Centralization/directional preference subgroup Paul Weiss, Cedar Hill Physical Therapy 18 March 2010 Often times, RCT's for low back pain show a small treatment effect over a group with non-specific low back pain. However, there are several examples where subgroups of back pain patients have been shown to respond favorably to a particular treatment. In this study, the treatment group was given a mechanical diagnosis of either a derangement, posture syndrome or dysfunction. Of the three groups, a subset of the derangement classification has been shown to either centralize or have a directional preference, while other derangements are irreducible and do not demonstrate this examination response. Those who centralize or have a directional preference have a more favorable prognosis and are expected to respond positively to the McKenzie Method. I would be interested in seeing this study redone with a focus on those who centralize or have a directional preference. Identifying that subgroup and randomizing them into a McKenzie Method treatment or a usual treatment group could show a greater treatment effect. The study method presented included both people who would and would not be expected to respond rapidly to the McKenzie Method. This may have diluted the positive results expected in a well defined subgroup. (By definition, the dysfunction classification is expected to respond slowly to treatment.) Perhaps the authors could take the data collected and reexamine it. I would suggest identifying those patients who on initial examination did centralize or have a directional preference and compare their outcomes to those who did not have this finding and to those in the control group. Competing interests Paul Weiss, PT, Dip MDT is the proprietor of Cedar Hill Physical Therapy. He has completed the McKenzie Diploma program and utilizes this method of treatment in his private practice.