“Constraint should be reserved for cases where there are no other options. These liners can compromise fixation and they don’t always work, ” argues Doug Padgett. “Failure with constrained liners is caused by either poor judgment or poor technique, ” counters Larry Dorr. “Dual mobility is hot stuff, but it’s going up against the tried and true constrained liner.”
This week’s Orthopaedic Crossfire® debate is “Use of Constrained Sockets in Revision THA: More Problems Than They Solve.” For the proposition is Douglas Padgett, M.D. from Hospital for Special Surgery in New York. Lawrence Dorr, M.D. of Keck Medical Center of USC in Los Angeles is in opposition. Moderating is Robert Trousdale, M.D. of the Mayo Clinic.
Dr. Padgett: “Larry, you’re wrong. Instability factors are complex; we know that for primary hips, patient, surgeon, and implant factors are all involved. But there are unique issues in revision surgery and the priorities are to fix it and make it stable so that it doesn’t pop out. Kevin Bozic has shown us the magnitude of the problem…instability is the number one reason for revision. The results of revision hip, however, in every single series: instability, instability, and instability. Why? What holds a hip in place? Soft tissue constraints. The role of soft tissues in reducing instability in primary hips—mostly observational work from our institution—noted that with enhanced soft tissue repairs dislocation rates decreased.”
“As for soft tissues in revision work, the predicate example…simple liner head exchange; at 15 years never had problems with instability. Take out the liner, remove the head, and put it back in without changing component position. What is the number one problem? Instability…suggesting there are soft tissue problems.”
“What about alignment? The Lewinnek safe zone is often misquoted. In our work on 7, 000 total hips we found that it doesn’t exist. Even if it did, can you hit it? The guys at Massachusetts General couldn’t. We used the robot and we hit it, but they still dislocated. Why is this? I would like to thank Larry for thinking about spinal-pelvic alignment, pelvic tilt, pelvic obliquity, as well as 3D images.”
“So why not go with more constraint? We were early adapters of this technology, and of the treatment in revision. We reported our success, along with John Callaghan from Iowa. Like most things it is subject to the effects of time. Merlot grapes are either going to become a $2, 000 bottle of wine or they are going to become red wine vinegar.”
“My concern is that these constrained liners can compromise fixation. And they don’t always work. You could have a simple problem like ring breakage…the big ball is out, the small ball is out, or the entire ball is out. What about dual mobility? It has had success in high risk groups, preventing dislocation in the fracture group…and it is increasingly used in revision. But there are problems with dual mobility including intraprosthetic dislocation.”
“In revision work we need to focus on fixation. Also, use bigger heads. A randomized controlled trial from Rush and Vancouver clearly demonstrated that larger heads were effective in reducing instability rates. It’s also important to repair the soft tissues, reestablishing the capsular, check range of motion, develop a robust capsular flap, reattach through drill holes, and consider prophylactic bracing. That is sketchy…I think it’s better to be stiff and stable than flexible and unstable.”
“In summary, I think constraint should be used only if there is truly no other option, such as in patients whose muscles are compromised or who have cognitive dysfunction. But constrained liners do cause more problems than they solve.”
Dr. Dorr: “We’re talking about patients in whom there is a loss of biological constraint of the hip. In a primary hip replacement you have this as well as mechanical constraint. In many revisions you don’t have good biological constraint. There is loss of the abductor function and a very weak or absent capsule. And let’s further define this patient as being 70 years old.”
“With this type of patient you can use a constrained liner if your surgical technique and judgment is good. It’s not difficult and every one of you can do it. If you hear of someone having 25% failure with constrained liners then either their judgment or their technique was not good.”
“First of all, the liner has to be press fit against the metal edge. You can’t worry about the thickness of the cement column. You can’t use a small liner inside a big cup, and try to get a 4mm cement column. Also, you need a mechanical interlock for the cement, which just means that you roughen up the plastic and the metal. And it’s best if you don’t use a hood.”
