Diagnose, treat ‘easy-to-miss’ intraprosthetic dissociation in failed dual mobility THA
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While dislocation and intraprosthetic dissociation rates in dual mobility total hip arthroplasty are low, it is crucial to diagnose and treat these “easy-to-miss” presentations to avoid further surgery, according to presenter.
“Dual mobility decreases dislocation rates for both primary and revision hip arthroplasty, but we've all seen that they can also dislocate,” Rafael J. Sierra, MD, said in his presentation at the Current Concepts in Joint Replacement Meeting. “They will present in two ways: either as a large head dislocation, that’s when the large polyethylene head dislocates from the metal liner or shell, or as an intraprosthetic dissociation (IPD), where the smaller head dissociates from the larger polyethylene head,” he said.
Modular dual mobility THA implants can dissociate during dislocation or at the time of reduction, according to Sierra. However, it is uncommon for IPD to be associated with wear of the inner constraining ring, and overall incidences of dislocation and IPD are low (3% and 0.7%, respectively), he added.
Sierra said X-rays are often required to determine if a dual mobility implant is present. Carefully look for eccentricity of the femoral head within the acetabulum, dissociated polyethylene or a “halo” around the femoral head, he said. While not recommended for every patient, a CT scan or MRI will show the dissociated polyethylene, he noted.
“Remember that they are easy to miss,” Sierra said.
When it is clear that a dislocation of the dual mobility implant is present, Sierra encouraged surgeons to perform closed reduction in the OR under general anesthesia and under fluoroscopic control to check for possible IPD, where acetabular revision should be considered.
“I urge you to think about not putting simply another dual mobility head and reducing these,” Sierra said. “The French have shown [a] one out of five failure rate at 5 years, and in our series – I got to say – we had an 80% failure rate when we simply put another dual mobility head. So, consider acetabular revision, sometimes a femoral revision as well, to increase offset, as needed,” he added.
“The overall rates of dual mobility dislocation are fairly low, but it's critical to identify whether you have a large bearing dislocation or a dissociation on X-ray,” Sierra concluded. “And if you are going to think about another dual mobility or constraint liner, then make sure that the acetabular and femoral components are well positioned and free of impingement,” he said.
Collapse
Sierra RJ, et al. Failed dual mobility with intraprosthetic dislocation: Making the diagnosis and solving the problem. Presented at: Current Concepts in Joint Replacement Meeting; Dec. 7-10, 2022; Orlando (hybrid meeting).
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