This study aimed to measure treatment expectations of patients in a Family Medicine clinic after watching a video with short demonstrations of one active and two placebo treatments that have all been used in previous clinical trials of osteopathic manipulative treatment (OMT). In a previous study, Slicho provided information on treatment expectations of the general population measured through a postal survey with descriptions representing High-Velocity Low-Amplitude (HVLA), sub-therapeutic ultrasound, light touch, and standard care. Slicho found that study participants more strongly agreed with HVLA as a way to logically treat low back pain, but responses did not differ for other aspects of treatment expectations . In the current study, participants were asked to respond to the same statements after viewing two minute filmed demonstrations of the treatments. The investigators realize a better study design of measuring placebo effect would be to have the participants experience the treatments. This study, however, was conducted to provide pilot data on a topic that is under-researched, but vital to successfully conducting clinical trials of OMT. This represents an elementary step in identifying an appropriate placebo for OMT clinical trials.
Analysis revealed a significant difference in participant responses to the statement "I believe this treatment would allow me to get better quicker" after viewing the three treatments. Post hoc analysis demonstrated that participants responded more positively with the statement after viewing the High-Velocity Low-Amplitude treatment than after viewing the light touch treatment. There were no differences between responses after viewing the High-Velocity Low-Amplitude and ultrasound treatments or between ultrasound and light touch treatments.
There was also a significant difference between responses for the statement "I believe this treatment would make me more able to do the things I want to do." Again, post hoc analysis revealed a difference existed in participant responses after viewing the High-Velocity Low-Amplitude treatment and the light touch treatment such that participants responded more positively with the High-Velocity Low-Amplitude treatment. There were no other differences between responses to this statement. These results suggest the sub-therapeutic ultrasound might be a more suitable placebo than LT since there were significantly different expectations between the HVLA and the light touch treatments, but not between HVLA and ultrasound.
Prior experience with manipulative treatment
The expectation of treatment and hence the placebo effect may change with a person's previous experience with manipulative treatment. In this study participants were asked if they had ever had osteopathic manipulative treatment or chiropractic treatment. Participants that had received manipulative treatment (non-naïve) were compared to participants who had never received manipulative treatment (naïve) on all four statements. There were differences between responses from naïve and non-naive participants for the statement "I believe this treatment would allow me to get better quicker," after viewing the ultrasound treatment. Participants who were naïve to manipulative treatment responded more favourably than those who were non-naïve, suggesting that naïve participants had a greater expectation of treatment after viewing the ultrasound treatment than did non-naïve participants. The difference in responses between naïve and non-naïve participants for the statement "This seems like a logical way to treat low back pain" approached significance, again suggesting that naïve participants may have had a greater expectation of treatment after viewing the ultrasound treatment. No differences were found between naïve and non-naïve participants after viewing the light touch treatment for any of the statements. These results suggest that differences in treatment expectations between naïve and non-naïve research participants can have important implications in selecting the appropriate placebo for manipulative treatment clinical trials. Research study participants' experience with manipulative treatment should be measured and controlled for through statistical analysis or controlled for in the study design.
There are several limitations to this current study. First, a convenience sample was utilized. Participates in this study were patients in a Family Medicine clinic and were asked to participate if they would be waiting at least 10 minutes before being seen by their physician. This recruitment process was used to ensure minimal interruption of clinic operations. The use of a convenience sample minimizes the generalizability of the study findings to the general population. Second, participants were recruited from a clinic associated with an osteopathic medical school. This may further limit generalizability because patients at an osteopathic medical school had self reported poorer health than the general population . However, this clinic population is representative of subjects commonly used in OMT clinical research studies. Finally, study participants did not experience the different treatments. This study measured treatment expectations from watching a short demonstration of the treatments. Actually experiencing the treatments would provide additional stimuli to participants and potentially change their expectations.
This study is only an initial step in identifying the best placebo for OMT clinical trials. Measuring expectations of benefits after viewing a two minute demonstration of a treatment cannot replace measuring expectations of benefits after actually receiving a treatment. Further research into the placebo effect, particularly for manipulative treatments, is needed. The most appropriate placebo for OMT clinical trials cannot be truly determined until a better understanding of treatment expectation, physician/patient interaction in osteopathic medicine, other factors involved in the placebo effect, and a patient's experience with manipulative treatment is achieved. A point of interest would be to determine if the amount of prior experience with manipulative treatment is correlated with treatment expectations. Additionally, prior experience with manipulative treatment may have different effects across different countries with variations in OMT practitioner training. The video demonstrations also do not control for the effect of touch or sound during the treatments. Actually applying the sub-therapeutic ultrasound on the skin with gel could potentially change treatment expectations. The presented results, however, provide an elementary analysis of potential placebo treatments in OMT clinical trials and provide the opportunity to seek funding for more definitive research studies. The next step is to research the way participants respond to these issues after actually experiencing OMT and placebo treatments.