Outcome after laminectomy for lumbar spinal stenosis

Transcription

1 J Neurosurg 81: , 1994 Outcome after laminectomy for lumbar spinal stenosis Part II: Radiographic changes and clinical correlations GERALD F. TUITE, M.D., STEPHEN E. DORAN, M.D., JOSEPH D. STERN, M.D., JOHN E. MCGILLICUDDY, M.D., STEPHEN M. PAPADOPOULOS, M.D., CRAIG A. LUNDQUIST, M.D., DOTUN I. OYEDIJO, B.S., SUSAN V. GRUBE, R.N., HOLLY S. GILMER, M.D., M. ANTHONY SCHORK, PH.D., STEVEN E. SWANSON, M.D., AND JULIAN T. HOFF, M.D. Section of Neurosurgery and Department of Radiology, University of Michigan Hospital; Department of Biostatistics, School of Public Health, University of Michigan; and Department of Neurosurgery, St. Joseph Mercy Hospital, Ann Arbor, Michigan The pre- and postoperative lumbar spine radiographs of 119 patients who underwent decompressive lumbar laminectomy were studied to evaluate radiographic changes and to correlate them with clinical outcome. An accurate and reproducible method was used for measuring pre- and postoperative radiographs that were separated by an average interval of 4.6 years. Levels of the spine that underwent laminectomy showed greater change in spondylolisthesis, disc space angle, and disc space height than unoperated levels. Outcome correlated with radiographic changes at operated and unoperated levels. This study demonstrates that radiographic changes are greater at operated than at unoperated levels and that some postoperative symptoms do correlate with these changes. Lumbar fusion should be considered in some patients who undergo decompressive laminectomy. The efficacy of and unequivocal indications for lumbar fusion can only be determined from randomized, prospective, controlled trials, however, and these studies have not yet been undertaken. KEY WORDS spinal stenosis lumbar spine decompressive lumbar laminectomy radiographs outcome D ECOMPRESSIVE lumbar laminectomy for lumbar spinal stenosis is one of the most commonly performed operations in the United States, particularly in the elderly. Since its original descriptions, this operation has appeared to provide excellent results. 8,27,28,53 Recently, however, its indications have been questioned because of concern about the relationship between decompressive laminectomy and long-term spinal instability. 5,23,25,40,42,44 Consequently, interest in performing spinal fusion concomitantly with decompression has increased. This trend, along with the advent of new fusion techniques, has led to an exponential increase in the rate of lumbar fusion. 48,49 The argument that spinal fusion is necessary with lumbar laminectomy hinges on the definition of lumbar instability. Spinal instability is a widely used term that does not have established criteria. 2,52 The most widely accepted method of diagnosing clinical instability requires interpretation of standard lumbar spine radiographs. 52 Unfortunately, the incidence of radiographic instability after lumbar laminectomy is difficult to determine because researchers methods of selecting patients and interpreting radiographs have been inconsistent. 48,49 We report the results of radiographic analyses of the changes in lumbar spine radiographs in a representative sample of patients who underwent standard laminectomy for lumbar stenosis. The relationship of these radiographic changes to clinical outcome is also described. J. Neurosurg. / Volume 81 / November,

2 G. F. Tuite, et al. FIG. 1. Drawings indicating the method for measuring the percent of spondylolisthesis (listhesis) (upper left), disc space height percent (upper right), and the disc space angle (lower). The percentages of spondylolisthesis and disc space angle are displayed as positive values in these diagrams; negative values correspond to spondylolisthesis and angulation in the opposite direction. Clinical Material and Methods Patient Selection Criteria Our study group consisted of 119 patients who comprised the core study population of a clinical outcome study, the results of which are reported elsewhere. 