The outcome of spinal decompression surgery 5 years on

Abstract

Decompression surgery is an increasingly common operation for the treatment of lumbar spinal stenosis. Although good relief from leg pain is expected after surgery, long term results of pain relief and function are more uncertain. This study prospectively followed a cohort of patients presenting with the signs and symptoms of spinal stenosis, who underwent decompression surgery to ascertain the long term outcome with respect to pain and function using visual analogue pain scores, the Oswestry Disability Index, and the Short Form 36, a general health questionnaire. From an initial pool of 84 recruited patients, 7 withdrew from surgical intervention; of the remaining 77, 51 (66%) returned for follow up assessments at 5 years. In these responders, a significant improvement was observed in back and leg pain, which was sustained for at least 1 year (P < 0.01). A significant improvement was also seen in physical function (P < 0.05) as assessed by Oswestry and SF-36. Although an initial improvement was noted in social function, this was not observed at 5 years. This study has demonstrated that decompression surgery is successful in relieving symptoms of lumbar spinal stenosis. Physical function, back and leg pain are significantly improved after 5 years but initial significant improvements in social function diminish over time.

Introduction

Degenerative lumbar spinal stenosis, due to hypertrophy of the ligamentum flavum and facet joints, is a narrowing of the lateral root canal of the spine. It may result in nerve root ischemia and neurogenic claudication. Typical symptoms of unilateral or bilateral leg pain and neurogenic claudication may only be brought on by ambulation and spinal posture and neurological deficits may be absent on clinical examination. It is a leading cause of disability and discomfort [5].

Although many studies support the use of surgical intervention for spinal stenosis [13, 14, 27, 42], the long term natural history of the disease is unclear. It has been suggested that the majority of patients have stable symptoms, with only 15% of patients deteriorating significantly over 3 years [19] and less than 20% of patients treated non-operatively electing to undergo surgery due to refractory pain [37]. This questions the need for surgery. Further, in those having operative interventions there is still limited information on long term outcomes beyond 2–3 years [14].

In order to fully appreciate the effectiveness of surgical intervention, the long term outcome has to be determined. Many spinal interventions appear to have excellent early post-operative results [2, 3, 14, 40], but there is a temporal decline in benefit [21, 35, 41]. This would then indicate that conservative options may provide a viable option. Ciol et al. [8] has suggested that spinal stenosis was the fastest growing cause for surgery in patients over 65 years, this combined with the findings of Yamashita et al. [42] which suggests that age may impact outcome, indicates a need for further research. This is further supported by the Maine study [4, 5] which suggested that early improvements in symptoms as a result of surgery diminished with time. Within our own institution we have demonstrated good early results in outcome following spinal decompression surgery [30, 31]; however, in view of these current findings, we decided it was appropriate to review the long term impact of their surgery on their pain and function.

Methods

Patients presenting to the Spinal Clinic at the Charing Cross Hospital with the signs, symptoms and MRI findings of spinal stenosis as a result of degenerative changes were eligible for inclusion in this study. Stenosis due to trauma, malignancy and infection were excluded. Written informed consent was obtained from all subjects. A total of 84 subjects (41 female and 43 male, with a mean age of 52.8 ± 14.0 years) out of 135 approached were recruited into this study between September 1997 and 1999, which gave a recruitment rate of 62%. Of the 51 subjects who did not take part in the study, 35 declined participation, and the remainder were excluded on account of their age (over 80 years), language problems, confused state of mind, and coexisting pathology. Base line measures were obtained on the 84 patients recruited into this study at 6 weeks prior to surgery at a pre-admission clinic.

Twenty of the 84 subjects had had previous surgery; 15 had had previous decompression surgery and the remaining 9 had had a discectomy. Of the subjects recruited, 77 underwent surgery; the remaining 7 subjects opted not to go through with their surgery choosing a conservative management approach and were therefore not included in the subsequent analysis. 72 subjects (94% of original recruited surgical population) were re-assessed at 6 weeks, 68 (88%) were reviewed at 6 months, 65 subjects (84%) completed their 1 year review and 51 subjects (66%) their 5 year review. Where possible, reviews were performed during the patient’s post-operative follow-up appointments at the clinic; where patients were unable to attend questionnaires were posted to the patient for completion. Review assessments were performed by an independent observer and the questionnaires were completed by the patient. Patient drop out from the study was primarily a result of either patients moving out of the area or returning to full time employment and having insufficient time to complete the study.

