People with low back pain typically need to feel 'much better' to consider intervention worthwhile: an observational study

Question: How much of an effect do five common physiotherapy interventions need to have for patients with low back pain to perceive they are worth their cost, discomfort, risk, and incovenience? Are there any differences between the interventions? Do specific characteristics of people with low back pain predict the smallest important difference? Design: Cross-sectional, observational study. Participants: 77 patients with non-specific low back pain who had not yet commenced physiotherapy intervention. Outcome measures: The smallest worthwhile effect was measured in terms of global perceived change (0 to 4) and percentage perceived change. Results: Participants perceived that intervention would have to make them 'much better', which corresponded to 1.7 (SD 0.7) on the 4-point scale, or improve their symptoms by 42% (SD 23), to make it worthwhile. There was little distinction made between interventions, regardless of whether smallest worthwhile effects were quantified as global perceived change (p = 0.09) or percentage perceived change (p = 1.00). Severity of symptoms independently (p = 0.01) predicted percentage perceived change explaining 9% of the variance, so that for each increase in severity of symptoms of 1 point out of 10 there was an increase of 4% in the percentage perceived change that participants considered would make intervention worthwhile. Conclusions: Typically people with low back pain feel that physiotherapy intervention must reduce their symptoms by 42%, or make them feel 'much better' for intervention to be worthwhile. [Ferreira ML, Ferreira PH, Herbert RD, Latimer J (2009) People with low back pain typically need to feel 'much better' to consider intervention worthwhile: an observational study. Australian Journal of Physiotherapy 55: 123-127]