69728_Szpalski_Ch23.qxcl 8/9/06 8:31 PM Page 201 X STOP Interspinous Implant for Lumbar Spinal Decompression Jim F. Zucherman, Patrick Simons, and Jake Timothy Neurogcnic intcnnittent claudication (NIC) secondary to lumbar spinal stenosis (LSS) is a posture-dependent complaint and it typically affects patients at the age of 50 years or older. NIC is defined as pain or numbness in the buttocks, thighs, and/or lower legs caused by decrease of the spinal canal area and brought on by either prolonged standing or exercise in the erect posture. The symptom is typically relieved by various maneu vers that flex the lumbar spine, which increases the spinal canal area significantly(l-9). Dccomprcssive surgery widi or without fusion is tlie current gold standard treatment for moderate to severe symptomatic LSS. INTERSPINOUS PROCESS DECOMPRESSION (IPD) A new minimally invasive, stand-alone alternative to conservative and standard surgical decomprcssivc treatments has been dcveloped(10-13). The interspinous implant (X STOP, St. Francis Medical Technologies Inc., Alanicda CA) is placed between the spinous processes to prevent extension of tiie symptomatic levels, yet allowing flexion, axial rotation, and lateral bending (Fig. 23.1)(14). Eliminating the symptomatic extension at the abnormal segment and keeping it in diat position would maintain the asymptomatic state and allow the more normal spinal segments to function normally. The patient would no longer be forced to keep the entire lumbar spine in flexion just to maintain enough space at die localized stcnotic areas. Because the load-bearing element is anterior to the retained stipraspinous ligament a candlever effect results unloading the middle column of the spine while restoring height loss from degenerative ciianges. Tliis is bom out by biomechanical testing mentioned later. Also the retained pos terior supraspinous ligament prevents kyphotic defomilty as is verified by the radiographic studies mcndoncd later. The load that is taken up by tiic device is taken from die middle column of the spine, which has deteriorated from its inability to efficiently handle loads over the years. This then may allow slowing of the degenerative pnxiess or even some rccovei7 of inflamed chronically overloaded dssues over dme as is evidenced by the persistence of benefitfrom the device FIGURE 23.1 widi a 78% success rate at 4-year follow-up bascdlon implant. X STOP interspinous 201 -C)
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69728_Szpalski_Ch23.qxcl 8/9/06 8:31 PM Page 201
XSTOP Interspinous Implant forLumbar Spinal DecompressionJim F. Zucherman, Patrick Simons, and Jake Timothy
Neurogcnic intcnnittent claudication (NIC) secondary to lumbar spinal stenosis (LSS) isa posture-dependent complaint and it typically affects patients at the age of 50 years orolder. NIC is defined as pain or numbness in the buttocks, thighs, and/or lower legscaused by decrease of the spinal canal area andbrought on by either prolonged standingor exercise in the erect posture. The symptom is typically relieved by various maneuvers that flex the lumbar spine, which increases the spinal canalareasignificantly(l-9).
Dccomprcssive surgery widior without fusion is tlie currentgold standard treatmentfor moderate to severe symptomatic LSS.
INTERSPINOUS PROCESS DECOMPRESSION (IPD)
A new minimally invasive, stand-alone alternative to conservative and standard surgicaldecomprcssivc treatments has been dcveloped(10-13). The interspinous implant(X STOP, St. Francis Medical Technologies Inc., Alanicda CA) is placed between thespinous processes to prevent extension of tiie symptomatic levels, yet allowing flexion,axial rotation, and lateral bending (Fig. 23.1)(14). Eliminating the symptomaticextension at the abnormal segment and keeping it in diat position would maintain theasymptomatic state and allow the more normal spinal segments to function normally.The patient would no longer be forced tokeep the entire lumbar spine in flexion just tomaintain enough space at die localized stcnoticareas.
