Methods
Patients
This prospective single-center study was approved by the Ethics Committee of Kuopio University Hospital, and the patients provided informed consent. The study included 84 patients with both clinically and radiologically defined LSS who had been selected for surgical treatment. Selection for surgery was made by an orthopedist or neurosurgeon at the Kuopio University Hospital, Kuopio, Finland. The inclusion criteria were as follows: 1) the presence of severe back, buttock, lower extremity pain, and/or neurogenic claudication with radiographic evidence (computed tomography, magnetic resonance imaging (MRI), myelography) of compression of the cauda equina or exiting nerve roots by degenerative changes (ligamentum flavum, facet joints, osteophytes, and/or disc material); and 2) clinical and radiological evaluation by a surgeon, indicating that the patient had degenerative LSS with symptoms that could be relieved by operative treatment. Additionally, all patients had a history of ineffective response to conservative treatment over three months. Patients with only back pain were not included.
The exclusion criteria were as follows: emergency or urgent spinal surgery precluding recruitment and protocol investigations; cognitive impairment prohibiting completion of the questionnaires or other failures in cooperation, and the presence of metallic particles in the body preventing the magnetic resonance imaging investigation. A previous spine operation or coexisting disc herniation was not an exclusion criterion, but the main diagnosis of the study patient had to be LSS. The surgeons sent the information of eligible patients to the Department of Physical and Rehabilitation Medicine, for further study organization. In four of these patients, recordings of standardized tests were not completed and these patients were excluded. Finally the study included 80 patients (mean age 63 ± 11 years, 44% male).
MRI
MRI of the lumbar spine was performed with a 1.5-T imager (Vision; Siemens Medical Solutions, Erlangen, Germany) and a dedicated receive-only spine coil. All patients were evaluated prospectively by applying the same study protocol for study purposes. The imaging protocol conformed to the requirements of the American College of Radiology for the performance of MRI of the adult spine.[10] The following sequences were used: (a) sagittal T1-weighted spin-echo (repetition time/echo time (TR/TE) 600/12 ms; flip angle, 150°; 4-mm sections; intersection gap, 0.4 mm; field of view (FOV), 290 mm; rectangular FOV, 80%; three signals acquired per data line; matrix 288 × 512) (b) sagittal T2-weighted fast spin-echo (3500/120; flip angle, 180°; echo train length of five; 4-mm sections; intersection gap, 0.4 mm; FOV 290 mm; rectangular FOV, 63%; two signals acquired; matrix 180 × 512); (c) transverse T1-weighted spin-echo (700/15; flip angle, 90°; 4-mm sections; intersection gap, 0.4 mm; FOV, 250 mm; rectangular FOV, 80%; two signals acquired per data line; matrix 288 × 512); and (d) transverse T2-weighted fast spin-echo (5000/120; flip angle, 180°; echo train length of 15; 4-mm sections; intersection gap, 0.4 mm; FOV, 250 mm; rectangular FOV, 100%; three signals acquired per data line; matrix 330 × 512).
The entire lumbar spine was studied on the sagittal images (T12-S1), including parasagittal imaging of all the neural foramina bilaterally. Transverse images were obtained from the inferior aspect of L1 to the inferior aspect of S1, and the orientation of the sections was planned parallel to the major axis of each disc. In all sequences, a saturation band was placed over the abdominal vessels.
Image Analysis
Image evaluation was performed with Numaris software (Siemens Medical Systems) by a neuroradiologist with 15 years of experience with spinal MRI (T.S.). Image analysis was performed independently without knowledge of the patient clinical symptoms and data. Each level from the inferior aspect of L1 to the inferior aspect of S1 was analyzed separately. For the visual image evaluation, the central canal was visually classified into three grades: 0 = normal or mild changes (ligamentum flavum hypertrophy and/or osteophytes and/or or disk bulging without narrowing of the central spinal canal), 1 = moderate stenosis (central spinal canal is narrowed but spinal fluid is still clearly visible between the nerve roots in the dural sac), 2 = severe stenosis (central spinal canal is narrowed and there is only a faint amount of spinal fluid or no fluid between the nerve roots in the dural sac) (Figure 1). Patients who had severe stenosis at least two levels in the visual analysis were classified as having the multilevel spinal stenosis. For the quantitative image evaluation, each level was first assessed visually. The borders of the dural sac were manually traced in the image with smallest cross-sectional area upon visual examination. According to the smallest area, patients were divided into three groups: 1) patients with dural sac area less than 75 mm2; 2) patients with dural sac area form 75–100 mm2; and 3) patients with dural sac area greater than 100 mm2.[11] In statistical analyses, the highest degree of stenosis was used for both the visually and quantitatively measured stenoses.
Figure 1.
Axial T2-weighted model images of representative cases that were used to grade central spinal canal in visual assessment. a) normal central spinal canal; b) moderate central spinal canal stenosis; c) severe central spinal canal stenosis.
Assessment of Preoperative Symptoms and Functional Disability
The overall current low back and leg pain intensity was assessed by a self-administered VAS (range 0–100 mm) in a sitting position during study visits. VAS was proven as a valid index for experimental and clinical assessments of chronic pain.[12] According to the score range (0–100 range), four groups were established: scores 0–20 (minimal), 21–40 (moderate), 41–60 (severe), and over 60 (crippled). Back pain at rest (during last week) and leg pain while walking (during last week) were measured separately with a numeric rating scale ranging from 0 to 10 (NRS-11).[9] The questions about pain were anchored on the left (0) with the phrase "No pain" and on the right (10) with the phrase "intolerable pain".
Subjective disability was measured by the validated Finnish version of the ODI, where 0% represents no disability and 100% extreme debilitating disability. This ODI score (0–100 range) were also classified in four groups: scores 0–20 (minimal), 21–40 (moderate), 41–60 (severe), and over 60 (crippled).[3,6,13]
Depression was assessed with the Finnish version of the 21-item BDI with scores ranging from 0–63.[8,14] The cutoff point for depression was set at 15/63. The BDI score was classified into two groups: scores 0–14 (normal mood), and 15 or more (indicating elevated depressive symptoms).[15]
The treadmill test was supervised by a physiotherapist. The patient was asked to keep a straight, upright position during walking on ram without elevation. The starting speed was 0.67 m/s for the first 10 min (400 m), then 1 m/s for the next 10 min (600 m), with a maximum result 1,000 m in 20 min. If the patient was not able to start with a speed of 0.67 m/s, another test with a starting speed of 0.5 m/s was applied. The walking distance scale ranged from 0 to 1000 m.
Statistical Analyses
Associations between the quantitative evaluation of the radiological stenosis in MRI and the continuous ODI, VAS, BDI, and walking capacity were analyzed using Spearman correlation coefficients. The visual assessments were analyzed using t-test. Non-parametric tests were used when no assumption of normal distribution could be made. Statistical analysis was performed using SPSS for Windows (version 19.0; SPSS, IBM, Chicago IL, USA). Statistical significance was set at a P <0.05.
BMC Musculoskelet Disord. 2014;15(348) © 2014 BioMed Central, Ltd.
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