Page 44 - ISAKOS 2018 Newsletter Volume 2

CURRENT CONCEPTS
Shorter Stems and Stemless Implants in Shoulder Replacement Surgery
In addition, these fractures are more commonly metaphyseal and often can be treated either nonoperatively or with cerclage fixation without the use of a long stem. Radiographically evident stress resorption occurs in association with a substantial number of stemmed implants, and Razfar et al.1, using finite image analysis, showed that this finding might be avoided with use of short-stem implants. Those authors also proposed a classification system for stem lengths on the basis of their work (Fig. 2). The advantages noted above may offer significant improvements in the outcomes of shoulder arthroplasty.
Similarly, short-stem implants are inappropriate for the treatment of the majority of proximal humeral fractures because of the presence of concomitant metaphyseal comminution. For this reason, a “bail out” option (i.e., the availability of a stemmed prosthesis system in the operating room) is absolutely necessary in cases of planned short-stem arthroplasty. Failure to respect this precaution will increase the risk of implant failure (Fig. 2). Surgeons who support the use of a lesser tuberosity osteotomy to manage the subscapularis need to understand that this procedure can also possibly compromise implant fixation. Also while positioning of the implant has the advantage of being independent of the humeral diaphysis, both short-stem and stemless implants have been noted to be malpositioned in a substantial number of cases2.
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Limitations
Perhaps the greatest limitation of shorter stems is the excellent long-term results associated with standard-length stems. Long-term loosening rates for traditional devices have been widely reported as <1%, and the success that has been achieved with these devices may be difficult to duplicate. Both short-stem and stemless devices share several limitations. Polyethylene debris resulting from glenoid wear increases the risk of loosening of all humeral components, and migration of this debris into an implant interface with only metaphyseal fixation potentially could increase long-term loosening rates. As there is no diaphyseal fixation, metaphyseal bone quality is critical. It must be understood that as many as 30% of patients will not have adequate bone quality to support these devices, and often the decision about which implant to use must be made at the time of surgery on the basis of fairly arbitrary criteria such as the “thumb test.” The excellent results associated with short-stem implants have been achieved because of strict adherence to the requirement for high-quality metaphyseal bone. Patients with rheumatoid arthritis may be at higher risk of fracture.
Short-stem designs offer several advantages over stemless components in terms of metaphyseal fixation. First, the rate of loosening of short-stem components approaches 0%, and the larger surface area available for fixation may prove beneficial. Second, most short-stem systems on the market offer a range of humeral inclination angles and therefore can compensate for a variety of proximal humeral geometries. Third, the fixed geometry of a stem corrects for excessive varus or valgus humeral osteotomy, an error commonly seen in association with stemless implants. Fourth, many currently available stemless designs are not convertible secondary to the implant collar. As platform systems offer many of the same advantages as short-stem or stemless implants in terms of revision, many of the advantages reported in association with these implants may in fact be imaginary.
Results
Between 2004 and 2013, approximately 10,000 short- stem and stemless shoulder prostheses were implanted worldwide1. Premature loosening has been virtually unreported, and short-stem and stemless implants have been discussed in several comprehensive reviews3-5. The only 2 publications that raised concerns regarding loosening of short-stem implants noted the potential need for a porous coating on implants with metaphyseal fixation.
42 ISAKOS NEWSLETTER 2018: VOLUME II