Glenoid Erosion

Glenoid erosion after hemiarthroplasty is a multifactorial problem.¹ It may occur early or late and does not seem to be related to any readily identifiable risk factor. This problem occurs when the metallic prosthetic humeral head erodes into the softer glenoid bone (Fig. 35-1). Initially, pain may be the sole manifestation of this problem. As the erosion progresses medially, the normal length-tension relationships of the rotator cuff may become compromised and result in substantial weakness (Fig. 35-2).

Figure 35-1 Radiograph demonstrating osseous glenoid erosion after hemiarthroplasty.

Figure 35-2 Severe medialization of the humeral head caused by progressive glenoid erosion.

Glenoid erosion may be central or peripheral. If the rotator cuff is intact, as in primary osteoarthritis, the erosion is usually central or, less commonly, posterior (Fig. 35-3). If the rotator cuff is deficient, the erosion is generally superior (Fig. 35-4) or, less commonly, anterior (if the subscapularis is deficient; Fig. 35-5).

Figure 35-3 Computed tomogram demonstrating central glenoid erosion after hemiarthroplasty for primary osteoarthritis.

Figure 35-4 Superior glenoid erosion in a patient who has undergone hemiarthroplasty for rotator cuff tear arthropathy.

Figure 35-5 A and B, Anterior superior glenoid erosion in a patient who has undergone hemiarthroplasty for anterior superior rotator cuff insufficiency.

Glenoid erosion is best treated by resurfacing of the glenoid if sufficient native glenoid bone is available for implantation of a glenoid component (see Chapter 36). Frequently, the humeral component will require revision for glenoid exposure, and two options are available to the surgeon. We may exchange the component for a smaller head size in an unconstrained arthroplasty (Fig. 35-6) or change to a reverse-design arthroplasty. In general, with a functioning rotator cuff, an unconstrained arthroplasty is performed for revision arthroplasty. If rotator cuff function is significantly compromised, revision to a reverse prosthesis is performed.

Figure 35-6 A, Pre-revision radiograph. B, Humeral revision in which the humeral stem has been exchanged and the humeral head exchanged for a smaller size.

Glenoid Component Failure

Glenoid component failure can vary from subtle loosening to migration of the component with severe glenoid bone loss (Fig. 35-7). Additionally, mechanical failure of the implant can necessitate revision surgery (Fig. 35-8). When considering revision surgery for failure of a glenoid component, the surgeon must first decide whether to simply remove the failed glenoid component or to remove the failed glenoid component and reconstruct the osseous glenoid. In debilitated patients seeking mainly pain relief without significant concern for function, isolated removal of the glenoid component is usually the best treatment option. In other patients, glenoid reconstruction with iliac crest bone graft is indicated. For patients undergoing revision with an unconstrained prosthesis, we reconstruct the glenoid with an iliac crest bone graft as the first stage. Six months later, after complete incorporation of the bone graft, if the shoulder is still painful, we perform the second stage, which consists of placement of a new glenoid component (Fig. 35-9). When performing revision surgery with a reverse-design prosthesis, glenoid reconstruction and revision can often be performed as a single stage, provided that the central post of the revision glenoid component can be firmly seated in native glenoid bone (Fig. 35-10).

Figure 35-7 Radiograph showing loosening of a glenoid component.

Figure 35-8 A and B, Mechanical failure of a glenoid implant.

Figure 35-9 Preoperative radiograph (A) and postoperative radiograph(B) after removal of a loose glenoid component and bone grafting of the residual osseous defect in the glenoid.

Figure 35-10 A, Preoperative radiograph. B, Postoperative radiograph after revision of a failed unconstrained shoulder arthroplasty to a reverse shoulder arthroplasty with bone grafting of the glenoid.

Just as in cases of glenoid erosion, patients requiring revision surgery for a problem with the glenoid component often require revision of the humeral component for glenoid exposure, and the surgeon can exchange the component for a smaller head size in an unconstrained arthroplasty or change to a reverse-design arthroplasty. As previously mentioned, in a patient with a functioning rotator cuff, an unconstrained arthroplasty is used for revision arthroplasty. If rotator cuff function is significantly compromised, revision to a reverse prosthesis is performed.

Reverse Glenoid Component

In our experience, failure of the glenoid component of a reverse prosthesis is less common than failure of the glenoid component of an unconstrained shoulder arthroplasty. The most common problem that we observe is inadvertent placement of the glenoid component in a superiorly oriented position (Fig. 35-11). This usually occurs when a superior surgical approach has been used to place the reverse prosthesis. Although this radiographic finding does not merit revision surgery in and of itself, revision is indicated if this problem evolves into early glenoid loosening (Fig. 35-12).

Figure 35-11 Superiorly oriented glenoid component after reverse shoulder arthroplasty performed through a superior approach.

Figure 35-12 Failure of the glenoid component in reverse shoulder arthroplasty. The glenoid component was initially placed in a superiorly directed orientation.