47 Patient selection methods, which will not be repeated here, provided an unbiased patient sample that is representative of patients undergoing decompressive lumbar laminectomy for lumbar spinal stenosis. The average interval between radiographs was years (range 2.0 to 8.6 years). Radiographic Techniques Postoperative radiographs in all patients were obtained by one of three trained technologists under the supervision of radiologists to ensure that standardized radiological methods were employed. Static radiographs were taken in the lateral decubitus (neutral lateral) and supine anteroposterior planes. Post- operative dynamic films were taken with the patient in the maximum flexed (sitting) and extended (standing) positions for the purpose of this study. Radiographic Analysis A total of six lumbosacral spine radiographs obtained in each patient were analyzed: two preoperative (anteroposterior and neutral lateral) and four postoperative (anteroposterior, neutral lateral, flexion, and extension). All radiographs were quantitatively analyzed by a radiologist or a neurosurgeon using a precise, reliable, and reproducible method, as FIG. 2. Drawing indicating the method for coding the data used in this study. Maximum values correspond to the maximum value of a measurement within the coded categories. Pooled data are generated by pooling all values that have the same code, regardless of level. described below. The investigator performing the analysis was not previously involved in the care of the patient and was blinded to the patient s clinical status. The radiographic method requires the investigator to mark eight points on the lateral image and six points on the anteroposterior image at each vertebral level. These points are then digitized and entered into a computer spreadsheet. The use of this spreadsheet allows for calculation of numerous measurements that will be discussed later in this manuscript. The percentage of spondylolisthesis and the disc space angle were measured on the anteroposterior, neutral lateral, and flexion/extension radiographs. Disc space height was also measured on the neutral lateral view (Fig. 1). Radiographic Coding Data for all measurements were recorded relative to lumbar spine disc spaces (including L1 2, L2 3, L3 4, L4 5, and L5 S1). Based on operative reports, the radiographic measurements were further stratified according to whether a laminectomy had been performed at that level. Measurements were coded as operative if a laminectomy had been performed on the lower half of the lamina above and/or the upper half of the lamina below (Fig. 2). For example, if a patient had the entire lamina of L-4 and L-5 and the lower half of L-3 removed at the time of surgery, all measurements at L3 4, L4 5, and L5 S1 would be considered operative. All data at other levels were considered unoperated. Data were analyzed by operated level, unoperated level, and overall (Fig. 2). Definition of Maximum and Pooled Values Because clinicians typically judge the presence of spinal instability on maximum radiographic measurements over the segments of interest, the data were fur- 708 J. Neurosurg. / Volume 81 / November, 1994

3 Radiographic changes after decompressive lumbar laminectomy ther stratified, as follows. For every radiographic measurement in each patient, the maximum absolute value at both operated and unoperated levels was determined. These maximum values allowed statistical comparisons to be made that eliminated differences in the distribution of operative levels between patients (Fig. 2). We pooled data from levels with the same surgical coding to further minimize the effect of differences in surgical distribution. We then compared these data pooled from levels with the same surgical coding (operated, unoperated, overall), thereby allowing for greater statistical power. Data Analysis Parametric data were compared using paired and independent t-test analysis as well as an analysis of variance, where appropriate. When performing pairwise comparisons, the Bonferroni adjustment for multiple comparison was used after an omnibus analysis of variance was performed. To assess associations between radiographic data and categorical clinical data, chi-square analysis was utilized after radiographic data were dichotomized. The transformation of radiographic data was performed such that a given measurement was assigned a binomial value (0, 1) based on whether it deviated from the norm. For some measurements, numeric cutoffs were based on values cited in previous literature to represent abnormal values. 