Placebo-control of acupuncture is used to evaluate and distinguish between the specific effects and the non-specific ones. During 'true' acupuncture treatment in general, the needles are inserted into acupoints and stimulated until deqi is evoked. In contrast, during placebo acupuncture, the needles are inserted into non-acupoints and/or superficially (so-called minimal acupuncture). A sham acupuncture needle with a blunt tip may be used in placebo acupuncture. Both minimal acupuncture and the placebo acupuncture with the sham acupuncture needle touching the skin would evoke activity in cutaneous afferent nerves. This afferent nerve activity has pronounced effects on the functional connectivity in the brain resulting in a 'limbic touch response'. Clinical studies showed that both acupuncture and minimal acupuncture procedures induced significant alleviation of migraine and that both procedures were equally effective. In other conditions such as low back pain and knee osteoarthritis, acupuncture was found to be more potent than minimal acupuncture and conventional non-acupuncture treatment. It is probable that the responses to 'true' acupuncture and minimal acupuncture are dependent on the aetiology of the pain. Furthermore, patients and healthy individuals may have different responses. In this paper, we argue that minimal acupuncture is not valid as an inert placebo-control despite its conceptual brilliance.

A photoplethysmographic (PPG) technique to assess blood flow in bone tissue has been developed and tested. The signal detected by the PPG consists of a constant-level (DC) component-which is related to the relative vascularization of the tissue-and a pulsatile (AC) component-which is synchronous with the pumping action of the heart. The PPG probe was applied on the skin over the patella. The probe uses near-infrared (804 nm) and green (560 nm) light sources and the AC component of the PPG signals of the two wavelengths was used to monitor pulsatile blood flow in the patellar bone and the overlying skin, respectively. Twenty healthy subjects were studied and arterial occlusion resulted in elimination of PPG signals at both wavelengths, whereas occlusion of skin blood flow by local surface pressure eliminated only the PPG signal at 560 nm. In a parallel study on a physical model with a rigid tube we showed that the AC component of the PPG signal originates from pulsations of blood flow in a rigid structure and not necessarily from volume pulsations. We conclude that pulsatile blood flow in the patellar bone can be assessed with the present PPG technique.

Randomized, placebo-controlled clinical trials are recommended for evaluation of a treatment's efficacy with the goal of separating the specific effects (verum) from the non-specific ones (placebo). In order to be able to carry out placebo-controlled acupuncture trials, minimal/sham acupuncture procedures and a sham acupuncture needle has been used with the intention of being inert. However, clinical and experimental results suggest that sham/minimal acupuncture is not inert since it is reported that both verum acupuncture and sham/minimal acupuncture induce a significant alleviation of pain. This alleviation is as pronounced as the alleviation obtained with standard treatment and more obvious than the one obtained with placebo medication or by the use of waiting list controls. These results also suggest that sham acupuncture needles evoke a physiological response. In healthy individuals sham acupuncture results in activation of limbic structures, whereas a deactivation is seen in patients with pain, i.e. results from healthy individuals do not reflect what is seen in clinical conditions. Also, depending on the etiology of pain (or any under clinical condition under investigation), the response to sham acupuncture is varying. The acupuncture ritual may also be seen as an emotional focused therapy allowing for psychological re-orientation. Sham needling in such context may be as powerful as verum acupuncture. We recommend that the evaluated effects of acupuncture could be compared with those of standard treatment, also taking the individual response into consideration, before its use or non-use is established.

During the last five years a large number of randomised controlled clinical trials (RCTs) have been published on the efficacy of acupuncture in different conditions. In most of these studies verum is compared with sham acupuncture. In general both verum and sham have been found to be effective, and often with little reported difference in outcome. This has repeatedly led to the conclusion that acupuncture is no more effective than placebo treatment. However, this conclusion is based on the assumption that sham acupuncture is inert. Since sham acupuncture evidently is merely another form of acupuncture from the physiological perspective, the assumption that sham is sham is incorrect and conclusions based on this assumption are therefore invalid. Clinical guidelines based on such conclusions may therefore exclude suffering patients from valuable treatments.

A randomized controlled study was conducted to evaluate the effect of acupuncture treatment in idiopathic anterior knee pain, a pain syndrome without known aetiology. Fifty-eight patients, clinically and radiologically examined, were randomly assigned to either deep or minimal superficial acupuncture treatment. The patients were treated twice weekly for a total of 15 treatments. The main outcome measurements were one leg vertical jump, functional score, daily VAS recording and skin temperature. Fifty-seven patients completed the study. Pain measurements on VAS decreased significantly within both groups; in the deep acupuncture group from 25 before treatments to 10 afterwards, and in the superficial (placebo) acupuncture group from 30 to 10. There was no significant difference between the groups. The improvement on the VAS recordings remained significant even after 3 and 6 months. Even though the pain decreased after sensory stimulation, neither the ability to jump on one leg, the functional score nor the skin temperature changed. This study shows that patients with idiopathic anterior knee pain benefit from both electroacupuncture treatment and subcutaneous needling. The pain-relieving effect remains for at least 6 months. Central pain inhibition, caused by either afferent stimulation or by non-specific therapeutic (placebo) effects, is a plausible explanation behind the treatment effects.