The Humeral Implant in Shoulder Arthroplasty
Humeral hemiarthroplasty, anatomic total shoulder arthroplasty, and reverse total shoulder arthroplasty all rely on a prosthetic articular surface fixed to the proximal humerus. Humeral implant designs have changed considerably as a result of improved understanding of proximal humeral anatomy and prosthetic biomechanics. Fixed, monoblock implants have been superseded by modular implants with variable inclination, offset, version, and stem length. Press-fit designs now commonly have surface coatings that allow bony ingrowth. Metaphyseal fixation is often favored over diaphyseal fixation. Both cemented and noncemented fixation continue to be used, and each of these techniques has advantages and disadvantages. Although aseptic loosening rarely requires revision, complications, such as osteolysis, stress shielding, radiolucent lines, and proximal humeral bone loss, can occur. Humeral periprosthetic fractures continue to be a disabling complication and are difficult to manage. Innovations such as short-stemmed implants, stemless implants, and platform stems are currently under clinical investigation.