36,51 However, this was possible to do only among measurements of vertebral body spondylolisthesis on the neutral lateral film (5%), and for the measurement of the amount of movement in flexion minus extension on a given film (5%). For the remainder of the radiographic measurements, assignment to a normal or abnormal category could not be performed based on previous studies. Values for the entire patient population were plotted for these measurements; each measurement approximated a normal distribution. Without an a priori or previously established definition of abnormal values for these measurements, cutoffs were established to define approximately 30% of the population with values greater than the cutoff (cutoff mean 0.52 standard deviation). If a value fell outside the designated cutoff, it was designated abnormal. (See, for example, Table 1.) Results Radiographic Analysis A comparison made of changes in pooled measurements on neutral lateral radiographs during the study interval revealed differences between operated and unoperated levels. The average progression of spondylolisthesis was 7.3% at operated levels and 4.2% at unoperated levels (p 0.01). Disc space angle changed more at operated levels than at unoperated levels (4.7% vs. 3.7%, p 0.01), and disc space collapse was more pronounced at operated levels than at unoperated levels (7.9% vs. 6.9%, p 0.01). J. Neurosurg. / Volume 81 / November,

4 G. F. Tuite, et al. However, changes in spondylolisthesis and disc space angle on anteroposterior films did not differ at operated versus unoperated levels. Change in spondylolisthesis and disc space angle on flexion/extension views also did not differ between operated and unoperated levels (Table 2). A comparison of changes in radiographs at levels undergoing laminectomy versus those that underwent laminectomy plus discectomy revealed only two differences. First, the decrease in disc space height on the neutral lateral film was greater at levels undergoing laminectomy and discectomy compared to laminectomy alone (10.8% vs. 7.9%, p 0.05). Second, spondylolisthesis on flexion/extension views was less at levels that underwent laminectomy plus discectomy compared to laminectomy alone (4.5% vs. 7.8%, p 0.05), as indicated in Table 2. In addition, a comparison of unoperated levels to those levels undergoing laminectomy and discectomy revealed that the decrease in disc space height at operated levels was greater in the laminectomy and discectomy group when compared to the unoperated group (10.8% vs. 6.9%, p 0.05). Progression of Spondylolisthesis. When spondylolisthesis is defined as a displacement of greater than 5% on the neutral lateral radiograph of one vertebral body upon another, 88% of patients had spondylolisthesis at some level before surgery. Furthermore, more patients had preoperative spondylolisthesis at future operative levels than at unoperated levels (80% vs. 54%, p 0.05). To study the progression of spondylolisthesis in patients with preoperative spondylolisthesis, we stratified operative and nonoperative data according to the presence of spondylolisthesis (5%) before surgery and compared the changes in spondylolisthesis on the neutral lateral radiographs between the two stratified groups. At unoperated levels, there was no difference in the change in spondylolisthesis after surgery between those levels that had preoperative spondylolisthesis and those that did not. This was also true when the data were analyzed at each operated level individually. When the data from all operative levels were pooled, however, there was greater progression of spondylolisthesis at those levels with preoperative spondylolisthesis than at those levels that did not have spondylolisthesis (7.9% vs. 5.2%, p 0.01). Changes appeared to be more likely at certain levels. Before surgery, spondylolisthesis on the lateral view was significantly greater at L4 5 than other levels (p 0.005). When overall changes after surgery on the neutral lateral view were compared, without considering the effect of operative intervention, the changes in spondylolisthesis at L3 4, L4 5, and L5 S1 were found to be greater than L1 2 and L2 3 (p 0.05); however, there was no difference between the changes in spondylolisthesis at these lower lumbar levels when these levels were compared to each other (p 0.05). At operated levels, there was greater change in spondylolisthesis at L3 4 through L5 S1 than at other levels after surgery (p 0.05), with L4 5 having greater change than L3 4 or L5 S1 (p 0.005). Changes in spondylolisthesis at unoperated levels on the neutral lateral view were not found to be different from each other (Table 3). Changes in disc space angle on the neutral lateral radiograph were also greater at the lower lumbar levels (p 0.05). Levels L4 5 and L5 S1 were found to have greater changes in disc space angle than others after surgery at operative levels; however, there was no difference between L4 5 and L5 S1 (p 0.005). 710 J. Neurosurg. / Volume 81 / November, 1994

