Functional disability after instrumented stabilization in lumbar degenerative spondylolisthesis: a follow-up study

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1 Functional disability after instrumented stabilization in lumbar degenerative spondylolisthesis: a follow-up study Paolo Gaetani a Enrico Aimar a Lorenzo Panella b Daniel Levi a Flavio Tancioni a Antonio Di Ieva a Alberto Debernardi a Patrizia Pisano a Riccardo Rodriguez y Baena a Departments of a Neurosurgery and b Rehabilitation, Istituto Clinico HUMANITAS, Milan, Italy Reprint requests to: Dr Paolo Gaetani Department of Neurosurgery Istituto Clinico Humanitas Mirasole S.p.A. Via Manzoni, Rozzano (Milan) - Italy paolo.gaetani@humanitas.it Accepted for publication: February 14, 26 Summary Low back pain (LBP) is a widespread health problem and a major contributor to increasing health costs and lost work days. Different pathologies cause LBP and one of these is lumbar degenerative spondylolisthesis (SPL). There are no generally accepted and standardized methods for assessing the outcome of patients treated for degenerative lumbar SPL. This study aims to assess quality of life after surgery for lumbar degenerative SPL through the adoption of outcome measures. We studied 76 patients treated, for degenerative lumbar SPL, with spinal stabilization, decompression and bilateral dorsolateral fusion, followed up for at least two years. We used the Roland-Morris (RM) scale and the Oswestry Disability Index (ODI) to assess the quality of life of the patients before surgery and at follow up. Each patient was pre-operatively studied through standard and dynamic x-rays, CT scan and MRI of lumbar column. Relationships between clinical, radiological and disability scores, grouped by categories, were tested. The sample comprised 25 males and 51 females. Mean age was 59.6 years (SD 12.2). The mean duration of symptoms (from clinical onset to surgery) was months (median 13, range 4-1 months). In about half of the cases, duration of symptoms before surgery was >12 months. At follow up, the fusion rate was 85.5%, and the ODI score was significantly reduced: an improvement of <2 points in 35.7% of patients, and of >2 points in 55.7%. On the RM scale, 59.4% of patients had a reduction >5 points, 13.1% a reduction of 2-4 points, and 27.5% an unchanged or worse score. There was no significant reduction in RM scale and ODI scores in patients with fusion versus pseudoarthrosis. Instrumental pedicle screw fixation and arthorodesis seem to be very effective in improving quality of life, as shown by the reduced disability scores at follow up. KEY WORDS: instrumented stabilization, lumbar spondylolisthesis, lumbar stenosis, quality of life measures. Introduction Ever since the first clinical description of the condition in 195 (1), degenerative spondylolisthesis (SPL) has been considered an important cause of low back pain (LBP). In addition to classification of vertebral slippage, the concept of vertebral instability, which is based on the characteristics of facet joints in relation to the vertebral load, has been introduced into clinical practice. Recent studies have shown that sagittal alignment of the facet joint (2-6) is an important factor influencing the development of degenerative SPL (7-9). Thus, SPL may be considered stable or unstable, depending on the capacity of the facet joints to bear physiological load without moving through an abnormal, and usually excessive, range of motion. Moreover, the development of SPL depends on degeneration of the intervertebral disc and the presence of segmental stenosis, both of which contribute to the progressive loss of disc biochemical properties and thus to progression of the listhesis. The treatment of degenerative SPL is still debated: few reports have analayzed non surgical management (1,11). In a recent prospective study, Matsunaga et al. (11) showed that conservative treatment may lead to progressive reduction of LBP and of radicular symptoms, and that surgical treatment is clearly indicated when neurological deficits are evident. Although good clinical results were reported in about 8% of patients undergoing surgical decompression without arthrodesis (12-15), recent studies have emphasized the importance of concomitant arthrodesis and instrumented stabilization (16-21). Spinal fusion with pedicle screw fixation is significantly more effective in reducing both LBP and radicular pain, providing immediate stability of the column, improving the rate of fusion, and leading to reestablishment of physiological lordosis (22). Spinal instrumentation has not been shown, in the previously published studies (17,22-25), to lead to better correction of vertebral alignment or to an improved functional outcome when compared to conservative treatment. Meanwhile, several authors have, instead, addressed the question of the influence of surgical treatment on activities of daily living (19,26-28). In order to verify whether quality of life is significantly influenced by surgery in cases of degenerative SPL, we analyzed the records of 76 patients using the Roland- Morris (RM) scale (29) and the Oswestry Disability Index (ODI) (3,31), both of which are widely accepted measurement methods for the follow-up evaluation of specific procedures in cases of lumbar spine pathology. Functional Neurology 26; 21(1):

