Arthrex Eclipse™ Shoulder Prosthesis

Inclusion Criteria: * The subject is \> 21 years of age * The subject has continued symptoms in target shoulder despite at least 3 months of other treatment modalities(e.g.: anti-inflammatory, physical therapy and steroid injections) * The subject has a diagnosis in the target shoulder of one or more of the following: osteoarthritis, avascular necrosis, post-traumatic arthritis, or rheumatoid arthritis. * The subject presents with pain and functional impairment in the index shoulder, measured by an Adjusted Constant Score of ≤50. Note: The Adjusted Constant Score will be calculated from the raw Constant Score to establish patient eligibility. * The subject is willing to receive implantation of the Arthrex™ Shoulder Prosthesis or Univers™ II Shoulder Prosthesis. * The subject must be physically and mentally willing and able to comply with all study procedures (including follow-up visits and radiographic assessments) until the conclusion of the study. * The subject has been informed of the nature of the study and provided written consent as approved by the sites local Institutional Review Board or Ethic Review Board. Exclusion Criteria: * The subject is likely a candidate for hemi-humeral arthroplasty (i.e.: Avascular Necrosis of the humeral head without glenoid involvement (Stages 0-3): Rotator Cuff Deficient Shoulder: Glenoid Bone deficiency/deformity that precludes glenoid replacement (Walch Type B2 or C) or Fractures of the Proximal Humerus, without Glenoid involvement. * The subject has immature bone as defined by the absence of cancellous bone patterning, a mature, thick cortex, and stress lines within the cancellous bone. * The subject has obvious defects in bone quality, such as cysts or lesions, in the humeral head of the target shoulder, as demonstrated by radiographic evaluation. * The subject has a target shoulder a rotator cuff that is not intact and not reconstructible. * The subject has Irreducible 3- and 4- part proximal humeral fractures of the target shoulder. * The subject has documented history of foreign-body sensitivity. * Subject with positive pregnancy test, or lactating, or intends to become pregnant during treatment period * The subject has history of Schizophrenia, Bipolar Disorder and/or Major Depressive Disorder as defined by DSM IV. * The subject is skeletally immature demonstrated radiographically by incomplete closure of proximal humeral epiphyses. * The subject is at high risk for poor healing or confounding outcomes \[(i.e.: clinically significant renal, hepatic, cardiac hematologic disease or endocrine disease)\] * The subject is on immune-stimulating or immunosuppressive agents * The subject has co-morbidity that reduces life expectancy \< 36 month. * The subject seeking or receiving workman's compensation for shoulder injury, * The subject is \> 350 lbs. * The subject engaged in heavy labor (e.g. repetitive lifting in the excess of more than 50 lbs.) * The subject has had surgery in the affected shoulder in the last 12 months (with the exception of diagnostic arthroscopy without reconstruction or repair procedures) * The subject is engaged in active sports participation. (e.g. weight lifting involving upper extremities or involved in contact sports) * The subject is taking medications known to potentially interfere with bone/soft tissue healing (e.g. steroids with the exception of topical and/or inhalers) * The subject is a prisoners or wards of the state * The subject has a history of alcohol and/or substance abuse as defined by DSM IV (Diagnostic and Statistical Manual Diploma in Social Medicine) * The subject has an active or chronic infection, either systemic or local. * The subject has pathologic fractures of the affected shoulder * The subject has acute trauma of the affected shoulder * The subject has osteoporosis defined as a bone density T score of \< or = -2.5. (A screening Questionnaire for osteoporosis, SCORE (Simple Calculated Osteoporosis Risk Estimation) and MORES (Male Osteoporosis Risk Estimation Score), will be used to screen patients who require a DEXA (dual energy x-ray absorptiometry) bone mineral density measurement.