Glenoid component

Glenoid Revision Not Requiring a Bone Graft

Glenoid erosion after hemiarthroplasty is a common indication for revision arthroplasty and occurs in two situations: (1) in patients with rotator cuff deficiency and superior glenoid erosion coupled with static superior (or anterior superior) humeral migration ( Fig. 40.1 ) and (2) in patients with an intact rotator cuff and painful symptomatic humeral erosion that is central, anterior, or posterior ( Fig. 40.2 ). Usually, the erosion is not severe enough to require a bone graft, but the surgeon should first determine the severity of the osseous glenoid defect with a preoperative computed tomography scan ( Fig. 40.3 ).

Unconstrained Shoulder Arthroplasty Cases Not Requiring a Glenoid Bone Graft

In patients with glenoid erosion after hemiarthroplasty and a functional rotator cuff, revision surgery from hemiarthroplasty to total shoulder arthroplasty is performed similar to cases of primary unconstrained shoulder arthroplasty. In such cases, if the humeral component is properly sized and positioned, the surgeon may be able to retain the humeral stem while performing revision surgery. This almost always necessitates changing the humeral head of the modular implant. It is important to know preoperatively the type of implant that the patient had and the radius of curvature of the various head sizes of this implant. A different brand of glenoid component can be coupled with the previous humeral head component if prosthetic mismatch can be calculated and respected during revision arthroplasty (see Chapter 12 for discussion of prosthetic mismatch and its implications in unconstrained shoulder arthroplasty). In general, radial mismatch of greater than 5.5 mm and less than 10 mm should be respected and the glenoid component size selected accordingly. If the humeral component is not properly sized or positioned or if adequate glenoid exposure cannot be obtained because of the humeral stem, the humeral component should be removed as described in Chapter 38 .

After glenoid exposure is achieved, implantation of a glenoid component proceeds as in cases of primary unconstrained arthroplasty with either a keeled or pegged glenoid component ( Fig. 40.4 ). The technique for insertion of an unconstrained glenoid component is detailed in Chapter 12 .

Reverse Shoulder Arthroplasty Cases Not Requiring a Glenoid Bone Graft

In patients with glenoid erosion after hemiarthroplasty and a nonfunctional rotator cuff, revision surgery from hemiarthroplasty to reverse shoulder arthroplasty is performed similar to cases of primary reverse shoulder arthroplasty. In such cases the hemiarthroplasty component is removed and the glenoid exposed as described in Chapter 38 . If a convertible implant had been placed primarily, removal of only the prosthetic humeral head may be necessary, leaving a well-fixed humeral stem (see Chapter 39 ). Implantation of a reverse glenoid component proceeds as in cases of primary reverse arthroplasty, as described later in this chapter and in detail in Chapter 22 .

Occasionally, revision of an unconstrained total shoulder arthroplasty to a reverse shoulder arthroplasty in a patient with minimal glenoid bone loss is indicated (i.e., late rotator cuff insufficiency). Most of these patients have a pegged glenoid that is well fixed or minimally loose. After the glenoid component is removed, the previously created central hole can be used for placement of a reverse glenoid component ( Fig. 40.5 ). The previously placed peripheral holes from the pegged unconstrained glenoid component may be ignored. The residual glenoid is reamed to a flat surface ( Fig. 40.6 ). We prefer the use of a revision-type base plate with a central screw in this scenario ( Fig. 40.7 ). The base plate is placed as described in Chapter 22 . Because using the previously placed hole in the glenoid places the reverse base plate more superior than desired, an inferior offset glenosphere is used ( Fig. 40.8 ). Fig. 40.9 shows the final construct.