The study included 102 patients with both clinically and radiologically defined lumbar spinal spinal stenosis (LSS) who had been selected for surgical treatment. The collection of the study cohort has been described in detail previously [5, 6]. Briefly, selection for surgery was made by an orthopaedist or neurosurgeon between October 2001 and October 2004 in Kuopio University Hospital, Kuopio, Finland. The inclusion criteria were: (1) presence of severe back, buttock, and/or lower extremity pain with radiographic (computed tomography, magnetic resonance imagining, myelography) evidence of compression of the cauda equina or exiting nerve roots by degenerative changes (ligamentum flavum, facet joints, osteophytes and/or disc material), and (2) the surgeon’s clinical evaluation that the patient had degenerative LSS that could be treated operatively. In addition, all patients had a history of ineffective response to conservative treatment over three months. At the 3-month follow-up, two of the 102 baseline patients had missing BDI and ODI data, thus the final sample size was 100.
The exclusion criteria were: emergency or urgent spinal operation precluding recruitment and protocol investigations; cognitive impairment prohibiting completion of the questionnaires or other failures in co- operation; and the presence of metallic particles in the body preventing the MRI investigation. The surgeons sent the information of eligible patients to the Department of Physical and Rehabilitation Medicine, which organized the study. A previous spine operation or co-existing disc herniation (N = 13) were not exclusion criteria. Sixteen patients (out of 100 study patients) had previously undergone one or more lumbar spine operations. Seventeen patients had only lateral spinal stenosis.
All the 100 patients had open or microscopic decompressive surgery with (N = 19) or without (N = 81) arthrodesis or with extirpation of disc herniation (N = 7). Decompressive surgery included laminotomy, hemilaminectomy or laminectomy with undercutting facetectomy. Decompression was done at 1 level in 23 patients, 2 levels in 51 patients, 3 levels in 24 patients and 4 levels in 2 patients. The most common level for decompression was L4-L5. Of the 19 cases with concomitant degenerative spondylolistesis leading to posterolateral fusion, three reached two levels, and the remaining 16 cases were single level.
The study was approved by the Ethics Committee of Kuopio University Hospital, and the patients provided informed consent.
Retrospective outcome scale measurement
In the retrospective analysis, surgical outcome was evaluated from the medical records by two independent researchers blinded for the prospective questionnaire data. Patient outcome was graded as 2 = good if the clinical condition had clearly improved which was the case when the patient was satisfied to the surgical treatment and symptom free, 1 = moderate if it had only slightly improved symptoms and the patient was not fully satisfied to the surgical treatment, 0 = poor if it had not improved symptoms or was worse than before the surgical treatment which was the case if the patient was totally dissatisfied to the surgical treatment (Retrospective 3-point scale). The judgement was based on the information in the medical records during the postoperative 3-month clinical check-up when the surgeon met the patient and patient told for the surgeon about how he or she was doing and how satisfied patient was to surgical treatment. To assess the inter-rater repeatability of the retrospective scale, the evaluation of the patient files was repeated completely for all patients (N = 100) by an independent senior neurosurgeon blinded for the previous evaluation. To assess the intrarater repeatability, the retrospective evaluation of the patient files was repeated completely (N = 100) of at least 2 months after the first evaluation by the first independent researcher, who was again blinded for previous results and prospective questionnaire data.
Prospective outcome scale measurements
Overall back and leg pain intensity was assessed by a self-administered Visual analogue scale (VAS) (range 0–100 mm). This has been proved to be a valid index of experimental, clinical and chronic pain . Subjective disability was measured by the validated Finnish version of the Oswestry Disability Index, where 0 % represents no disability and 100 % extreme debilitating disability [8, 9]. Depression was assessed with the Finnish version of the 21-item BDI with scores ranging from 0 to 63 [10, 11]. Patients completed the ODI, VAS and BDI questionnaires at the baseline and 3 month after operation.
Associations between the retrospective 3-point surgical outcome scale and the prospectively measured (baseline, 3-month follow-up and change) ODI, VAS and BDI were analysed using Spearman correlation coefficients. We analysed separately analysis for patients with the only isolated lateral spinal stenosis to study possible difference outcomes in the central and lateral spinal stenosis patients. The inter-rater and intra-rater repeatability of the retrospective scale was analysed by calculating kappa coefficients (κ). Statistical significance was set at the P < 0.05 level.