The prevalence of degenerative spine disease will increase with the aging of the population and symptomatic lumbar spinal stenosis will continue to be one of the most frequent indications for spinal surgery [1, 10, 14]. Despite the increasing socioeconomic impact of lumbar spinal stenosis an accurate diagnosis remains difficult to make. Studies evaluating the likelihood that surgery will be performed display wide geographic variations, highlighting the lack of specific and reliable diagnostic tools, and a clinical consensus regarding therapy [1, 15].
The history of neurogenic claudication and assessment of radiological parameters continue to play a pivotal role in clinical practice, and serve as indicators for further therapeutic treatment such as surgery, even though the accuracy of these tools is controversial [7, 14–17].
The aim of this clinical study was to determine the coherence of MR-imaging parameters and subjective clinical affliction, with the objectively measured walking distance in patients with symptomatic lumbar spinal stenosis, in order to examine if these parameters can serve as reliable tools in clinical decision making. Furthermore, the influence of clinical and sociodemographic parameters on the walking capacity was assessed in order to determine if symptomatic lumbar spinal stenosis displays a multi-factorial nature with respect to its causes, diagnosis, and treatment.
In our study the subjective assessment of functional performance in terms of the estimated walking distance differed from objective findings as shown in table 2. The determined Kappa coefficient indicates a significant agreement, but the value of 0.121 is relatively low. That confirms that the subjective assessment of maximal walking distance by the patients does not adequately reflect the reality. Thus, the subjective history of neurogenic claudication cannot serve as a reliable screening tool and leads to the conclusion that in addition to the evaluation of pain records, the walking distance should be verified by the clinical staff. Treadmill gait analysis can serve as a reliable established method if available [16, 18, 19].
Furthermore, our results could not reveal any significant correlations between the objectively measured walking distance using gait analysis, and the cross sectional area of the dural tube measured by MRI in patients with lumbar spinal stenosis.
The displayed correlation between the objectively measured walking distance and dural sac narrowing at L1/2 is not expected to be clinically relevant.
Our results are consistent with recent studies demonstrating that there is little relationship between central canal size and clinical symptoms among persons with a clinical diagnosis of LSS, and that MRI does not sufficiently differentiate between clinical spinal stenosis and controls [20, 21]. In comparison to the study of Haig et al. and Geisser et al. our study population displayed more severe clinical symptoms. Taken together, this underlines that our results apply to a broad patient population independent of the clinical affliction.
The correlation between spinal stenosis and clinical symptoms has been the subject of continuing controversy. While some authors acknowledge a correlation only for certain groups of patients others have reported an influence of spinal canal dimensions in multilevel foraminal narrowing [1, 3, 17, 22–24]. None of these studies demonstrated a clear association between the degree of narrowing and clinical symptoms nor could cutoff values be determined.
Furthermore, studies evaluating MR-imaging in asymptomatic patients demonstrate spinal narrowing in 21–28%, indicating a low coherence of MRI parameters and clinical symptoms in accordance to our study [25, 26].
Some authors have attributed general fitness, age, muscle strength, and pain coping strategies to radiographic severity and non-operative outcome of patients with spinal stenosis . Others correlated obesity and depressive situation with worse spine related symptoms [7, 9, 10].
Although several authors question the diagnostic accuracy of MRI findings because narrowing of the dural sac cannot easily be assessed due to specific imaging modalities (lack of spinal stress during scanning), it is the leading modality in the imaging of spinal disease. MRI is more likely to show bony as well as ligamentous structures without the risks and discomfort of myelograms [11, 27].
Correlation analysis of clinical parameters, the depression status and the subjective functional back capacity with the absolute walking distance are shown in table 3. In bivariate analysis, a reduced functional capacity (FFbH-R) correlated with the absolute walking distance on the treadmill. However, as only one out of the 12 items of the FFbH-R refers to running, further parameters of behavioral dysfunction in respect to avoiding pain and walking should be examined. Moreover, our data displayed a significant negative correlation between walking distance and BMI. Takahashi et al. assumed that obesity provoked lordosis and led to a narrowing of the spinal canal with subsequent aggravation and functional loss . It should be noted that people who are overweight (BMI > 25) suffer more frequently from back pain than people with normal weight .
