Last week, as most weeks, we had a number of patients come in for clinical evaluation of failed shoulder joint replacements that had been performed elsewhere. Each of the three cases below illustrates an important point.
The x-rays from the first case show a recurrently unstable reverse total shoulder. Note the absence of bone at the lateral aspect of the proximal humerus. This makes it likely that the posterior soft tissues are deficient - a factor that may be contributing to the posterior instability seen on the axillary view.
There are many other factors that can contribute to reverse total shoulder instability, one of which is polyethylene wear. Note that in the x-ray below taken after the shoulder was reduced, the glenosphere does not sit in a centered position in relation to the humeral cup. This pattern suggestions wear of the inferior aspect of the polyethylene liner - a known contributor to instability.
The second case illustrates a not uncommon problem with hybrid (metal and polyethylene) glenoid components. Because metal and poly have different elastic moduli, they deform differently when load is applied. Here we can see a fatigue fracture of a metal fixation post and osteolysis of the glenoid bone.
In the third case, we can see that a large humeral stem could not be fully seated in the humeral canal so that the humeral head remained proud or high in respect to the greater tuberosity. This, in turn, gave rise to rocking horse loosening of the glenoid component.
The tight fit of the humeral stem is always more evident on the axillary view.
Comment: Each of these cases has a lesson to teach. It is important that we spread the knowledge learned from failures so that they can be prevented in the future.
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