LUMBAR DECOMPRESSION. Murat Cosar, MD, Larry T. Khoo, MD, Christopher A. Yeung, MD, and Anthony T. Yeung, MD

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1 A Comprison of the Degree of Lterl Reess n Forminl Enlrgement With Fet Preservtion in the Tretment of Lumr Stenosis With Stnr Surgil Tools Versus Novel Powere Filing Instrument: A Cver Stuy Murt Cosr, MD, Lrry T. Khoo, MD, Christopher A. Yeung, MD, n Anthony T. Yeung, MD ABSTRACT Bkgroun The SurgiFile (SurgiFile, In., Crls, Cliforni) is speilize tool esigne for the tretment of lterl reess n forminl stenosis tht llows surgeons to internlly expn n eompress the entire length of the neurl formen while preserving the integrity of the overlying fet omplex. Methos We use two veri speimens in this stuy. After they remove the lmin n spinous proesses of L2, L3, L4, n L5 from the orsl spine, fellowship-trine spinl surgeons use the stnr tools n the SurgiFile to the est of their experiene n ility on lternting sies of eh level to eompress the lterl reess n neurl formen while still preserving t lest 50% of the orsl fet omplex. Using preopertive n postopertive fine-ut CT sns with xil n sgittl reonstrutions, we evlute the egree of eompression n the mount of preserve fet omplex using nlytil tests n reoring the mesurements. Results The ifferene etween the proximl reess n lterl formen of the groups ws sttistilly signifint in the xil CT imges. On sgittl reonstrution CT imges, the ifferene etween the two groups ws signifint (P < 0.05, Wiloxon) only for the lterl formen. Although strong tren towr etter re hnge ws evient for the proximl reess mesurements in the experimentl tool sies, this i not hieve sttistil signifine. Mrosopi n CT sns mesurements showe tht the mount of fetetomy for equte eompression with the SurgiFile ws less thn the mount hieve with the stnr tools. Conlusions For the tretment of spinl stenosis, this novel powere-file instrument provies surgeons with new mens of eompressing the lterl reess n neurl formin. In this veri stuy, proeures performe with the SurgiFile tool showe sttistilly superior egree of eompression s ompre with the stnr surgil instruments n tehniques. Key Wors Forminl stenosis, lterl reess, spinl stenosis, spinl surgery. SAS Journl. Autumn 2007; 1: DOI: SASJ NT-R1 INTRODUCTION The entrl spinl nl n formen re efine y oth ony strutures (verterl oy, fets, peiles) n soft tissue strutures (ligmentum flvum, fet psules, interverterl is nnulus). With the ging proess, egenertive hnges our in the spine, using nrrowing of the entrl spinl nl re, the proximl formen (eg, lterl reess) n the lterl spet of the spinl formin. With progressive ging, y the ehyrtion of nuleus pulposus, the re etween iniviul vertere ereses. A erese in the is height n often le to impingement of the verterl enpltes n fet joints, resulting in sponylosis n the formtion of retive osteophytes. 1 3 Consequently, the formtion of mrginl enplte osteophytes, susiene n suluxtion of the fet proesses, seonry loss of forminl height, n thikening of the ligmentum flvum re the mjor egenertive hnges tht le to nrrowing of the entrl nl n neurl formen (Tle 1). Clssilly, lminetomy, lminotomy, n forminotomy hve een use in vrying omintions to tret spinl stenosis. 1,4 7 The egree of eompression, espeilly for the proximl reess n neurl formen, re limite y the egree of fet resetion. Wheres most eompressions o not le 135 AUTUMN 2007 VOLUME 01 ISSUE 04

2 Tle 1 The Preopertive n Postopertive Forminl Heights on Axil CT Sns (mm) Proximl Reess Lterl Formen Preop Postop Preop Postop Preop Postop Preop Postop Cver 1 L Cver 1 L Cver 1 L Cver 1 L5 S Cver 2 L Cver 2 L Cver 2 L Cver 2 L5 S Averge to postopertive spinl instility, over 30% to 50% of these proeures n result in erly or elye sponylolisthesis. 8,9 For suh ses, spinl fusion my lso e require to support the primry eompressive proeures. 4,9 18 As result of this lne etween the egree of eompression n the mount of inue postopertive spinl instility, inomplete eompression of the exiting nerves remins one of the most ommon uses of file k synrome in the literture. 