Knee 3). Buckling, as an

Knee Osteoarthritis (KOA), the most common degenerative osteoarticular disease, is characterized by arthralgia, stiffness, limitation of motion, decreased quadriceps strength and functional impairment. Recently, the sensation of knee instability was also reported by the patients with KOA during activities of daily living especially in the elderly population(1).The sudden loss of knee stability at the time of weight bearing is a condition called buckling, shifting, or giving way of the knee(2, 3). Buckling, as an important issue in orthopedic literature(4), occurs mostly in persons with knee pain and often was seen as evidences of an internal derangement, such as anterior cruciate ligament tear or as a complication of surgery(5).

Unfortunately; knee giving way has been less considered and often neglected in the KOA despite numerous problems for the patients. Mechanical instability and episodes of buckling or shifting may develop in patients with KOA even before activity-related pain(6). Knee instability has a great impact on patients’ performance and disrupts their quality of life and causes more severe limitations in the patients’ physical activity (7, 8). Nguyen et al, in a longitudinal study on 2120 participants with KOA, reported 18% knee buckling, 27% knee instability without buckling, and 9% both buckling and instability which significantly associated with fear of falling, poor balance and activity limitations(9).

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Also,Knee buckling and low knee confidence were associated with poor physical function(10).Knee buckling in patients with KOA increases the chance of falls and fractures, including femoral neck fractures, because of bone density reduction in the elderly patients(11). The development of KOA is associated with inability to stand and walk and other functional disabilities which exacerbated by buckling in the patients(12). Due to severe consequences of instability, the patients often have been seeking physical therapy and exercise training for treatment. It is clear that the complications of knee instability impose a lot of health care costs on the health system.KOA with joint instability and motor disabilities, also, affects the cardio respiratory health of the affected patients, increases the incidence of cardiovascular disease(13). However, the prevalence of knee buckling in the Iran and its effect on physicalfunction has not been studied.

We sought to determine the knee buckling frequency in the past three months among the patients with KOA, the rate of fall in the patients with knee buckling and the relationship of buckling with physical function.