2 P. Gaetani et al. Materials and methods Eighty-five patients were surgically treated (spinal stabilization, arthrodesis and decompression) for degenerative lumbar SPL at the Department of Neurosurgery at the Istituto Clinico Humanitas, Milan (Italy), between January 1999 and June 21. Clinical and radiological follow-up data were available in 76 cases, and these cases constitute the present series. Inclusion criteria were: presence of severe LBP, radicular symptoms or neurological deficits resulting from lumbar instability related to degenerative SPL; diagnosis of lumbar instability based on plain AP and lateral flexion and extension x-rays, CT scan and MRI findings; at least 4 months of previous conservative treatment (rest, pharmacotherapy and/or physical therapy). Excluded from the study were patients with isthmic spondylolisthesis, degenerative neurological disorders, age >8 years, presence of severe diabetes complicated by polyneuropathy, diagnosis of rheumatological disesaes, or other medical conditions precluding surgery. Neuroradiological assessment In all cases, the following radiological characteristics were considered: on plain and dynamic x-rays of lumbar column, the degree and the angle of vertebral slippage were classified according to Meyerding et al. (32). For analysis of results, the patients were divided into two groups: Meyerding classes I and II, and Meyerding class III; CT scan data were classified considering the presence or absence of lumbar stenosis; the presence of a degenerated, protruded or herniated disc; and the presence of air (vacuum sign) in the facet joints (Fig. 1a); on MRI, we analyzed facet joint orientation and tropism according to Dai et al. (7). On the basis of the degree of joint tropism, patients were further divided into two groups: those with joint tropism <1 and those with joint tropism >1. Surgical procedure Three neurosurgeons performed all surgical procedures in the same hospital: instrumented stabilization with pedicle screws was performed using the Spine System Evolution 4 (B. Braun, Aesculap, Milan, Italy), followed by decompression (spinosectomy, bilateral laminectomy, partial facetectomy and foraminotomy) and arthrodesis. The disc spaces were inspected in all cases and discectomy was performed in cases of herniated disc material. Posterolateral interbody fusion was not used in cases requiring discectomy. Spinal arthrodesis was performed in all cases according to McNab and Dall (33): the osseous surfaces of transverse and articular processes were decorticated using a high-speed drill; bone obtained by the posterior decompression was packed over the decorticated surfaces. All patients, 4-6 days after surgery, were admitted to the rehabilitation unit where they stayed until discharge. Data collection and analysis On admission, or in the week preceding surgery, patients were requested to fill in a detailed activities of daily living questionnaire. The questionnaire included the RM scale and ODI, which consisted of 24 and 1 items respectively: the RM scale is sensitive to functional changes in patients with low-level disability, whereas the ODI is more sensitive in patients with high levels of disability (34). On admission, the patients were examined and their clinical and neurological status was recorded. For analysis of the results, we considered the following age groups: <3 years, 31-5 years, years, and >65 years. As regards the duration of symptoms before surgery, patients were subdivided into three groups: <6 months, 6-12 months, and >12 months. Linear visual analogue scale (VAS) for LBP and for radicular pain (VAS Leg pain) were used in order to assess pain. For analysis of the results, VAS scores were A B C Figure 1 - a) CT scan image of concomitant segmental lumbar stenosis and the presence of vacuum in facet joints; b) MRI, sagittal view showing the spondylolisthesis at L4-L5 level; c) CT, sagittal view of the same case. 32 Functional Neurology 26; 21(1): 31-37

3 Outcome in degenerative spondylolisthesis considered both as continuous variables and divided in two groups: <5 and >5. In view of the peculiarity of degenerative instability and long-term clinical histories, to analyze data from the present study, we calculated an ODI cut-off score of 5 as indicative of a good condition. Follow up In all cases, a clinical and radiological evaluation was performed 24 months after surgery. In addition, in patients observed for longer periods a final follow-up evaluation of RM scale and ODI scores was obtained either by on-the-spot compiling of questionnaires or by phone interviews (conducted by independent evaluators) in the case of patients who were unable to reach the hospital for a medical examination (e.g., because they lived too far away). Any bias arising from telephone interviews would appear to be irrelevant as regards the validity of the protocol validity given that in >9% of cases the scores at final follow up were similar to those