Osteoarthritis (OA) is the most common joint disorder (1). OA is seen 7 times more than rheumatoid artritis. It is the most important cause of disability seen with advanced age (1). It's a degenerative joint disease, usually associated with progressing age and characterized by biochemical and morphological changes in the synovial membrane and joint capsule, erosion of the joint cartilage, hypertrophy of the joint edges, subchondral sclerosis (2).

OA, an important public health problem, affects the knee joint most frequently (3). While the most important risk factor is age, there are many other risk factors such as race, sex, obesity, genetics and trauma. In osteoarthritis; joint is damaged due to the imbalance between formation and destruction. It causes progressive joint damage, pain, physical disability, and psychological disorders (4). The clinical characteristics of OA include pain, stiffness, limitation of motion, crepitation, varying degrees of inflammation and effusion, disability, functional disability, loss of daily living activities, deterioration in quality of life. (4,5). Pain is diminished by increased resting and alleviated by movement but advanced stages may also include resting pain and night pain. (6) In painful, swollen joints; loss of function is inevitable. The loss of function is specific to the site which is being involved. In knee OA, difficulty in squatting and climbing stairs, walking distance reduction and fatigue, antalgic gait can be seen (7). These complaints are often associated with instability. With increasing age, the frequency of OA also increases. The presence of knee OA in addition to the complications associated with aging especially affects the quality of life negatively. In addition to the physiological effects of advancing age; pain, functional restriction, loss of proprioception and instability due to knee OA may lead to a decrease in balance and, consequently, to falls, which may lead to undesirable outcomes. The determination of the balance problems in OA patients is also important in planning the treatment protocol to be given and also in evaluating the effectiveness of the treatment. There are valid and reliable scales in Turkish language which assess balance.

However, validity and reliability specific to the disease are also important for doing the assessment safeley in that population.

The Fullerton Advanced Balance Scale (FAB) was developed by Debbie Rose in 2006 to evaluate patients with a high risk of falling. The test uses dynamic and static equilibrium in different situations to determine balance problems in the elderly. The test has 10 parameters. These are: feet adjacent and eyes closed standing, reaching out forward to reach a shoulder-length object, turning in right and left directions in 360 degrees, stepping and passing over a 15.24 cm-length stair, tandem march, standing on one leg, eyes closed standing on the foam, double feet bounce, walking with head turning, reactive postural control. In this scale, which is scored between 0-40, a score between 0 and 4 is given for each item (8).

According to the power analysis,a total number of 84 knee osteoarthritis patients, aged between 40 and 65 years of age will be included in the study. Individuals will be given written and oral information about the study and their written approvals will be obtained. \* The Turkish version of the Fullerton Advanced Balance Scale (FAB) was obtained with permission from Debbie Rose who developed the scale and it is used on the elderly before. Study pattern: Familiarization will be made to the physiotherapists before the study. Information about the all scales will be given in detail with practical application. The study will be performed on 3 different days and by a single physiotherapist. 1st Evaluation: All evaluations of the individuals included in the study will be done by the physiotherapist (sociodemographic evaluations, implementation of FAB-T and other balance scales). In addition, to determine the acceptability of the FAB-T scale, the time during the FAB-T application will be recorded. 2nd Evaluation: The same individuals will be visited by the same physiotherapist at least 7 days after the first evaluation and only the FAB-T scale will be applied. 3rd Evaluation: After 6 weeks of treatment, the FAB-T scale will be applied to all individuals included in the study. The first two evaluations will be made for all participants. After the second evaluation is completed, 34 volunteer individuals who will be randomly choosen among 84 individuals will be given a 6-week exercise training program. According to this 6 week program, individuals will be admitted to the exercise training program for 45-60 minutes with a physiotherapist for 3 days in a week. The exercise program will consist of a warm-up, a strenght training and a cool-down section. Various exercise methods (clinical pilates exercises) and tools will be utilized to improve balance and mobility. Third assessment will be applied only to individuals participating in the 6-week exercise training program. With the study design, the reliability of testing and retesting ability of the FAB-T scale, its validity with respect to its correlation with other balance scales, its acceptability with the application period and its sensitivity to change after 6 weeks of treatment will be evaluated.