People with knee osteoarthritis (OA) frequently complain of knee instability. This study will test whether certain exercises can improve knee stability, reduce pain, and improve physical function in people with knee OA.

Study hypotheses: 1) Participants in the stability training group will demonstrate less pain and higher levels of physical function, based on self-report measures of pain and function (WOMAC, Lower Extremity Function Scale), and less time to complete the Get Up and Go test, a physical performance measure of function. 2) During walking and the step down task, participants in the stability training group will demonstrate greater knee motion during weight bearing, greater vertical ground reaction forces and loading rates, and reduced ratios of co-contraction between quadriceps/hamsting and tibialis anterior/gastrocnemius muscle pairs compared to the standard group. Participants in the stability group will also demonstrate greater step lengths, single limb support times, and average walking velocity compared to the standard group.

Traditional exercise therapy for knee OA primarily focuses on lower limb strength and joint motion deficits. Recent evidence has suggested that changes in lower limb biomechanical factors during weight bearing activities may have substantial impact on physical function and disease progression in individuals with knee OA. The effectiveness of exercise therapy programs might be improved by incorporating balance and agility training techniques (knee stability training). The aim of this trial is to test the effectiveness of supplementing traditional exercise therapy with knee stability training techniques tailored for individuals with knee OA.

Participants will be randomly assigned to one of two groups. The first group will participate in a standard rehabilitation program of traditional exercise therapy for knee OA. The second group will participate in a standard rehabilitation program supplemented with a knee stability program. Study visits will occur at study entry, 2 months, 6 months, and 1 year. At each study visit, changes in pain, physical function, and biomechanical factors will be assessed. This study will last for one year.

Inclusion Criteria:

• Meet the 1986 American College of Rheumatology (ACR) clinical criteria for knee osteoarthritis
• Grade II or greater Kellgren and Lawrence radiographic changes

Exclusion Criteria:

• History of two or more falls within the year prior to study entry
• Unable to walk a distance of 100 feet without an assistive device or a rest period
• Total knee arthroplasty
• Uncontrolled hypertension
• History of cardiovascular disease
• History of neurological disorders that affect lower extremity function such as stroke or peripheral neuropathy
• Corticosteroid injection to the quadriceps or patellar tendon in the past month, or 3 or more within the past year
• Quadriceps tendon rupture, patellar tendon rupture, or patellar fracture that could place them at risk of re-injury during quadriceps strength testing
• Pregnancy