obtained at 24 months. Therefore, we here report only the 24-month follow-up data of the series. In our analysis of these 24-month follow-up results, we considered the differences between pre- and post-operative ODI scores, with a reduction of 2 points being deemed clinically significant. Thus, as regards the ODI score, we divided the results into: ODI increased or reduced by 2 points (defined unsuccessful); ODI reduced by 4-2 points; and ODI reduced by >2 points. The RM scale identifies a greater amount of changes and is probably associated with the self-rated improvement in patients with lumbar problems (35). In the pre-operative assessment, the patients were subdivided into two groups according to RM scale score: <15 points, and >15 points. At follow up, the patients were classified according to RM scale score as follows: those in whom the RM score was increased, unchanged or reduced by 1 point, (defined failures); those in whom the score was reduced by 2 to 5 points; and those in whom it was reduced by >5 points. Post-operative control x-rays were obtained at 2 months and at 24 months of follow up: AP and standing flexion/extension lateral x-ray images allowed us to measure the extent of the vertebral slippage (in mm), the sagittal motion (in mm) and the angular motion (in degrees). In accordance with Fischgrund et al. (23), arthrodesis was deemed successful if a bilateral continuity in the fusion mass between the transverse processes was detected. Pseudoarthrosis was deemed present when there was no continuity in the fusion mass or when the lateral flexion-extension showed >2 of angular motion or >2 mm of sagittal motion. Radiological assessment was performed by independent radiologists. Statistical analysis Statistical analysis was performed using the SPSS for Windows. The ANOVA and Student s t-test were used to compare the continuous variables (RM scale, ODI and VAS scores, age, joint tropism). The relationship between clinical, radiological and disability scores grouped by categories, were tested using the Chi-square and contingency coefficient tests and by multivariate analysis. Significance was accepted at p<.5. Results Pre-operative assessment and patient characteristics The pre-operative general data are reported in Table I. Of the 76 patients, 25 were males and 51 females. Mean age was 59.6 years (SD 12.2). The mean duration of symptoms (from clinical onset to surgery) was months (median 13, range 4-1 months). In about half the cases, duration of symptoms before surgery was >12 months. L4-L5 was the most frequent level of maximal instability (47.4%). Radicular symptoms were recorded in 57.9% of cases; Table I - General clinical and radiological characteristics of the 76 cases enrolled in the study. Mean age (years) 6.6 SD:12.2 Sex Male % Female % Level of maximal instability L1-L % L2-L % L3-L % L4-L % L5-S % Duration of pre-operative symptoms < 6 months % 7-12 months % > 12 months % Mean follow up (months) 28.2 range: Main clinical sign Radicular pain % LBP % Neurological deficit % Vertebral slippage (acc. to ref. 32) Meyerding classes 1 and % Meyerding class % Vacuum sign in facet joints on CT scan Positive % Negative % Segmental stenosis Presence of stenosis % No stenosis % Joint tropism < % > % Pre-operative RM scale score <15 points % >15 points % Pre-operative ODI score <5 points % >5 points % Post-operative differences in RM scale score unchanged or worsened % decrease < 5 points % decrease > 5 points % Post-operative differences in ODI score unchanged or worsened 6 7.9% decrease < 2 points % decrease > 2 points % Abbreviations: LBP=low back pain; RM=Roland-Morris; ODI=Oswestry Disability Index. Functional Neurology 26; 21(1):

4 P. Gaetani et al. in 3.3% of cases LBP with postural exacerbation was the main clinical sign, as opposed to neurological deficits in 11.8% of cases. CT scan showed the presence of vacuum sign on facet joints in 62.7% of cases. Segmental stenosis was shown in 55.3% of cases. The intervertebral disc at the site of maximal instability was degenerated in 38.9% of cases, protruded in 51.4% and herniated in 9.7% of cases. Joint tropism, calculated on MRI, showed wide variability: the mean value was 9.1 (SD 6.1). VAS Leg pain score. Mean VAS Leg pain score before surgery was 7.2 (SD 2.4). Higher VAS Leg pain scores were found to be directly related to increasing age (p:.46). VAS LBP score. Mean VAS LBP score was 7.6 (SD 1.7). Higher VAS LBP scores also showed a significant relationship with increasing age (p:.44). The Oswestry Low Back Pain Disability Index. The mean pre-operative ODI score was 49.4 (SD 16.8). Pre-operative ODI scores did not correlate with the age of the patients. When the cut-off score of 5 was applied, the multiple regression and the logistic analysis of pre-operative ODI score groups (matched for other clinical and radiological parameters) showed significant correlations with the extent of vertebral slippage (p:.12) and the presence of segmental stenosis (p:.46): 71.4% of patients with preoperative ODI scores <5 were classified as Meyerding classes I and II. Sixty percent of patients with pre-operative ODI scores <5 had