5 Radiographic changes after decompressive lumbar laminectomy In addition, there were no differences in disc space angle changes at unoperated levels, and there were no significant differences between measurements at different levels on postoperative flexion/extension radiographs. Maximum Values. Maximum changes on neutral lateral and anteroposterior radiographs at operated levels were compared to the changes at unoperated levels (Table 4). The maximum change at operated levels was greater than the maximum change at unoperated levels for spondylolisthesis, disc space height and disc space angle on the neutral lateral radiograph (p 0.05). Similarly, the maximum changes in spondylolisthesis on postoperative flexion/extension views were compared at operated and unoperated levels. The maximum change in spondylolisthesis at operated levels during flexion and extension was greater than the maximum change at unoperated levels (10.0% vs. 6.8%, p 0.01). Radiographic and Clinical Correlations Correlation of Gender and Age to Radiographic Findings. More women than men were found to have an abnormal preoperative spondylolisthesis at some level of their spine (45% vs. 25%, p 0.05) (see Clinical Material and Methods section for definition of abnormal ). When considering only operated levels, women also had more abnormal spondylolisthesis than men before and after surgery (before: 45% vs. 20%, p 0.05; after: 50% vs. 25%, p 0.05). More importantly, women were more likely to develop a progression of spondylolisthesis at operative levels (46% women, 22% men, p 0.01). At unoperated levels, there was no gender difference in the change in spondylolisthesis (p 0.05). Older patients were found to develop more change in spondylolisthesis, as indicated on anteroposterior films: 33% of patients over 60 years old developed an abnormal spondylolisthesis and 9% of patients under 60 had a similar change (p 0.05). There was no correlation of age to other radiographic abnormalities. Correlation of Low-Back Pain With Radiographic Findings. Patients with a primary complaint of lowback pain were more likely to have abnormal disc space angles preoperatively. Fifty-two percent of patients with a primary complaint of back pain had abnormal disc space angles on a neutral lateral film, and 39% of those with a different chief complaint had an abnormal disc space angle (p 0.05). This finding was specific to operated levels: 43% of those with a chief complaint of back pain had abnormal disc space angles and 34% of those with leg pain had abnormal disc angles at operated levels (p 0.05). The frequency of back pain after surgery correlated with the change in spondylolisthesis on the neutral lateral view. Forty-seven percent of patients with an abnormal change in spondylolisthesis at operated levels complained of constant low-back pain after surgery, and only 22% of those patients with less frequent pain had an abnormal change (p 0.05). The frequency of postoperative low-back pain was also found to be related to spondylolisthesis seen on anteroposterior views after surgery. Fifty-one percent of patients who complained of low-back pain that lasted at least 12 hours per day after surgery had an abnormal spondylolisthesis at operated levels, but only 36% of those who complained of less frequent back pain had abnormal values (p 0.05). This association was also specific to operated levels; however, similar associations of low-back pain to other radiographic measurements at unoperated levels were not demonstrated. Correlation of Leg Pain and Walking Abilities With Radiographic Findings. Patients walking abilities at the study interval were found to correlate with changes in spondylolisthesis and disc space height at operated levels on the neutral lateral radiographs. Twenty-four percent of patients who could walk two blocks or more had an abnormal change in the percentage of spondylolisthesis on neutral lateral films, and 56% of those who were unable to walk two blocks had the same abnormal change in spondylolisthesis (p 0.05). Forty-six percent of patients with neurogenic claudication after surgery had an abnormal J. Neurosurg. / Volume 81 / November,

