Knee osteoarthritis (OA) is a major cause of disability, especially for older people, as well as a burden on healthcare resources
[1, 2]. Age is the strongest predictor of knee OA and therefore increasing age and extended life expectancy will result in a greater occurrence of the disease
. The impact of OA can be severe and profound, and OA often results in both direct and indirect medical expenses. In the United States, the total cost of arthritis and other rheumatic conditions in 1997 was $116.3 billion, comprising direct costs of $51.1 billion (hospitals, doctors, transportation, nursing homes, and so on) and indirect costs of $65.2 billion (primarily lost wages and lost productivity)
Patients with knee OA experience pain and loss of function. At present, there is no cure for knee OA. The management of knee OA is broadly divided into nonpharmacological, pharmacological, and surgical treatments
. Surgical treatments are often recommended if other treatments are ineffective and functional disability affects the patient’s quality of life. Pharmacological management includes control of pain and improvement in function and quality of life. However, pharmacological agents used to treat the symptoms of knee OA are associated with various sideeffects
. Exercise is recommended for the nonpharmacological management of knee OA
, but many forms of exercise may betoo intense, uncomfortable, or monotonous for older adults to maintain over an extended period of time
. In 2012, the American College of Rheumatology conditionally recommended tai chi for patients with knee OA
. Tai chi is a popular form of exercise among older adults, especially in Asia; it encompasses balance, aerobics, flexibility, and weight-bearing exercise with meditation and deep breathing. Tai chi involves a series of slow, smooth, and graceful movements, with an emphasis on smooth coordination of the eyes, head, body, and upper and lower extremities
There are five primary types of tai chi (Yang style, Wu style, Chen style, Hao style, and Sun style), and each style takes a different approach in terms of the movements and forms. For every type of tai chi, there are many forms, such as the 24-, 36-, and 48- form Yang styles. The biomechanical characteristics, in terms of joint loading, muscle activity, and range of lower limb motion, of the tai chi movements in the intervention programs from the published studies have not been investigated. Without an understanding of tai chi biomechanics, the mechanisms of the effects of tai chi intervention for OA management would be unknown. Recently our research team has studied the biomechanical characteristics of some of the most representative tai chi movements
[10, 11]. The understanding of the biomechanics of these tai chi movements gained from our studies and other published work
 provides the scientific basis for developing an innovative tai chi rehabilitation program (ITCRP) specifically for OA patients.
Most previous studies
[13, 14] of regular tai chi programs only focus on pain relief and maintenance of the range of motionof the joint for knee OA, rarely considering the importance of neuromuscular control. Thus, it is not known whether exercise interventions influence factors associated with progression of OA. This study will not only examine the effects of a tai chi intervention on knee pain andrange of motion, but will also focus on joint biomechanics, muscle strength, proprioception tests of knee and ankle, and neuromuscular response. Hence, we aim to investigate the efficacy of a 6-month ITCRP compared with a 6-month health education program on a broad range of outcomes in patients with knee OA.