Abstract
Leg pain/numbness and gait disturbance, two major symptoms in the lower extremities of lumbar spinal stenosis (LSS), are generally expected to be alleviated by decompression surgery. However, the paucity of information available to patients before surgery about specific predictors has resulted in some of them being dissatisfied with the surgical outcome when the major symptoms remain after the procedure. This prospective, observational study sought to identify the predictors of the outcome of a decompression surgery: modified fenestration with restorative spinoplasty. Of 109 consecutive LSS patients who underwent the decompression surgery, 89 (56 males and 33 females) completed the 2 year follow-up. Both leg pain/numbness and gait disturbance determined by the Japanese Orthopedic Association scoring system were significantly improved at 2 years after surgery compared to those preoperative, regardless of potential predictors including gender, preoperative presence of resting numbness in the leg, drop foot, cauda equina syndrome, degenerative spinal deformity or myelographic filling defect, or the number of decompressed levels. However, 27 (30.3%) and 13 (14.6%) patients showed residual leg pain/numbness and gait disturbance, respectively. Among the variables examined, the preoperative resting numbness was associated with residual leg pain/numbness and gait disturbance, and the preoperative drop foot was associated with residual gait disturbance, which was confirmed by logistic regression analysis after adjustment for age and gender. This is the first study to identify specific predictors for these two remaining major symptoms of LSS after decompression surgery, and consideration could be given to including this in the informed consent.
Keywords: Lumbar spinal stenosis, Decompression surgery, Outcome, Predictor
Introduction
Lumbar spinal stenosis (LSS) is a degenerative disorder causing neurological symptoms in the lower extremities such as leg pain/numbness and gait disturbance, both of which dramatically deteriorate the patients’ quality of life [3, 4, 17]. With elderly populations growing worldwide, degenerative LSS has become the most frequent indication for spine surgery [12]. The most common surgery is decompression of the lumbar spine, which is performed mainly to reduce the above symptoms in the lower extremities. In fact, a prospective study revealed that the surgery generally resulted in a more preferable greater outcome than non-surgical treatments in the LSS patients [20]. However, about 20–40% of patients have been reported to be dissatisfied with the result due to residual symptoms [1, 8, 9]. To avoid the discrepancy between a patient’s expectations and actual surgical outcome, a surgeon should preoperatively inform the patient in detail of the possible post-surgery outcome of the major symptoms such as leg pain/numbness and gait disturbance.
There have been several reports on the factors that could predict the outcome of LSS surgeries [7–9, 15, 19]; however, some of the surgeries included arthrodesis in addition to decompression. Furthermore, the outcomes were evaluated using several validated measures, so that they covered a broad range including low back pain, psychological status, patients’ satisfaction, quality of life, etc. other than symptoms in the lower extremities. Hence, the predictors identified are rather ambiguous such as the presence of other comorbidities, patient’s assessment of his/her health, subclinical vascular factors and illness behavior. Since little has been known about the specific predictors of outcomes in the lower extremities after decompression surgery, this study sought to identify the factors associated with two major symptoms in the lower extremities of LSS patients: leg pain/numbness and gait disturbance, after a minimally invasive decompression surgery.
Materials and methods
Patients
Consecutive patients, who were blinded to the study, were entered into this prospective observational study from January 2000 through December 2002. Symptoms of leg pain/numbness and/or gait disturbance in LSS patients, which did not respond to conservative therapies for more than 3 months, were considered to be indications for the decompression surgery [10]. The LSS was confirmed by plain radiographs, magnetic resonance imaging and myelography followed by contrast-enhanced computed tomography scan. The patients with severe spinal deformity (spondylolisthesis with Meyerding grades ≥II or lumbar scoliosis with Cobb angle >20 degrees), spondylolysis, post-traumatic stenosis or re-stenosis after prior decompression surgery were excluded, because they were indicated for an additional arthrodesis surgery. A total of 109 patients who met the criteria underwent our original decompression surgery called modified fenestration with restorative spinoplasty [11]. They were allowed to sit up and walk on the 1st or 2nd postoperative day with a soft lumbar support. Examinations were performed preoperatively and at 2 years after surgery. The study was conducted with the approval of the institutional review board (IRB) and all participants (blinded) provided written informed consent.