6 G. F. Tuite, et al. change in disc space height at operated levels; and an abnormal change was seen in 22% of those without neurogenic claudication (p 0.05). Similar correlations of neurogenic claudication to spondylolisthesis and disc space height were not found at unoperated levels. Correlation of Current Outcome and Need for Further Surgery With Radiographic Findings. The patients current assessment of their surgical outcome did not correlate with radiographic measurements or changes in measurements at operated levels. However, patients with less favorable outcomes were more likely to have abnormal radiographic measurements at unoperated levels (p 0.05). The need for additional surgery also correlated with changes at initially unoperated levels. Four of the 18 patients who required additional laminectomy were found to have an abnormal change in spondylolisthesis on neutral lateral radiographs at initially unoperated levels; however, only two of the 98 patients who did not require additional surgery developed an abnormal progression of spondylolisthesis at unoperated levels (p 0.05). In all of those patients with an abnormal progression of spondylolisthesis that required further surgery, the additional laminectomy included the area of progression. Other Clinical Outcomes Without Correlation to Radiographic Findings. There were no significant correlations of history of smoking, duration of preoperative symptoms, or interval between studies and the radiographic findings. Discussion Radiographic Changes at Operated Versus Unoperated Levels To attribute radiographic changes to lumbar laminectomy, an extensive comparison of radiographic data at operated and unoperated levels was performed. This study is the first to make such a comparison, and our results suggest that many radiographic findings are specific to surgical levels that undergo laminectomy. Operated levels have more spondylolisthesis, disc space angulation, and decrease in disc space height as seen on lateral films than unoperated levels. These radiographic abnormalities at levels of lumbar spinal stenosis are indicative of the severity of the degenerative process at those levels. We found that operated levels have a greater change in radiographic measurements after surgery than unoperated levels. There was a significantly greater change in spondylolisthesis, disc space angulation, and disc space collapse at operated levels than at unoperated levels on the neutral film. Contrary to the suggestion of previous authors, 13,19,22,33 we did not find that the effect of discectomy in addition to decompressive lumbar laminectomy increased the propensity for progression of spondylolisthesis. To make these radiographic comparisons more relevant to clinical practice, maximum changes over operated and unoperated levels were compared. The results of this comparison indicated that the maximum change in spondylolisthesis, disc space angle, and disc space height on the neutral lateral film was greater at operated levels than at unoperated levels. Additionally, the maximum change in spondylolisthesis on lateral flexion/extension images was greater at operated than at unoperated levels. Our findings suggest that surgical levels are more likely to develop progressive spinal deformity than those that do not undergo decompressive lumbar laminectomy. However, it is possible that the propensity for change at operated levels is more of a reflection of the severity of spinal degeneration at those levels rather than an effect that is specific to decompressive lumbar laminectomy. Progression of Spondylolisthesis Our study confirms a widely held belief that spinal levels with preoperative degenerative spondylolisthesis are more likely to develop progressive spondylolisthesis after laminectomy. 24,25,29,45,46 We found that operated levels which had spondylolisthesis (5%) prior to surgery had an average change in spondylolisthesis of 7.9%, but levels without spondylolisthesis changed by only 5.2%. This change was specific to surgical levels; the same effect was not demonstrated at unoperated levels. These findings are in agreement with previous studies of degenerative spondylolisthesis. Johnsson, et al., 25 found a significantly higher rate of progressive spondylolisthesis in patients with preoperative spondylolisthesis, but their results were difficult to interpret because of patient selection bias. Other authors 29,45,46 have made similar associations, but none has provided statistical comparisons. Propensity for Radiographic Change at Specific Levels Previous studies 9,12,15,17,20,32,34,38,43,54 have clearly demonstrated a propensity for preoperative degenerative spondylolisthesis at the L4 5 interspace; our study confirms this finding. However, little is known about the likelihood of change in radiographs after surgery. We found that progression of spondylolisthesis was more common at the lower lumbar levels, with L4 5 having a significantly greater change than other levels. This finding is in agreement with biomechanical studies and clinical impressions that the L4 5 interspace is more likely to develop spinal deformities; an effect that has been attributed to differences in facet joint orientation as well as the insertion of the iliolumbar ligament, although our study did not address these possible etiologies. 