Development and validation of a functional disability index for chronic low back pain.

OBJECTIVE To develop a valid and reliable functional disability scale for chronic low back pain (CLBP). METHODS Inpatients and outpatients suffering from low back pain (LBP) for at least 3 months were selected randomly. Patients with inflammatory LBP were not recruited. Interrater reliability and Cronbach's α were examined. Face, content, convergent and divergent validities were investigated. Factor Analysis and pearson's correlation coefficients (r) were performed. RESULTS 112 patients (71 females) with a mean age of 39.93 (SD: 12.92) answered the 66 questions on the provisional scale. Elimination left 18 daily activity questions. The interrater reliability of the scale was 0.79 and Cronbach's α was 0.90. Face and content validities were determined. It showed good convergence with the Quebec Back Pain Disability Scale (r: 0.82), the Oswestry Disability Index (r: 0.76), Waddell's Functional Index (r: 0.68), and the Visual Analog Scale of Handicap (VAS-handicap) (r: 0.49) The scale showed no significant or fair relationship (divergence) with VAS-lumbar, VAS-radicular, Beck Depression Inventory, morning stiffness, night pain, finger tip-ground distance, radicular pain duration, or modified Schöber's index. The scale had two main factors. First represents activities implicating forward bending and second represents standing activities. CONCLUSION A practical functional disability scale for CLBP was developed and validated.