Doug Padgett says, “Constrained liners are problematic. We looked at 70 liners and found a mean length of implantation of only 26 months. We noted a tremendous amount of wear on both the outer and inner rims.” “But some do need a constraint, ” argues John Callaghan. “And when we looked at the tripolar design out to ten years there was a 93% success rate.”
This week’s Orthopaedic Crossfire® debate is “Constrained Liners in Revision THA: More Problems than They Solve.” For the proposition is Douglas E. Padgett, M.D. of Hospital for Special Surgery (HSS); against the proposition is John J. Callaghan, M.D. from the University of Iowa. Moderating is Daniel J. Berry, M.D. from Mayo Clinic in Minnesota.
Dr. Padgett: “Today’s thesis is that it’s better to avoid/prevent than treat in terms of instability, and constrained liners are the last resort. Dislocation remains a problem for surgeon and patient. Kevin Bozic has taught us that instability remains the number one reason for revision in the U.S. It’s so prevalent that at the Hip Clinic at the University of Iowa they are very proactive in this regard. This was noted by Dr. Callaghan recently, who advised a patient, ‘And when your hip pops out, go to the ER and ask for the resident on call and tell them you came from Mayo.’”
“The factors associated with instability are complex, and include patient, surgeon, and implant issues. Thirty years of THA [total hip arthroplasty] data from Mayo on the cumulative dislocation rate show that head size influences instability; the cumulative risk was estimated to be about 7% at 25 years. If you dislocate once you have at least a 50% chance of dislocating again.”
“And bracing? The data is awful…there’s about a 50/50 chance that bracing will help. If you determine that the cause of instability is component orientation, then changing components should solve the problem. Unfortunately, it was only successful in 70% of cases in the original Mayo study.”
“This led us to the age of constraint…poor results with revision. Most manufacturers had at least one type of constrained design. Our group—and John—reported on the high success rate at two to three years (94-96%). Unfortunately this is subject to the effect of time. At HSS we wrote up the modes of failure of the constrained implants whether they were pulled out of pelvis, whether or not they re-dislocated, whether there were material problems.”
“We looked at our retrieval collection—70 liners. The mean length of implantation was only 26 months in this group. The indications for the use of these constrained liners were: prophylaxis in a third and prevention of recurrent instability in another third. We noted a tremendous amount of wear on both the outer and inner rims. Obviously, with these well-functioning liners that were removed for infection, there was no difference in the extent of damage between the two.”
“Recently we had a 71-year-old female with rheumatoid arthritis who at four years postop had recurrent dislocations. It was revised to a dual mobility last year, had a closed reduction in the ER. The liner was sitting in the flank, so I’m not sure if the dual mobility is going to solve the problem.”
“If we do a critical analysis of the unstable THR [total hip replacement] I would suggest using these radiographic criteria: looking at the socket, stem, and true lateral to assess version. In most cases you will find a problem. We looked at 700 hips from our registry; the biggest issue was the failure to reconstruct proper offset on both the socket and the femoral head side.”
“We found that at our institution the majority of unstable hips were in sub-optimal implant position. We now advise that if it’s sub-optimal, fix it! The options are to revise the cup, revise the stem, use larger diameter heads, and potentially offset liners. In a case of recurrent instability following revision we had a retroverted cup…we revised the cup. In another case there was a retroverted stem; we revised the stem.”
“Constraint should be used when there is no other option. In conclusion, constrained liners create more problems than they solve.”
Dr. Callaghan: “There’s no question that larger head sizes can control a lot of the problems today. The larger heads don’t appear to be wearing. In a hip simulator they do still show that there’s more wear with these larger heads, but I’m not sure we can say that this will definitely be the case with larger heads.”
“Our biggest problem now is becoming the trunion issues with the larger heads…especially as you get up around 40mm. There is good clinical evidence showing that big heads are not enough. In work by Lachiewicz where they used 36 and 40mm heads there was a 4.6% early dislocation rate. Beaule was one of the first to use large heads in revision surgery; he had a 9% prevalence of dislocation.”
