Suspicion is of the essence with taper corrosion diagnosis

Pain without mechanical explanation may signal taper corrosion.

The risk of taper corrosion following total hip arthroplasty has recently garnered the attention of the orthopedic community. In interviews with Orthopedics Today, sources questioned whether current attention to this phenomenon is due to an increase in occurrence of taper corrosion or a greater awareness among orthopedic surgeons of the problem.

“Right now, [we are trying] to figure out how much of this is a real increase in the rate of taper corrosion vs. just increased awareness,” Tad M. Mabry, MD, consultant and assistant professor of orthopedic surgery at Mayo Clinic, told Orthopedics Today. “Were there patients in years past that we just said, ‘well, they have trochanteric bursitis and that is that,’ and we never investigated for it?”

This increased interest in taper corrosion has led surgeons to consider how and why it occurs, how to treat it and the implant-related factors, Mabry said.

Source: Jamey DeBerry, MAA

Multiple causes of taper corrosion

Thomas P. Schmalzried, MD, Section Editor, Joint Reconstruction for Orthopedics Today, said taper corrosion may not be caused by one specific factor.

A consistent feature associated with taper corrosion is the inclusion of a cobalt-chrome femoral head with a modular connection to a femoral stem, according to Mabry.

“It seems like the mixture of a cobalt-chrome femoral head with a modular junction or the dual modular-neck total hip implants that had a cobalt-chrome modular junction, that seems to be ... a key component to [taper corrosion] taking place so far,” Mabry said.

Wayne G. Paprosky, MD, FACS, suggested surgeons who choose a metal head for THA dry the taper and the inside of the femoral ball to reduce the risk of taper corrosion.

Several sources told Orthopedics Today assembly of the taper junction may also contribute to later corrosion.

“If you assemble the taper in clean conditions as per the manufacturers’ recommendations, you are not going to get mechanical-assisted crevice corrosion,” Schmalzried said.

He said to properly seat the ball and engage the taper, manufacturers recommend the force of the axial blow be directed in line with the neck, which can be a challenge to achieve with small incisions.

“When [taper corrosion] happens, what that says is the conditions the taper was intended to have were not met and therefore the taper breaks down over time,” Schmalzried said.

Changes in design

Changes to the design of the tapers, which inadvertently made these more flexible, and the creation of dual modular necks have also led to mechanically assisted crevice corrosion, according to William L. Griffin, MD, co-director of OrthoCarolina Hip and Knee Center and chair of OrthoCarolina Research Institute.

“We did not have [dual modular necks] 10 years ago. So, I think that was a self-inflicted attempt to make a design improvement,” Griffin said. “It may help the biomechanics of the hip joint, but it hurts the biomechanics of the prosthesis itself and is prone to corrosion,” he said.

Use of larger femoral heads can also increase loading on the taper, Michael M. Morlock, PhD, professor at Hamburg University of Technology in Hamburg, Germany, said.

“The main reason for taper corrosion is always that the micromotion, the relative motion at the junction between the head and the stem, is too large,” Morlock told Orthopedics Today. “That is one of the reasons why the frequency has been increasing over the years especially since the surgeons in the U.S. have started using larger femoral heads in which ... the load the taper connection has to sustain is higher due to the higher friction moment of larger heads. That means the risk that there is micromotion is [greater].”

However, research has shown it is not the size of the head that leads to a higher risk of taper corrosion, but increased offset at the neck and increased load, which places more stress on the taper junction, Griffin said.

“There is a good award-winning paper from the Hip Society that showed that it was not necessarily head size, but taper design, component materials and the length of time of implantation that creates the increased risk of corrosion,” he told Orthopedics Today, noting this study by Triantafyllopoulos and colleagues was published in 2016.

Misdiagnosis possible

Although there may be a high incidence of taper corrosion after THA at specific centers due to use of a specific stem design, in general it is a rare occurrence with an incidence of less than 1% in the United States, Griffin said.

Diagnosis of taper corrosion may not be straightforward because patients present with symptoms that range from slight stiffness, discomfort or muscle weakness or slight to severe pain without any other mechanical explanation, according to Paprosky, a professor of orthopedic surgery at Rush University Medical Center.

Schmalzried told Orthopedics Today some patients may be asymptomatic.

Often taper corrosion may be misdiagnosed as trochanteric bursitis, according to Mabry, or it could be missed on radiological exam because it may present as a small amount of osteolysis.