Surgical procedure

All of the subjects underwent posterior decompression surgery through a midline approach, 83% had a bilateral decompression performed whilst the remainder had a unilateral decompression. The decompression involved a partial laminectomy, removal of ligamentum flavum and undercutting facetectomy. Midline structures were preserved. Five subjects also underwent a fusion with instrumentation due to the presence of a degenerative spondylolisthesis. Evidence has suggested that the outcome of surgery for spinal stenosis in these patients is improved by fusion [15]. 77% of subjects had two or more levels decompressed whilst the remainder had only one level decompressed. All patients returned from surgery to an orthopaedic ward. Post-operative mobilisation was supervised by a physiotherapist, however, other than this patients were not routinely required to attend the hospital for any post-operative rehabilitation. The five subjects who underwent fusion received a lumbar corset, which was worn when mobilising for 3 months. All patients were encouraged to mobilise as pain and other symptoms allowed. Patients were discharged to their own homes when safely mobile and followed up in a spinal clinic at regular intervals.

Clinical assessment of patients

This was done in accordance with the original study protocol [30], which included anamnestic information and pain diagrams. At the 5 year review, patients were asked to identify their pain sites on a pain drawing [32] and to rate their current resting pain levels, and their worst and usual pain levels over the past week on a 10 cm visual analogue scale (with back and leg pain considered separately) with the mean value of current, worse and usual pain used in the analysis. In addition patients, completed the Short Form SF-36 Health Survey Questionnaire—a validated general health questionnaire [7, 12], and the Oswestry Disability Index (version 2.1) [11]—a disease specific disability index.

Analysis

All statistical analyses were performed on the statistical package STATA version 8.0 (Stata corp., TX, USA) on a personal computer. All analyses were performed according to a statistical analysis plan that was agreed before any data were seen. In order to investigate whether missing follow-up data were informative, Student’s t tests and χ² tests were used to compare subjects who had attended follow-up with those who had not. Comparisons were made in terms of baseline leg pain, age, gender, smoking status and previous surgery. The primary outcome measure was leg pain with secondary outcomes including average back pain, Oswestry disability index (ODI) and the SF-36 sub-categories of physical and social functioning, relative to baseline pre-operative values using paired Student’s t tests. Normality plots were used to check the distribution of all differences in the outcome variables. Linear regression models were used to assess whether improvement in outcome had been confounded by age, sex, smoking status and previous surgery at baseline. The threshold for statistical significance was set at P < 0.01 to account for the multiple testing performed on the data.

Results

Missing data

There was little evidence to suggest that either leg pain or age were related to missing follow-up data status. However, there was some evidence to suggest that men were more likely to fail to complete their follow-up reviews compared with females but this was only statistically significant for the 6 week appointment when 23% of men did not attend compared with 5% of women (P = 0.016). Similarly there was weak evidence to suggest that smokers were consistently better at completing their follow-up reviews; however this was only strongly significant at the 5 year review (P = 0.007) where 19% of smokers failed to attend compared with 49% of non-smokers. There was no strong evidence to suggest that previous surgery related to missing data, although the data did indicate that people who had received previous surgery were more likely to complete their follow-up reviews.

Pain

Figure 1 illustrates the changes in back and leg pain over the 5 year period. A statistically significant improvement in leg pain was observed from baseline at all three review stages (P < 0.01). Similarly, back pain appeared to reduce significantly (P < 0.01). However, as can be observed from Fig. 1 there was some deterioration in pain level at 5 years but the level of pain was still significantly improved from baseline, although the clinical impact of this reduction is questionable. Regression modeling indicated that these improvements in leg and back pain could not be explained by differences in age, sex, smoking status or previous surgery with all regression P values falling markedly above the threshold for significance of 0.01.

Fig. 1.

Changes in back and leg pain over 5 years, mean and standard error presented with Student’s t test P values for difference from baseline, n = 72 at baseline, 68 at 6 weeks, 65 at 1 year and 51 at 5 years

Oswestry Disability Index

Minimal changes were observed in ODI score between baseline and 6 weeks; however, at 1 year statistically significant improvements were observed (P = 0.002) which were maintained at 5 years (P = 0.015) (see Fig. 2). The clinical relevance of these changes is less clear. Again, improvements did not appear to relate to age, sex, smoking status or previous surgery (P > 0.05).

Fig. 2.

