This is a rare complication of anatomic shoulder arthroplasty. Dissociation of the humeral component from the stem is very rarely seen, especially when the fixation method is a morse taper. The following case illustrates the problem of "modularity". The more complexity is added to the prosthesis the higher the chances of failure of the implant. This patient had a Smith and Nephew Promos prosthesis implanted in his shoulder and he did well for quite some time, until he felt a snap at approximately 10 years after surgery. The following x-rays were taken in our office at the time of first evaluation which indicate a dissociation of the stem from the head. The FDA has issued a Class 2 Device Recall for this particular implant.
As seen in the picture above this design can have multiple modes of failure at the head / stem interface due to the complexity of the fixation. In addition, the entire stem is porous coated which makes it extremely difficult to revise and unnecessary as non coating or proximal coating is enough for fixation of the humeral stem and press fitting.
The idea in this case was to avoid conversion to a reverse TSA as the glenoid component was well fixed and there was intact rotator cuff at the time of surgery. Such a revision would have been very difficult as removal of the glenoid fixed component can lead to glenoid bone defect and extraction of the stem would have required extensile humeral osteotomy as it was porous coates in its entire length
The picture above shows the broken screw at the inclination set
The picture above shows the improved design/inclination set that was used for salvage of the construct.
Luckily, the retained broken screw was removed from the stem without damaging the threads of the stem
The patient had the least aggressive approach, which was to downsize the humeral head, retain the glenoid component, as it was well fixed despite the radiolucent lines and implant the new small head with the new inclination set.
At 6 weeks postop the patient had 170 assistive forward elevation, no limitation in internal rotation and no pain.