lumbar segmental stenosis. Roland-Morris Scale. The mean pre-operative RM score was 14.2 (SD 4.8). Pre-operative RM scores did not correlate with the age of the patients. When we considered the pre-operative RM score groups (<15 and >15 points), multivariate analysis with logistic regression showed a relationship between RM score group and extent of vertebral slippage as classified according to Meyerding et al. Indeed, a higher percentage (73.7%) of patients with RM score <15 were found to show a low degree of vertebral slippage (Meyerding classes I and II). Pre-operative RM score group did not correlate with type of symptoms, but the presence of air in the facet joints was associated with higher percentages of patients with elevated pre-operative RM and ODI scores (Fig. 2). Operative data and complication rate. Surgery was conducted at a single level in 61 cases, at two levels in 14 cases, and at three levels in one case. In three cases complications of the instrumental stabilization system were recorded: in one case there was exceptional bilateral disruption of pedicle screws, and in two cases displacement of the titanium bars, requiring surgical revision of the system. These patients were not excluded from follow-up analysis. In one case, a dural tear was conservatively treated, successfully, and in three cases wound infection necessitated prolonged specific antibiotic treatment. No operative deaths were recorded. Procedure-related outcome Radiological follow-up. At 24-month follow up, fusion was observed in 65 cases (85.5%), and pseudoarthrosis in the remaining 11 cases (14.5%). Vertebral slippage, assessed post-surgically, did not differ significantly from pre-surgical levels, and in the majority of cases the degree of vertebral slippage remained unchanged; conversely, a significant reduction of both sagittal and angular motion was recorded. Pain evaluation (VAS). Figure 3 shows that the mean scores of both VAS LBP and Leg pain at follow up were significantly reduced (p:.1). Pre-op. 1 Follow-up VAS Back Pain VAS Leg *p<.1 (ANOVA and Student s t test) Figure 3 - Bar graph representation of mean pre-operative and follow-up VAS scores. % 8 6 RM <15 RM >15 % 1 8 ODI <5 ODI > A Normal facet joint Vacuum sign B Normal facet joint Vacuum sign Figure 2 - Bar graph representation of (A) pre-operative Roland-Morris scale score (cut off of 15); and (B) pre-operative ODI score (cut off of 5) and the radiological finding of vacuum sign in facet joints. 34 Functional Neurology 26; 21(1): 31-37

5 Outcome in degenerative spondylolisthesis Oswestry Disability Index. Overall ODI score at 24- month follow up was significantly reduced (Fig. 4); 8.6% of patients had an unchanged ODI score, 35.7% an improvement of <2 points and 55.7% an improvement of >2 points. The difference in ODI score at follow up was correlated with the presence of pre-operative radicular pain (Table II): 61.4% of patients with pre-operative radicular pain showed an ODI score reduction >2 points, while 39.1% of patients with pre-operative LBP showed a significantly improved ODI score. The presence of radiological fusion at follow up did not correlate with a significant reduction in ODI scores. Roland-Morris Scale. Overall RM score at follow up was significantly reduced (Fig. 5): 59.4% of patients recorded a reduction of >5 points, 13.1% a reduction of 2-4 points, and 27.5% an unchanged or worse RM score. Multivariate analysis of RM score changes at follow up (Table III) showed that in 61.4% of patients with pre-operative radicular pain, RM score was significantly reduced (>5 points). The reduction of RM score at follow up was not dependent on the presence of fusion. Similarly, the presence of disc protrusion or herniation requiring a discectomy, like the presence of significant degenerative changes in the intervertebral disc space, had no influence on pre- and post-operative RM and ODI scores. Discussion There are no generally accepted and standardized methods for assessing the outcome of patients treated for degenerative lumbar SPL: it is clearly paradoxical that the main clinical sign associated with this condition (pain) cannot be evaluated objectively, whereas the symptoms and signs that best lend themselves to objective evaluation are often much less consequential from the point of view of a patient s quality of daily living. Factors predictive of surgical success in cases of lumbar disc surgery have been studied by several authors: 8 7 Pre-op. Follow-up 18 Pre-op. Follow-up ODI *p<.1 (ANOVA and Student s t test) Figure 4 - Bar graph representation of mean pre-operative and follow-up ODI scores. Roland-Morris *p<.1 (ANOVA and Student s t test) Figure 5 - Bar graph representation of mean pre-operative and follow-up Roland Morris scores. Table II - Relationship between type of presentation and modifications in Oswestry Disability Index (ODI) score at follow up. Clinical presentation Total ODI N. Unchanged < 2 points > 2 points Radicular pain 44 2 (4.5%) 15 (34.1%) 27 (61.4%) Low back pain 23 2 (8.7%) 12 (52.2%) 19 (39.1%) Neurological deficit (22.2%) 11 (11.1%) 16 (66.7%) Table III - Relationship between type of presentation and modifications in Roland-Morris (RM) scale score at follow up. Clinical presentation Total RM scale score N. Unchanged < 5 points > 5 points Radicular pain 44 9 (2.4%) 8 (18.2%) 27 (61.4%) Low back pain 23 7 (3.4%) 4 (17.4%) 12 (52.2%) Neurological deficit 19 3 (33.3%) 1 (11.1%) 15 (55.6%) Functional Neurology 26; 21(1):

