Saturday, September 21, 2013

Conversion of anatomic to reverse total shoulder

Revision to reverse shoulder arthroplasty with retention of the humeral component Good outcome in 14 patients followed for a mean of 2.5 years

The authors point out that revision surgery for failed shoulder arthroplasty often requires removal of the humeral component and that this removal can carry a significant risk of fracture and bone loss. This is a problem that can be avoided if surgeons fix the humeral component using impaction grafting rather than using cement or bone ingrowth into trabecular metal. An impaction grafted humeral component can be removed with minimal risk of fracture or bone loss. This paves the way for conversion to a reverse total shoulder if that is indicated.

However, when the humeral component is cemented or when bone has grown into trabecular metal, removal of the humeral component is risky. It is interesting that, rather than adopting impaction grafting, vendors have developed "newer modular systems" that "allow conversion from anatomic to reverse shoulder arthroplasty with retention of a well-fixed humeral stem".

These authors report 14 cases of failed hemiarthroplasty due to rotator cuff deficiency and painful pseudoparalysis (in 13 women) in which revision to reverse shoulder arthroplasty was performed with retention of the humeral component using modular systems. 

The problem with this approach is that unless the humeral body/stem system is modular, placing a reverse humeral cup on a body/stem placed for anatomic arthroplasty will result in lengthening of the humerus with the attendant risks of neurologic complications and acromial fracture. In this series of 14 revisions, the humeral lengthening ranged from 9 mm to 48 mm with an average of 26 mm.

So, an alternative to expensive complex modular stems that will allow for anatomic to reverse conversion is a well done basic, impaction grafted humeral component that, should failure occur, allows for straightforward removal followed by the insertion of the reverse total shoulder system of choice, rather than one dictated by the extant stem.

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