13,19,20 Figure 1 We present our initil evlution of new surgil tool, the SurgiFile (SurgiFile, In., Crls, Cliforni), whih employs thin powere-file le esigne to slip into the proximl reess n then internlly expn the neurl formen long its entire ourse y shving off enrohing osteophytes n impinging fet eges while mximlly preserving the overlying fet joint omplex. We ompre the effetiveness of this tool in hieving neurl eompression with tht of stnr surgil tehniques in veri lumr experimentl stuy. Tehnil Properties of the SurgiFile Tool The SurgiFile is novel surgil tool for eompression of the neurl formen while spring the overlying fet joint omplex s muh s possile n proteting the unerlying neurl elements (Figure 1). Its ptente toroil rive funtionlly onverts stnr rotting motor rive s ylinril spinning motion (ie, Stryker TPS, Ansph emx, Mis Rex Legen) into smooth osillting liner motion tht is use to iretly rive speilly rete file le. This is omplishe without using ms or gers, therey elivering riving fore to the utting le with minimum torque, het, n energy loss. One n equte surgil exposure of the spinl lmin hs een me vi smll lminotomy or lminetomy, the thin osillting le of the evie is then use to expn the neurl formen from insie out, tehnique tht is in iret ontrst with the stnr pproh of outsie-in eompression for tretment of spinl stenosis (Figure 2). The SurgiFile tool is emonstrte with the thin re of the expose () utting surfe, () min toroil rive oy, () irrigtion inlet, n () the surgil rill motor. The surfe of the utting le ontins smll rise uttingones tht effetively shve hr ortil one into smll miron-size prtiles tht re wshe wy y the flow of sline solution provie y the integrte irrigtion pump n elivere through smll portl within the shft of the le. With the use of stnr sution tips, the surgeon is le to vne the tool progressively through the length of the neurl orrior with minimum of stoppges or exhnges euse the prtiles re too smll to log the sution tips. Finlly, the SurgiFile n e rotte roun the orsl spets of the formen, thus llowing the surgeon to eompress not only the osteophytes on the roof of the orrior ut lso those long the sie wlls of the formen. The SurgiFile mintins the integrity of the stilizing fet omplex uring forminl eompression euse it works using n insie-out tehnique n oes not require resetion of the overlying joint to gin ess to the meil n lterl forminl res (Tle 2). This 136 AUTUMN 2007 VOLUME 01 ISSUE 04

3 Figure 2 e e one winows) were otine to visulize n oument the size of the lterl reess n neurl formen t the L2 3, L3 4, L4 5, n L5 S1 levels. The vers were heke to ensure tht there ws no eformity or severe osteoporosis or prior spinl surgil eompression tht oul onfoun the experimentl results. The meil-lterl height of the neurl formen n reess were mesure on xil CT one winow slies. The level of the proximl reess ws efine s the re immeitely jent to the meil orer of the superior rtiulting fet proess n the meil orer of the peile. The level of the lterl formen ws efine s the re immeitely sujent to the lterl spet of the inferior rtiulting fet proess n lterl orer of the peile (Figure 3). On sgittl reonstrutions, ross-setionl re mesurements were otine t the level of the proximl reess n lterl formen s well. These mesurements were lulte with the i of stnr omputer-se visuliztion n imge nlysis softwre t the L2 3, L3 4, L4 5, n L5 S1 levels. () The SurgiFile tool is emonstrte here ompleting n insie-to-outsie eompression long the entire length of the neurl forminl orrior. Beuse only the orsl surfe of the working le is tive, the SurgiFile tip n e use iretly over the expose () thel s n nerve root. () SurgiFile sie. () Stnr sie. (e) Fet joint. pility is in strk ontrst to stnr tehniques, whih require resetion of the overlying fet omplex with either rill or Kerrison rongeurs to provie ess to the unerlying neurl formen. Even with ggressive unerutting, suh stnr surgil tehniques often result in signifint resetion of the fet omplex, therey ontriuting to the phenomenon of postopertive spinl instility, whih n e voie with the use of the SurgiFile for eompression. MATERIALS AND METHODS In two veri lumr segments, preopertive xil n sgittl CT sns (5 mm overlpping, nonontrst sequenes, Three experiene fellowship trine neurologil n orthopei spinl surgeons performe the experimentl eompressions. During the opertive portion of the proeure, the surgeons use stnr miline pproh with superiostel exposure of the L2 S1 lmin n susequent plement of self-retining retrtors. The issetion ws rrie out more lterlly thn for usul lminetomy proeures to provie full exposure of the fet omplex. The spinous proesses were then resete with miline lminetomy performe to the level of the meil fet using stnr Kerrison rongeurs