These authors assessed the timing and location of cortical bone resorption after total shoulder arthroplasty with an uncemented rectangular stem and investigate its effect on shoulder function up to 5 years after implantation.
They evaluated 133 arthroplasties performed between June 2003 and September 2006.
Twenty-two patients (17%) showed full-thickness cortical bone resorption, 21 of whom were diagnosed with zone 2 resorption. The maximum craniocaudal distance of full resorption averaged 19.1 mm (range, 5.6-46.7 mm). The median distance progressed significantly from 9.6 mm to 13.8 mm between 6 and 12 months (P . .005). The risk of bone resorption was 3.1 times higher for posttraumatic OA patients than for those with primary OA. The occurrence of bone resorption increased significantly
with increasing stem diameters relative to the humeral diameter.
with increasing stem diameters relative to the humeral diameter.
Comment: The authors concluded that bone resorption is a "radiographic phenomenon without significant impairment of function or need for revision within 5 years after surgery" there can be no question that loss of humeral bone stock can be a problem with respect to risk of fracture, loosening and increased difficulty of revision.
The desire to achieve cement less fixation of the humeral stem has led implant companies to develop porous surfaces, trabecular metal, and large stems (such has that shown below).
The difficulties associated with bone resorption with such a prosthesis can be envisioned on this film showing the absence of lateral cortical bone three years after prosthesis implantation. It would be difficult to remove this stem without fracturing the humerus.
We avoid the problem of stress shielding and bone resorption by using impaction grafting for the fixation of the humeral component. See yesterday's post to see the quality of the humeral bone almost three years after implantation with excellent bone quality around the prosthesis.
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