48.1 Introduction

The number of primary shoulder arthroplasties being performed throughout the world increases exponentially every year. Many of these procedures are now indicated for younger, more high-demand patients who want to continue their activities. In addition, with increasing life expectancies, we can expect more primary and, ultimately, even more revision procedures of all types in the future. The most common indications for revision shoulder arthroplasty include glenoid component loosening, rotator cuff failure, subscapularis failure after instability, and infection. ¹

Revision procedures that require removal of well-fixed humeral or glenoid components are difficult and have an increased risk of complications including intraoperative fractures, more extensive soft-tissue damage, increased blood loss, and surgical time. ² In an effort to diminish these risks, many implant designs are now convertible especially on the humeral side (unipolar convertibility; Fig. 48.1 ). Some systems are convertible on both the humerus and the glenoid (bipolar convertibility; Fig. 48.2 ).

48.2 Goals of Procedure

Convertible shoulder arthroplasty components facilitate revision surgery when used in the index arthroplasty procedure. Convertible-type implants can be unipolar (platform stem on the humeral side) or bipolar (convertible components on the humeral and glenoid side). Most of the present-day third- and fourth-generation shoulder arthroplasty systems consist of humeral platform stems of all types and lengths that are adaptable to anatomic or reverse components.

Several present-day shoulder arthroplasty systems have both convertible humeral components and metal-backed glenoid components that can also be adapted for use as an anatomic glenoid component or a glenosphere for use in reverse shoulder arthroplasty (RSA). Implant systems like these can be used to carry out primary hemiarthroplasty (HA) or anatomic shoulder arthroplasty successfully and can be revised to RSA if needed in the future.

48.3 Advantages

The advantage of these convertible component systems is the fact the revision cases can be made much easier because in most cases the well-fixed humeral stem does not need to be removed. Removing a well-fixed stem can be difficult and can result in intraoperative humeral fractures and increased blood loss and surgical time.

In cases of bipolar convertible systems, the glenoid component can be exchanged without removing the well-fixed metal baseplate in most cases. This is extremely helpful in that it reduces the risk of glenoid bone deformity and/or loss that would require possible bone graft or even patient-specific implants during the revision procedure.

48.4 Indications

In patients who are indicated for anatomic shoulder arthroplasty for glenohumeral osteoarthritis, HA for acute trauma, avascular necrosis, or any other primary arthritic condition, surgeons should consider using implant systems that are convertible. This convertibility gives the surgeon an important advantage in any revision procedures that may be necessary in the future. This is especially important as younger, more active patients are now being indicated for anatomic shoulder arthroplasty or HA. These patients are at risk for revision surgery in the future, and convertible implants may be particularly beneficial in these clinical situations.

48.5 Contraindications

There are no absolute contraindications to usage of convertible implants; however, the surgeon should never compromise the index procedure for the sake of a convertible situation. In all orthopaedic procedures, the first procedure is the best opportunity for success, so humeral stem and glenoid baseplate positioning should not be altered from what is best in the index procedure in order to create a more convertible situation. Placing the glenoid baseplate in a bipolar convertible system in an excessive superior or inferior position or with excessive tilt may compromise the outcome of the primary procedure and any subsequent revision procedure. Similarly, placing a platform humeral stem in an abnormal height or version to accommodate a later convertible revision should not be done.