Lumbar laminectomy for spinal stenosis is one of the

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1 J Neurosurg Spine 18: , 2013 AANS, 2013 Radiographic predictors of delayed instability following decompression without fusion for degenerative Grade I lumbar spondylolisthesis Clinical article Claire Blumenthal, 1,2 Jill Curran, M.S., 2 Edward C. Benzel, M.D., 3 Rachel Potter, B.A., 2 Subu N. Magge, M.D., 4 J. Frederick Harrington Jr., M.D., 5 Jean-Valery Coumans, M.D., 6 and Zoher Ghogawala, M.D. 2,4 1 Harvard University, Cambridge; 4 Department of Neurosurgery, Lahey Clinic Medical Center, Burlington; and 6 Department of Neurosurgery, Massachusetts General Hospital, Boston, Massachusetts; 2 Wallace Clinical Trials Center, Greenwich Hospital, Greenwich, Connecticut; 3 Department of Neurosurgery, Cleveland Clinic, Cleveland, Ohio; and 5 Department of Neurosurgery, University of New Mexico, Albuquerque, New Mexico Object. It is not known whether adding fusion to lumbar decompression is necessary for all patients undergoing surgery for degenerative lumbar spondylolisthesis with symptomatic stenosis. Determining specific radiographic traits that might predict delayed instability following decompression surgery might guide clinical decision making regarding the utility of up-front fusion in patients with degenerative Grade I spondylolisthesis. Methods. Patients with Grade I degenerative lumbar spondylolisthesis (3 14 mm) with symptomatic stenosis were prospectively enrolled from a single site between May 2002 and September 2009 and treated with decompressive laminectomy without fusion. Patients with mechanical back pain or with gross motion (> 3 mm) on flexionextension lumbar radiographs were excluded. The baseline radiographic variables measured included amount of slippage, disc height, facet angle, motion at spondylolisthesis (flexion-extension), and sagittal rotation angle. Data were analyzed using multivariate forward selection stepwise logistic regression, chi-square tests, Student t-test, and ANOVA. Results. Forty patients were enrolled and treated with laminectomy without fusion, and all patients had complete radiographic data sets that were available for analysis. Reoperation was performed in 15 (37.5%) of 40 patients, with a mean follow-up duration of 3.6 years. Reoperation was performed for pain caused by instability at the index level in all 15 cases. Using multivariate stepwise logistic regression with a threshold p value of 0.35, motion at spondylolisthesis, disc height, and facet angle were predictors of reoperation following surgery. Facet angle > 50 was associated with a 39% rate of reoperation, disc height > 6.5 mm was associated with a 45% rate of reoperation, and motion at spondylolisthesis > 1.25 mm was associated with a 54% rate of reoperation. Patients with all 3 risk factors for instability had a 75% rate of reoperation, whereas patients with no risk factors for instability had a 0% rate of reoperation (p = 0.14). Conclusions. Patients with motion at spondylolisthesis > 1.25 mm, disc height > 6.5 mm, and facet angle > 50 are more likely to experience instability following decompression surgery for Grade I lumbar spondylolisthesis. Identification of key risk factors for instability might improve patient selection for decompression without fusion surgery. Clinical trial registration no.: NCT ( Key Words degenerative lumbar spondylolisthesis reoperation radiographic predictor outcome laminectomy Lumbar laminectomy for spinal stenosis is one of the most common spine operations performed in people over the age of 65 years in the US. 21 The choice Abbreviations used in this paper: ODI = Oswestry Disability Index; PCS = physical component summary; SF-36 = 36-Item Short- Form Health Survey; SPORT = Spine Patient Outcomes Research Trial. of surgical treatment for degenerative lumbar spondylolisthesis with symptomatic stenosis represents a clinical dilemma for many practicing surgeons. Although there is evidence to support the use of fusion when performing a decompressive laminectomy, 9,12,17,24 there are limited data regarding the comparative effectiveness of performing a lumbar fusion with laminectomy versus laminectomy alone in actual US practice. Particularly for the elderly, 340 J Neurosurg: Spine / Volume 18 / April 2013