6 P. Gaetani et al. Waddell et al. (36) stated that return to pre-operative work conditions is the most important outcome measure of medical care; Donceel et al. (37), using the predictive model of fitness for work at one year, showed that preoperative ODI is inversely related to poor outcome. In the present study we have addressed the question of whether surgery in cases of degenerative SPL of the lumbar tract may significantly reduce RM and ODI scores. Figures 3-5 show that there is a significant reduction of VAS LBP and VAS Leg pain after surgery and that RM scale and ODI scores at follow up are also significantly reduced (about 5%). This indicates that there is a significant post-surgical improvement in the quality of activities of daily living. Reduction of the RM scale scores at follow up was less pronounced than reduction of ODI scores: indeed while only 8.6% of cases had unchanged or worse ODI scores, 27% of patients recorded unchanged RM scale scores. This may seem contradictory, but we should stress that the characteristics of the two questionnaires are different, and also point out that our data are consistent, in the field of degenerative SPL, with those reported by Baker et al. (35) and Leclaire et al. (34), which showed that the RM scale is more sensitive to functional changes than the ODI in patients with low-level disability, whereas the ODI is more sensitive in more severely disabled patients. The second question addressed in the present study concerned the possibility of identifying clinical or radiological parameters significantly related to pre- and postoperative disability and pain scores. Sato et al. (38) showed that facet joint tropism, measured as the difference of angles between the right and left facet, was significantly increased in cases of degenerative instability when compared to controls, and was also correlated with the degree of disc degeneration. The results of the present study confirm this observation. Two important pre-operative patterns influence both the ODI and RM scale scores: the presence of air in the facet joint and the degree of vertebral slippage, while the presence of segmental stenosis, which implies a high level of disability, is related only to pre-operative ODI scores. As previously reported (23,39), fusion at short- or medium-term follow up is not related to a better clinical outcome. In our series, the RM scale and ODI score reductions did not differ significantly when considering fusion vs pseudoarthrosis, although this could be an effect of the duration (medium) of the follow-up period (19). On the other hand, we showed that decompression and fusion may be effective in degenerative SPL patients with radicular pain or neurological deficits, but less so in those with LBP alone (Table II): this is explained by the decompressive effect of laminectomy per se and by the consequent effect on quality of life in patients who are functionally impaired by radicular symptoms. As regards the decision to operate surgically, age has frequently been considered a major limiting factor: many degenerative SPL patients are in the older age groups and could run the risk of a high complication rate due to concomitant pathologies or osteoporosis. However, the results of the present study suggest that age, per se, is not a limiting factor for surgery: in fact, while age clearly influences the pre-operative pain scores [we found a significant correlation with pre-operative VAS LBP (p:.44) and VAS Leg pain (p:.46)], the pre-operative RM scale and ODI score groups were not found to be influenced by age. At follow up, reduction of the RM scale score was higher in older patients (r=.73, p:.247), whereas ODI score reduction was not correlated with age group (r=.51; p:.6). Age group distribution also showed a relationship with the presence of lumbar stenosis (p:.7). All this means that surgery could be an option also in older groups of patients presenting with high pre-operative disability scores. In conclusion, instrumental pedicle screw fixation with arthrodesis seems to be very effective in improving the functional disability of patients treated for degenerative SPL, as shown by the reduction of both the ODI and the RM scale scores at follow up. The decision of whether or not to operate should be based both on the severity of symptoms and on the correlation between symptoms and radiological findings, such as the degree of vertebral slippage and the presence of vacuum in the facet joints. Decompression and fusion may be effective in degenerative SPL patients with radicular pain or neurological deficits, but less so in those with LBP alone. The occurrence of fusion after surgery is not significantly related to a better outcome in medium-term follow-up analysis. References 11. Macnab I. 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