1. CONCLUSION It’s clear that shoulder prosthesis is efficient in comfort and function restoration, and its main visible benefits are pain relief and the possibility to realize daily activities. The indications to these procedures are in constant evolution and multiple variables should be considered. The most important variable is the specific pathology in surgery’s moment and its possible progression after the arthroplasty as well. Due to the big variability of results measure scales used, it would be recommended a homogenization that will permit to establish valid comparisons between different cases. It is useful to stand out the importance of a supervised rehabilitation and the need of a maximum stimulation of patient collaboration to obtain a satisfactory result. Felizardo, Cristiano; Gomes, Rodolfo; Carvalho, Sérgio; Salta, Sidónio PATHOLOGIES The most common pathologies are osteoarthritis, rheumatoid arthritis, osteonecrosis, rotator cuff tear and complex humeral fracture. Although treatment depends on each case, surgery usually comes as the best solution. The hemiarthroplasty is most effective in early stages of osteonecrosis, in cases of complex humeral fractures and is also viable in some rotator cuff tears. The total arthroplasty, reversed or anatomical, is more effective in patients with osteoarthritis since degeneration is global, in advanced stages of osteonecrosis and in some rotator cuff tears.  Harder procedure.  Long surgery.  Frequent rupture of involving muscles.  The damage of the polyethylene component may cause lack of stability in both components.  The glenoid damage associated with loss of bone.  Less consistent to pain relief.  The glenoid progressive erosion can imply worst results with time. DisadvantagesDisadvantages  More efficient in pain relief.  Better support point to active mobility.  Easy procedure.  Short surgical period.  Smaller risk of lack of stability.  Can convert in total arthroplasty, if necessary. AdvantagesAdvantages Total ArthroplastyHemiarthroplasty IMPLANT FIXATION  Cemented: it is the most frequently used and is considered as standard. It’s preferable when there is risk of osseous breaking down, like in osteoporosis or rheumatoid arthritis.  Biological fixation: implant surfaces are coated with a porous surface or hydroxyapatite, in order to promote osseointegration into the implant.  With pressure (press-fit).  With screws (glenoid component). The biological non-cemented fixation of the humeral component is indicated to young patients with good osseous quality, and, also, in older patients with little complications. The glenoid component can be, or not, cemented. In the majority of cases, the cement is adopted. ACKNOWLEDGEMENTS: ACKNOWLEDGEMENTS: Prof. João Folgado. MATERIALS  Humeral Biomaterials: - Stainless steel. - Cobalt-chromium alloy. - Titanium alloy. - Hydroxyapatite.  Glenoid implant: - Metallic materials - Polymeric material: ultra high weight polyethylene.  Polymeric biomaterials requirements: - Biocompatibility, the possibility of being sterilized without changing physical and mechanical properties and without being degraded. Prostheses Hemiarthroplasty Total Arthroplasty AnatomicalReverse PROBLEMS  Mechanical failures - Few different kinds of prostheses to all sizes of arms and shoulders. - Constant friction.  Biological reactions to the implants: - Unexpected incompatibilities even in the humeral part or in the glenoidal labrum. - A septic loosening. INTRODUCTION The shoulder is a complex articulation, a synovial joint type ball-and-socket. The vast amplitude of different movements causes this articulation to be more unstable with a higher risk of displacement or other injury compared to others on the human body. This motivates the research and development of prosthesis in order to minimize the effects associated with these pathologies. Major problems caused by the implants are mechanical failures of the materials and biological reactions to the implant. Although shoulder prosthesis demonstrates to be efficient in comfort and functions restoration, the success and reliability depends among a complex number of variables.