A prosthesis assembly for use with a scapula in one embodiment includes an acromion spacer unit, a first articulation surface on an inferior surface of the acromion spacer unit, a bone contacting surface on a superior surface of the acromion spacer unit, and a bone mounting member extending sideways from the acromion spacer unit and oriented such that when the acromion spacer unit is mounted on a scapula, the acromion spacer unit is positioned at a height above the height of a midpoint of a glenoid fossa of the scapula.
