Saturday, April 25, 2020

Reverse total shoulder - humeral stress shielding

Short-term evaluation of humeral stress shielding following reverse shoulder arthroplasty using press-fit fixation compared with cemented fixation

These authors compared the functional outcomes and humeral stress shielding of a reverse shoulder arthroplasty (RSA) placed with either cement or press-fit fixation. The stems were identical in geometry and coating with the only variable being whether the stems were secured with cement or by a press-fit technique. 

At minimum of two year followup, they found no significant differences in ranges of motion or functional outcomes between the two groups. 

Proximal lateral stress shielding was more common in the press-fit group (68%) than in the cemented group (25%). 

The authors concluded that at short-term follow-up, there were no differences in functional outcomes or stem loosening between press-fit fixation and cemented fixation of an RSA humeral stem. Proximal stress shielding was more common with press-fit fixation with the stem in this study, but the overall changes were considered low in 97% of cases. They pointed out that further study is needed to evaluate the mid- to long-term differences regarding stress shielding.

Comment: Humeral stress shielding results when the humeral prosthesis applies loads localized to some areas of the bone with unloading of other areas, resulting in bone resorption. It seems likely that cement helps even out the load distribution from prosthesis to bone.

Another way to even out the load distribution is to select a stem without a large metaphysical flare and of a size that is too small for a secure press fit in the patient's humerus (i.e. providing a small filling ratio).
The implant is then secured with impaction autografting or allografting to spread the load from the humeral component to the humerus

This approach can minimize stress shielding

by reducing the filling ratio (the ratio of the implant width (red line) to the humerus width (blue line))

This approach also has the advantages of bone preservation and of facilitating revision, should it become necessary.

To see a YouTube of our technique for a reverse total shoulder arthroplasty, click on this link.
How you can support research in shoulder surgery Click on this link.

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

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