Anand Murthi, Chief, Shoulder and Elbow Surgery, MedStar Union Memorial Hospital
The ideal humeral component for shoulder arthroplasty provides long-term fixation while preserving proximal bone stock for revision surgery. Traditional stemmed humeral prostheses achieve fixation through either cementation or a press-fit coating. However, humeral component loosening has been reported in 7-15 percent of patients, and periprosthetic fractures occur in up to 3 percent of patients.TSA implant design is constantly evolving, and stems of humeral components have become shorter. Stemless implants were first released in 2004 in Europe, and eight stemless shoulder arthroplasty systems are currently available. Stemless humeral implants have the potential to mitigate some humeral-sided complications. These implants preserve proximal bone stock because the humeral canal is not violated during implantation. Additional potential benefits include decreased intraoperative blood loss and surgical time; easier component extraction during revision surgery; the flexibility to place the component in any version, inclination, and offset; decreased risk of intraoperative humeral shaft fractures; and reduced stress shielding.
Despite these benefits, stemless humeral components have their own unique risks and limitations. Making a humeral head osteotomy without a referencing stem can be more challenging than with stemmed components. Early loosening may occur in the osteopenic bone if initial metaphyseal bone fixation is not sufficient prior to component osseous in growth or on growth.
Initial radiographic outcomes with stemless humeral components have been encouraging. One study of 70 radiographically assessed shoulders with stemless humeral prostheses concluded that stemless prostheses reliably reproduced native anatomy. However, there was a tendency for surgeons to place the component in varus. In a prospective follow-up study, the authors reported the more accurate establishment of native anatomy. Subsequent studies radiographically comparing stemmed and stemless implants have found no significant differences in anatomic restoration with respect to center of rotation, humeral head height, humeral head medial offset, lateral humeral offset, and neck-shaft angle at short- and long-term follow up.
Multiple small prospective studies and randomized trials have found comparable functional and clinical outcomes for stemless and total stemmed arthroplasty at short-term follow-up. Recently, a study compared implant survival in patients with isolated primary osteoarthritis, 761 patients treated with stemless implants versus 4398 patients treated with stemmed implants. The revision rate was comparable between the groups, with percentage of 2.8 and 2.6, respectively. There was no difference in 6-year unadjusted survival rates between the groups, 0.953 and 0.958, respectively. Long-term radiographic and clinical studies are limited with these relatively new implants, but one prospective cohort study with mean follow-up of 9 years reported on 17 of 49 patients who received total shoulder replacement and 32 who received hemiarthroplasty with stemless implants. The authors found a significant improvement in postoperative pain and function cores and active range of motion. No revision surgery was observed as a result of loosening or countersinking of the humeral implant.
Stemless total shoulder arthroplasty may be indicated in patients with primary osteoarthritis, post-traumatic arthritis, inflammatory arthropathies, and instability arthropathy, especially in younger patients where future revision surgery may be anticipated. Early studies found low survival rates with the initial designs, which may have resulted from a steep learning curve with new implants. Over the last decade, however, advancements in surgical techniques and changes in stemless humeral components that rely on metaphyseal press fitting have provided longer implant survival. Careful preoperative evaluation of metaphyseal bone quality is critical when considering a stemless implant. Stemless shoulder arthroplasty is contraindicated when early metaphyseal fixation is at risk, including with osteoporotic or osteopenic bone and in the setting of 4-part proximal humerus fractures.
Stemless implants have been shown to appropriately reproduce native anatomy and, compared to stemmed total shoulder arthroplasty, have equivalent survival rates, functional outcomes, and clinical results with potential for easier revision and lower incidence of humeral component complications. These humeral implants offer another option for the shoulder surgeon when planning for shoulder arthroplasty.