2 Radiographic predictors of reoperation following laminectomy the optimal surgical treatment is unclear. Many surgeons perform laminectomy without fusion for many of these patients. We previously reported higher rates of reoperation following laminectomy alone versus laminectomy with lumbar spinal fusion. 11 Specifically, we found nearly a 3-fold increase in reoperations for patients treated with laminectomy alone compared with patients in whom a fusion was added to a laminectomy. Despite higher rates of reoperation, laminectomy without fusion has been found to be associated with fewer complications and good functional outcomes. 14,18,20 Defining risk factors for failure following laminectomy may make it easier to separate patients who are optimal candidates for laminectomy from those who are most at risk for developing delayed instability. The objective of this study was to identify specific radiographic traits that predict delayed instability following decompression surgery. We prospectively collected preoperative radiographic data to identify risk factors for developing spinal instability following laminectomy with long-term follow-up. Methods Clinical Data and Eligibility Patients with Grade I degenerative lumbar spondylolisthesis (3 14 mm) were prospectively enrolled from a single site between May 2002 and September Patients years of age with symptomatic lumbar neurogenic claudication with or without radiculopathy were eligible. Patients with mechanical back pain, gross motion (> 3 mm) on flexion-extension lumbar radiographs, history of previous lumbar spinal surgery, or serious medical illness (American Society of Anesthesiologists Class III or higher) were excluded. Mechanical back pain was defined as back pain produced by standing for > 5 min or by lifting > 20 lbs. This type of back pain was relieved in all patients by lying supine. Approval from the institutional review board at Greenwich Hospital was obtained prior to initiating the study. Informed consent was obtained in all patients. This clinical trial is registered as the Greenwich Lumbar Stenosis SLIP Study (clinical trial registration no. NCT , Radiographic Measurements In all patients lumbar flexion-extension plain radiographs, lumbar CT scans, and lumbar MRI studies were performed prior to surgery. Two independent neuroradiologists examined each film to confirm eligibility for the study. Baseline radiographic variables measured included amount of slippage, disc height, facet angle, motion at spondylolisthesis (flexion-extension), and sagittal rotation angle. 14 Preoperative CT images were used to calculate facet angle as described previously. 10 Figure 1 demonstrates how these measurements were made. For purposes of analysis, radiographic measurements were made by 2 independent radiologists as well as the principal spine surgeon investigator (Z.G.). J Neurosurg: Spine / Volume 18 / April 2013 Outcomes Assessments Outcomes assessments (ODI 8 and SF-36) were obtained preoperatively and then postoperatively at 6 weeks, 3 months, 6 months, and 1, 2, 3, 4, and 5 years. The PCS scores were calculated from the SF The outcomes assessments were either completed by patients in the office or mailed, completed at home, and returned to the office. Any discrepancy in the questionnaires was addressed by the research study coordinator, who was not directly involved in patient care. Surgical Treatment All patients underwent surgery at the discretion of the surgeon and patient. Decompressive laminectomy with facet sparing was performed in all cases. 10 All reoperations consisted of posterolateral fusion with or without interbody fusion performed at the index level for instability. Data Analysis The data were analyzed using commercially available software (Stata version 11.2, Stata Corp.). Statistical analysis was performed using the chi-square test to compare categorical variables and the Student t-test to compare continuous variables. Repeated-measures ANOVA was used to assess improvement in outcomes over time. A p value < 0.05 was considered statistically significant. Multivariate regression was used to determine which radiographic variables were predictors of reoperation. For the purpose of building a multivariate logistic model, forward selection stepwise regression with a threshold p value of 0.35 was used. Results Patient Population Forty patients met inclusion criteria and were enrolled from a single site between 2002 and All patients were treated with traditional open lumbar laminectomy without fusion by 1 surgeon (Z.G.). No minimally invasive techniques were applied to this study population. For this study, radiographic measurements were completed in all patients. The average age was 68.2 years, and 30 (75%) of the 40 patients were female. The average baseline SF- 36 PCS score was 36.1 ± 7.0 and the average baseline ODI score was 33.7 ± 15.2 (Table 1). Reoperation Data The reoperation rate was 15 (37.5%) of 40, with a mean follow-up of 3.6 years. Four of these 15 patients underwent reoperation within 6 months of the index procedure. Reoperation was performed for mechanical lowback pain presumably caused by instability at the index level in all 15 cases. Baseline patient demographic and radiographic features were similar between groups with and without reoperations, with the exception of baseline motion at spondylolisthesis (p = 0.02) (see Table 1). Postoperative Complications There were 2 complications (5%) within 30 days of surgery. There was 1 major wound infection resulting in readmission to the hospital. Another patient experienced 341

