Augmented glenoid components for B2 and B3 glenoids

An augmented glenoid component is used by some surgeons in cases of posterior bone loss and retroversion.

Its insertion requires concentric reaming of the anterior glenoid

followed by the removal of additional posterior bone to fit the back of the selected component using either an oscillating rasp

or a superior/inferior scraper

The size of posterior augment ranges from 3 to 7 mm. The amount of bone removed in a case using a 7 mm augment is shown below.

The authors of Factors Associated with Functional Improvement After Posteriorly Augmented Total Shoulder Arthroplasty sought to identify pre- and postoperative factors that impact range of motion and function after augmented TSA in patients with B2 or B3 glenoid morphology.

An individual highly experienced shoulder surgeon performed 1,044 consecutive anatomic TSAs. Of these 88% were performed using a standard (non-augmented) glenoid component. 121 (12%) were performed with posteriorly augmented, stepped glenoid components; the indications for the use of an augmented component were not specified.

50 patients (57%)(41 B2 and 9 B3 glenoids) with minimum 2 year followup were included in the analysis. Two patients having posterior dislocation were excluded.

There was strong agreement among the observers for preoperative and postoperative glenoid version as measured on plain x-rays.

There was strong agreement for plain X-ray measurements of humeral decentering preoperatively and moderate agreement for this measurement postoperatively.

Range of motion was improved over preoperative values.  

Preoperative glenoid retroversion did not significantly affect the postoperative range of motion. 

Postoperative glenoid component retroversion and residual posterior subluxation relative to the scapular body or glenoid face did not correlate with range of motion in any plane.

Preoperative shoulder SANE and VAS scores were missing from this study. The mean postoperative VAS score was 0.5 and mean SANE score was 94.5  

Posterior subluxation relative to the glenoid face was moderately associated with lower SANE scores.

While the amount of posterior decentering of the humeral head was reduced from a mean of 21 percent before surgery to 3 percent after surgery, the amount of glenoid version was only changed by 7 degrees (24 degrees to 17 degrees).  

Comment: The questions needing answers are 

(1) how important is version correction to a value of 15 degrees or less as proposed by some authors?

(2) while it is evident that postoperative posterior decentering can lead to eccentric loading and rocking horse loosening of the glenoid component

is "correction" of glenoid version necessary for re-centering the humeral head on the glenoid?
(3) are the results of anatomic shoulder arthroplasty with a standard glenoid component for B2 and B3 glenoids inferior to those for glenoid types A1 or A2?
(4) are the clinical results of anatomic shoulder arthroplasty for B2 and B3 glenoids using an augmented component superior to those obtained with a standard glenoid component?

Some of the answers may be found in Anatomic Total Shoulder Arthroplasty with All-Polyethylene Glenoid Component for Primary Osteoarthritis with Glenoid Deficiencies.These authors sought to evaluate the ability of shoulder arthroplasty using a standard glenoid component to improve patient self-assessed comfort and function and to correct preoperative humeral-head decentering on the face of the glenoid in patients with primary glenohumeral arthritis and type-B2 or B3 glenoids. They identified 66 shoulders with type-B2 glenoids (n = 40) or type-B3 glenoids (n = 26) undergoing total shoulder arthroplasties with a non-augmented glenoid component inserted without attempting to normalize glenoid version and with clinical and radiographic follow-up at a minimum of 2 years.

Shoulder pathoanatomy was characterized on the axillary "truth" view in terms of glenoid version (angle between lines G and S) and humeral head decentering on the face of the glenoid (distance between line P - the perpendicular bisector of line segment G - and the center of the humeral head, C). Preoperative CT scans and computer planning software were not used in this case series.

This method allowed direct comparison of glenoid version and humeral decentering before and after the arthroplasty

The Simple Shoulder Test (SST) score improved from 3.2  points preoperatively to 9.9  points postoperatively at a mean time of 2.8 years for type-B2 glenoids and from 3.0 points preoperatively to 9.4 points postoperatively at a mean time of 2.9 years for type-B3 glenoids. These patient reported outcomes were as good as those achieved with other glenoid types.

These outcomes were achieved without changing glenoid version: postoperative glenoid version was not significantly different from preoperative glenoid version.

The humeral head centering on the glenoid was restored without the use of an augmented component: the mean humeral-head decentering on the glenoid face was reduced for type-B2 glenoids from 14% preoperatively to 1% postoperatively and for type-B3 glenoids from 4% preoperatively to 1% postoperatively.

The rates of bone integration into the central peg for type-B2 glenoids (83%) and type-B3 glenoids (81%) were not inferior to those for other glenoid types (A1 67%, A2 85%, B1 74%, D 75%).

Anterior penetration of the glenoid neck by the central peg of the glenoid component was observed in 2 (11%) of 19 of the type-B1 glenoids, in 6 (15%) of 40 of the type-B2 glenoids, and in 6 (23%) of 26 of the type-B3 glenoids. Perforation of the glenoid by the central peg was not associated with inferior clinical or radiographic outcomes. Twelve of the 14 shoulders with glenoid neck penetration had ingrowth of bone between the flanges of the central peg with no radiographic evidence of component loosening. The final mean SST score for the 14 shoulders with central peg penetration was 9.4 points, a value not significantly different from that for all of the type-B2 and B3 glenoids (9.7 points).

These minimum 2-year outcomes for 40 shoulders with type-B2 glenoids and 26 shoulders with type-B3 glenoids do not appear to be inferior to the minimum 2-year results reported recently for a combined group of 71 shoulders with type-B2 or B3 glenoid anatomy treated with posteriorly augmented glenoids inserted using preoperative CT scans and 3-dimensional planning software (see this link).

This study demonstrates that good two year clinical outcomes can be achieved for B2 and B3 glenoid components using a standard (non-augmented) glenoid component inserted without changing glenoid version.

Further clinical research will be required to establish clinical practice guidelines and appropriate use criteria for augmented glenoid components. 

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