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Chapter 8
Methods
Study population
Patients in this study were participants in the Felix Trial, a double-blind multi center randomized trial among patients with a history of intermittent neurogenic claudication (INC) based on LSS, as seen on MRI. Patients included in the trial were aged 40 to 85 years and were subjected to at least 3 months of conservative therapy. The medical ethics committee at each of the five participating hospitals approved of the Felix Trial protocol (including the use of the MRI for scientific purposes), which is available with the full text of this article at BMJ.com.12, 13 Written informed consent was obtained from all patients.
MRI protocol and evaluation
All patients included in the trial underwent MRI at time of initial diagnosis. The extent of spinal stenosis was graded according to the grading system for spinal stenosis developed by Schizas et al.14 The grading system allows for the classification of lumbar spinal stenosis in four grades: grade A, no or minor stenosis; grade B, moderate stenosis; grade C, severe stenosis and grade D, extreme stenosis. Grade A is further divided into four subcategories (Figure 1).14 In our analysis we used the four category Schizas scale (grades A, B, C and D) and two dichotomized Schizas scales (whereas grade A was scored as ‘no to mild stenosis’ and grade B, C and D were scored as ‘stenosis present’ and the alternative whereas grade A and B were scored ‘as no to mild stenosis’ and grade C and D were scored as ‘stenosis present’). Presence of tortuosity of the caudal nerves and presence or absence of epidural fat were also scored. Facet hypertrophy was assessed using the recommended grading system developed by Weishaupt et al., which ranges from grade 0, no facet hypertrophy, to grade 3, severe hypertrophy (Figure 1).15, 16
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