Monday, May 27, 2013

Conversion of anatomic shoulder arthroplasty to a reverse total shoulder

Conversion of shoulder arthroplasty to reverse implants: clinical and radiological results using a modular system

These authors report results of an anatomic -> reverse arthroplasty system in18 patients having revision of a hemiarthroplasty implanted for fracture and 8 patients having revision of anatomical total shoulder. In the fracture group, the primary reason for failure of the index arthroplasty was cuff or tuberosity failure. In the failed total shoulder group, again all cases were related to failure of the rotator cuff.

The lesson here is clear – cuff integrity is essential to the function of an anatomic arthroplasty, whether for fracture or arthritis. Individuals with frail cuff – tuberosity conditions may be better treated with a primary reverse or a CTA arthroplasty, depending on individual situation including the status of the coracoacromial arch and the patient’s activity level and fall risk. It is obviously best to do the best operation the first time.

There is no question that the revision of a well-fixed humeral stem carries with it substantial risk of fracture and bone loss. The challenge is that in the revision of an anatomic arthroplasty to a reverse usually requires lowering of the humeral implant in the humeral shaft to accommodate the lowering of the articulation with the inferiorly placed glenosphere. In the system used by the authors, this appears to be accomplished by a modular stem that allows adjustment of the height of the humeral body. It is not clear the degree to which the system allows for modification of humeral version, which can be critical to the stability of a reverse total shoulder.

In this series the metal backed glenoid was also modular, allowing for exchange of an anatomic polyethylene surface for a glenosphere. While this seems at first glace to be attractive, we must recall that the failure rate of metal backed glenoids is higher than that of all polyethylene glenoids.

So, as we consider our approaches to patients requiring shoulder arthroplasty, we must consider how to ‘get it right the first time’ with conventional prostheses in contrast to the value added by using a more complex implant at the initial surgery with the goal of making revision easier.

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