Inclusion Criteria:  Patients ≥55-85 years Moderate-severe primary OA of the glenohumeral joint according to Samilson and Prieto, by measuring the lower osteophyte (32) Eligible for surgery with standard TSA  Exclusion Criteria:  Surgical need for bonegraft Previous shoulder fracture (fracture of the proximal humerus or glenoid fracture) Planned other upper extremity surgery within six months Rheumatoid arthritis or other types of arthritis not diagnosed as primary glenohumeral OA Cancer diagnosis and receiving chemo-, immuno- or radiotherapy Neurological diseases affecting shoulder mobility (e.g. disability after previous stroke, multiple sclerosis, Parkinson's, Alzheimer's disease) Other reasons for exclusion (i.e. mentally unable to participate) or planned absence for more than 14 days in the first 3 months after baseline test. Unable to communicate in the participating countries respective languages