Overall, Tai Chi appears to reduce pain and improve physical function for people with knee OA. The measures of benefit include patient-reported outcomes as well as physician assessments and several physical function tests. We also observed significant benefits in the measures of depression and self-efficacy that appeared durable for participants who continued to practice Tai Chi beyond the 12-week intervention period. Thus, in this first long term follow-up trial of Tai Chi for knee OA, the Tai Chi group seems to have developed a general sense of well being, suggesting that there may be synergy between the physical and mental components of this discipline. These findings are promising because there are few efficacious long-lasting treatments for knee OA (2
There have been several previous trials testing the effects of Tai Chi for OA (13
). However, interpretation of their results is limited by low levels of adherence (13
) short follow up (13
), deployment of varying Tai Chi styles (13
), and inclusion of heterogeneous types of OA (13
). Nevertheless, our results are consistent with some of their positive findings for improvements in pain (36
) and function (13
). Our findings are also consistent with prior studies showing benefits of Tai Chi on self-efficacy, depression and quality of life (9
). However, our study did not show any improvement in balance tests as was shown in a number of other studies (9
Recent efforts have suggested that there is the minimal clinically important difference for WOMAC scores from both pharmacological and rehabilitation trials (40
). In our trial, the Tai Chi group had a 75% improvement of WOMAC pain over baseline (57% greater than control) and 72% improvement of WOMAC function over baseline (46% greater than control). Thus, our study shows that Tai Chi gives more than the minimally perceptible improvement for patients.
Most of our participants were significantly overweight with an average BMI of 30 kg/m2
. It is well known that significant weight reduction can improve symptoms of knee OA (42
). However, there was no significant weight reduction for either group during the trial. In addition, the two groups did not differ in medication usage, and it is unlikely that the difference in outcomes between the groups was attributable to changes in medication patterns occurring over the course of the trial.
Explanatory theories from eastern and western literature provide a supposed rationale for the effectiveness of Tai Chi to treat knee OA (43
). While the biological mechanisms by which Tai Chi may improve the clinical consequence of knee OA still remain unknown, synergy between its physical and mental components likely plays a major role. First, Tai Chi may enhance cardiovascular benefits, muscular strength, balance, coordination, and physical function (9
). All of these are thought to be able to reduce joint pain. As the severity of pain is directly correlated with the degree of muscle weakness (43
), stronger muscles and better coordination improve the stability of the joints and lessen pain. Increased peri-articular muscle strength may also protect joints from traumatic impacts. Second, evidence suggests that the mind-body component may influence immune, endocrine, neurochemical and autonomic functioning (44
). Third, controlled breathing and movements promotes a restful state and mental tranquility. These influences may help break the arthritis “pain cycle” (45
). Improving self-efficacy, social function and depression can also help people build confidence, get support and overcome fears of pain. Together, these can lead to improved physical, psychological and psychosocial well-being and overall quality of life (46
Our study had some limitations: First, the attention group appears to have had more severe knee OA, as measured by WOMAC physical function, radiography scores and self-reported comorbidities at baseline. This difference likely occurred by chance as a result of the relatively small sample size, rather than as a problem with the randomization procedures. Regression adjustment for these baseline differences did not change any of the conclusions. The possibility exists that some unidentified confounding factors were not measured in our trial, such as socio-economic status and knee malalignment and these factors will be considered in our future work. Second, we could not mask the participants to treatment assignment. While an elaborate sham treatment might accomplish such blinding, no validated approach for this currently exists. As a result, participants’ a priori beliefs and expectations with respect to Tai Chi could have biased their subjective outcome assessments. Therefore, we attempted to minimize such expectations by maintaining a stance of equipoise regarding the likely benefits of the two interventions. By de-emphasizing our specific interest in Tai Chi, participant expectations would have been reduced. In addition, we tested to see if expectations might have produced any bias. We found that the baseline outcome expectations of benefit from an exercise intervention were similar in both groups (Tai Chi= 4.1 [SD 0.6], control = 4.3 [SD 0.4]). Furthermore, total session attendance was similar in both groups (89% control, 85% Tai Chi) indicating that our neutral presentation of the interventions may have succeeded. A third limitation, instruction by a single Tai Chi master, might limit generalizability. However, we only made minor modifications to the movements of the classical Yang Style to avoid knee injury. Thus, it should not be difficult for other instructors to implement and for participants to practice at home, so that the benefits of Tai Chi may be extended to the general population. Finally, even though the patients were instructed not to communicate to the blinded assessors about their treatment assignments, there is the possibility that leakage of information did occur even though the study physician reported no such leakage.
In conclusion, 12-week Tai Chi appears to reduce pain and improve physical function, self-efficacy, depression and health status for knee OA. These observations emphasize a need to further evaluate Tai Chi’s biological mechanisms and approaches to extend its benefits to a broader population. Further studies should replicate these results and deepen our understanding of this therapeutic modality.