Is THA instability best mitigated with dual mobility systems or larger femoral heads?
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Tool of choice for surgeons
Instability is best mitigated with dual mobility heads inside anatomic dual mobility shells.
Large heads are better than small ones, but not good enough.
Dislocation has not occurred following any of my last 800 total hips (primaries and revisions) performed employing ‘anatomic’ dual mobility acetabular components (thin shells [3 mm] without screw holes, smooth and polished on the inside and porous-textured on the outside). This does not include the use of ‘modular’ dual mobility components which are problematic in other ways, including obligatorily smaller heads, more neck impingement and corrosion issues. Previously, I preferred more standard ‘fixed-bearing designs’ where the poly liner locks into the socket. In that type of construct, my THA dislocation rate was 1% despite using large heads (as large as possible, depending on the outer diameter of the socket). I am fully convinced that anatomic dual mobility acetabular components will become the tool of choice in the future for hip surgeons unwilling to accept any THA instability.
William B. Macaulay Jr., MD, is the William and Susan Jaffe professor of orthopedic surgery, chief of the division of adult reconstructive surgery in the department of orthopedic surgery and medical director of International Patient Services at NYU Langone Health in New York.
Both may be effective
Instability after THA can be a complicated problem. It is first essential to determine the underlying cause of the instability to correctly address it. In situations where the implant is in an appropriate position both on the acetabular and femoral side and the patient has the appropriate offset and leg length, but the patient continues to have instability, a dual mobility or larger femoral head are both excellent options. Although both options have been shown to be effective in multiple studies, my belief is dual mobility gives you the advantage of having a larger overall head size with a greater jump distance and thus, more stability. Dual mobility comes with its own additional risks, such as disassociation of the two heads, extra bearing surface articulation and additional cost. In patients whose primary reason for revision is instability, I think it is more important to address the problem that we know exists opposed to worrying about a problem that might occur. Some studies will argue that dislocation rates are similar in revisions with dual mobility or large heads, but, when comparing revisions specifically for dislocations, most studies show dual mobility wins.
When revising hips for instability, I believe dual mobility is the way to go.
- Hartzler MA, et al. Clin Orthop Relat Res. 2018;doi:10.1007/s11999.0000000000000035.
- Hoskins W, et al. J Arthroplasty. 2021;doi:10.1016/j.arth.2021.05.008.
James A. Germano, MD, is the chairman of orthopedics at Long Island Jewish Valley Stream Hospital, Orlin and Cohen Medical Group, Northwell Health in New York.