Source: Cuthbert R, et al. EFORT Open Rev. 2019; doi:10.1302/2058-5241.4.180089.
Disclosures: Abdel reports he receives royalties from Stryker. Della Valle reports he is a consultant for DePuy Synthes and received research support related to dual mobility implants from Zimmer Biomet and Stryker. Markel reports he is a consultant for Smith & Nephew and Stryker. Peters reports he receives royalties from and is a consultant for Zimmer Biomet. Sculco reports no relevant financial disclosures.
September 22, 2021
10 min read
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Surgical optimization is important in use of dual mobility implants

Source: Cuthbert R, et al. EFORT Open Rev. 2019; doi:10.1302/2058-5241.4.180089.
Disclosures: Abdel reports he receives royalties from Stryker. Della Valle reports he is a consultant for DePuy Synthes and received research support related to dual mobility implants from Zimmer Biomet and Stryker. Markel reports he is a consultant for Smith & Nephew and Stryker. Peters reports he receives royalties from and is a consultant for Zimmer Biomet. Sculco reports no relevant financial disclosures.
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Instability has been cited as the most common cause of revision after total hip arthroplasty, with rates of 1% to 4% after primary THA and 10% to 15% after revision THA, according to sources who spoke with Orthopedics Today.

“[Hip instability] is probably the number one complication that we deal with in hip arthroplasty today,” Christopher L. Peters, MD, chief of adult reconstruction at the University of Utah, told Orthopedics Today. “Although there have been a number of strategies employed to try and reduce that, such as anterior approach total hip replacement, it remains an unsolved problem and there certainly are populations of patients we see that have higher dislocation rates.”

Among the patients at higher risk for dislocation after THA are older female patients, according to Thomas P. Sculco, MD, surgeon in chief emeritus at Hospital for Special Surgery.

“They tend to be a little bit more lax, and their proprioception is not quite so good, so their limb control of the leg is not always as good,” Sculco said. “They will put their leg into a bad position and they will dislocate the hip, particularly your thinner, elderly female patients.”

Matthew P. Abdel, MD, the Andrew A. and Mary S. Sugg professor of orthopedic surgery at Mayo Clinic in Rochester, Minnesota, said patients with neurologic disorders, such as Alzheimer’s disease, advanced dementia or nerve issues that lead to weak control of the hip, are also at a higher risk of dislocation. A higher risk of dislocation can be found among patients with previous femur or femoral neck fractures who are converted to THA, Abdel said.

Thomas P. Sculco

Some surgeons have also found a higher rate of dislocation among patients who have spinal-pelvic mobility issues, which is a relatively new area of investigation, according to Peters.

“The last 5 years or so a lot more attention is being paid to patients that have had prior spinal fusion or who have severe arthritis resulting in lumbosacral spine stiffness and, therefore, [they have] reduced pelvic mobility, which leads to an increased risk for dislocation,” Peters said.

Greater risk for dislocation is also linked with patients with good preoperative range of motion, patients who engage in activities that require high range of motion postoperatively, such as yoga and Pilates, as well as with patients who undergo revision THA surgery, according to Craig J. Della Valle, MD, professor of orthopedic surgery and chief of adult reconstructive surgery at Rush University Medical Center.

“In general, patients undergoing revision surgery are at higher risk for dislocation and particularly in instances where they have been multiply operated on and they have damage to their abductor musculature,” Della Valle, who is an Orthopedics Today Editorial Board Member, said.

Enter the dual mobility implant

As a way to reduce the risk of instability after THA, the dual mobility THA implant was introduced in the mid-1970s in France, which incorporated “an additional bearing with the interposition of a mobile polyethylene layer between the prosthetic head and the acetabular shell”, according to a publication by Rory Cuthbert, BSc, MBBS, and colleagues.

However, the advent of the dual mobility implant was short lived due to accelerated wear of the polyethylene acetabular liner, Sculco said.

“[Dual mobility] was sort of abandoned. Then, there was a resurgence about 10 years ago,” he told Orthopedics Today.

This resurgence led to different designs of dual mobility implants that were introduced in the United States, which provided several advantages in primary, as well as revision THA, according to sources interviewed.

