These authors report on a multicenter review of primary total shoulders performed with either the Arthrex Univers traditional-length stem (below left) or the Arthrex Apex short-stem (below right)
postoperatively in 58 Univers II stems and 56 Apex stems.
The clinical outcomes between the groups were similar, for example the SST improved 6.1 points from 3.6 to 9.7 for the Univers II and 5.5 points and from 4.1 to 9.6 for the Apex.
Anatomic alignment was achieved in 98% of Univers II stems but only 86% of the Apex stems (P = .015).
Cortical thinning was more common in the medial metaphysis with the Univers II stem (74%) than with the Apex stem (50%; P = .008). Increased stem diameter relative to the size of the humeral canal was associated with higher rate of proximal medial cortical thinning or osteopenia.
Partial calcar osteolysis was seen in 31% of the Univers II stems and in 23% of the Apex stems (P = .348) (see blue arrow on film below at right).
Comment: It is well recognized that grit blasted stems can shunt loads applied to the humeral head past the proximal humerus resulting in osteolysis and stress-shielding. It is also recognized that short stems provide less control of the position of the stem in the canal. The findings of this study are consistent with these observations.
For decades now, we've been very pleased with the use of a standard length smooth stemmed humeral component fixed in place using impaction autografting. This approach avoids problems of stress shielding on one hand and stem malposition on the other.
We avoid ingrowth surfaces and tight diaphyseal fit of the distal stem in our approach to humeral fixation. Instead we attempt to prevent stress shielding using impaction grafting to distribute the load evenly from the prosthesis to the humerus. For more about impaction grafting see this link.
Shown below is a diagram of an impaction grafted stem and an x-ray of an impaction grafted stem 6 years after total shoulder arthroplasty with no evidence of stress shielding.
To emphasize the point, see below the x-rays of of a patient with a stiff painful right shoulder after a hemiarthroplasty using an ingrowth stem performed five years prior to presenting to us for revision arthroplasty.
Note that the distal two thirds of the stem is tightly impacted in the humeral diaphysis so that forces applied to the prosthetic head bypass the proximal one third of the bone. As a result of this stress shielding bone has been lost from the humerus above the diaphyseal metaphyseal junction (red arrows).
Interestingly, this prosthesis has a bone ingrowth surface in its metaphyseal portion. Should it require removal, there may be a risk of tuberosity fracture.
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