“Failures are caused by altering that technique. You try to tilt the liner to change the version because your component position isn’t good…or you use too small (or big) of a liner. So my technical tips are to use a power drill to scratch the implant so that you get the mechanical interlock. Use the cement with more liquid because you’ve got to get that to press fit. If you let the cement get doughy then you’ll have trouble getting the liner all the way into the cup. And if you have rotational pegs take them off with a carbide bit and leave the pressurization on until the cement is hard outside of the body.”
“I don’t like a hood because it can increase impingement. We get really good range of motion with this if the components are in good position. And when we cement, we put the ring halfway in because if you get cement into the ring groove then you’re not going to be able to get the ring to seat and lock into the plastic afterwards.”
“Dual mobility is hot stuff and it’s going up against the tried and true constrained liner. So in this match up the constrained liner is going to show everyone exactly what it can do. It can be done in all primaries and revisions, you won’t have any dislocations, and it will last forever.”
Moderator Trousdale: “So Doug what is your absolute indication for a constrained liner?”
Dr. Padgett: “In the revision setting it would be in those who are muscularly compromised…or perhaps the patient that has global soft tissue deficiency.”
Moderator Trousdale: “Larry, what about the position of the native socket in revision hip/instability situations?”
Dr. Dorr: “You can’t compensate for bad component position with a constrained liner. Nor can you tilt the liner to try and change the version of the cup. That’s going to cause failure…it’s going to cause impingement and flip out. The cement isn’t that strong. It’s got to be press fit against the metal shell.”
Moderator Trousdale: “Does fixation of the socket matter? Are you happy to put in a constrained liner into a well positioned socket that’s well fixed or can you put a constrained liner in ‘fresh’ into a complex revision surgery?”
Dr. Dorr: “You can always cement it into a well fixed cup. I’ve used it for 20 years and only had 3 failures; 2 of them were my own fault. But let’s say you’ve got a bad revision situation with bad acetabular bone and you have compromised fixation of the cup…and then you use the constrained liner. If I had to do it in that situation because I had no medius and no capsule and I needed mechanical constraint, I’d put that patient in a cast postoperatively to let the bone heal and to get some static control.”
Moderator Trousdale: “Doug, how would you handle that?”
Dr. Padgett: “The priority there would be fixation. I would lean towards not using a constrained liner, and I would use a big head if there are any soft tissues to repair the capsule. I would probably use a brace. I’d use a cup that can mate with a favorable constraining device such that if the patient becomes unstable later then I’d feel confident that there is a good option.”
Moderator Trousdale: “Larry, can you cement a constrained liner into a solid cobalt-chrome monopiece cup that was a metal-metal bearing?”
Dr. Dorr: “Sure. You can scratch it up and get the mechanical interlock.”
Moderator Trousdale: “Titanium scratches pretty well, but what are your tricks for scratching cobalt-chrome?”
Dr. Dorr: “Just use a carbide bit with an Anspach or a Midas.”
Dr. Padgett: “It may be easier to make multiple perforations in it…to actually drill right into the cobalt-chrome cup.”
Moderator Trousdale: “We grouped constrained liners all in the same category. Are some better performers than others? Also, please comment on the range of motion patients get with various constrained liners.”
Dr. Padgett: “They run the gamut from the less constrained dual mobility options to the more constraining of the tripolar designs. I think the ones that are simply ring-locked may be less predictable in their success. The most success we’ve had is with the tripolar design.”
Moderator Trousdale: “Larry, regarding the cup you showed, how much flexion does that patient get before the neck impinges on the constrained locking ring?”
Dr. Dorr: “If you have a good combined anteversion of your cup and stem—and remember that the cup itself is usually not the problem as far as dislocation. There are papers showing that the combined anteversion causes dislocation. So if your combined anteversion is good, and you cement in a liner without a hood, then the range of motion isn’t much different.”
Moderator Trousdale: “Thank you, gentlemen.”
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