J Manipulative Physiol Ther 2005 (Nov); 28 (9): 662–666 ~ FULL TEXT
Howard Vernon, DC, PhD, FCCS, Katherine MacAdam, DC,
Victoria Marshall, BSc, DC, Maryse Pion, BScPT, DC,
Magdalena Sadowska, DC
Canadian Memorial Chiropractic College,
Toronto, Ontario, Canada.
OBJECTIVE: To develop a sham manipulation procedure for the cervical spine for use in randomized clinical trials of cervical disorders.
METHODS: A single-group, single-intervention study design was used. Adult neck pain subjects underwent a screening examination that included palpation for a site of cervical spine joint dysfunction. Eligible subjects underwent measurements of regional cervical ranges of motion as well as pressure algometry (tenderness) at the site of cervical joint dysfunction. Subjects were instructed that they would receive one of several types of manipulative procedures. A newly developed sham manipulation was delivered once. Subjects were then remeasured for ranges of motion and tenderness. They were asked if they had experienced any pain during the procedure, if they had experienced a "cavitation" sound, and if they thought that the procedure they received was a "real" manipulation. Finally, they were debriefed as to the deception involved in this study. A prior level of 65% was set for endorsement that the procedure was a real manipulation. Changes in pre-post measures of ranges of motion and tenderness were analyzed descriptively for clinically important differences.
RESULTS: Twenty eligible subjects were included (12 males, 8 females) with an average age of 30.4 (2.8) years. Twelve of the subjects were not students, with 3 of these having no prior experience with chiropractic treatment; 8 were students. Of the total sample (N = 19), 8 (42.1%) indicated that the procedure was a "real adjustment"; of the 12 nonstudents, 8 (58.3%) indicated similarly. None of the procedures in the final sample resulted in a cavitation, and none of the subjects registered the procedure as painful. None of the measures for ranges of motion or tenderness showed clinically important changes.
From the Full-Text Article:
The issue of placebo treatment in chiropractic is controversial. Clinical studies, especially randomized clinical trials, of chiropractic treatment or care may be complicated by the presence of what have been described as nonspecific treatment factors such as expectation of benefit, general manual contact, and other health-related beliefs. These have been regarded by many in the profession as beneficial. [1–3] Their removal in the designs of protocolized studies has been seen by some as a weakness, in that these trials fail to retain fidelity to the circumstances of real-world practice.
On the other hand, studies of joint manipulation alone (once or in series) have been criticized for the lack of a control procedure that could minimize these nonspecific effects and equalize the level of outcome expectation by subjects who have consented to participate.  This applies to both lower-level analytical studies (often of a single dose of intervention), whose objective might be to elucidate some mechanism of action of manipulation, as well as to higher-level clinical studies of the efficacy of a series of manipulation treatments for spinal pain disorders.
The ethical justification for the use of a placebo group in clinical trials lies in the concept of “clinical equipoise,”  which, when justified, permits investigators to, as Freedman  states, “have no ‘treatment preference’ throughout the course of the trial.” The arguments presented above on the need for placebo-controlled research in spinal manipulation, as well as the lack of such trials in key clinical areas, establish the general basis for clinical equipoise in this field of work. Once this is accepted, the need for a valid placebo maneuver becomes paramount and the issues that distinguish this type of placebo from the kind of inert pill used in drug trials become obvious.
Hawk et al [6–8] have noted that the development of placebo manipulation procedures by researchers in manipulative therapy has been challenging. They identified two important objectives of placebo manipulation procedures: (1) the equalization of the nonspecific effect of physical touch between groups of subjects, and (2) the blinding of the subject as to the nature of the treatment. They identified the essence of such a placebo maneuver in that it “increase(es) the believability of the intervention, thus equalizing the effect of expectation of improvement between groups.” 
Sham manual or manual-type treatments have been used in trials of chiropractic manipulation for low back pain, [6–10] headache, [11, 12] primary dysmenorrhea, [14, 13] hypertension, [15, 16] phobia,  nocturnal enuresis,  asthma, [19, 20] and otitis media.  The trials in the latter three disorders involved pediatric patients, so the level of success in achieving a true placebo condition in these trials is not applicable to adults.