n n irpowere surgil rill with mthstik it tthment. One the miline eompression ws hieve, the surgeons performe lterl reess n forminl eompression in rotting fshion using either stnr surgil tools (surgil rill with mthstik tthment/kerrison rongeurs/urettes) or the SurgiFile le (with only initil use of urettes n Kerrisons to enter the proximl reess). The extent of the eompression Tle 2 The Preopertive n Postopertive Forminl Are on Sgittl CT Sns (mm2) Proximl Reess Lterl Formen Preop Postop Preop Postop Preop Postop Preop Postop Cver 1 L Cver 1 L Cver 1 L Cver 1 L5 S Cver 2 L Cver 2 L Cver 2 L Cver 2 L5 S Averge 1, , , , , , , , AUTUMN 2007 VOLUME 01 ISSUE 04

4 Figure 3 Tle 3 Preop n Postop Forminl Length Inrese on Axil CT Sns (%) Proximl Reess Lterl Formen Cver 1 L Cver 1 L Cver 1 L Cver 1 L5 S Cver 2 L Cver 2 L Cver 2 L Cver 2 L5 S Averge 1, , , , Tle 4 Preop n Postop Forminl Are Inrese on Sgittl CT Sns (%) The lnmrks of the neurl formen re shown in the xil CT sn imge. () Lterl formen; () proximl reess. ws stoppe when the opertive surgeon oserve tht no more fet oul e sfely resete to mintin segmentl stility (more thn 50%) or tht the proximl reess n neurl formen h een ompletely eompresse, s onfirme y Wooson elevtors n nerve hooks. The eompressions were rrie out on sie-to-sie omprison etween the ontrol n experimentl groups. The SurgiFile tool ws use in the leftsie lumr formin in the first ver (four levels: L2 3, L3 4, L4 5, n L5 S1) n the right-sie lumr formin in the seon ver. In eh spinl level Wooson elevtors were use intropertively for quntittive ssessment of the eompression (poor/goo). The surgeons etermine the extent of fet resetion hieve (less thn 25%, 25% to 50%, 50% to 75%, or more thn 75%). After the eompression proeure, the two vers were re-imge y CT fine-ut snning using the sme protool s we use preopertively. The line-riologist ws lso etermine n reore these mesurements. RESULTS The forminl length n re in the meil n lterl prts of the lumr verterl formin were mesure efore n fter lminetomy, n the forminl eompression ws ssesse using xil n sgittl CT sns in onjuntion with omputerize imge viewing n nlysis softwre (Tles 3 n 4; Figure 4, 4). Compring the rw preopertive n postopertive t, we oserve ler solute numeril inrese in the forminl height on xil imging n in the ross-setionl re on sgittl imging in oth the stnr n SurgiFile groups. After the sizes of reess n lterl formin were mesure on xil n sgittl CT sns, the Proximl Reess Lterl Formen Cver 1 L Cver 1 L Cver 1 L Cver 1 L5 S Cver 2 L Cver 2 L Cver 2 L Cver 2 L5 S Averge 93,5 59,5 73,625 10,5 perentge of hnge in the height n ross-setionl re for the proximl reess n lterl formen ws lulte for the stnr n SurgiFile groups, respetively (Figure 5, 5, 5, 5). As preite, n solute inrese ws seen in terms of perent hnge for oth groups s well (Figure 6, 6). The results of the sttistil nlysis revele tht the perentge of hnge in the proximl reess n lterl forminl height on xil CT sns ws signifintly higher in the SurgiFile group (P < 0.05, Wiloxon). Similrly, the perentge of hnge in the lterl forminl ross-setionl sgittl res ws signifintly higher in the SurgiFile group (P < 0.05, Wiloxon). Although we oserve ler n strong tren towr lrger solute ross-setionl res in the postopertive group t the level of the proximl reess, these ifferenes i not hieve sttistil signifine (P = 0.263, Wiloxon). On xil n sgittl CT imges, the fet omplex n intervening joint line oul e seen. 138 AUTUMN 2007 VOLUME 01 ISSUE 04

5 Figure Preop Postop Preop Postop Preop Postop Preop Postop Figure 5 Meil formen Lterl formen Preop Postop Preop Postop Preop Postop Preop Postop Meil formen Lterl formen () Axil A-P forminl sizes; n () sgittl forminl res re shown. However, the fet volumes oul not e mesure with solute ertinty ue to the onstrints of the imging tehnique n the nlysis softwre. Qulittively, however, more of the fet omplex ws mintine t nerly every level in the SurgiFile group, s seen on CT imging n iret visul inspetion (Figure 7, 7). DISCUSSION In this ver stuy, we ompre the stnr tools (rill, Kerisson ronguers, n others) with novel tool SurgiFile tht ws speifilly esigne for the trement of reess n forminl stenosis with the im of mximl eompression while mintining the integrity of the overlying fet omplex. The eginning of the surgil proeures (removl of spinous proess, lminetomy) ws similr in oth the experimentl n ontrol groups. After the