“Sometimes people do not pay much attention when they see a little bit of osteolysis, but from an orthopedic surgeon and radiologist standpoint, if they see a little bit of osteolysis around otherwise well-fixed implants that have a cobalt-chrome junction in them, I think one has to at least start thinking about whether taper corrosion could be involved,” he said.

Orthopedic surgeons have become comfortable with modular heads in the past 40 years, so they may not automatically suspect taper corrosion as the reason for unexplained hip pain after THA with a cobalt-chrome femoral head, according to Griffin.

“Taper corrosion is not the first thing they think of when somebody starts having pain,” Griffin said. “They may be looking for back pain or infection and, if they are unable to identify why the patient hurts, it is a good idea to go ahead and check metal ion levels.”

Infection vs taper corrosion

Although orthopedic surgeons are accustomed to evaluating metal ion levels in patients with metal-on-metal hips, Griffin said they may not order metal ion level tests for unexplained pain with metal-on-polyethylene femoral heads as these implants are not usually associated with the same problems as metal-on-metal articulations.

However, patients who present with pain without a mechanical explanation should be assessed for infection and taper corrosion because these conditions can develop either separately or in conjunction with one another, Mabry said.

“You still have that exact concern about infection and you would have to specifically search for that,” Mabry said, and noted that in patients who underwent THA with a modular junction that included cobalt chrome, taper corrosion should be added to the list of factors that may potentially contribute to postoperative problems.

“It is important that people know that there is nowhere that says you cannot have both,” he said.

According to Paprosky, surgeons should review the patient’s C-reactive protein and erythrocyte sedimentation rate to help rule out infection, as well as perform metal ion level studies to check for serum levels of cobalt and chromium. Patients with elevated cobalt and chromium levels should then undergo metal artifact reduction sequence (MARS) MRI, which can help identify fluid collection or damage to the muscles, he said.

“If you have normal metal ion levels, you would not get a MARS MRI scan. But, if you have a metal-on-polyethylene articulation, there should not be any elevation of metal ions and, even if you get levels in the one to two range, you should be thinking about taper corrosion,” Griffin said.

Patients who have elevated ions and a fluid collection on MARS MRI scan should have ion tests and MRI scans repeated in 6 months, which will give the surgeon an understanding over time and can indicate whether the process is progressing, according to Schmalzried.

“If the clinical condition, ion levels and MRI findings are essentially unchanged, annual assessments are generally sufficient,” he said.

‘Time is of the essence’

Taper corrosion also has no time frame for occurrence, according to Paprosky, who told Orthopedics Today patients who are hypersensitive to metal debris from an implant may present with symptoms sooner.

“One of the tricks is there is certainly nothing that is unique or specific to it,” Mabry said. “One of the most important things is for people to understand that condition is out there as a cause of pain and/or weakness after hip replacement and it can present fairly early, within a few months, or it can present many years afterward.”

Once a patient is diagnosed with taper corrosion, “time is of the essence” to prevent further complications, such as damage to the tissues, muscles and bones around the hip joint, Mabry said.

“We do not know the full answer right now, but the consideration is that it is a process that is not going to stop, and it is not ever going to get better on its own. It is only going to get worse,” he said.

Schmalzried said surgeons must decide whether MARS MRI results are “significant enough to recommend revision surgery.”

“There is not a good, non-surgical treatment, so to speak, so I think you would have to look at all factors related to the patient,” Mabry said. “Oftentimes, in general terms, I think for many patients, earlier surgery would be better to try to prevent further damage to the soft tissue that we have no good way to fix.”

Chrome-cobalt femoral heads with an incidental finding of taper corrosion seen during revision THA in a patient with no symptoms or signs of mechanical damage are best treated by cleaning off the taper and replacing the cobalt-chrome head with a ceramic head that has a titanium sleeve, Griffin said.

“The other situation is when you have one of the dual modular necks and taper corrosion occurs at the base of the neck-stem junction,” he said. “Most of those implants have been recalled, so if it develops from that modular junction, you generally have to revise the femoral component, which may be well-fixed and may require an extended trochanteric osteotomy to get the stem out.”

If MARS MRI shows fluid collection or some damage to the muscle, surgeons should “be prepared for the situation where there may not be any abductor muscles,” Griffin said.

Common complications

If the amount of corrosion stays below a certain threshold, Morlock noted the patient may not realize corrosion is occurring at the junction.

However, Griffin said, “even low levels of ions from taper corrosion can cause significant damage to the tissues.”