Another radiographic finding related to a reverse glenoid component is inferior scapular notching. This finding can be related to excessive superior placement of the reverse glenoid component (Fig. 35-13). Notching, even when it is severe, has not been shown to cause loosening of the glenoid component, and revision surgery is unnecessary in the absence of glenoid loosening.

Figure 35-13 Scapular notching after reverse shoulder arthroplasty in which the glenoid component was placed superiorly on the glenoid face. The red line indicates the original border of the glenoid.

Unconstrained Humeral Components

The main problem that leads us to revise an unconstrained humeral component is placement of a humeral head prosthesis that is too large (Fig. 35-14). This can lead to stiffness, glenoid problems, and rotator cuff problems. If the stem of the humeral implant is acceptably positioned, the humeral head is simply exchanged for a smaller size.

Figure 35-14 Unconstrained shoulder arthroplasty with an excessively large humeral head component.

Less frequently, a humeral implant will be improperly positioned, generally with respect to humeral version. Problems with humeral component version can lead to instability of the component; nonconcentric glenoid loading, wear, and loosening; and failure of subscapularis repair. These scenarios are indications for revision of the humeral component.

Reverse Humeral Components

Even in cases in which a reverse humeral component is properly positioned, the deltoid muscle can “stretch out” and result in loss of prosthetic stability and, ultimately, dislocation. Patients most at risk for this complication are those with proximal humeral bone loss (Fig. 35-15). In such cases it is sometimes necessary to add more length to the humeral component to restore prosthetic stability via restoration of deltoid tension. This can usually be accomplished by exchanging the primarily placed polyethylene liner for a thicker liner or adding a metallic augment, or both (Fig. 35-16). Tensioning the deltoid by adding length to the prosthesis almost never requires removal of the humeral stem. In cases in which use of a metallic augment and the thickest polyethylene liner fails to stabilize the prosthesis, multiple metallic augments can be stacked together and secured with a custom-manufactured screw (Fig. 35-17).

Figure 35-15 Patient with severe proximal humeral bone loss resulting in dislocation of the reverse prosthesis.

Figure 35-16 A, Pre-revision radiograph. B, Radiograph after revision of a dislocated reverse prosthesis by adding a metallic augment with a thicker polyethylene spacer to increase deltoid tension and prosthetic stability.

Figure 35-17 Use of multiple metallic augments to stabi-lize a dislocated reverse prosthesis. This requires the use of a custom-manufactured screw to hold the augments together.

Subscapularis Problems

Occasionally, subscapularis dehiscence will develop after unconstrained shoulder arthroplasty. In many circumstances, postoperative failure of a subscapularis repair will be asymptomatic or minimally symptomatic and is a contraindication to revision surgery. If the patient has early (<6 weeks postoperatively) subscapularis failure without instability, subscapularis repair with retention of all components can be considered, provided that they are appropriately sized and positioned. If the patient complains only of weakness and pain without instability and has chronic subscapularis insufficiency, a subcoracoid pectoralis major transfer with retention of all components can be considered, provided that they are appropriately sized and positioned.

If subscapularis insufficiency is coupled with either dynamic or static anterior instability after unconstrained shoulder arthroplasty, our experience has been that revision to a reverse-design prosthesis is the only reliable way of restoring glenohumeral stability (Fig. 35-18).

Figure 35-18 Case in which a patient with subscapularis insufficiency and dynamic glenohumeral prosthetic instability (A) underwent revision with a reverse prosthesis (B).

Other Rotator Cuff Problems

The development of rotator cuff insufficiency after unconstrained shoulder arthroplasty is very rare. In cases in which a patient has sustained a massive (two or more tendons) rotator cuff tear after unconstrained shoulder arthroplasty that has resulted in severe dysfunction and static or dynamic glenohumeral prosthetic instability, revision to a reverse-design prosthesis can be considered (Fig. 35-19).

Figure 35-19 A, Patient with a massive irreparable rotator cuff tear after an unconstrained total shoulder arthroplasty. B, Static superior migration of the humerus required revision to a reverse prosthesis.

Instability

Glenohumeral instability after unconstrained shoulder arthroplasty usually occurs in one of two scenarios. First, instability can occur with rotator cuff insufficiency, as previously mentioned. Second, instability can occur in patients who have undergone unconstrained shoulder arthroplasty for primary osteoarthritis with posterior glenoid wear and posterior capsular distention (Fig. 35-20). In these cases we have found soft tissue procedures unpredictable in restoration of glenohumeral stability. We opt for revision to a reverse-design prosthesis (Fig. 35-21).

Figure 35-20 Posterior dislocation of a total shoulder arthroplasty performed for primary osteoarthritis in a patient with severe posterior glenoid wear.

Figure 35-21 Revision of a posteriorly dislocated unconstrained total shoulder arthroplasty to a reverse prosthesis.

A less common problem causing instability is an unconstrained humeral implant positioned in incorrect version (Fig. 35-22). This is an indication for revision of the humeral component and placement of the revision component in correct humeral version.

Figure 35-22 Computed tomogram of a patient with a humeral component placed in excessive anteversion that resulted in anterior instability.