Wednesday, May 24, 2017

Managing arthritic posterior instability

Many approaches have been suggested for managing the posteriorly decentered humeral head that has come to rest in a pathological posterior concavity. These include posterior bone grafting (a technically difficult procedure with associated problems of hardware failure and graft resorption), reaming the anterior ‘high side” (a procedure that sacrifices bone stock without improving stability), posteriorly augmented plastic glenoid components (devices than increase the force and pressure on the posterior polyethylene with the associated risks of cold flow and increased ‘rocking horse’ lever arm) , and reverse total shoulder (with its associated risks and limitations).

Here are the preoperative x-rays on a heavy set, active patient.  The AP view suggests 'standard' osteoarthritis.

However the axillary 'truth' view shows severe posterior decentering into a pathologic glenoid concavity resulting from severe posterior erosion.

Our approach to this pathoanatomy is to convert the biconcavity into a single concavity by conservative reaming without attempting to change glenoid version, to insert a standard (non-augmented) all polyethylene glenoid, and then to manage any tendency for excessive posterior translation using an anteriorly eccentric humeral head and a rotator interval plication.

The postoperative AP view is shown below

Along with the axillary view that shows the anteriorly eccentric humeral head component to be centered in the glenoid component, which has been inserted in retroversion. Note the slight anterior penetration of the central peg.

At surgery the shoulder was stable to posteriorly directed forces applied to the humeral head. Postoperatively, the patient was able to participate fully in the standard post total shoulder rehabilitation program, including assisted flexion on the evening of surgery.

Of note in this approach is that the head is stabilized in large part by the posterior soft tissues (blue arrows in the figure below),
rather than by loading the posterior aspect of an augmented glenoid component.

Time will tell the best approach for managing this complex pathology. Stay tuned!
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