Because the load-bearing element is anterior to theretained stipraspinous ligament a candlever effect resultsunloading the middle column of the spine while restoringheight loss from degenerative ciianges. Tliis is bom out bybiomechanical testing mentioned later. Also theretained posterior supraspinous ligament prevents kyphotic defomilty asis verified by the radiographic studies mcndoncd later. Theload that is taken up by tiic device is taken from die middlecolumn of the spine, which has deteriorated from its inabilityto efficiently handle loads over the years. This then mayallow slowing of the degenerative pnxiess or even somerccovei7 of inflamed chronically overloaded dssues overdmeas is evidenced by the persistence of benefit from the device FIGURE 23.1widi a 78% success rate at 4-year follow-up bascdlon implant.
X STOP interspinous
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Oswcstry Disability Index (ODI) scores(15). Because sagittal balance effect is minimal,motionlimitation is minimal, and adjacent discand facet joint pressures are unaffected,there is no reason to believe the devicewill adversely affect the natural history of adjacent segments.
Biomechanical studies have shown that, in extension, the implant significandyincreases the canal area by 18%, the subarticular diameter by 50%, the canaldiameter by10%, the foraminal area by 25%, and the foraminal width by 41%.These dimensions werenot affected at adjacent levels. This is the primarymechanism of action(16). Wardlaw et al.reported equal results in their clinical study evaluating positional magnetic resonanceimaging (MRI) changes after X STOP implantation(17,18). Further studies have alsodemonstrated that that, at the implanted level, the implant significantly reduces the pressure on the facets, in the nucleus pulposus, and in the posterior annulus of the disc, without influence on adjacent levels(l6,19,20).
SURGICAL PROCEDURE
Patients may be operated on under local anesthesia with light intravenous sedation,placed in either lateral decubitus or prone posidon. A 4- to 8-cm midline incision ismade exposing the spinous processes at the appropriate disc level, which is confirmedradiographically. The supraspinous ligament and its attachments are preserved, whichis of paramount importance to prevent postoperative kyphosis and also to serve tostabilize the implant. The interspinous ligament is pierced, but retained, and theimplant is placed between the spinous processes. The spinous processes are not modi-fied to allow implantadon, but in cases where hypertrophied facets protrude posteriorly, they should be trimmed without interfering its integrity in funcdon (Rg. 23.2).The spinal canal is not violated, and neither laminotomy, nor laminectomy, norforaminotomy is performed. Removal of any pordon of the ligamentum flavum isunnecessary.
CLINICAL RESULTS IN LITERATURE
XSTOP Prospective Randomized Multicenter Study
Based on very promising results ofa clinical pilot study oftensymptomadc LSS padentstreated with the X STOP, a United States Food and Drug Administradon (US FDA)prospective randomized clinical muldcenter study was undertaken, comparing the interspinous implant with conservative (nonoperadve) treatment for the management ofNIC.Study results demonstrated a clinically andstadsdcally significant difference favoring the interspinous implant. Two years after the surgery, 60% of the padents reportedthat their symptoms were significandy improved, compared to 18% of the controlpadents. Regarding physical funcdon, 57% of X STOP patients reported significantimprovement, compared to15% ofcontrol padents. Among X STOP padents, 73% weresatisfied or very satisfied with their treatment compared to 36% of the control grouppadents (Table 23.1)(21).
Of interest, 39 patients with grade I degeneradve spondylolisthesis were treated inthe U.S. study with the X STOP and 22 padents were treated nonoperadvely. Using15-point improvement over baseline scores in the Zurich Claudicadon Quesdonnaire
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CHAPTER 23 X STOPInterspinous Implant for Lumbar Spinal Decompression
f
!k
FIGURE 23.2 TheXSTOP interspinous process decompression (iPD) implant procedure.
(ZCQi as the criterion of clinical success, 69% of the X STOP patients had a successfuloutcome at 2-year follow-up, compared to 9% of the control patients. The meanimprovement score for the39 X STOPpatients was 26points. Therewere no significantdifferences in the mean percentage of slip between X STOP and control patients atbaseline or at 2-year follow-up. The X ^OP represents a significantly less invasivealternative therapy for these patients, resulting in verygoodclinical outcomes, and mostimportantly, no evidence that the implant results in any instability of the motionsegment. In this study, more than a third of the patients treated with the X STOPimplant suffered from a degenerative spondylolisthesis up to grade 1 (out of4). Spondy-lolisthesis patients are mosdy treated with an instrumented spinal fusion. Analysis of
®this subgroup showed that the XSTOP procedure is as effective as that applied on ^patientswithout spondylolisthesis(22). "W
Furthermore, Implicito etal.(23) reported on their subanalysis of the X STOPpatients in this study, comparing 63 one-level and 33 double-level IPD patients. Withthe current surgical options, NIC patients treated surgically at multiple levels typicallyhave worse outcomes than those treated at one level. TWs study showed that bothX STOP groups had significant improvements postoperatively [p < 0.0001). Thesuccess rate of the one-level IPD patients was 56%m and for the two-level IPD patientsit was 73%, with no significant difference between the success rates, showing theX STOP to be an effective way to surgically treat patients with NIC at more thanone level.
