Barret H, et al. - Fifty-eight pyrocarbon interposition shoulder arthroplasties (PISAs) implanted in 56 patients between 2010 and 2015, were prospectively watched by the researchers in order to assess survival and midterm outcomes of PISA in arthritic patients younger than 65 years. The survival rate was 90% at a mean follow-up of 47 ± 15 months. Six patients needed conversion to reverse total shoulder prosthesis for painful glenoid erosion (n = 2) and humeral erosion with greater tuberosity stress fractures (n = 4). From 36 ± 14 points to 70 ± 15 points and 32% ± 14% to 75% ± 19%, the mean Constant score and subjective shoulder value significantly rose, respectively. In 78% of the cases with increased pain scores, humeral medialization was seen. Uncorrected anteroposterior implant subluxation (12 cases) was related to lower Constant score and lower subjective shoulder value. No risk factors for glenoid or humeral erosion were discovered. Therefore, at midterm follow-up, PISA does not protect from progressive glenoid erosion and could result in greater tuberosity erosion and stress fractures. Longer follow-up is needed to see whether PISA survival will be better than that of hemiarthroplasty.