Glenoid retroversion, "correction" and perforation - what matters?

Risk of Perforation Is High During Corrective Reaming of Retroverted Glenoids: A Computer Simulation Study

These authors used a computer simulation to examine the effects of anterior glenoid reaming to  address glenoid retroversion in 71 shoulders having anatomic shoulder arthroplasty for arthritis with a biconcave retroverted glenoids with posterior subluxation of the humeral head.

Forty-four of 71 glenoids (62.5%) had < 25° of native retroversion. 

Anatomic glenoid implants were then virtually implanted using three-dimensional CT software that allows for preoperative shoulder arthroplasty planning to correct native retroversion to 15° or 10° of retroversion using both a central peg with an inverted triangle peg configuration or a keel. 

They found that correction to 15° of retroversion required 5±3 mm of reaming, and correction to 10° of retroversion required 8±3 mm of reaming to obtain at least 80%seating. 

Peripheral peg perforation with correction to 15° occurred in 15 of 27 (56%) glenoids with > 25° of retroversion compared with 10 of 44 (23%) of glenoids with < 25° of retroversion. There was no difference in perforation with keeled components. 

When correcting to 15°, glenoids with higher native version (> 25°) had a greater risk of poor bone quality support (10 of 27 [37%]) when compared with glenoids with less version (four of 44 [9%].  

Comment: When dealing with a retroverted glenoid

there are several options for positioning an anatomic glenoid.

(1) Insert in anatomic version without reaming, leaving the posterior aspect of the component unsupported

(2) Reaming in anatomic version, sacrificing anterior glenoid bone and reducing the quality of bone supporting the component

(3) Inserting a technically challenging posterior bone graft to support the component

(4) Using a posteriorly augmented polyethylene component

accepting the risk of increased posterior bone loss should the component fail.

(5) Avoiding excessive reaming 

and instead, inserting the component without specific attempt to change glenoid version, reaming only enough to produce a single concavity.

 Then using an anteriorly eccentric humeral head

and rotator interval plication 

to manage any tendency for posterior instability as shown below

While (as shown above) there can be some peg perforation, but this has not been associated with component failure using this method.

The results of this approach are described in 

Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty? and below.

This remains our preferred method for managing the B2 glenoid.

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Is glenoid peg perforation a problem?

Glenoid perforation with pegged components during total shoulder arthroplasty.

These authors sought to determine if glenoid peg perforation was associated with an increased rate of glenoid component loosening and whether glenoid peg perforation was associated with inferior clinical outcomes. They performed a case-control retrospective review comparing 25 total shoulder arthroplasties (TSAs) in which one or multiple pegs perforated the medial glenoid vault (uncontained group) with 25 TSAs without peg perforation (contained group). Average clinical follow-up was more than 5 years.

Initially the authors had intended to obtain radiographs at two or more years after surgery. However, a large number of patients were unable to obtain satisfactory x-rays and this aspect of the study was abandoned.

No patient in either group was known to have had revision for glenoid loosening. 

Two (8%) patients in the uncontained group required revision for rotator cuff tears. The glenoid components were secure in both.

Penn and ASES scores were significantly lower in the unconfined group. Pain and satisfaction subscores were similar between the groups, but function subscores were significantly lower in the unconfined group.

Comment: Readers may be interested in a previous post discussing glenoid perforation and its possible consequences.

As the authors point out, shoulders with severe glenoid erosion accompanied by eccentric posterior glenoid wear and anterior soft tissue contractors have more severe forms of glenohumeral arthritis than those with small amounts of medial erosion. On one hand, it is not surprising that thin glenoids are more likely to be perforated. On the other hand, it is not surprising that shoulder arthroplasty for these severely deformed glenohumeral joints will have poorer results than those with minimal deformity. In this regard it would be of interest to know the pre surgery Penn scores and the radiographic pathoanatomy prior to surgery for each of the two groups.

It seems likely that the poorer functional results in the 25 TSAs with peg penetration were due to disease severity and not to the peg penetration. This view is somewhat reinforced by the observation that both shoulders requiring revision for cuff failure were in the penetration (uncontained) group.

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Glenoid component in total shoulder - perforation

Perforation tolerance of glenoid implants to abnormal glenoid retroversion, anteversion, and medialization.

The authors opine that it is important to avoid perforating the glenoid vault during insertion of the glenoid implant. To our knowledge, it has not been demonstrated that perforation predisposes the glenoid component to failure. What does predispose the glenoid to failure, as discussed in previous posts, is poor contouring of the underlying bone, poor cement technique, excessive reaming that removes supporting bone, and failure to balance the humeral head on the glenoid.

The authors made 3-dimensional models of 15 glenoid implants and and virtually implanted into 3-dimensional reconstructed models of 40 nonarthritic scapulae. It is of importance to note that the pathoanatomy of arthritic glenoids is quite different from 'nonarthritic scapulae' so the clinical relevance of the findings is unclear.

They found that the overall mean increased retroversion tolerated before perforation was 19°, increased anteversion was 16°, and abnormal version fully corrected by eccentric reaming was 17°.

It is furthermore of interest that the average glenoid retroversion in reported series of patients with arthritis is between 8 and 27 degrees Would it be better in the cases with more than 17 degrees of retroversion to (a) avoid using a glenoid component, (b) ream to normalize the version anyway, or (c ) accept the retroversion and use soft tissue balance to stabilize the joint?

In each patient the surgeon has many choices to make, including whether or not to insert a glenoid component, which glenoid component to use, how to manage the tradeoff between reaming and contouring and change of glenoid orientation. In our practice, 'perforation' of the fixation pegs is a minor concern, subordinate to the contouring of the glenoid surface, preservation of glenoid bone stock and good cement technique. Our approach is summarized here.

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