16,26,30 We found no level-specific differences in spondylolisthesis on postoperative flexion/extension radiographs; but there was a trend toward more movement in lower levels of the lumbar spine. This trend has been confirmed in previous cadaveric studies and radiographic analyses of asymptomatic individuals, 712 J. Neurosurg. / Volume 81 / November, 1994

7 Radiographic changes after decompressive lumbar laminectomy with the lower lumbar spine generally showing more change from flexion to extension than the upper spine. 1,18,35,50,55 Correlation of Symptoms and Outcome to Radiographic Change The indications for lumbar fusion as an adjuvant to decompressive lumbar laminectomy most often hinge on the presence of spinal deformity on standard radiographs. 4,7,10,14,33 Justification for fusion is based on radiographic measurements before surgery as well as the changes in these values after decompressive lumbar laminectomy. Most previous studies have attempted to compare outcome between groups of patients with and without spondylolisthesis. Several studies have indicated that patients with degenerative spondylolisthesis have a less favorable outcome after decompressive lumbar laminectomy than those without spondylolisthesis. 5,20 However, we found no difference in outcome between our patients with and without preoperative spondylolisthesis. We also compared outcome to the remainder of our preoperative radiographic measurements and found no significant correlations. We did not correlate the degree of lumbar spinal stenosis on myelogram or postmyelogram computerized tomography to clinical outcome. Significant correlations of outcome to radiographic changes after decompressive lumbar laminectomy have been demonstrated in our study, however. The incidence of postoperative back pain, leg pain, and neurogenic claudication was greater in patients who had a significant change in spondylolisthesis at operated levels after surgery. Patients assessment of outcome and the need for further surgery were related to the change in spondylolisthesis at unoperated levels; however, no correlation could be made with changes at operated levels. These correlations of outcome and pain to radiographic changes are the first significant correlations to be reported. Correlation of change in Radiographs to Other Factors In our study, women were more likely to have degenerative spondylolisthesis before surgery. This finding is specific to operated levels and has been well documented in previous studies, L4 5 being the most frequently involved level. 12,17,21,38 More importantly, our study showed a greater propensity for women to have progression of spondylolisthesis at operated levels. Some authors 23,41 have found that younger patients have a greater progression of spondylolisthesis, while other authors 23,37,41 have published contradictory data. In our patient group, we found no relationship of age to the change in spondylolisthesis on lateral views; in fact, our finding that older patients had a greater change in spondylolisthesis on anteroposterior views was the only significant correlation of age to radiographs. Similarly, other authors have found radiographic changes to be related to the duration of preoperative symptoms and to the duration of follow-up interval; however, we did not find such a correlation. 31 Tobacco use is known to hasten lumbar disc degeneration, and some authors have suggested that spinal deformity after decompressive lumbar laminectomy is more common in smokers. 3 We were unable to correlate smoking with any radiographic measurements taken before or after surgery, however. Role for Lumbar Fusion Changes in radiographic measurements are more pronounced at operated than unoperated levels after decompressive lumbar laminectomy, and according to our comparisons, some of these radiographic changes correlate with patients functional status after surgery. These findings, as well as previous studies, suggest that efforts to reduce the likelihood of postoperative spinal deformity may enhance outcome after decompressive lumbar laminectomy. 