Sagittal Balance
The requirement to maintain proper sagittal alignment andbalance inpatients receivingspinal implants iswell understood. Experience with lumbar fusion procedures thatcausea flat back hasoverwhelmin^y resulted in unacceptable clinical outcomes. Three different radiologic studies were therefore undertaken to measure any possible effect of theX STOP on sagittal alignment. In the U.S. study, x-rays were taken at each follow-upvisit for both X STOP and control patients and measurements were made of the lum-bosacral angle (LI toSI) andthetreated intervertebral angle. At2-year follow-up, therewere no significant differences iii the mean scores between the two groups of patients.Preoperative x-rays from a subset ofX STOP patients were also compared to standingfilms taken at 2-year follow-up. In 23 patients with single-level implants, the change inthe intervertebral angle was only 0.5 degree (±2.0 degrees), and the change in the
-0-
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CHAPTER 23 XSTOP Interspinous Implant for Lumbar Spinal Decompression
lumbosacral angle was 0.1 degree (±3.8 degrees). Similar values were recorded for18 patientswith double-level implants.
Interim data from an ongoingstudy beingconducted at the University of Aberdeenby Waidlaw and Smith(24) have been recendy presented, in whichpreoperadve imageswerecomparedto post implantimages obtainedin a posidonal MRI scanner. In additionto confirming in vivo the increases in the area of the foramen and canal that were measured in the preclinical in vitro cadaver study, results of this study confirm a change inangulation for both the lumbosacral angle and intervertebral an^e of between 1 and 2degrees. These three studies confirm that the X STOP results in only minimal changesto sagittal alignment. This due is to preserving the supraspinous ligament and itsoriginalinserdons. This ligament is a very robust structure receiving the confluence of thelumbodorsal fascia and itspreservadon prevents overdistracdon of thesegment.
XSTOP Versus Decompressive Laminectomy
The success rate of decompressive surgery varies gready due to a number of factorssuch as padent selecdon, surgical technique, and outcome measures. An attemptedmeta-analysis of 74 surgical LSS studies reported a mean rate of good to excellentoutcomesof 64%in the firstyear(25).
Compared to literature-reported outcomes ofdecompressive surgery therearesignificantdifferences in operadve time, esdmated blood loss, hospital stay, complicadon rate,and reoperadon rates, favoring the X STOP IPD(26-38) (Table 23.2).
During the course of the U.S. study, 24 padents in the control group underwentdecompressive laminectomy for the relief of their stenosis symptoms and outcomes areavailable for 22 padents. At a mean follow-up dme of 12.8 months outcomes for thesepadents were very similar to outcomes of the X STOP padents at 2-year follow-up.Sixty-four percent had clinically significant improvement in Symptom Severity Domainof ZCQj 68% had clinically significandy improvement in Physical Funcdon Domain ofZCQj and 60% were satisfied with the outcome of their treatment. Furthermore, Katzet al.(39) published a large series of surgically treated spinal stenosis patients using theZCQ^outcomes tool. When the same success criteria that were used in the X STOPseries are applied to Dr. Katz's series, the results in all threedomains are equivalent fortwo surgical procedures(40).
