Sunday, August 12, 2018

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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