Shoulder osteoarthritis (OA) is a frequent problem in our aging population and is believed to occur in up to 20% of the population. Different types of glenoid morphology are associated with shoulder OA, depending on the amount and localization of the glenoid erosion as well as the amount and direction of Humeral Head Migration. Total shoulder arthroplasty (TSA) has been shown to relieve the pain and improve joint function of patients with OA. However, several complications such as component loosening and polyethylene damage has been reported and it has been revealed that 7.3% of glenoids may show signs of asymptomatic radiographic loosening annually after primary anatomic TSA. The mechanism of such fixation failure is still unclear. The main goal of this study is evaluating in-vivo glenohumeral contact patterns in patients with osteoarthritic glenoids before and after TSA, to unravel the high rate of glenoid component loosening.