Abstract
A conceptually new, to the North American market, acetabular design is currently available when performing a total hip arthroplasty – the dual mobility socket. Essentially this is a press-fit acetabular component with a polished surface (either modular or monoblock) that articulates with a large polyethylene head with a 28 mm ball inserted into that polyethylene in a similar fashion to a bipolar design.
Proponents of this design advocate its use to reduce the risk of dislocation, and it is being offered as an alternative to constrained liners and also as a potential prophylactic application in revision and high risk patients.
The concerns regarding this construct include:
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Wear - A large polyethylene head articulating against a polished metal surface may have much greater wear than a conventional metal against polyethylene bearing. Hip simulator data has shown this previously. Additionally there are two articulating surfaces, potentially leading to a greater combined wear than one would see with just a singular surface.
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Clinical data - At present there are predominately short term published reports on this implant, many from the same centers. There are no control groups with other implants in these same “at risk” patients. There is no registry data to date on this implant.
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Patient Population - A difficult question to answer is which patient is at risk for dislocation and if one was going to apply this new technology, which patient would receive it? In the original published series, 26% of patients undergoing THA had this implant. Does the increased risk of wear and osteolysis warrant the use of this implant in a primary setting?
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Unique complication - A unique complication has been described labeled intra-prosthetic dislocation. This occurs when the inner femoral ball disassociates from the polyethylene. The incidence has been reported up to 2% in some series. This complication alone equals the current rate of hip instability in a Medicare database with a conventional total hip replacement.
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Cost - In our current era of containing health care costs, this implant is offered to most at a significant cost premium to a more conventional total hip construct, without evidence of superiority, or for that matter equivalence at this point.
There are many options available to both manage and to prevent hip instability. Any new implant must show equivalence to current devices on the many fronts of wear, fixation, mid-term results, complications and costs.