In their systematic review, Ernst and Harkness  noted that the small number of trials using a “placebo” maneuver precludes making definitive conclusions, although they urged a continuation of the development of sham-controlled trials. Ernst and Harkness opined that the extant sham-controlled trials have not shown a consistently greater effect for manipulation as compared with the placebo,  but this conclusion referred to a wide range of clinical conditions, with the highest-quality trials addressing asthma and primary dysmenorrhea. Others have concluded that manipulation has shown a superior effect as compared with placebo treatments in subjects with low back pain. 
The challenge faced by researchers wishing to use a placebo manipulation procedure is to develop and validate a sham manipulation procedure that has high fidelity to a subject's perceptions of a “real” manipulation, while insuring that this procedure is as therapeutically inert as possible. Triano et al [9, 10] addressed this challenge by focusing on the level of force applied to the spine during manipulation. They developed a low-force manual manipulation procedure that was shown to be successful as a “sham” manipulation in several trials involving the lumbar spine.
Other procedures used for sham treatments have included the use of an inactivated manipulation device, [6–8, 16, 18] low-force, non–rotary thrust technique, [9, 13, 14] and soft tissue techniques. [10–12, 15, 19–21]
Other challenges identified by these researchers include the apparent requirement of a “cracking sound” to signify a real manipulation and the fact that there may be a difference between what might be successful as a sham procedure on one occasion as compared with what is required for a series of treatments, such as in a randomized controlled trial of a program of care. Finally, there has been concern that the placebo maneuver in some studies has actually produced some level of therapeutic benefit, resulting in the lack of statistically significant difference between real and placebo manipulation groups.
No clinical trial has yet used a manual cervical sham manipulation, although Bove and Nilsson  did use a manual control therapy (soft tissue therapy) in their study of manipulation for tension-type headaches and Sterling et al  used a cervical sham mobilization procedure in their single-intervention study.
The purpose of our study was to validate a novel cervical sham manipulation used in a single application. In this investigation, we hypothesized that the sham manual manipulation would succeed as a placebo in that (1) it would have no significant treatment effect and that (2) subjects would be unsuccessful in determining if they received a sham treatment.
This study was designed to determine if a novel sham cervical manipulative procedure was “effective” to the extent that it resulted in no significant change in clinical status, but was perceived by subjects to be a real manipulation. Should these objectives be met, then this maneuver could be considered for use as a placebo chiropractic treatment in future randomized clinical trials for treatment of neck-related disorders.
Several limitations must be considered with these results. The sample size was small, limiting its ability to achieve the predicted level of agreement by subjects on whether they considered that the maneuver was a real manipulation. Furthermore, the sample was composed of two groups who had unequal experience with chiropractic treatment. It can certainly be concluded here that future studies should not employ students currently in a chiropractic program, although they may profess that they have not previously had a cervical manipulation.
Nonstudents in this sample (63%) were much more likely to have the perception that the procedure was a real adjustment. The level of agreement among these participants was just short of our target level.
Even if the target level of deception had been achieved, if the proposed maneuver actually produced some important change in physical findings such as ranges of motion and local tenderness, then it would fail to achieve overall practicability as a sham procedure. The procedure used in this study appears to produce no important change in either a positive (therapeutic) or negative (harm) direction. That is, it appears to be therapeutically inert and, thus, qualifies for that aspect of a placebo maneuver.
Participants provided helpful information on which aspects of the intervention made them feel that the procedure was a real manipulation. Most patients believed that the absence of a cracking sound was the biggest indicator that the procedure was not real. A couple of patients believed that the sham adjustment actually produced a specific correction to the vertebrae.
Several researchers have remarked on the issue of the cracking sound accompanying what is presumed to be a successful manipulation of the spine. [6–8] Some subjects (in previous studies and in the present one) have indicated that the absence of this sound convinces them that the procedure is not a real manipulation. Future research on sham cracking sounds might lead to greater success in subject believability. We undertook the present study without such contrivances to determine what level of success could be obtained solely by a procedure involving manual contacts and apparent thrusting. Our results come close to full success, so perhaps additional elements are not necessary.
The sham cervical manipulation studied here appears to approximate the necessary features of a placebo maneuver in that it is perceived by a majority of nonstudent neck pain subjects to be a real manipulation, although it does not produce any important change in cervical status. The small sample size of nonstudent participants precludes a strong recommendation for this procedure at this time.