In a 2019 systematic review of English and French high-level studies, Nicolas Reina, MD, PhD, and colleagues found patients who received a dual mobility construct for primary and revision THA had a statistically significant decrease in the risk of dislocation, of re-revision or revision for dislocation and of polyethylene wear compared with patients who received non-dual mobility articulations.

“In the primary and revision setting, the English and French spoken literature supported [dual mobility constructs] in a variety of different settings,” Abdel said. “The complications and the risks are still in case reports of small numbers. They do not come out in these big systematic reviews because they are so rare, and they do not happen frequently.”

Reduced dislocation risk

According to Abdel, the reduction in dislocation with use of dual mobility prostheses is due in part to the larger head size.

Matthew P. Abdel

“The actual effective head size is bigger because you have a small head that sits on the trunnion — the hip stem — and then a larger head that is on top of that,” Abdel told Orthopedics Today.

Peters noted the larger head size increases the jump distance of the femoral head, which allows for greater range of motion before either impingement occurs or the femoral head escapes from the acetabulum.

In addition, “There is the theoretical contribution of the dual articulations also adding to some protection against dislocation,” Peters said. “So, by virtue of being able to go to a larger diameter head and then also the dual mobility articulation itself, those things probably contribute to reducing dislocation.”

Dual mobility implants may also have the potential to provide better motion to patients, according to David C. Markel, MD, Michigan Market President of The CORE Institute.

Della Valle said better motion may allow some patients to return to pre-surgical activities that may typically lead to dislocation with use of a conventional hip bearing.

“A lot of patients in the Midwest like to water ski. That always make me nervous, so I will use a dual mobility bearing in patients who are going to get back to those types of activities,” Della Valle said.

Lack of long-term data

However, as is the case with any newer device, longer term data are still needed for dual mobility hip implants, according to Markel. He said one area of interest is the long-term economic impact that dual mobility implants may have on the health care system. Although higher cost has been found to be associated with dual mobility hip implants, Markel noted several studies have reported that dual mobility implants may have equal or less cost compared with conventional THA implants.

“Despite a potentially increased cost of the mobile bearing implant, by limiting a complication like dislocation, the overall cost to a [health] system or to a value-based care system is improved. Using an implant to prevent or avoid a complication is cost-effective,” Markel told Orthopedics Today.

Regarding patient outcomes, Peters said some patients may experience residual anterior hip pain due to irritation caused by the large diameter nature of the dual mobility articulation or possible malseating of the dual mobility articular insert.

“It may be a bit design-specific, but, nevertheless, with a number of designs, there have been reports of malseating of these implants occasionally leading to clinical problems,” Peters said.

Abdel said more research is needed into the appropriate size of the inner head of the dual mobility implant, as well as whether the implant liner should be flush or elevated in relation to the cup.

Adverse local tissue reaction

The short- to mid-term data currently available have also shown conflicting results with regard to the possibilities of implant corrosion and adverse local tissue reaction, which may occur at the interface between the outer titanium acetabular component and the inner cobalt-chromium, modular dual mobility insert, according to Peters.

“The ion levels in most of these studies have been relatively low, but there are some reports on higher ion levels in some of these modular dual mobility implants,” Peters said. “But clinically, it does not seem to be a major problem, at least at short- to mid-term follow-up.”

Sculco said longer-term research should focus on identifying the possibility of polyethylene wear, as well as whether metallic debris is being generated between a titanium shell and a cobalt chromium liner.

“That coupling looks extremely stable and there is little, if any, motion between those two surfaces. It is not like you have a metal head against a metal shell, but still that needs to be further evaluated as we get out to 10 years to be sure that those metal levels, cobalt and chromium particularly, are not starting to elevate,” Sculco said.

Intraprosthetic dissociation

Some reports have also shown a risk of intraprosthetic dissociation among patients with dual mobility THA implants, Peters said, which occurs “when there is a dislocation event with a dual mobility implant and, either during the dislocation or, probably more commonly, during the relocation attempt, there is a dissociation between the outer diameter polyethylene ball and the inner diameter typically ceramic ball,” he said.

Although rare, in patients with dual mobility implants who present with dislocations, to prevent the plastic liner from dislodging upon reinsertion, surgeons should use intraoperative fluoroscopy, Sculco said.