Data elements
The severity of leg pain/numbness or gait disturbance was evaluated as four grades according to the Japanese Orthopedic Association (JOA) scoring system [5]: 0 (none), 1 (occasionally mild), 2 (always present or sometimes severe) and 3 (always severe) for leg pain/numbness; and 0 (none), 1 (able to walk >500 m with pain/numbness/weakness), 2 (unable to walk 500 m due to pain/numbness/weakness) and 3 (unable to walk 100 m due to pain/numbness/weakness) for gait disturbance. The presence of a residual symptom was defined as a JOA score of 0 or 1 at 2 years after surgery, regardless of the preoperative score. In addition, a score of 2 after 2 years and of 2 or 3 preoperatively were also regarded as the presence of a residual symptom. Potential predictors of outcome included age, gender, preoperative presence of resting numbness in the leg, drop foot [manual muscle test (MMT) score below 3 out of 5 in the tibialis anterior and/or peroneal muscle], cauda equina syndrome (urinary retention, perineal anesthesia or symptoms in bilateral lower extremities), degenerative spinal deformity (spondylolisthesis with more than 5% anterior slippage by the Taillard method [16] and/or lumbar scoliosis with more than 10 degrees of Cobb angle) on plain radiographs, a complete filling defect on myelography in the standing position and the number of decompressed levels. Radiographic findings were independently evaluated by three spine surgeons and were determined with the agreement of at least two of them.
Analyses
Statistical analyses were performed using the SPSS 16.0J for Windows. A P value of <0.05 was considered to be statistically significant and all reported P values were two sided. Paired t test was used to examine the difference between the preoperative and postoperative JOA scores. Association of age, gender, preoperative presence of the above findings or the number of decompressed levels with residual leg pain/numbness or gait disturbance was evaluated by chi-square test in the stratified subgroups. Logistic regression analysis was performed to estimate odds ratio (OR) and the associated 95% confidence interval (CI) after adjustment for age and gender.
Results
Comparison of preoperative and postoperative scores
Of the 109 patients enrolled, 101 (93%) could be followed postoperatively for 2 years. The reasons for the eight dropouts were two deaths from lung cancer and heart failure, three moved to distant areas and three lost contact. Twelve other patients who showed symptoms in the lower extremities due to cerebral infarction, myelopathy or dementia during the postoperative follow-up period were excluded. Symptoms in the lower extremities of the remaining 89 patients (56 males and 33 females; mean ± SD, 66.3 ± 11.2 years) were surveyed 2 years after surgery. There was no complication in the surgical procedure except for slight dural tears in four patients, which were repaired without additional treatment. During the follow-up period, a superficial infection, a pseudomembranous enteritis, a disc herniation at the operated level and a compression vertebral fracture occurred, all of which were cured with conservative therapies. None of the patients underwent spinal re-operation because of progression of stenosis or instability.
The background data of the 89 patients are shown in Table 1. Comparison of preoperative and postoperative JOA scores on symptoms in the lower extremities of all the patients revealed that both leg pain/numbness (1.0–2.0) and gait disturbance (0.7–2.4) were significantly improved by surgery (Table 1). The stratified comparisons by gender, preoperative presence of the above findings and the number of decompressed levels showed that the JOA scores of both symptoms were significantly improved by the surgery in all subgroups. However, the subgroup with preoperative drop foot showed somewhat less improvement in both leg pain/numbness (P = 0.009) and gait disturbance (P = 0.007) than other subgroups (P < 0.0001).
Table 1.