Changes in Oswestry Disability Index score over 5 years, mean and standard error presented with Student’s t test P values for difference from baseline. N = 72 at baseline, 68 at 6 weeks, 65 at 1 year and 51 at 5 years

SF∼36 General Health Questionnaire

Table 1 gives the results for the physical and social functioning scores from the SF-36 assessment. For physical functioning, strongly significant improvement was observed at 1 year (P = 0.004) with some borderline evidence to suggest significant benefit at 5 years (P = 0.028). For social functioning, significant improvement only emerged at 1 year (P < 0.001) and appeared to diminish beyond this. Regression analysis did not indicate that SF-36 score improvements were associated with age, sex, smoking status or previous surgery.

Table 1.

SF-36 physical and social functioning scores over 5 years

	Physical function	Social function
Baseline	28.8 ± 24.4	40.8 ± 26.9
6 weeks post-op	32.2 ± 22.4	36.2 ± 31.3
1 year post-op	39.4 ± 30.8	59.0 ± 32.5
5 years post-op	33.9 ± 26.2	43.9 ± 33.2

All values given as mean ± standard deviation

Discussion

This study reviewed the long term outcome in an established cohort of patients from whom prospective outcome data had been collected prior to and following a decompression procedure. Unfortunately only a 61% return rate was achieved, limiting the interpretation of these findings but there was little evidence to suggest that subjects who did not complete their follow-up were different from those who did. In agreement with previously published data, this study confirms that surgery achieved an initial improvement in pain and function at 1 year, and also demonstrated significant, although diminished improvement in symptoms at the 5 year review [6, 17, 42]. A limitation of this study was that it only looked at surgical management; however, a recent randomised controlled study from Finland highlighted a greater reduction in disability and pain in those receiving the surgical intervention as opposed to conservative intervention for spinal stenosis, but also that this improvement diminished at the 2 year follow up [26] A further limitation of the current study was the inclusion of different decompressive procedures performed by different surgeons, ideally the analysis could account for this but this would require a larger study population or a more procedure-specific study. Similarly, all patients requiring decompressive surgery were included, regardless of whether this was a result of a degenerative spondylolisthesis or just severe degeneration. A small number had had previous surgery; however, this was noted to have limited impact on the outcome findings.

The objective of decompression surgery is to relieve leg pain and it is not surprising that improvement in leg pain was observed, a finding that is not unique to this study [6, 9, 17]. A significant improvement in back pain was also seen, similarly this is not new. Routinely patients are told that the surgery aims to relieve leg pain/symptoms only, thus patients are encouraged not to expect such an improvement. It is of interest that improvements in both pain sites deteriorate with time. Some may advocate inadequate decompression at the time of surgery (but this is not consistent with the initial improvements observed), progression of the underlying spondylosis condition and inactivity combined with ageing [34, 36] as the cause for this deterioration. Work by Atlas et al [6] comparing the long term outcome of spinal stenosis suggests that it may be an inevitable part of the disease process but suggested that this effect was less marked in those who had surgical intervention. The answer to this dilemma is beyond the scope of this study and requires further research in the form of randomised controlled studies, ideally with a control population that permits the natural course of the disease to be assessed. Recent reviews of post-operative practice have noted clear inconsistencies within and between surgeons with regard to post-operative management and advice [[29]]. This can make patients uncertain and reluctant to return to normal activities. Combined with the deconditioned state many patients present with [1, 16, 23, 25, 33, 39] this may explain the low improvements in function observed. This lack of post-operative advice has now been addressed in the form of a patient education booklet [28], the value of which is currently being explored in a randomised controlled study.

Whilst many of our outcome measures demonstrate significant improvement, the clinical relevance of these changes is less clear. Of interest here is the finding that social function, unlike physical function, did not demonstrate significant improvement at the 5 year review, returning to pre-operative levels. This may be due to other co-morbidities, but may reflect more a lack of confidence in their spine and a lack of education as noted above. Patient’s perception of general health status is known to predict outcome in decompression surgery [22], and this in turn is influenced by other psychosocial factors including depression [18, 24, 38]. Sex and smoking status were not related to outcome, which is of interest considering the relationship between smoking and back pain [10, 20].

To summarise, this prospective cohort study documenting the outcome of decompressive surgery showed that physical function assessed by ODI and back and leg pain were significantly improved after surgery but that these improvements had deteriorated slightly by 5 years. In particular, early improvements in social functioning observed at 1 year were not sustained. From this study we feel confident in being able to advise our patients before surgery that they can expect an improvement in the level of pain that they experience and in their physical abilities. This study provides new long-term data and suggests that patients should be informed that early benefits may diminish slightly with time, however, these findings do only represent a 66% return in the long term review data.