These authors report on 24 patients having total shoulder arthroplasty using a posteriorly augmented glenoid for arthritis with posterior glenoid wear. The degree of posterior wear and retroversion before surgery are not presented.
At two years after surgery, 60% of the shoulders had a periglenoid radiolucent line with an average radiographic line score of 1.10.
One glenoid was radiographically loose.
Two shoulders demonstrated superior subluxation.
Three were anteriorly subluxated.
Comment: These results speak to the challenges inherent in the use of posteriorly augmented components.
One of the rarely discussed concerns is the effects of using thick posterior polyethylene to manage the posteriorly directed loads applied when the arm is elevated to the functional position of forward elevation, which is known to create the risk of functional decentering.
This is best explained by noting that when the arm is at the side with a posteriorly augmented glenoid, the net humeral joint reaction force (red arrow) is centered.
However, when the arm is elevated to a functional position, the net humeral joint reaction force (red arrow) is directed posteriorly against the posteriorly augmented polyethylene, subjecting it to the risk of cold flow.
It is possible that these mechanisms contributed to the development of lucent lines and instability with posteriorly augmented glenoid components in the series presented.
Our approach to the retroverted glenoid is simple - see this link..
(1) We do not rely on preoperative CT scans because they cannot image the shoulder in the functional position of forward elevation. Instead we prefer the simple standardized axillary view taken with the arm elevated 90 degrees in the plane of the scapula as shown below (this shoulder demonstrates the bad arthritic triad).
(2) We do not use preoperative planning software or patient specific drill guides, but rather ream the glenoid conservatively without trying to 'normalize' glenoid version as shown in this link.
(3) Finally, in a total shoulder arthroplasty for a retroverted glenoid, we place a standard glenoid component on the conservatively reamed glenoid, using an anteriorly eccentric humeral humeral head component if necessary to achieve centering of the articulation.
This type of reconstruction is shown below on an axillary view taken with the arm in the functional position of forward elevation. Note the centered humeral head and the lack of glenoid lucent lines after two years of implantation.
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