3 C. Blumenthal et al. Fig. 1. A D: Flexion and extension digital plain radiographic images were used to determine motion at the level of spondylolisthesis (1.46 motion in this case example [A and B]). Sagittal rotation angle was also calculated from digital flexion-extension images. The angles in extension (C) and flexion (D) were used to generate a sagittal rotation angle of 7 in this case example. E G: Lumbar CT scans. Disc height (E) was measured on preoperative lumbar CT scans by using a midsagittal image and measuring the distance from the midpoint of the endplate at the level of spondylolisthesis. Facet angle (F) was measured by calculating the angle generated by connecting the 2 end points of each facet on a preoperative axial lumbar CT (midcut through the disc) and a line connecting the 2 dorsal points of each facet joint. When the facet angles were different (right side vs left side), the average value was used (57.5 in this example). A facet-sparing procedure was used in all cases (G). a new sensory deficit within 30 days of surgery. Neither patient underwent a reoperation. There were no CSF leaks in either group. There were no 30-day complications for any of the patients who underwent a reoperation. Risk Factors for Instability Using multivariate forward selection stepwise logistic regression with a threshold p value of 0.35, motion at spondylolisthesis, disc height, and facet angle were predictors of reoperation following surgery, with p values of 0.033, 0.102, and 0.187, respectively (Table 2). Higher risk of reoperation was observed with each of the radiographic predictors determined. Facet angle > 50 was associated with a 39% rate of reoperation, disc height > 6.5 mm was associated with a 45% rate of reoperation, and motion at spondylolisthesis > 1.25 mm was associated with a 54% rate of reoperation. Patients with all 3 risk factors for instability had a 75% rate of reoperation, whereas patients with no risk factors had a 0% rate of reoperation (p = 0.14) (Fig. 2). Outcomes Assessment Significant improvements following lumbar laminectomy were observed and persisted through 5 years of 342 J Neurosurg: Spine / Volume 18 / April 2013

4 Radiographic predictors of reoperation following laminectomy TABLE 1: Demographic and radiographic features of the total group and the no reoperation and reoperation cohorts in 40 patients with lumbar spondylolisthesis* Feature All Laminectomy No Reop Reop no. of patients age (yrs) 68.2 ± ± ± 7.3 no. female (%) 30 (75.0) 17 (68.0) 13 (86.7) facet angle ( ) 57.4 ± ± ± 13.0 motion at spondylolisthesis (mm) 1.1 ± ± ± 1.0 extent of slippage (mm) 6.3 ± ± ± 1.8 disc height (mm) 6.9 ± ± ± 3.0 sagittal rotation angle ( ) 10.9 ± ± ± 7.6 SF-36 score 36.1 ± ± ± 7.1 ODI score 33.7 ± ± ± 15.7 * Values are expressed as the mean ± SD, unless otherwise noted. Value represents statistically significant difference between no reoperation and reoperation groups (p = 0.02). follow-up. Improvement was documented using both ODI and SF-36 PCS outcomes assessments (p < 0.001) (Fig. 3). The 15 patients who ultimately underwent fusion for delayed instability had a trend toward worse ODI and SF- 36 PCS scores at 3 and 6 months postoperatively (delayed instability was diagnosed and treated in 11 of 15 patients after 6 months) (Fig. 4). Patients who underwent a reoperation experienced statistically significant improvements in both disease-specific (ODI; p < 0.01) and quality of life (SF-36 PCS; p < 0.001) outcomes 1 year following reoperation (Fig. 5). Discussion We found a relatively high rate of reoperation following laminectomy without fusion when treating patients with degenerative Grade I lumbar spondylolisthesis with symptomatic lumbar spinal stenosis. We were able to identify 3 risk factors for reoperation: 1) motion at spondylolisthesis > 1.25 mm; 2) disc height > 6.5 mm; and 3) facet angle > 50. These risk factors for instability were identified from a prospective cohort in which all patients were treated initially with laminectomy without fusion. In this study, patients with no risk factors for instability had a minimal chance of requiring fusion at the index level of laminectomy, whereas patients with 3 risk factors had a 75% chance of developing delayed instability. Comparative Studies: Fusion Versus No Fusion for Grade I Lumbar Spondylolisthesis A number of studies have examined the question of whether laminectomy alone or laminectomy with fusion is the most effective surgical treatment for patients with degenerative Grade I lumbar spondylolisthesis. 2,12,17,24 The current evidence points in favor of fusion added to laminectomy, but the results of studies have been inconsistent and most studies have not included validated outcome measures. In the most recent lumbar fusion guidelines that were published regarding the use of fusion for degenerative disease of the lumbar spine, fusion was recommended, but a treatment guideline could not be provided due to insufficient evidence. 