Outcomeand complications of long fusions to the sacrum inadult spine deformity: Luque-galveston, combinediliac and sacral screws, and sacral fixation. Spine.2002;27:776-786.


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