“King and Ries have shown that the problem becomes greater when your abductors are off. In one group of 28mm heads there was an absent abductor and a 40% dislocation rate. In another group of 36mm heads there was an absent abductor and a 33% dislocation rate. We must remember to always check the patient during the physical exam and ensure that their abductor is functioning. With metal-metal we’ve been seeing situations where the abductors are completely necrotic. I’ve been putting in constrained liners in a number of those folks.”
“So why have constrained liners gotten a bad rap? There are different kinds of constrained liners; some capture between the head and polyethylene and some capture at a distant site. When you look at those that capture between the head and the liner there’s no question a very high re-dislocation rate. We looked at those with tripolar type of designs and found that about 70-90% of the movement is at the bipolar, so they don’t actually lose the constraint. When we looked at the tripolar design out to ten years there was a 93% success rate; it was only the younger patients that had failures.
“The acetabular and femoral revision rates at ten years were reasonable (5% and 3%)…just a bit higher than in revision surgery, but these were also complex cases. Osteolysis was low (2%). You can also cement a liner into the shell if you use a number of techniques.”
“Yes, we had failures, but they were related to technique such as an abducted cup, one where there was an extended lip down inferiorly (the bipolar will pop out of the tripolar), and you can’t put it on a bunch of bone graft.”
“Some people do need a constraint. Doug would sleep a lot easier if he would use it on occasion. We are still liberal with the use of constrained liners with elderly patients, especially in people with deficient abductor musculature.”
Moderator Berry: “Can we come to some agreement on current indications for a constrained implant? Doug?”
Dr. Padgett: “I think that would be neuromuscular patients and perhaps those with deficient abductors.”
Moderator Berry: “How about the patient who’s got all the other implants and you can’t determine why they’re coming out?”
Dr. Padgett: “That becomes problematic in my hands because that’s not going to prevent dislocation. The issue I have with constrained liners is that when they dislocate that’s not a, ‘I’m going to Dr. Doug’s clinic at New York Hospital.’ Rather we’re not able to successfully close reduce those patients and they buy themselves another operation. My concern is the overutilization of this technology. So I don’t think identification of what you see as the high risk patients—like a hyper mobile woman who’s undergoing primary hip replacement. As a prophylactic measure I think that is overused.”
Moderator Berry: “Good point. Just because you’re afraid that someone might become a dislocator you’re worried about overusing technology that has accompanying risks? John, who do you think should not get a constrained liner?”
Dr. Callaghan: “Any patient under age 50 I would try these other things…tripolar, dual mobility. Maybe I’ll be back in there, but I’ll accept it in those patients…with those other patients I mentioned I just want one operation. You should avoid constrained liners when you do a big acetabular revision. You’ve got all these screws in there—and screws can be problematic—and you have bone graft. I think nowadays you should put a tripolar in and see how it does…if you must revise so be it.”
Moderator Berry: “Let’s say you’ve done a big acetabular revision and you’re worried about cup fixation. That’s the one you’re going to worry about going to constrained because that’s going to stretch those interfaces in that first year?”
Dr. Callaghan: “Absolutely.”
Moderator Berry: “Give me you’re top technical tips on avoiding failure of a constrained implant.”
Dr. Callaghan: “I used to think that the extended lip on the tripolar was a bad idea. Now I think it’s a very good idea…because usually there’s going to be one direction that’s the biggest problem for the patient. The problem with some of the newer cups—even the tripolar one—is that they have a rim on both sides and you can impinge on the other side of that. I don’t use those; I use the old style. I put the extended lip in the direction that the patient’s been dislocating. I accept the fact that you could have a problem the other way.”
Dr. Callaghan: “Absolutely.”
Moderator Berry: “Doug?”
Dr. Padgett: “You heard what John said. You ignore that and do the opposite. Don’t use an elevated liner because in our series that’s where they all wore…and you have broken rings, poly wear, etc. I think that it actually has been an advantage with the lower profile devices.”
Dr. Callaghan: “There’s not enough experience with those yet for you to have in your lab, but you’ll get more of those.”
Moderator Berry: “So we all agree that constrained implants are more at risk for impingement than nonconstrained, just by virtue of the way they’re designed. Would you agree that if you’re going to do constrained you should put trials in and try to figure out how to position them?”
Dr. Callaghan: “I agree.”
Dr. Padgett: “I agree 100%.
Moderator Berry: “Thank you both.”
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