Comparison of preoperative and postoperative JOA scores on symptoms in lower extremities
| n | Leg pain/numbness | Gait disturbance | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Preop. (SD) | Postop. (SD) | Change (SD) | P value | Preop. (SD) | Postop. (SD) | Change (SD) | P value | |||
| All | 89 | 1.0 (0.5) | 2.0 (0.8) | 10 (0.8) | <0.0001 | 0.7 (0.8) | 2.4 (0.8) | 1.8 (1.0) | <0.0001 | |
| Gender | Male | 56 | 1.0 (0.6) | 2.1 (0.8) | 1.1 (0.8) | <0.0001 | 0.7 (0.8) | 2.4 (0.8) | 1.7 (0.9) | <0.0001 |
| Female | 33 | 0.9 (0.4) | 1.8 (0.8) | 0.9 (0.8) | <0.0001 | 0.6 (0.8) | 2.4 (0.8) | 1.8 (1.0) | <0.0001 | |
| Resting numbness | (+) | 40 | 0.9 (0.5) | 1.4 (0.7) | 0.6 (0.7) | <0.0001 | 0.6 (0.7) | 2.2 (0.9) | 1.6 (1.0) | <0.0001 |
| (–) | 49 | 1.1 (0.6) | 2.5 (0.5) | 1.4 (0.6) | <0.0001 | 0.8 (0.8) | 2.7 (0.6) | 1.9 (0.9) | <0.0001 | |
| Drop foot | (+) | 9 | 0.9 (0.8) | 1.9 (0.6) | 1.0 (0.9) | 0.009 | 0.6 (0.9) | 1.9 (1.2) | 1.3 (1.1) | 0.007 |
| (–) | 80 | 0.9 (0.5) | 2.0 (0.8) | 1.0 (0.8) | <0.0001 | 0.7 (0.8) | 2.5 (0.7) | 1.8 (0.9) | <0.0001 | |
| Cauda equina syndrome | (+) | 66 | 0.9 (0.5) | 1.9 (2.2) | 1.0 (0.8) | <0.0001 | 0.6 (0.7) | 2.4 (0.8) | 1.8 (0.9) | <0.0001 |
| (–) | 23 | 1.0 (0.7) | 2.2 (0.9) | 1.0 (0.8) | <0.0001 | 0.9 (0.9) | 2.4 (0.7) | 1.5 (1.0) | <0.0001 | |
| Degenerative spinal deformity | (+) | 47 | 1.0 (0.6) | 2.0 (0.8) | 1.0 (0.8) | <0.0001 | 0.7 (0.8) | 2.4 (0.7) | 1.7 (0.9) | <0.0001 |
| (–) | 42 | 0.9 (0.4) | 2.0 (0.9) | 1.1 (0.9) | <0.0001 | 0.6 (0.7) | 2.5 (1.0) | 1.9 (1.0) | <0.0001 | |
| Complete filling defect | (+) | 56 | 0.9 (0.6) | 1.9 (0.8) | 1.0 (0.8) | <0.0001 | 0.7 (0.8) | 2.4 (0.8) | 1.7 (1.0) | <0.0001 |
| (–) | 33 | 1.0 (0.5) | 2.2 (0.9) | 1.2 (0.7) | <0.0001 | 0.7 (0.8) | 2.5 (0.8) | 1.8 (0.9) | <0.0001 | |
| Number of decompressed levels | 1 | 50 | 1.0 (0.5) | 2.1 (0.7) | 1.1 (0.7) | <0.0001 | 0.9 (0.8) | 2.6 (0.6) | 1.7 (0.8) | <0.0001 |
| ≥2 | 39 | 0.9 (0.6) | 1.9 (0.8) | 0.9 (0.9) | <0.0001 | 0.4 (0.7) | 2.2 (0.9) | 1.8 (1.2) | <0.0001 | |
P value was determined by the paired t test
Predictors of the residual symptoms in lower extremities
According to the definition of residual symptoms as above, 27 (30.3%) and 13 (14.6%) patients showed residual leg pain/numbness and gait disturbance, respectively (Table 2). To identify the predictors of residual symptoms in the lower extremities, we compared the number (percentage) of patients with and without residual symptoms in the stratified subgroup according to the variables. Among the variables, preoperative resting numbness was positively associated with both residual leg pain/numbness (P = 0.03) and residual gait disturbance (P = 0.02). Furthermore, preoperative drop foot was more strongly associated with residual gait disturbance (P = 0.0002), although not with residual leg pain/numbness. Age, gender, preoperative presence of cauda equina syndrome, degenerative spinal deformity, myelographic complete filling defect or the number of decompressed levels was not associated with either of the residual symptoms in the lower extremities.
