Here’s some data for the Duraloc focal constraint design, 16% dislocation rate, I think this is Craig’s paper (Della Valle CJ, J Arthroplasty 2005). The S-ROM, focal constraint, not the tripolar constraint, 18% dislocation rate (Berend KR, J Arthroplasty 2005). The Trilogy system, again, focal constraint, 12% dislocation rate (Andersen AV, ISRN Orthopedics 2013). Another Trilogy, focal constraint, 19% dislocation rate (Chalmers BP, J Arthroplasty 2016). And a tripolar system (Osteonics), 101 revision total hips using the tripolar 10.2-year follow-up—dislocation rate, 6% (Bremmer BR, J Arthroplasty 2003).
I think there is a place for the constrained liner in some of these more complex revisions we do. We did demonstrate joint stability in over 96%; there are issues in this more complex group of patients that can cause a problem.
When you look at tripolar constrained sockets, they are probably best for those with severe neuromuscular disease; Parkinson’s and things like that; those with an absent abductor mechanism—although Craig had some data where the dual mobility looks good in those patients; patients that fail with the dual mobility. And I have concerns about the use of these dissimilar metals in the modular systems as we look long term.
Moderator Trousdale: Routine primary total hip replacement, fair to say no role for dual mobility?
Dr. Della Valle: In my practice, no role.
Dr. Sculco: I believe there is a role for dual mobility in the primary hip and I’m talking about the older female patient.
Moderator Trousdale: Yeah, so high-risk instability patient.
Dr. Sculco:Right, that high-risk primary population is a good place for dual mobility.
Moderator Trousdale: Craig, for routine revision surgery, they’re all high risk for instability, of course, but no terrible back problems, no muscle problems, fixed bearing is the gold standard for total hip?
Dr. Della Valle: I’d still think so. I’m still using a large head, but I wouldn’t fault someone for using a dual mobility in a revision.
Dr. Sculco: Yeah. I agree with that. I think if it’s a chip shot revision, bone quality is good, soft tissues are good, dual mobility is an option and the modular dual mobility is a very good option for it and I would not again fault for using it.
Moderator Trousdale: Tom brought up the corrosion issue so let me give a clinical scenario: 60-year-old patient, trunnion problem, abductor mechanisms compromised, certainly ultra-high risk for instability…
Dr. Della Valle: So that’s the exact scenario where I worry because I want to be able to monitor that patient post-operatively. If we use a modular dual mobility design we are putting in another junction that could potentially generate cobalt or chromium. So, if I’m trying to monitor them, I try to avoid using a modular dual mobility in that specific scenario. They also are high risk for dislocation and if they are abductor deficient then I might actually use a constrained liner because I don’t want to put in that extra metal-metal modular interface.
Dr. Sculco: Yeah, I think that’s actually the ideal setting for a constrained acetabular component. Very poor soft tissues, the abductor mechanisms have been mucked up, the bone is not great, you’re worried about the metal-on-metal potential problem. I think that is the ideal setting for a constrained socket.
