Wednesday, September 20, 2017

The problem with tight-fitting humeral stems - diaphyseal incarceration

Here is the x-ray of a middle aged lady with glenohumeral arthritis.

She had a total shoulder arthroplasty at which time her rotator cuff was reported to be normal. A large diameter humeral stem was used that was incompletely seated in the humeral canal because of diaphyseal incarceration, leaving the humeral head high above the tuberosity.

Three months after surgery she presented to us for consultation regarding weakness and pain. On examination she had pseudoparalysis and these x-rays.
We converted the failed anatomic arthroplasty to a reverse total shoulder.  A year later she has a comfortable and functional shoulder.
Comment: The point here is that a stem that fits tightly in the diaphysis may be difficult to seat completely. A high humeral head can put the rotator cuff at risk and lead to cuff failure and pseudoparalysis.

Our approach to humeral fixation uses a relatively thin and smooth stem fixed with impaction autografting as shown below from a case we did yesterday. This avoids the problem of incarceration in the diaphysis and distributes the load evenly to avoid stress shielding. With this approach no short stem, trabecular metal or ingrowth surface is required or desired

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