TABLE 23.2 XSTOP Decompression Versus Laminectomy
Operative andHospitallzation Details
XSTOP Laminectomy
AverageOR time (minutes) 27-54 104-224
Average blood loss (mL) 46 120-1,040Average lengthof hospital stay < 24 hours-2 days 7-8 daysOperadve or device-related 7% 20% (with arthrodesis)
Both the multicenter randomized clinical trial (RCT) study in the United StatesandStromqvist et al.,(41) as part of the Swedishnational registerof lumbar surgery, used theSF-36 to evaluate general health outcomes after surgical treatment. A comparisonbetween two matched subsets of patients, 90 each, showed that the postoperative scoreswere improved for both group's in all domains except for general health 1 year aftersurgery. Mean postoperative scores in the two physical and emotional domainsimproved more markedlyfor the X STOP group{42).
Okumu and Hannibal(43) evaluated the cost and effectiveness of X STOP andlaminectomy surgery during index hospitalization for the treatment of 33 patientswith LSS in the United States. Patients were matched for age, number of levelstreated, and preoperative disability. It was shown that X STOP is significantly morecost-effective than laminectomy for the treatment of single- and double-level LSS(Table 23.3).
Turner etal.(25) reported on complications such as dural tears, neural injuries,deep wound infections, pulmonary embolism, myocardial infarction, and death in theirmeta-analysis of 74 LSS surgery studies, lb date, with the exception of a death thatoccurred 3 days postoperatively and was determined to be unrelated to the X STOPimplant, there were no complications of this nature reported during or after theX STOP procedure.
German Registry
In Germany, a registry is being maintained to gather prospective data on NIC patients,whoare treated with theX STOP implant in general practice. Patients are assessed pre-and postoperatively using thevalidated, condition-specific ZCQ. The ZCQ^is the onlyvalidated LSS-specific outcomes measure(46,47). TTie questionnaire consists of threedomains: Symptom Severity (SS), Physical Function (PF), and PatientSatisfaction (PS),lb date 212 patients have been evaluated 1 year after surgery with very good results(Table 23.4). Two patients hada reoperation because of lack ofefficacy and onebecauseof dislocation of the implant.
TABLE 23.3 XSTOP Versus Laminectomy; Average Hospital Costs for Single- andDouble-Level Lumbar Spinal Stenosis(LSS)
Li addition to the German results presented here, Katz ctal.(33) reported otitcomeswith 2-year follow-up on 197 NIC patients treated widi a lumbar laminectomy using thesame success criteria in a patient population similar to those enrolled in the registry.
Tlic German X STOP patients show higlicr ZCQ^ success rates compared to thescores of thelaminectomy patients reported byKatz et al. (Eg. 23.3).
European Clinical Experience
Aprospective clinical evaluation of 15 patients with 3-and 6-month follow-up was carriedout byWardlaw(46) Inconjunction widi pre- andpostoperadve posldonal MRI scan measurements. All cases demonstrated clinical improvement and the X STOP implantincreased die cross-secdonal area of the dural sac and exit foramina without affectingoverall movement of die lumbai' spine.
Hcijnen and Kramer(47) reported on the satisfaction of 14padents with NIC, whowere treated widi the X STOP implant.One patient died of a non-backrelated disorder.Eleven of the other 13 padents expressed a great satisfaction. They arc free of NICsymptoms and all but one would undergo the surgery again, if the choice had to bemade again.
SCIENTIFIC EVIDENCE X STOP IN PERSPECTIVETO WORLDWIDE LITERATURE
Surgery for Degenerative Lumbar Spondylosis
Gibson and Waddcll(48) evaluated the current scientificevidenceon the effectiveness of surgicalinterventions fordegencradvc lumbar spondylosis, involving surgicalprocedures of spinal decompression, nerve root decompression,and fusion of adjacentvertebra.
Thirty-one published RCTs of all forms of surgicaltreatment for degenerative lumbarspondylosis were iden-dfied. There is moderate evidence that instrumcntadoncan incrcasc the fusion rate, but strong evidence diat itdoes not improve clinical outcomes.
Tlic trials varied a lot in quality: only in 16, morerecent, trials there was some form of centralized
Symptom
SeverityPatient
Satisfaction
• X STOP s Laminectomy
FIGURE 23.3 Zurich Claudication Questionnaire (ZCQ) success rates: X STOP versusiaminectomy patients reported by Katzet ai.