24 The lack of clear evidencebased research to guide clinicians in the surgical treatment of degenerative spondylolisthesis is highlighted by the striking regional variation in the utilization of fusion (> 20-fold among Medicare enrollees in ). 29 Cost-Effectiveness: Complications, Costs, and Overall Outcome Although the addition of fusion to laminectomy has been shown to result in better functional and radiographic outcomes 2,12,17 and fewer reoperations, 11,16 it has also been associated with more complications 4,5,7,20 and greater costs. 5,7,20 In one study, the complication rate and hospital charges among Medicare patients with fusion were TABLE 2: Multivariate analysis using forward selection stepwise logistic regression in patients with lumbar spondylolisthesis* Reop Group OR SE z Score p Value 95% CI motion at spondylolisthesis in mm (flexion extension) disc height in mm (>6.5 vs 6.5) facet angle (30 50, 51 70, ) * Threshold p value of J Neurosurg: Spine / Volume 18 / April

5 C. Blumenthal et al. Fig. 2. Bar graph showing the percentage of patients with 0, 1, 2, or 3 risk factors requiring a reoperation. Risk factors are defined as facet angle > 50, disc height > 6.5 mm, and motion at spondylolisthesis > 1.25 mm. Of the patients with 3 risk factors, 75% required a reoperation compared with none of the patients with 0 risk factors (p = 0.14). 1.9 and 1.5 times higher, respectively, than in those who had surgery without fusion. 5 From 1992 to 2003, spending for lumbar discectomy/laminectomy decreased by > 10% whereas spending for lumbar fusion increased by > 500%. 29 By 2003, Medicare spending on lumbar fusion reached $482 million. 29 In addition, from 1990 to 2001, the rate of lumbar fusion increased 220%. The greatest rise in fusion rates was among the elderly population, in which complications are expected to be higher. 6 Lumbar fusions are frequently associated with increased risk of major complications, including excessive blood loss and neural injury, compared with laminectomy alone. 4,13 In a recent study, 22 43% of patients who underwent laminectomy with fusion were found to have at least 1 complication following surgery. Similarly, Malter et al. 20 found an 18% complication rate among fusion Fig. 4. Graphs showing change in scores from preoperatively to 6 months postoperatively. The ODI (upper panel; lower score is better) and SF-36 PCS (lower panel; higher score is better) assessments are shown prior to surgery, at 6 weeks, and at 3 and 6 months following surgery. patients compared with a 7% rate of complications in patients with laminectomy alone. Kuntz et al. 19 found instrumented fusion to be more costly when compared with other treatment options for Fig. 3. Graphs showing long-term follow-up scores in the total population. The ODI (upper panel; lower score is better) and SF-36 PCS (lower panel; higher score is better) assessments are shown prior to surgery, at 6 months, and at 1, 2, 3, 4, and 5 years following surgery (p < 0.001). Fig. 5. Bar graphs showing improvement in ODI (upper panel; p < 0.01) and SF-36 PCS (lower panel; p < 0.001) scores at 1 year following reoperation in 15 patients. 344 J Neurosurg: Spine / Volume 18 / April 2013

6 Radiographic predictors of reoperation following laminectomy lumbar spinal stenosis. In the SPORT findings, the incremental cost per quality-adjusted life-year gained for surgical treatment relative to nonoperative care for degenerative spondylolisthesis was $115,600, which is above the cost-effectiveness willingness to pay threshold for most industrialized nations. In the SPORT series, the vast majority (95%) of patients were treated with laminectomy and fusion; however, the incremental cost-effectiveness ratio for those treated with laminectomy alone was $38,900, which is well under what is considered costeffective in most industrialized nations. 27 In addition, there were no differences in outcome (quality-adjusted life-years gained) between those treated with or without fusion in the SPORT series. Aging Population From 2005 to 2025, the population over the age of 65 years is predicted to increase 73%. 3 Both degenerative spondylolisthesis and spinal stenosis are prevalent in older patients. 1,15,26 Over a 10-year period, from 1998 to 2008, the average age of patients undergoing spinal fusion increased by 5.4 years. 23 Deyo et al. 6 reported a 230% increase in lumbar fusions in adults over 60 years of age compared with 180% among adults years old and 120% among those years old. As the American population ages, it is likely that more elderly patients with lumbar spondylolisthesis will be eligible for treatment. Defining which patients are best suited for less invasive procedures including laminectomy without fusion will become a priority for multiple stakeholders. Multiple studies suggest that laminectomy alone might reduce complications for the elderly population in particular. Laminectomy alone has been found to minimize surgery-related trauma and postoperative morbidity in elderly patients. 