Poly vs Hybrid Glenoid in Stemless aTSA

Inclusion Criteria: \- In order to be eligible to participate in this study, a subject must meet all of the following criteria: 1. Both genders; 2. Age 18 years old; 3. Life expectancy over 5 years; 4. Patient has symptomatic shoulder osteoarthritis for more than 1 year and is submitted to previous conservative non-surgical treatments; 5. Patient is requiring primary unilateral or staged bilateral anatomic arthroplasty based on physical examination, medical history and X ray examination. (In cases where bilateral aTSA's are indicated, the patient will be included for the second aTSA again when the patient meets the inclusion criteria); 6. Good bone quality evaluated by the investigator on the basis of a risk factors analysis and the intraoperative estimation; 7. A diagnosis in the target shoulder of osteoarthritis; according to the classification of Walch, the glenoid should be a type A1, A2 or B1. Retroversion should not exceed 15 degrees. 8. Patient is willing and able to complete scheduled follow-up evaluations as described in the Informed Consent; 9. Patient has participated in the Informed Consent process and has signed the Informed Consent form previously approved by the Ethics Committee. Exclusion Criteria: 1. Patient requiring revision shoulder arthroplasty; 2. Osteoporosis with a history of non-traumatic fractures; 3. Steroid injections within the previous 6 months; 4. Contralateral shoulder replacement within the previous 3 months; 5. Meta-epiphyseal bony defect (including large cysts); 6. Significant proven or suspicious infection of the target shoulder or any serious infectious disease 7. Significant neurological or musculoskeletal disorders that may compromise functional recovery; 8. Known or suspicious hypersensitivity to the metal or other materials of the implant; 9. Unwillingness or inability (i.e. alcoholism, infirmity) to comply with rehabilitation and to return for follow-up visits and any psychiatric illness that would prevent comprehension of the details and nature of the study; 10. Any systemic disease which may affect outcome. 11. Active or metastatic neoplastic disease 12. Chemotherapy and/or radiotherapy within the last 6 months 13. Previous organ transplant 14. Participation in any clinical research study that may interfere with this study 15. A current or prior DSM-5 diagnosis of schizophrenia, delusional disorder, schizoaffective disorder, psychotic disorder or bipolar disorder. 16. Current substance use disorder (excluding nicotine/tabacco use disorder) or moderate or severe alcohol use disorder. 17. Imminent suicide risk. 18. Any other psychiatric condition that renders the individual unsuitable for the study according to the study physicians judgment