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208 NON-FUSION TECHNOLOGIES IN SPINE SURGERY
randomization scheme or assignment system. Eighteen of the 31 trials had the recommended follow-up for surgical studies of at least2 years. Only 6 trials reportedon thesurgical treatment for spinal stenosis and/or nerve root decompression. Just 1 of the6 trials was an RCT with a large pauent population, it concerns the prospectiverandomized clinical multicenter study, comparing the X STOP interspinous implantwith conservative (nonoperative) treatment(21) (Table 23.5).
Turner et al.(25) also reported on the poor scienddc quality of the published studiesin their attempted meta-analysis of 74 surgical therapy studies for LSS. None of the74 studies were randomized and just 3 studies were clearly prospective.
CONCLUSION
The decompression of the lumbarspine withX STOPIPD implant offers a well-proven,safe, effective, and cost-effective treatment of patients suffering from NIC secondary toLSS. The X STOPcanbe implanted withlocal anesthetic, and manypatients can returnhome within 24 hours after surgery.
In brief,regardingX STOP decompression of the lumbar spine:
• It is clinically well proven as an effective treatment for symptoms of LSS with orwithout degenerative spondylolisthesis.
• It is safe.
• It has a short surgery timeand can be made under local anesthesia.• It is minimally invasive.
TABLE 23.5 Scientific Review on DegenerativeSpondylosis; The Cochrane Review 2005
No. Randomized Controlled Trials 16
No. Clinical Controlled Trials 15
TOTAL 31
Six trials on spinal and nerve root stenosis
Author Year No. Patients Randomized Subject
Herkowitz 1991 50 No Decompression vs.decompression with fusion
Postacchini 1993 70 No Differentsurgical
BridweUdecompression techniques
1993 44 No Decompressionvs.
Grobdecompressionwith fusion
1995 45 No Decompression vs.decompression with fusion
Amundsen 2000 31 No SurgicalDecompressionvs.conservative
Zucherman 2004 200 Yes X STOP vs. conservative
treatment incl. epiduralinjections
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CHAPTER 23 X STOPInterspinous Implant for Lumbar Spinal Decompression 209
• It can be implanted during a short stationaryor ambulatorystay.
• There is an immediate and subsistentreliefof pain.• It is cost-effective.
The X STOP implant offers the benefits of decompression, yet with a low-riskprofile, for NIC patients.
The comparative analyses suggest that the outcomes of the X STOP decompressionmay at least be comparable to outcomes reported in the literature for decompressivelaminectomy. However, mainly due to flaws in studies on decompressive treatments, nodefinitive conclusions can be drawn.
ACKNOWLEDGMENT
For partidpadon in the German registry: Dr. D. Werner, Arkade Privatklinik, Nieder-schmalkalden; Dr. P. Simons, Medi^^k Klinik, Cologne; Dr. P. Krause, OrthopadischeSchmerztherapie, Munich; Dr. G. Godde, Gemeinschaftspraxis Konigsallee, Diisseldorf;and Dr. P. Mark, Westend Krankenhaus, Berlin.
2. Schoastrom N, Lindahl S, Willen J, HanssonT.Dynamic changes in the dimensions of the lumbar spinal canal: an experimental study in vitro.J Orthop Res 1989; 7:115-121.
3. Verbiest H. A radicularsyndrome from developmental narrowing of the lumbar vertebral canal.J BoneJoint SurgBr 1954;36: 230-237.
4. Willen J, Danielson B, Gaulitz A, Niklason T,Schonsirom N, Hansson T. Dynamic effects onthe lumbar spinal canal: axially loaded CT-myelography and MRI in padents with sciadcaand/or neurogenic daudicadon. Spine1997; 22:2968-2976.
5. Blau JN, Logue V. The natural history of intermittent daudicadon of the cauda equina. A longterm foUow-up study. Brain 1978; 101:211-222.
6. Chung SS, Lee CS, Kim SH, Chung MW. AhnJM. Effect of low back posture on the morphology of the spinal canal. Skeletal Radiol 2000; 29:217-223.
7. DongC, Porter RW. Walking and cycling tests inneurogenic and intermittent daudicadon. Spine1989;14:965-969.
8. Inuhisa A, An HS, Lim TH, Hasegawa T,Haughton VM, Nowicki BH. Anatomic changes
of thespinalcanaland intervertebral foramen associated with flexion-extension movement Spine1996;21:2412-2420.