18,25 Lumbar fusions are associated with higher rates of complications and 30-day mortality compared with laminectomy in Medicare patients. 7 Many elderly patients have a higher propensity to develop complications, and minimizing risk in this group is particularly important. Sanderson and Wood 25 examined degenerative spondylolisthesis in the elderly population and found that only 15.8% of patients experienced increased slippage following laminectomy, which was not always associated with back pain. Although the current study suggests a higher rate of instability following laminectomy alone, identifying specific risk factors that might help select those who would do well with a laminectomy alone would be valuable for surgeons and patients. J Neurosurg: Spine / Volume 18 / April 2013 Limitations and Strengths The sample size in this study was small (40 patients) and may not be representative of the majority of patients with degenerative lumbar spondylolisthesis treated in actual practice. One major variable that was not measured in this study was the body mass index. Future studies examining surgical outcome following lumbar spine surgery should include this information. All of the operations performed in this study were performed using an open technique. It is possible that minimally invasive laminotomies that preserve the interspinous process ligaments would provide greater stability in these patients. The use of reoperation as an end point is subjective both for the surgeon and the patient. Reoperation to treat possible delayed instability is a complex decision. In the current study, all patients with a single exception chose to undergo reoperation for instability when the surgeon identified delayed instability and recommended reoperation. Prospectively collected validated outcomes assessments demonstrated that the patients who underwent reoperation improved following fusion. This provides some evidence that the symptoms were related to delayed instability. The independent review of all images was done prospectively. It is therefore unlikely that any bias was introduced because the independent radiology evaluation of each study was done as patients were enrolled in the study. The most important strength of the study is the long-term follow-up. Conclusions Patients with motion at spondylolisthesis > 1.25 mm, disc height > 6.5 mm, and facet angle > 50 are more likely to experience instability following decompression-only surgery for Grade I lumbar spondylolisthesis. Although fusion for treating delayed instability was associated with significant improvement in outcome, the identification of risk factors for developing instability up front might help improve patient selection for decompression alone and reduce the number of reoperations following treatment for Grade I degenerative lumbar spondylolisthesis. Disclosure Funding was received from the Greenwich Lumbar Stenosis SLIP Study Fund (Grant No. GH384) and the Jean and David Wallace Foundation (Grant No. GH382). The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. Author contributions to the study and manuscript preparation include the following. Conception and design: Ghogawala, Benzel, Magge, Harrington, Coumans. Acquisition of data: Ghogawala, Blumenthal, Benzel. Analysis and interpretation of data: Ghogawala, Blumenthal, Curran, Potter. Drafting the article: Ghogawala, Blumenthal, Curran. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Ghogawala. Statistical analysis: Curran. Study supervision: Ghogawala. Acknowledgments The authors acknowledge the late Richard H. Velaj, M.D., and Scott J. Sullivan, M.D., for performing the independent radiological review, as well as Ellyn Wasserberger for assistance in organizing the database. References 1. Babb A, Carlson WO: Spinal stenosis. S D Med 59: , Bridwell KH, Sedgewick TA, O Brien MF, Lenke LG, Baldus C: The role of fusion and instrumentation in the treatment of degenerative spondylolisthesis with spinal stenosis. J Spinal Disord 6: , Colwill JM, Cultice JM, Kruse RL: Will generalist physician supply meet demands of an increasing and aging population? Health Aff (Millwood) 27:w232 w241,

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Qual Life Res 10: , Weinstein JN, Lurie JD, Olson PR, Bronner KK, Fisher ES: United States trends and regional variations in lumbar spine surgery: Spine (Phila Pa 1976) 31: , 2006 Manuscript submitted May 31, Accepted January 7, Portions of this work were presented in abstract form at the Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves, Orlando, Florida, March 9, Please include this information when citing this paper: published online February 1, 2013; DOI: / SPINE Address correspondence to: Zoher Ghogawala, M.D., Department of Neurosurgery, Lahey Clinic Medical Center, 41 Mall Road, Burlington, Massachusetts zoher.ghogawala@lahey. org. 346 J Neurosurg: Spine / Volume 18 / April 2013