lminetomy step, the surgeons use the SurgiFile for forminl eompression on one sie of the lumr segment n the stnr tools (rill, Kerrison, urettes) on the other sie. The linly evlute results suggest tht the SurgiFile tool mintins the stility of the vertere with qulittively greter preservtion of the overlying fet omplex while eompressing the neurl elements. Centrl nl stenosis is fr less ommon thn the synromes of lterl reess n forminl stenosis from fet hypertrophy in omintion with enrohment of the interverterl iss. Deompression of the trversing n exiting roots is ommon gol in opertive tretment for spinl stenosis. Beuse the fet joint forms the orsl orer of oth the proximl n lterl neurl formen, Comprison of sgittl CT sns showing () meil proximl reess res efore (left) n fter (right) use of SurgiFile tool; () lterl forminl res efore (left) n fter (right) use of SurgiFile tool; () meil forminl res efore (left) n fter (right) use of stnr tools; n () lterl forminl res efore (left) n fter (right) use of stnr tools. 139 AUTUMN 2007 VOLUME 01 ISSUE 04

6 Figure 6 Figure Meil formen Lterl formen Meil formen Lterl formen () Postopertive hnge in Axil A-P forminl istne; n () perentge of hnge in the sgittl forminl re. suessful nerve eompression typilly mntes some ony resetion of the joint omplex. This effet is lssilly hieve with omintion of rilling n unerutting with Kerisson ronguers in n ngle fshion. 5,8,19,20 Due to the outsie-in pproh use in tritionl spinl surgery, ertin egree of fet joint violtion n estiliztion is inevitle uring most opertions for spinl stenosis. Consequently, uring lssil eompression of the ffete neurl elements in spinl stenosis using stnr surgil tools, itrogeni estiliztion of the operte spinl segments n our erly or e progressive over time. The lne etween these two opposing gols results in the ommonly enountere linil prolems of either persistent riulopthy when the neurl elements re not equtely eompresse or spinl instility n k pin when the formen is fully eompresse n too muh of the fet joint omplex hs een resete. 5 7,13,17 We think tht the SurgiFile tool my llow surgeons to perform n internl eompression not only of the jent lmin t the level of the surgil proeure ut lso of the entire neurl formen. After initilly reting enough lminotomy exposure with stnr urrettes n Kerrisons, the surgeons oul mneuver the SurgiFile ngle tip in the sme mnner s with Wooson to engge the internl surfe of the lminofet juntion unersurfe. Then, through the osillting tion of the SurgiFile, the surgeon n rpily n sfely file own the inner ortex of the lmin to wien the spinl () Preopertive mrosopi visul omprison of the SurgiFile versus the stnr sies emonstrtes the greter fet preservtion overll in the SurgiFile sie fter neurl eompression; () Postopertive omprisons of the; () Stnr sie on xil CT emonstrtes greter qulittive preservtion of the fet joints; n the () SurgiFile sie. nl. The SurgiFile is thus shiele to protet the unerlying neurl strutures. The SurgiFile tip oul e steere rostrlly n ully to unerut further the jent lmin while preserving the outer ortex of the lmin with its funtionlly importnt musulo-ligmentous tthments. The surgeon enters the lterl reess or proximl spet of the neurl formen with the tip of the SurgiFile tool. The tool is then use to hieve n internl eompression from the insie out of the neurl formen while mximlly preserving the rtiulting surfe of the fet joint omplex. Beuse the tool n e rotte roun the yliner of the nerve root, the impinging fets n e eompresse oth rostrlly n ully long 140 AUTUMN 2007 VOLUME 01 ISSUE 04

7 the sie wlls of the neurl formen. Beuse the inferior surfe of the SurgiFile tip is smooth, it oul e psse sfely long the surfe of the existing nerve root ll the wy to the lterl formen to hieve omplete eompression long the entire length of the forminl yliner. Both of these opertive mneuvers re unique to the SurgiFile tool. Finlly, the risk of invertent url injury uring eompression ppers to e less for the SurgiFile le with its protete unersurfe s ompre to the iting ege of the Kerrison rongeurs or the more perilous tip of the spinning rill it. We think tht the potentil for neurl injury with the SurgiFile le is less thn tht for stnr tools euse of the smooth unersurfe re n ovl-shpe eges. A smll mount of risk might result from the het generte y the evie uring osilltion, ut this n e eliminte y wshing the opertion re with sline through