This prospective study will evaluate the Bigliani/Flatow prosthesis. The aims of this study are to establish the safety, effectiveness, and value of the prosthetic system, and to collect information from expert shoulder surgeons as to features of the implants, instruments, and techniques which may be further improved. In this study, the investigators hypothesize that this prosthetic device will significantly improve long-term patient-based outcomes, functional status and quality of life.

Over the last two decades, total shoulder joint replacement - or arthroplasty - has become a commonly performed procedure for the treatment of painful arthritis of the shoulder, and numerous studies have demonstrated its success. During this time, much has been learned about the efficacy, as well as the complications, of the procedure, and since its introduction in the 1950's, shoulder arthroplasty has undergone an evolution in design. The value of such innovations has not yet been determined and will depend on the results of long term follow-up studies. The purpose of this study is to provide follow-up information and design modification directives.

Inclusion Criteria:

• Patient must be 18 years of age or over.
• Patient must have signed The Informed Consent and Release of Medical Information forms.
• The patient can be a man, postmenopausal woman, or a woman who is likely to become pregnant but is using adequate contraceptive precautions (defined as oral contraceptives, intrauterine devices, surgical contraception or a combination of a condom and spermicide).
• Patient needs a total shoulder arthroplasty (humeral head and glenoid).
• Patient has a diagnosis of primary osteoarthritis.

Exclusion Criteria:

• Obstacles, which pose an inordinately high surgical risk, in the judgment of the certified surgeon.
• Class IV or higher anesthetic risk.
• Patient has a recent history of psychiatric disease (including drug or alcohol abuse) that is likely to impair the compliance with the study protocol.
• Patient has had a shoulder fracture.
• Patient had previous shoulder surgeries with the exception of an arthroscopic debridement procedure.
• The patients has a massive rotator cuff tear (rupture >3 cm or total cicatrisation) demonstrated at time of the surgery that precludes the total shoulder replacement.

Subjects will be recruited when the decision to undergo shoulder arthroplasty is made. The surgeon will confirm that the subject is appropriate for inclusion in the study. The surgeon will confirm that the subject is appropriate for inclusion in the study.