These authors suggest that modularity in reverse shoulder arthroplasty provides surgical flexibility and facilitates less-complex revision surgery, but that the potential for fatigue fracture is higher with modular components.
They studied 8 humeral trays of nearly identical designs: 4 made of Ti-6Al-4V (Ti) and 4 made of CoCrMo (CoCr),
Both types of implant are still on the market.
Some of the results of this retrieval study are shown here.
They concluded that fatigue failure is possible for some reverse shoulder components and is likely exacerbated by fillet radius, tray thickness, and material choice.
Comment: This report shows how important it is for the surgeon to understand the material and the geometry of the components he or she plans to use.
We've actually put up a post previously on this exact topic; it is reproduced below
Three years ago a patient had a reverse total shoulder. Post operative films shown below
Within the first month the glenosphere dissociated from the baseplate requiring revision as shown below.
With a year or so, he developed pain and clunking in his shoulder and had these radiographic findings (problem is subtle, can you see it?)
He came to see us at which time we obtained these films.
In this cases, the stem of the tray had fatigued and fractured.
We were able to obtain a Chrome-Cobalt humeral tray and used it in our revision, shown below. We also resected the heterotopic bone and cultured the wound for Propionibacterium. There was no growth on these cultures.
In the current wave of enthusiasm for implanting reverse total shoulders, it is important to recognize that this is a technically demanding procedure and that each implant system has its own nuances for fixation of the glenoid base plate, glenosphere, humeral stem, humeral tray and humeral poly. This case also demonstrates that the forces at the articulation are large - enough to result in fatigue fracture of the stem of the tray. It also points out the importance of understand the metallurgy of the implant.
Our practice is to use an impaction grafted non-modular monoblock prosthesis , which avoids the risk of tray failure
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