the irrigtion inlet of the evie. This moel of the SurgiFile evie is suitle for some ses of minimlly invsive surgery, ut if the ngle of the le is inrese, it oul e use in most minimlly invsive surgery ses. In this ver stuy, we performe fetetomy t ll levels n emonstrte n inrese in the size of the proximl reess n lterl formin overll in oth the SurgiFile n stnrtool groups fter forminotomy. However, the verge inreses in the tul height (mm) n ross-setionl res (mm 2 ) t oth the proximl reess n lterl formin were greter in the SurgiFile group thn in the ontrol group. Anlysis of the ifferenes in perent hnge for proximl reess n lterl forminl height on xil CT sns lso revele sttistilly signifint ifferenes etween the SurgiFile n stnr groups (P < 0.05, Wiloxon). As eompression of the proximl formen or lterl reess n e reily hieve vi oth existing stnr surgil tools n the SurgiFile le, the perent hnge etween two groups for proximl reess res ws not signifint (P = 0.263, Wiloxon). Wheres eompression with stnr tools h to e stoppe more meilly to voi exessive resetion of the fet, the SurgiFile utting le ws esily rotte n psse long the nerve out to the lterl orer of the formen. Consequently, the mile n outer setions of the neurl formen were fr less effetively eompresse in the stnr group. As result, the perent hnge in the lterl forminl ross-setionl res ws sttistilly greter with the SurgiFile thn with the stnr tools (P < 0.05, Wiloxon). Beuse the SurgiFile worke from the insie-out s oppose to the outsie-in tehnique of unerutting with Kerrison rongeurs n rill its, we were le to oserve fr greter egree of fet preservtion in the SurgiFile group on gross visul inspetion n on CT xil sn imges (Figure 7, 7). Bse on exmples from the linil n iomehnil literture, greter preservtion of the funtionl fet joint woul likely erese the risk of itrogeni postlminetomy instility n therey voi the nee for simultneous or susequent spinl fusion. 8,9 With the inresing populrity of less invsive spinl surgil tehniques, the SurgiFile le will lso llow surgeons to eompress spinl stenosis through minimlly invsive lminotomy exposure. Beuse the le n shve off spurs n the internl spets of the fet n lmin, the outer orties of the ony spinl ntomy, with its funtionlly importnt musulr n ligmentous tthments, remin intt. This tehnique my offer the itionl enefits of erese musle trum n loo loss, more rpi postopertive reovery, n etter long-term funtion for oler ptients with lumr stenosis. In ses of lumr totl is replement, preexisting isese n previous surgil resetion of the fet re reltive ontrinitions. The minimlly invsive insie-out type of eompression hievle with the SurgiFile le my e prtiulrly relevnt in the emerging ge of spinl rthroplsty, for whih the primry ojetive is to mintin the overll motion n ynmi stility of the spinl segment. Bse on these finings n our initil experiene with the SurgiFile le, we elieve tht it offers severl potentil linil vntges over the existing stnr surgil tools use for spinl eompression. These vntges inlue more effetive reess n forminl eompression, etter fet preservtion, erese iniene of postopertive or itrogeni instility, n less nee for susequent rthroesis n stiliztion. Ultimtely, the SurgiFile le my funmentlly lter the mnner in whih surgeons tret spinl stenosis, therey reuing the risk, moriity, n omplition rtes of these proeures. Murt Cosr,, MD, Lrry T. Khoo, MD, Christopher A. Yeung, MD, n Anthony T. Yeung, MD From the Deprtment of Neurosurgery, Cnkkle 18 Mrt University of Meil Shool, Cnkkle, Turkey (Cosr), the Division of Neurosurgery, UCLA, Los Angeles, Cliforni (Khoo), n the Arizon Institute for Minimlly Invsive Spine Cre, Phoenix, Arizon (C.A. Yeung n A.T. Yeung). Aress orresponene n reprint requests to Murt Cosr, MD, Cnkkle 18 Mrt University, Fulty of Meiine, Deprtment of Neurosurgery, Cnkkle, Turkey (emil:rosr@hotmil.om). This sumission ws reeive July 3, 2007 n epte on Otoer 18, Note: There re no outsie funing soures for uthors of this stuy. This stuy ws pprove y the Institutionl Review Bor. REFERENCES 1. Herno A, Sri T, Suomlinen O. The egree of eompressive relief n its reltion to linil outome in ptients unergoing surgery for lumr spinl stenosis. Spine. 1999;24: Johnsson KE, Rosen I, Uen A. The nturl ourse of lumr spinl stenosis. Clin Orthop. 1992;279: Ktz JN, Dlgs M, Stuki G, Lipson SJ. Dignosis of lumr spinl stenosis. 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