Table 2.
Number (percentage) of patients with and without residual symptoms in the lower extremities
| Leg pain/numbness | Gait disturbance | ||||||
|---|---|---|---|---|---|---|---|
| (+) | (–) | P value | (+) | (–) | P value | ||
| n = 27 | n = 62 | n = 13 | n = 76 | ||||
| Mean age (years) | 72.0 | 68.1 | 0.10 | 64.6 | 69.1 | 0.10 | |
| Gender | Male | 17 (30.4) | 39 (69.6) | 0.26 | 10 (17.9) | 46 (82.1) | 0.26 |
| Female | 10 (30.3) | 23 (69.7) | 3 (9.0) | 30 (91.0) | |||
| Resting numbness | (+) | 26 (65.0) | 14 (35.0) | 0.03* | 9 (22.5) | 31 (77.5) | 0.02* |
| (–) | 1 (2.0) | 48 (98.0) | 4 (8.2) | 45 (91.8) | |||
| Drop foot | (+) | 4 (44.4) | 5 (55.6) | 0.33 | 5 (55.6) | 4 (44.4) | 0.0002* |
| (–) | 23 (28.8) | 57 (61.2) | 8 (10.0) | 72 (90.0) | |||
| Cauda equina syndrome | (+) | 23 (34.8) | 43 (65.2) | 0.11 | 9 (13.6) | 57 (86.4) | 0.66 |
| (–) | 4 (17.4) | 19 (82.6) | 4 (17.4) | 19 (82.6) | |||
| Degenerative spinal deformity | (+) | 17 (36.2) | 30 (63.8) | 0.60 | 7 (14.9) | 40 (55.1) | 0.60 |
| (–) | 10 (23.8) | 32 (76.2) | 6 (14.3) | 36 (55.7) | |||
| Complete filling defect | (+) | 21 (37.5) | 35 (62.5) | 0.06 | 8 (14.3) | 48 (85.7) | 0.91 |
| (–) | 6 (18.2) | 27 (81.8) | 5 (15.2) | 28 (84.8) | |||
| Number of decompressed levels | 1 | 11 (22.0) | 39 (78.0) | 0.05 | 4 (8.0) | 46 (92.0) | 0.05 |
| ≥2 | 16 (41.0) | 23 (59.0) | 9 (23.1) | 30 (76.9) | |||
P value was determined by the chi-square test
To further identify the principal predictors, we further performed logistic regression analysis after adjustment for age and gender to estimate OR and 95% CI. We confirmed the significant association of resting numbness with residual leg pain/numbness and gait disturbance, as well as the significant association of drop foot with residual gait disturbance (Table 3).
Table 3.
Logistic regression analyses for odds ratio (OR) and 95% confidence interval (CI) of the variables for residual symptoms in the lower extremities
| Leg pain/numbness | Gait disturbance | |||
|---|---|---|---|---|
| OR | (95% CI) | OR | (95% CI) | |
| Resting numbness | 85.6* | (15.9–1603.1) | 4.5* | (1.2–23.2) |
| Drop foot | 2.1 | (0.5–9.0) | 11.6* | (2.5–59.1) |
| Cauda equina syndrome | 2.6 | (0.09–4.1) | 1.3 | (0.006–2.5) |
| Degenerative spinal deformity | 0.7 | (0.1–4.9) | 0.6 | (0.1–2.2) |
| Complete filling defect | 2.2 | (0.9–2.4) | 1.4 | (0.004–2.3) |
| Number of decompressed levels | 2.5 | (1.0–2.7) | 4.2 | (0.06–9.8) |
Data were calculated by logistic regression analysis after adjustment for age and gender, *P < 0.01
Discussion
This prospective observational study for the first time identified the specific predictors for the remaining major symptoms of LSS after decompression surgery: leg pain/numbness and gait disturbance. Preoperative resting numbness was found to be a predictor of both residual leg pain/numbness and gait disturbance, and preoperative drop foot was a predictor of residual gait disturbance. It would seem to be natural that preoperative resting numbness eventually leads to postoperative leg pain/numbness. In fact, 65.0% (26 of 40 patients) of patients with preoperative resting numbness still showed residual leg pain/numbness 2 years after the operation (Table 2). Numbness caused by LSS has been reported to be more difficult to alleviate by surgery than other neurological symptoms such as muscle weakness or pain [2, 6]. Also, it is not surprising that preoperative drop foot eventually leads to postoperative gait disturbance. More than half (55.6%; 5 of 9 patients) the patients with preoperative drop foot showed residual gait disturbance (Table 2). A previous study on the surgical outcome of LSS patients with drop foot revealed that especially those with a preoperative MMT score of 0 or 1 for ankle dorsiflexion exhibited poor alleviation of this disorder [1]. In the present study as well, there were three patients with an MMT score of 0 or 1, and all of them showed residual gait disturbance due to the unchanged drop foot (data not shown). Furthermore, comparison of preoperative and postoperative JOA scores revealed that the subgroup with preoperative drop foot showed less improvement of symptoms in the lower