The subgroup analysis suggested that the acupuncture group had superior short and long-term pain scores compared with the sham acupuncture and usual care groups. The acupuncture group also showed a trend toward better physical function scores when compared with the various control groups in both the short and the long term. When compared with usual care and no acupuncture, the analysis had insufficient studies to detect a significant change in both physical function and pain (see Appendix).
The funnel plots did not reveal obvious asymmetry of pain and physical function scores in either the short or the long term (see Appendix). Consistently, the Egger test suggested a lack of publication bias for both pain (p = 0.88) and physical function (p = 0.69) scores (see Appendix). The funnel plots of the time subgroups are also depicted in the Appendix. According to this analysis, the included studies were relatively comprehensive and yielded statistically reliable results.
This meta-analysis demonstrates that acupuncture can result in both short and long-term improvement in function in patients with chronic knee pain due to osteoarthritis, but that the effect of pain relief is not sustained in the long term. Acupuncture tends to have better outcomes than sham acupuncture, usual care, and no intervention. These favorable effects of acupuncture involve complex interactions with the patient, including empathy, intention, care, and attention, that cannot be achieved by medications alone or by no intervention13. In addition, endogenous chemicals released during the acupuncture process, such as enkephalin, dynorphin, and gamma-aminobutyric acid, may have distinct effects for patients with chronic knee pain13-16.
Marked heterogeneity was a limitation of the analysis of the RCTs included in this study. The heterogeneity among studies was evaluated using I2 inconsistency tests, in which values of >50% were considered to indicate high heterogeneity. One possible reason for the observed heterogeneity is that the various acupuncturists performed the treatment without a standardized protocol and according to their individual training and experiences. The variety of control interventions included in this study (sham acupuncture, usual care, and no intervention) may also have led to heterogeneity.
Previous meta-analyses have drawn various conclusions depending on the types of control interventions used for comparison1,5,10. Although Manheimer et al. also showed that the pooled effects of acupuncture were significantly superior to those of sham treatment, the effects were believed to be clinically irrelevant5. In addition, a recent meta-analysis of individual patient data showed that acupuncture was associated with chronic pain relief when compared with sham acupuncture and with no acupuncture35; those results are in agreement with our findings.
The current study revealed some new findings that differ from those of previous reports. First, when acupuncture was compared with all control interventions simultaneously, pain relief was not found to be sustained over time. In contrast, no previous systematic reviews evaluated the effect of pooled control interventions on pain relief.
Although the 2 abovementioned recent studies did not support acupuncture treatment, the results of our meta-analysis are mainly positive. No evidence exists that positive attitudes contributed to the previous positive results, although an expectation effect was identified and may have affected the results. Moreover, the patients who held positive attitudes were randomly assigned to the control and treatment groups, so the expectation effect was attenuated.
This meta-analysis has some limitations. First, the included RCTs compared a variety of control interventions; therefore, definite conclusions regarding the various control interventions are not possible. Larger and higher-quality trials are needed to confirm these conclusions. Second, to avoid the expectation effect, future studies should consider the patients’ attitudes regarding acupuncture prior to treatment. Third, the results were based on unadjusted estimates; a more precise analysis should be conducted if individual patient data are available, allowing adjustment for age, sex, ethnicity, and geographical location. Finally, the lack of standardization of acupuncture treatment protocols also limits our findings.
In conclusion, we believe that acupuncture can provide superior pain relief and functional improvement compared with sham acupuncture, usual care, and no intervention in the short term. The effect on pain relief does not appear to be maintained in the long term. Finally, the placebo effect of acupuncture may contribute to its beneficial outcomes.
A table showing the PRISMA checklist and figures comparing acupuncture with sham treatment, usual care, and no intervention and showing funnel plots (overall and at each time interval) are available with the online version of this article as a data supplement at jbjs.org.
Investigation performed at the Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Medical College of Zhejiang University, Hangzhou, People’s Republic of China
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