We present a case report of a patient, affected by post-polio syndrome and cuff tear arthropathy of his right shoulder, who underwent reverse shoulder arthroplasty. A previous radial deficiency was unmasked in the post-operative follow-up, with passive elbow bending when the forearm was put in an antigravitational position. A precise preoperative neurological evaluation is mandatory in shoulder replacement in order to estimate the functional outcome after surgery.