extremities than other subgroups (Table 1). Taken together, resting numbness and drop foot may be derived from less reversible neurological disorders, so that they are difficult to restore by decompression. The preoperative durations of these symptoms may influence the surgical outcomes, which we should examine as a next task. More interesting is that preoperative resting numbness, a sensory disorder, was identified as a predictor of residual gait disturbance, which is a motor disorder. Although the underlying mechanism remains unclear, we speculate a possible involvement of irreversible peripheral neural damage that is related to both resting numbness and gait disturbance.
In addition to resting numbness and drop foot, the number of decompressed levels also showed a trend toward positive association with residual leg pain/numbness and residual gait disturbance, although not statistically significant (Table 2, P = 0.05 in both symptoms; Table 3, OR = 2.5 and 4.2, respectively). Although the present comparison was performed between a single level of decompression and two or more levels of decompression, a comparison between one or two levels (n = 80) and three or more levels (n = 9) showed a significant association of the number of decompressed levels with residual leg pain/numbness (P = 0.01, OR = 7.5, 95% CI = 1.6–50.0), but not with residual gait disturbance (P = 0.50, OR = 1.3, 95% CI = 0.1–6.3) (data not shown in the tables). Indeed, there is greater possibility of multiple levels of decompression to cause surgical invasion, which may eventually result in the residual symptoms. Alternatively, independently of the surgery itself, residual symptoms may be derived from irreversible symptoms of the preoperative disorders, since the multi-level canal stenosis, which is an indication of multi-level decompression, may cause more damages to the nerve root, cauda equina and the blood circulation [13, 14, 18]. Hence, unlike preoperative symptoms such as resting numbness and drop foot, the number of decompressed levels may not be suitable for the predictor. In fact, previous reports on the relationship between the number of decompressed levels and the surgical outcome have been controversial, depending on the outcome measures including standardized instruments and self-reported satisfaction by patients [7, 9].
As the decompression surgery, the present study utilized our original technique called modified fenestration with restorative spinoplasty. Since this technique was developed to achieve good visibility of the spinal canal and safe decompression even in patients with narrow and steep facet joints, the ability to decompress the spinal canal and nerve roots is sufficient, similar to conventional laminectomy/foraminotomy techniques [11]. Hence, we believe that the present results obtained using this unique technique are applicable generally to typical decompression surgeries.
Although approximately 30 and 15% of patients were shown to have residual symptoms after the decompression surgery, respectively (Table 2), the present residual symptoms were defined according to our original criteria based on the JOA score and were not completely or directly linked with the dissatisfaction of the patients. Indeed, there are other factors such as back pain and psychological status to be considererd for the recommendation of the surgery. Furthermore, since the JOA scores of leg pain/numbness and gait disturbance were significantly improved after the surgery, regardless of the presence or absence of these predictors (Table 1), decompression surgery is definitely worth performing to decrease the severity of these symptoms. Hence, the present study suggests that it is desirable for this surgery to be performed before the onset of resting numbness or drop foot at least to prevent residual symptoms in the lower extremities. Even in the presence of these preoperative predictors, however, we encourage this surgery with sufficient informed consent, including the findings obtained from this study, to avoid misunderstanding or over-expectation of the patient with regard to the surgical outcome.
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