9. Penning L, WilminkJT. Posture-dependent bilateral compression of L4 or L5 nerve roots in facethypertrophy. A dynamic CT-myelographic study.Spine 1987; 12:488-500.
10. ZuchermanJF, Hsu KY, Hartjen CA, MehalicTF, Implidto DA, Mardn MJ et al. A prospecdverandomized muld-centcr study for the treatmentof lumbar spinal stenosis with the X STOP interspinous implant: 1-year results. Eur SpineJ 2004;13: 22-31.
11. Zucherman JF, Hsu KY, Hartjen CA, MehalicTF, Implidto DA, Mardn MJ et al. Treatment ofLSS with an interspinous spacer. In: Trans IntMeeting on Advanced Spine lechniques 2002,Montreux.
12. Zucherman JF, Hsu KY, Harqen CA, MehalicTF, Implidto DA, Martin MJ et al. Treatment ofLSSwith an interspinous spacer. In: Trans NorthAmericanSpineSodety 2002, Montreal.
13. Zucherman JF, Hsu KY, Hargen CA, MehalicTF, Implidto DA, Mardn MJ et al. TreatmentofLSS with an interspinous spacer. In: TransEurospine 2002. Nantes, France.
"0^
69728_Szpalski_Ch23.qxd 8/9/06 8:31 PM Page 210
210
14. Lindsey DP, Swanson KE, Fuchs P, Hsu KY,ZuchermanJF, Tiferby SA.The effects of an inter-spinous implant on the kinematics of the instrumented and adjacent levels in the lumbar spine.Spine2003; 28:2192-2197.
15. Kondrashov D, Hsu K, Zucherman J. Subm.J Spinal Disord.[Ql]
16. Richards, J, Majumdar, S et al. The treatmentmechanismof an interspinousprocess implantforlumbar neurogenic intermitten claudicadon.Spine 2005; 30: 744-749.
17. Wardlaw D, Smith F, Pope M etal. Change inspinal canal and nerve root foraminal measurements before and six months following inserdonof the X STOP Interspinous ProcessDistracdonDevice in reladon to early clinical outcome. In:Trans ISMISS 2004, Zurich, Switzerland.
18. Siddiqui M, Karadimas E, Nicol M etal. Theposidonal MRI changes in the lumbar spine following inserdon of a novel interspinous processdistracdon device. In: Trans WorldSpine 2005,Rio deJaneiro, Brazil.
19. Swanson KE, Lindsey DP, Hsu KY, ZuchermanJF, Yerby SA. The effects of an interspinousimplant on intervertebral disc pressures. Spine2003; 28:26-32.
20. Wiseman CM, LindseyDP, Fredrick AD, YerbySA. The effect of an interspinous process implanton facet loading during extension. Spine 2005;30: 903-907.
21. ZuchermanJF, Hsu KY, Harqen CA, Mehalic TF,Implicito DA, Martin MJ etal. A muldcenter,prospecdve, randomized trial evaluadng theX STOP interspinous process decompressionsystemfor the treatment of neurogenic intermittentclaudicadon: two-year follow-up results. Spine2005; 15; 30:1351-1358.
22. Anderson PA. The effectof spondylolisthesis onthe outcomes of lumbar neurogenic intermittentclaudicadon padents treated with interspinousprocess decompression (IPD). In: Trans ISSLS2005 New York.
23. Implicito D, Martin M, Ozuna R. Outcomes ofneurogenic intermittent claudicadon padentstreated with interspinous process decompressionas a funcdon of numberof levels treated. SpineJ2005; 5: IS-90S.
24. Siddiqui M, Nicol M, Karadimas E, Smith F,Wardlaw D. The posidonal magnedc resonanceimaging changes in the lumbar spine followinginserdon of a novel interspinous process decompression device. Spine (in press).[^]
NON-FUSION TECHNOLOGIES IN SPINE SURGERY
25. TurnerJA, Ersek M, Herron L, Deyo R. Surgeryfor LSS. Attempted meta-analysis of the literature.Spine 1992; 17:1-8.
26. BenzRJ, Ibrahim ZG, AfsharP, Garfin SR. Predictingcomplicadons in elderly padents undergoing lumbar decompression. Clin Orthop 2001;384:116-121.