Craig J. Della Valle

“You cannot treat [dual mobility implants] like a regular dislocation of the hip. They are much more complicated and that is a disadvantage,” he said. “If you get a dislocation of a dual mobility, you have to be careful when you reduce them that you do not knock off the plastic liner from the prosthetic femoral head.”

Identify high-risk patients

Despite the need for more research in this area, some proponents of dual mobility THA favor using these hip systems in every patient.

“Although most people would tell you it is completely crazy, I do not think that it is, because I think the risk of dislocation for many patients is probably higher than the theoretical concerns with dual mobility,” Della Valle told Orthopedics Today.

Although patients at high risk for dislocation do benefit from dual mobility implants, Peters said the majority of patients who undergo THA will not experience a dislocation and will have good outcomes when treated with “a tried-and-true implant.”

He said, “To take the leap to using what I would say is still a fairly new technology with unknown longer-term clinical results and potentially longer-term adverse consequences due to the modularity of the system, I do not think that would be a wise choice.”

For surgeons who are interested in using dual mobility implants in patients undergoing THA, Della Valle noted it is important to identify whether the patient is at high risk for a complication.

“If you look at a patient, for example, with a seizure disorder or someone who has had a spinal fusion or something where you know they are at high risk for dislocation, I would not be afraid to use dual mobility in that situation. If they have probably a 2% or more risk of dislocation, then it makes sense to use the dual mobility,” Della Valle said.

Technical pearls for implantation

When performing THA with a dual mobility implant, Markel said surgeons need to be sure there is no debris or tissue in the cup when they reduce a hip that has a large head. Otherwise, the outer bearing will bind up, he said.

“You have to make sure that you wash it out well,” Markel said. “I have a little trick where I fill it up with fluid before I relocate it to hopefully float anything out when it relocates.”

David C. Markel

Della Valle recommends against the use of skirted heads with a dual mobility implant, which could potentially lead to more wear and restrict range of motion. Surgeons should be aware that if they choose to use a monoblock dual mobility cup, the actual implants are oftentimes larger than the stated size on the box, he said.

“Say, for example, you are putting in a 50-mm monoblock dual mobility cup. That cup may be closer to 52-mm in diameter, and you have to understand what that difference is so that you can ream appropriately, particularly if you think the patient has softer bone, to avoid the risk of periprosthetic fracture,” Della Valle said.

Although dual mobility implants may be known to reduce the risk of dislocation, Sculco said surgeons should check the stability of the implant after it is put together, as too much laxity may lead to complications.

Similarly, surgeons should optimize the position of the implants and be sure the modular dual mobility liner is not malpositioned in the shell, according to Della Valle. This can be achieved by having good exposure of the acetabulum and making sure the dual mobility liner is perfectly seated, he said.

“I do not think [dual mobility] is going to compensate for malposition of the implant,” Della Valle said. “We still always need to be meticulous and careful with getting the position of the implants right, as well as trialing intraoperatively to make sure that everything else has been optimized, including leg length, offset and impingement.”

Good addition to armamentarium

Although performing THA with a dual mobility implant may seem complicated, Peters said since the acetabular component insertion is fairly standard, it is not much different than with a conventional implant. He said the biggest difference in clinical workflow is most surgeons will trial a dual mobility implant system or both a dual mobility system and a non-modular larger diameter femoral head to assess how much more stability they are gaining with a dual mobility articulation.

“Otherwise, there is a little extra time on the back table to assemble the two-piece femoral head, but most surgical techs can be trained in that fairly quickly and safely,” Peters said. “The use of [these systems] does not interrupt our normal surgical workflow, whether it is a primary case or a revision case.”

As surgeons decide and start to add dual mobility implants into their armamentarium, Abdel said they must understand the strengths and weaknesses of these constructs.

Peters recommended that surgeons who hope to include dual mobility THA in their offerings keep an eye toward longer-term clinical results.

Despite the current unknowns, Sculco said dual mobility hip implants are an important adjunct when it comes to THA surgery.

“It is a nice technique to have in your armamentarium when you are approaching hip replacements and, particularly, in a higher risk population,” Sculco said. “There is a learning curve in terms of putting the monobloc dual mobility in, but it is not anything that someone who does hip replacements cannot master quickly.”

Click here to read the Point/Counter, "Is THA instability best mitigated with dual mobility systems or larger femoral heads?"