60.1 Goals of Procedure

Platform shoulder arthroplasty systems allow for conversion of an anatomic total shoulder arthroplasty (ATSA) to a reverse total shoulder arthroplasty (RTSA) without necessitating the removal of a well-fixed, well-positioned humeral stem and the associated risks of proximal humeral bone loss. Failed ATSA resulting in instability due to either progressive rotator cuff failure or component malpositioning may not be amenable to an anatomic revision procedure. An RTSA establishes a stable fulcrum to optimize shoulder biomechanics and provides inherent stability. Platform shoulder systems provide versatile options for preserving the humeral stem, which simplifies the revision procedure, minimizes patient morbidity, and conserves humeral bone stock while providing pain relief, improved functionality, and shoulder stability.

60.2 Advantages

Converting from an ATSA to an RTSA while preserving a well-fixed, well-positioned humeral stem avoids the technical challenges and significant morbidity associated with stem exchange. Exchanging either a cemented or uncemented humeral stem is technically challenging and associated with high rates of iatrogenic fracture, loss of proximal humeral bone stock, prolonged operative time, increased blood loss, and neurovascular injury. Furthermore, additional procedures such as humeral shaft corticotomy, strut grafting, and a more extensile approach are often necessary. Patients with a failed ATSA resulting in shoulder instability may benefit from the inherent stability provided by the constraint of an RTSA ( Fig. 60.1 ). As these patients are often osteopenic with poor bone quality, converting to an RTSA while preserving the humeral stem can preserve valuable bone stock, minimize morbidity, optimize function, and provide substantial pain relief.

60.3 Indications

Indications for converting from a failed ATSA to an RTSA most commonly include instability, component malposition, delayed failure or insufficiency of the rotator cuff, and aseptic loosening of the glenoid. The direction of shoulder instability is often indicative of the underlying pathology. Anterior instability commonly results from subscapularis deficiency, which is among the most commonly encountered problems following shoulder arthroplasty. Anterosuperior instability typically results from progressive rotator cuff failure secondary to either attritional changes or trauma. Rotator cuff deficiency can result in superior migration of the humeral head, which may also contribute to glenoid component loosening. Component malposition is another common indication for revision. Posterior instability may result from component malpositioning whereby the humeral, glenoid, or the combined version is significantly retroverted. Additionally, a stem that is malpositioned too proximally, often secondary to a nonanatomic humeral head resection, may result in pain, limited function, and progressive cuff disease. Finally, aseptic loosening of the glenoid component is a frequent mode of failure in ATSA. Glenoid loosening is often accompanied by instability and attritional rotator cuff disease. Revision to an RTSA is often necessary when the loose component is symptomatic and associated with glenoid bone loss in the setting of a deficient rotator cuff.

60.4 Contraindications

Contraindications for converting from an ATSA to an RTSA with a platform system pertain chiefly to the specific implant and its position. Platform shoulder systems come in two different varieties: an “In-side” or “Inlay” system or an “On-top” or “Onlay” system. Inlay systems have a modular body that connects to the humeral stem, whereas Onlay systems have no modular component. Rather, the humeral tray connects directly to the stem. Several of the currently available components are listed in Table 60.1 . The modular body in Inlay systems allows for more flexible optimization of implant height and version. Onlay systems with malpositioned stems (either too proximally or retroverted) may result in unacceptable lengthening of the humerus or persistent instability. Finally, stem retention is obviously contraindicated when the stem is loose or when there is concern for infection.

Contraindications that apply to all revision situations include active infection, axillary nerve deficit, compromised deltoid function, and inadequate glenoid bone stock to support a glenosphere. Indolent infections should always be considered in revision shoulder arthroplasty and unexpected positive cultures frequently occur. Propionibacterium acnes is a frequent culprit and presents indolently with pain and may be difficult to culture.

60.5 Preoperative Planning/Position

Related posts:

45 Posterior Glenoid Wear in Total Shoulder Replacement: Eccentric Reaming 48 Convertible Components in Shoulder Arthroplasty 53 Internal Latissimus Transfer for Reverse Shoulder Arthroplasty 43 Stemless Anatomic Shoulder Replacement 47 Bone Grafting for B2/B3 Glenoid 39 Deltopectoral Approach for Shoulder Arthroplasty

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