Tai Chi and Physical Therapy for Knee Osteoarthritis

Inclusion Criteria: * Age 40 years and older * American College of Rheumatology criteria for symptomatic Knee OA: Pain on more than half the days of the past month during at least one of the following activities: walking, going up or down stairs, standing upright, or lying in bed at night;101 radiographic evidence of grade I-III tibiofemoral or patellofemoral OA: defined as the presence of osteophytes in the tibiofemoral compartment and /or the patellofemoral compartment, as assessed on standing anterior/posterior and lateral views101 * WOMAC pain subscale score \>= 40 (visual analog version) on at least 1 of 5 questions (range 0 to 100 each) * Clinical examination confirming knee pain or discomfort or instability referable to the knee joint * Physically able to participate in both the Tai Chi and Standard PT programs * Willing to undergo testing and intervention procedures and 1.willing to abstain from Tai Chi until completion of the program, if randomized to Standard PT regimen. 2. willing to abstain from Standard PT regimen until completion of the program, if randomized to Tai Chi Exclusion Criteria: * Prior experience with physical therapy, Tai Chi or other similar types of Complementary and Alternative Medicine in the past 1 year such as Qi gong and yoga since these share some of the principles of Tai Chi. * Serious medical conditions limiting the ability and safety to participate in either the Tai Chi or Standard PT regimen programs as determined by primary care physicians; these include dementia, neurological disease, symptomatic heart or vascular disease (angina, peripheral vascular disease, congestive heart failure), severe hypertension, recent stroke, severe insulin-dependent diabetes mellitus, psychiatric disease, renal disease, liver disease, active cancer and anemia * Any intra-articular steroid injections in the previous 3 months or reconstructive surgery on the affected knee * Any intra-articular Synvisc or Hyalgan injections in the previous 6 months * Inability to pass the Mini-Mental Status examination (with a score below 24)102 * Inability to walk without a cane or other assistive device 100% of the time during the baseline assessments * Enrollment in any other clinical trial within the last 30 days * Plan to permanently relocate from the region during the trial period * Positive pregnancy test or planning pregnancy within the study period * Not English-Speaking