27. Deyo RA, Gherkin DC, LoeserJD, Bigos SJ,Ciol MA. Morbidity and mortality in associadonwith operadons on the lumbar spine. J BoneJoint Surg Am 1992; 74:536-543.
28. Iguchi T, Kurihara A, Nakayama J, Sato K,Kurosaka M, Yamasaki K. Minimum 10-yearoutcomeof decompressive laminectomy for degenerative LSS.Spine2000; 25:1754-1759.
29. Postacchini F, Cinotd G, Perugia D, Gumina S.The surgical treatment of central lumbar stenosis. Muldple laminotomy compared with totallaminectomy. J Bone Joint Surg Br 1993; 75:386-392.
30. Hu RW,Jaglal S, Axcell T, Anderson G. A popu-ladon-basedstudy of reoperadons after back surgery. Spine 1997;22: 2265-2271.
31. Jonsson B, Annertz M, Sjoberg C, Stromqvist B.A prospecdve and coasecudve study of surgicallytreatedLSS.Part II: five-year follow-up by an independent observer.Spine 1997;22:2938-2944.
32. KatzJN, Lipson SJ, Larson MG, MclnnesJM,Fossel AH, Liang MH. The outcome of decompressive laminectomy for degeneradve lumbarstenosis. J Bone Joint Surg Am 1991; 73:809-816.
33. KatzJN, LipsonSJ,Chang LC, LevineSA,FosselAH, Liang MH. Seven- to 10-year outcome ofdecompressive surgery for degeneradve LSS.Spine 1996; 21:92-98.
34. Hu RW,Jaglal S,Axcell T, AnderssonG. A popu-ladon-basedstudy of reoperadons after back surgery.Spine 1997; 22: 2265-2271.
35.Jonsson B, Annertz M, SjobergC, Stromqvist B.A prospecdve and consecutive study of surgicallytreated LSS. Part II: Hve-year follow-up byan independent observer. Spine 1997; 22:2938-2944.
36. KatzJN, Lipson SJ, Larson MG etal. The outcomeof decompressive laminectomy for degeneradve lumbar stenosis. J Bone Joint Surg Am1991; 73:809-816.
37. KatzJN, Lipson SJ, Larson MG, MclnnesJM,Fossel AH, Liang MH. Seven- to 10-year outcome of decompressive surgery for degeneradveLSS. Spine 1996; 21: 92-98.
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38. TimothyJ, Pal D, RossS, MarksP. Early experiencewith the X-STOP a lumbarspinous processdistractor for the treatment of lumbar canal steno
41. Stromqvist B,Jonsson B,Fritzell P,Ha^ O, Lars-son BE, Lind B. The Swedish National Registerfor lumbar spine surgery: Swedish Society forSpinal Surgery. Acta Orthop Scand 2001; 72:99-106.
42. Stromqvist B,Zanoli G, ZuchermanJ, Hsu K.SF-36 profiles before and one yearafterspinal stenosis surgery: a prospective comparison of twotechniques in two nations. In: Trans Eurospine2004, ^rto,Portugal.
43. Okuma K, Hannibal M. Cost analysis of interspinous process decompression versus laminec-tomy for the treatment of lumbarspinalstenosis.In Trans ISSLS 2005, New \brk.
44. StuckiG, LiangMH, Fossel AH, KatzJN. Relativeresponsiveness of condition specific and generichealth status measures in degenerative lumbarspinal stenosis. J Clin Epidemiol 1995; 48:1369-1378.[Q4]
45. Stucki G, Daltroy L, LiangMH, Lipson SJ,FosselAH, KatzJN. Measurement properties of a self-administered outcome measure in lumbar spinalstenosis. Spine 1996; 21:796-803.[Q5]
46. Wardlaw D. Change in spinal canal and nerveroot foraminal measurements before and sixmonths following insertionof the X STOP Interspinous Process Distracdon Device in reladon toearly clinical outcome. In: Trans ISMISS 2004,2kirich, Switzerland.