5,6,25 Patients assessment of their overall outcome, however, correlated with radiographic changes at unoperated levels; this finding suggests that persistent symptoms may also be related to progressive degeneration at levels adjacent to the levels of previous surgery. Other authors have found evidence that the incidence of progressive spondylolisthesis occurs less frequently when instrumentation and fusion are used with decompressive lumbar laminectomy for the treatment of lumbar spinal stenosis. 11,12,17,20 These findings, in addition to our correlations, suggest that there is a role for fusion at the time of decompressive lumbar laminectomy in patients who are at greatest risk to develop progressive spondylolisthesis. However, previous studies that compared outcome of decompressive lumbar laminectomy with and without fusion provided no conclusive support for this statement. 6,11,17,20,25,29,31,39 We believe that there is a limited role for lumbar fusion in patients who undergo decompressive lumbar laminectomy for lumbar spinal stenosis, but the efficacy and indications for fusion have not yet been demonstrated. Undertaking randomized, prospective, controlled trials is essential to resolve this question. Conclusions Until definitive prospective studies are performed, we believe that the role for lumbar fusion in lumbar spinal stenosis should still be limited, but that consideration should be given to fusion in patients with a rate of spondylolisthesis greater than 10%, particularly in women. Furthermore, when patients have a poor result after decompressive lumbar laminectomy, we suggest that further stenosis or spinal deformity may account for persisting complaints rather than spinal instability amenable only to fusion. Acknowledgments The authors thank Susan Kirkpatrick for providing organizational skills, Linda Kalmbach for secretarial assistance, and the J. Neurosurg. / Volume 81 / November,

8 G. F. Tuite, et al. staff of the radiology department at St. Joseph Mercy Hospital for their generous and capable support. References 1. Alexander E Jr, Kelly DL Jr, Davis CH Jr, et al: Intact arch spondylolisthesis. A review of 50 cases and description of surgical treatment. J Neurosurg 63: , Ashton-Miller JA, Schultz A: Spine instability and segmental hypermobility biomechanics: a call for the definition and standard use of terms. Semin Spinal Surg 3: , Battié MC, Videman T, Gill K, et al: 1991 Volvo Award in clinical sciences. Smoking and lumbar intervertebral disc degeneration: an MRI study of identical twins. Spine 16: , Bradford DS, Boachie-Adjei O: Treatment of severe spondylolisthesis by anterior and posterior reduction and stabilization. A long-term follow-up study. J Bone Joint Surg (Am) 72: , Caputy AJ, Luessenhop AJ: Long-term evaluation of decompressive surgery for degenerative lumbar stenosis. 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9 Radiographic changes after decompressive lumbar laminectomy stenosis. Results of operative treatment. Acta Orthop Scand 53:79 85, Tile M, McNeil SR, Zarins RK, et al: Spinal stenosis. Results of treatment. Clin Orthop 115: , Tuite G, Stern J, Doran S, et al: Outcome after laminectomy for lumbar spinal stenosis. Part I: Clinical correlations. J Neurosurg 81: , Turner JA, Ersek M, Herron L, et al: Patient outcomes after lumbar spinal fusions. JAMA 268: , Turner JA, Herron L, Deyo RA: Meta-analysis of the results of lumbar spine fusion. Acta Orthop Scand (Suppl 251): , White AA III, Panjabi MM: The basic kinematics of the human spine. A review of past and current knowledge. Spine 3:12 20, White AA III, Panjabi MM: Clinical Biomechanics of the Spine. Philadelphia: JB Lippincott, 1990, pp Willner S: Lumbar spine fusion conclusions. Acta Orthop Scand (Suppl 251): , Wilson CB: Significance of the small lumbar spinal canal: cauda equina compression syndromes due to spondylosis. 3: Intermittent claudication. J Neurosurg 31: , Wiltse LL, Newman PH, Macnab I: Classification of spondylolisis and spondylolisthesis. Clin Orthop 117: 23 29, Yamamoto I, Panjabi MM, Crisco T, et al: Three-dimensional movements of the whole lumbar spine and lumbosacral joint. Spine 14: , 1989 Manuscript received November 10, Accepted in final form March 3, This study was supported by Grant R through the Shoecraft Endowment at the Catherine McAuley Health System. Address reprint requests to: Gerald F. Tuite, M.D., Section of Neurosurgery, University of Michigan Hospital, 1500 East Medical Center Drive, Taubman 2128, Ann Arbor, Michigan J. Neurosurg. / Volume 81 / November,