Forty percent of our patients suffered from depression, even though no correlation between depression and walking distance could be demonstrated in this study. Depression is reported to play a significant role in patients with unspecific chronic back pain . Chronic back pain is known to display a multi-factorial nature often accompanied by emotional distress [29, 30]. The high number of patients with depression may lead to the suggestion that depression may play a more active part in LSS than previously thought.
Fear avoidance behavior can be seen as the primary dysfunction in daily activities of patients suffering from unspecific low back pain [12, 31, 32]. The concurrence of FFbH-R, depression, and elevated BMI in our study suggests that patients may have noticed a restriction in walking ability after some 100 meters and attempt to avert pain through avoidance behavior by reduction of walking distances. Continuing avoidance of walking leads to further reduction in functional parameters, and body mass increases which in turn leads to depressive cognition and further avoidance behavior. Another explanation would be the lack of reliable diagnostic tools to clearly identify patients with lumbar spinal stenosis. This leads to the conclusion that the increasing diagnosis of LSS also contains patients who indeed display a spinal canal narrowing in radiological imaging, but suffer primarily from unspecific chronic back pain. This might be one reason why patients' satisfaction in terms of walking improvement after surgery including decompression of the spinal canal is limited, and therapy failures of 20–40% after decompressive surgery are reported in long-term outcome evaluations [4, 16, 33, 34].
However, in multivariate analysis, FFbH-R, depression, BMI, and central spinal stenosis were not statistically significant independent predictors for walking distance.
Our results point out that the patients' prognosis might depend upon additional factors, such as an increased BMI together with reduced functional capacity and ability to overcome fear avoidance. [4, 15, 35].
This is in accordance with studies showing that functional performance can simply be improved with non-surgical treatment options such as general fitness programs or pain coping strategies, but, of course, the pathomorphology remains unchanged [1, 6, 9, 13, 23, 24]. A recent longitudinal study demonstrated improved function and a decrease of pain in patients with LSS, without receiving any surgical intervention . This demonstrates that anatomy does not predict functional ability and emphasizes the idea that interventions to address pain and function may be more successful than those that manage anatomy. The influence of psychosocial issues should be evaluated before surgery and taken into consideration in the therapy concept. Therapy modalities, which strengthen a passive patient's attitude, should be omitted. In addition to weight reduction, an age-related cognitive behavioral therapy such as a multidisciplinary approach, should be chosen in order to compensate avoidance behavior as expressed in the low rated scores in functional back capacity. This would be consistent with our experience with therapy for chronic pain and disability in the aged population .
Some comments can be made on the population and the methods used in this study. The assessment of patients with symptomatic spinal stenosis remains difficult since the population is heterogeneous and patients often present with a high number of comorbidities. As described above we tried to address this issue by performing diagnostics to create a more homogeneous population, which is a major strength of this study.
The lack of objective research methodologies is a major deficit of the studies evaluating patients with spinal stenosis, and potentially, issues of mental overlay could render the results bias. We tried to balance this issue by using reliable tests and independent staff to objectively assess gait analysis and MRI data sets. However, before making any generalizations, it must be taken into account that a relatively high number of our study population suffered from depression. The influence of psychosocial issues on pain and disability in patients with LSS is likely huge, but relatively unstudied. Further research is needed to address this issue. A limitation of the study is the small number of patients (n = 63) and the consequent risk of a Type II error. With the given 63 complete data sets which were included in the analyses and 3 independent variables, small effects could probably not have been detected. It was attempted to minimize the influence of further potential effectors with inclusion and exclusion criteria.
A post hoc performed power analysis showed (1-beta)-values of less than 0.80. The restriction to few clinically relevant variables such as factors determining walking distance was accepted in order to counter this.