According to Paprosky, common complications include early bone loss with possible greater trochanter or lesser trochanter fracture. Further, extensive involvement of the acetabulum may occur which could lead to osteolysis that develops within the socket; minor abductor muscle loss; major abductor muscle loss which could lead to weakening; and complete muscle loss, as well as swelling of the joint from inflammation and dislocation, he said.

“If the taper corrosion is too massive, then the head can get dislocated from the stem,” Morlock said. “That, obviously, is then a big problem, since the patient has something like a major trauma when that is happening.”

Patients with high ion levels may develop a pseudotumor which, depending on the concentration of ions and susceptibility of the patient, may be small or big in size, Griffin said.

“Some patients are more susceptible than others, but ions can kill tissues, like muscles, bones, and there have even been reports of damage to the sciatic nerve from this kind of pseudotumor,” he said.

Surgeons should also be aware of the high postoperative complication rate seen in patients who undergo revision for severe taper corrosion with a dislocation rate of 20% to 25%, an infection rate of 11% and a recurrence rate of adverse reaction of about 6%, Griffin said.

Reduce taper connection loading

With so many unanswered questions, researchers seek to identify the patient-and implant-specific factors that influence taper corrosion, Mabry said.

Morlock said predicting the patient’s risks and the best prevention methods may be difficult to decipher because taper corrosion cannot be simulated in the laboratory setting.

“We are trying to understand how the surface of the taper plays a role in the corrosion process,” he said. “We are trying to understand how the diameter and the length of the taper influence the role of that, but we do know if you want to prevent it right now that the best way is to reduce the loading of the taper connection.”

As research continues to be conducted to find the answers to these questions, Griffin recommends orthopedic surgeons “know the implants [they] are using and their track records and know the implants [they] are evaluating in [their] office and have a high index of suspicion if [patients] have unexplained pain.”

A surgeon’s index of suspicion should be higher for a recalled implant than an implant that has been used for 20 years with no history of problems, Griffin said.

“I think having a low index to evaluate patients, typically starting off with just blood tests and then, depending on what those show or depending on your index of suspicion, adding in some type of advanced imaging like ultrasound or metal suppression MRIs, is important,” Mabry said.

Surgeons also should be careful with the offset and how they assemble the taper. They should avoid using large-diameter heads staying with metal with a 32-mm size or less. For ceramic, a 36-mm head is probably also okay, Morlock said. Use of ceramic heads instead of modular, cobalt-chrome femoral heads may also help reduce the rate of taper corrosion, he noted.

Schmalzried said, “Morlock’s large head position is not supported by other studies with polyethylene bearings. His statement is likely based on analysis of metal-metal hips, many with greater than 40-mm heads and monoblock (metal-bearing) sockets. Taper corrosion can occur regardless of head size, including 28 mm and 32 mm.”

If ceramic heads continue to produce positive outcomes, Mabry said the research into cobalt-chrome femoral heads may potentially be of historical interest.

“If we start to run into problems with ceramic heads for one reason or another and we need to go back to a different type of metallic femoral head, I think that would change the discussion in terms of trying to figure out what was the underlying cause of all of this,” Mabry said. – by Casey Tingle

• References:
• Martin JR, et al. J Arthroplasty. 2016;doi:10.1016/j.arth.2016.05.047.
• Triantafyllopoulos GK, et al. Clin Orthop Relat Res. 2016;doi:10.1007/s11999-015-4468-6.

• For more information:
• William L. Griffin, MD, can be reached at 2001 Vail Ave., Charlotte, NC 28207; email: william.griffin@orthocarolina.com.
• Tad M. Mabry, MD, can be reached at 200 1st St. SW, Rochester, MN 55902; email: madson.rhoda@mayo.edu.
• Michael M. Morlock, PhD, can be reached at Denickestrasse 15, 21073 Hamburg, Germany; email: morlock@tuhh.de.
• Wayne G. Paprosky, MD, FACS, can be reached at 25 N. Winfield Road, Suite 505, Winfield, IL 60190; email: stephanie.giase@rushortho.com.
• Thomas P. Schmalzried, MD, can be reached at Joint Replacement Institute at St. Vincent Medical Center, 2200 West Third St., Suite 400, Los Angeles, CA 90057; email: tpschmalzried@gmail.com.

Disclosures: Griffin reports he is a consultant for and receives royalties from DePuy Synthes, a Johnson & Johnson Company. Morlock reports he receives research support from DePuy Synthes and Ceramtec. Paprosky reports he is a consultant for and receives royalties from Stryker and Zimmer Biomet. Schmalzried reports he receives royalties from DePuy Synthes, a Johnson and Johnson Company. Mabry reports no relevant financial disclosures.

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