Overall, this systematic review suggests that t'ai chi may be an effective treatment for pain and physical function associated with knee OA, compared with attention control or routine care. However, several caveats must be considered. For joint stiffness, the evidence was not robust, and for a mixed population with hip or knee OA, the evidence is not sufficient to conclude whether t'ai chi was beneficial.
Our review aimed to update and complete the evidence by adding recent RCTs of t'ai chi as a method of treatment in patients with OA. Compared with two previous reviews,9 10
we identified four new RCTs with a low risk of bias11 13–15
and successfully updated the evidence for therapy. The results of our review are similar to the other two reviews.10 14
One previous review14
showed that t'ai chi may be beneficial for pain control in patients with knee OA, while the other review10
also reported some favourable effects of t'ai chi for musculoskeletal pain. However, both reviews expressed concern regarding the poor methodological quality of the included primary studies.
Previous systematic reviews have suggested that there are clinically important differences among various therapies, compared with various control groups, in OA pain reduction and functional improvement.2
The effect size of the pain reduction and the functional improvement in our review was higher than exercise, non-steroidal anti-inflammatory drugs and drug therapy; this effect is clinically significant.2
However, these results are difficult to compare quantitatively owing to the use of different assessment measures for evaluating pain and the use of different controls for evaluating the comparisons.
Limitations of this study include the potential incompleteness of the evidence reviewed. The distorting effects of publication and location bias on systematic reviews and meta-analyses are well documented.25–27
We are confident that our search strategy located all relevant data; however, some degree of uncertainty remains. Another possible source of bias is the fact that half of the included trials were performed in China and Korea, where apparently no negative studies have been reported.28
Our review may be affected by the potentially poor quality of the primary data and poor reporting of results, which were highly heterogeneous in virtually every respect.
The risk of bias in the studies was assessed based on the descriptions of sequence generation, allocation concealment, blinding, incomplete outcome measures and selective outcome reporting. Based on these assessments, the risk of bias varied across the included studies. Only three RCTs had a low risk of bias,13 14 17
and two studies had a moderate risk of bias.11 19
The other four RCTs were at high risk of being biased.12 15 16 18
Five RCTs employed allocation concealment,11 13 14 16 19
and four RCTs used an intention-to-treat analysis.13 14 17 19
Inappropriate allocation concealment and the lack of blinding exaggerate the results of outcome measures.29 30
Only two RCTs were at low risk of bias in selective outcome reporting.13 17
Even though the authors reported that they employed assessor blinding,11–14 17
some outcomes that they measured relied on the patient's subjective reporting, and so the patient's and assessor's blinding becomes unachievable and irrelevant. The main limitations of the included studies were small sample sizes, the inadequate control for non-specific effects and a lack of power calculations or adequate follow-up. Additionally, the fact that t'ai chi interventions cannot control for placebo effects limits generalisability. Second, adequate follow-ups of 6–12 months are advisable for future studies of t'ai chi for OA.
One could argue that the employment of the Cochrane risk-of-bias tool to assess the methodological bias in the clinical trial is not acceptable. This tool was recently recommended for assessing methodological quality in lieu of other scoring assessment tools, such as the Jadad scale.20
It has been proposed that using a quality score for clinical trials is not adequate.31 32
Although the inter-rater disagreements across the domains were reported in the Cochrane risk-of-bias tool, their overall reliability was fair.33 34
We also calculated our reliability for nine included trials with the Excel module (http://agreestat.com/agreestat.html
). Our inter-rater agreement for the individual domains of the risk-of-bias tool to nine included trials ranged from substantial to almost perfect (0.88 for random sequence generation; 0.70 for allocation concealment; 1.00 for patient blinding; 0.85 for assessor blinding; 0.88 for reporting drop-out or withdrawal; 0.69 or intention-to-treat analysis; and 0.71 for selective outcome reporting). Therefore, the Cochrane risk-of-bias tool may be the most comprehensive tool with fair reliability that is currently available.
Proponents of t'ai chi claim that it improves flexibility, strength and balance, especially in older people. Clearly, these claims need to be tested. The pooled results from six RCTs11–16
suggested that pain intensity was reduced when patients used t'ai chi, compared with attention control or routine care for knee OA. However, three RCTs found that t'ai chi had no significant effect on pain reduction when compared with hydrotherapy, waiting list, routine treatments or participation in bingo games in multiple joint OA.17–19
These results may be explained, in part, through inadequate blinding and control for non-specific effects in some of the positive studies, among other sources of bias.
Assuming that t'ai chi was beneficial for treating OA, the possible mechanisms of action may be of interest. Regular t'ai chi has been postulated to improve balance and reduce the likelihood of falls by improving muscle flexibility and trunk rotation. T'ai chi is a form of physical exercise combined with relaxation. Physical movement in t'ai chi can improve joint stability and aid in reducing excess weight, effectively decreasing joint pain, increasing function and reducing the advancement of OA.35 36
Furthermore, t'ai chi may also influence the psychosocial quality of life, which may have a positive influence on chronic pain.35 37
The question of whether t'ai chi is superior to other forms of therapeutic exercise is currently unanswered and is thus a topic for further investigation.
Four of the reviewed studies reported minor adverse events related to t'ai chi.11–13 17
T'ai chi appears to be generally safe, and serious adverse effects have not been reported. However, adverse effects were not the focus of this review and may require further research.
Future RCTs of t'ai chi for OA should adhere to accepted standards of trial methodology. The studies included in this review show a number of problems that have been noted by other reviews of trials examining the efficacy of t'ai chi, such as the expertise of t'ai chi practitioners, the pluralism of t'ai chi, the frequency and duration of treatment, the use of validated primary outcome measures and adequate statistical tests, and heterogeneous comparison groups.38 39
Furthermore, even though it is difficult to blind subjects to treatment, employing assessor blinding and allocation concealment are important for reducing bias. A clinical study is only truly useful if the intervention used can be replicated; hence, the type of t'ai chi employed is important. There are significant differences between the numerous forms of t'ai chi, and a clear description of the t'ai chi intervention should be provided together with a description of the level of expertise of the instructors.
In conclusion, there are encouraging results suggesting that t'ai chi may be effective in controlling pain and improving physical function in patients with knee OA. However, owing to the number of eligible RCTs and the often-poor quality of the available RCTs, the evidence is limited.