Managing Glenoid Bone Deficiency—The Augment Experience in Anatomic and Reverse Shoulder Arthroplasty

INDICATIONS

Indications and limitations for augmented aTSA glenoids remain incompletely defined. The most common indication for an augmented aTSA is osteoarthritis with a B2 glenoid. We recommend augments in the occurrence of any indication of significant eccentric glenoid wear. With the expertise of surgeons, deformities of up to 20° to 25° of deformity can be readily handled with good predictability. More severe deformities can be managed with augmented aTSA components, but early failure rates may be high. The most severe acquired deformities remain best managed with RTSA. Currently, we prefer RTSA when glenoid bone loss exceeds 25°. With the widespread availability of computed tomography (CT) scans with 3-dimensional (3-D) reconstruction, glenoid bone defects are increasingly recognized. When correcting deformity, surgeons should strive to limit residual retroversion to a maximum of 5°.¹³ Preoperative planning software and computer-assisted surgery (ExactechGPS) may allow surgeons to better define the limits of augmented glenoid fixation prior to the date of surgery. We routinely utilize computer-guided glenoid preparation to control glenoid version to within 5° of neutral position.

The differences between B3 and a true type C glenoid must be recognized. Although B3 glenoids may still be a candidate for an augmented anatomic glenoid component, type C glenoids are not. Developmental abnormalities of type C glenoid occur simultaneously with humeral deformities, including medialized posterior rotator cuff musculature. Correction of the joint line to neutral version may not replicate the non-diseased state of a dysplastic type shoulder. Davis and colleagues¹⁴ have proposed treating these patients by leaving both the humerus and glenoid in their native version without correction.

TECHNIQUE

The implant that we have the most experience with is an 8° full-wedge augmented glenoid component. Such an implant is typically utilized for B2 glenoids. We recommend that a high-quality CT scan be performed for preoperative planning. As a general rule, the starting point often lies close to the ridge of B2 glenoid and more anterior than the apparent glenoid center, which is viewed intraoperatively due to asymmetric posterior wear. Full-wedge component is utilized to ream the ridge separating the neo and paleoglenoids to create a flat surface. This condition is best achieved by drilling a pilot hole at the planned glenoid central peg position to prevent the reamer from sliding anteriorly during reaming. Glenoid preparation begins with the smallest reamer until the ridge has been flattened, and the reamer makes full contact with the glenoid. The reamer diameter is then increased based on glenoid size. Slightly downsizing the glenoid implant will require less reaming to achieve full backside support. Once the glenoid is properly reamed, the central and peripheral peg holes are drilled using the appropriate guides. Holes are then dried, and all-polyethylene or composite glenoid component (either partially or completely cemented) is installed using favored cementing techniques. The advantage of composite glenoid component is that the central cage allows for bone ingrowth and may potentially improve long-term implant survival. Press fit of the central cage requires no waiting time for glenoid cement hardening before proceeding to the humerus. When placing an augmented component, adequate glenoid exposure is imperative to allow in-line placement and appropriate seating of the component without impingement on adjacent retractors.

When using the step-augmented glenoid, the paleoglenoid is prepared in a similar fashion to a standard aTSA. Once the paleoglenoid has been reamed to a neutral position, a protector plate is placed onto the paleoglenoid. and a step-cut saw is used to prepare the posterior stepped bone cut. Peripheral pegs are then drilled, and the component is installed in routine fashion. When using hemi-wedge augments, the paleoglenoid is again prepared in a similar fashion as a standard glenoid component over a cannulated guidewire. The neoglenoid is subsequently prepared using a specialized angled reamer with a positive stop to prevent over-reaming. These glenoid implants improve rotational force neutralization given the absence of flat back against the glenoid. All 3 designs preserve bone when compared with eccentric reaming alone,¹⁵ with the half-augmented wedge preserving the most bone.

Table 1. Results of Various Augmented Glenoid Components in Anatomic Total Shoulder

Arthroplasty

RESULTS

In our institution, we first used all-polyethylene posteriorly augmented glenoid components in 2010. Between 2010 and 2015, 45 patients received an 8° all-polyethylene posterior augment, and 7 patients received a 16° augment. In 2015, we transitioned to the composite caged posterior augment. All patients in our database who received an augmented glenoid component experienced improvement in active forward elevation, external rotation, American Shoulder and Elbow Surgeons (ASES), and Constant scores (Table 1). Minimum follow-up was 1 year for patients receiving both an 8° cage (mean, 1.48 years) and an 8° all-polyethylene augment (mean, 3.18 years). Figures 2A-2C show a patient with significant posterior glenoid wear and humeral head subluxation treated with an 8° wedge composite posterior augment glenoid 3 years postoperative.

Continue to: COMPLICATIONS