Surgeons question risk of mixing, matching hip arthroplasty components

Despite warnings from orthopaedic manufacturers to only use components from the same manufacturer in total hip arthroplasty procedures, the practice of mixing and matching components from more than one manufacturer is common in Europe, according to sources who spoke with Orthopaedics Today Europe.

Keith Tucker, MB, BS, FRCS, orthopaedic surgeon of Norwich, United Kingdom, and colleagues recently conducted a study using data in the National Joint Registry of England and Wales to determine how many total hip arthroplasty (THA) procedures were completed by surgeons who mixed and matched components from different manufacturers. They found more than 93,000 cases, out of an approximate 620,000 total procedures performed between 2003 and 2013, in which components were mixed. More than 48,000 cases included stems and heads from one manufacturer mixed with polyethylene cemented cups from another manufacturer, Tucker noted.

Mixing, matching frequently done

Tucker told Orthopaedics Today Europe, however, that mixing and matching components from different manufacturers did not necessarily lead to a greater rate of revision or complications.

“The best hip replacement implant in the National Joint Registry of England and Wales that has the best performance is the Exeter stem (Stryker) used in combination with an acetabular component, the Elite Plus Cemented Cup (DePuy Synthes). That is the best combination. A huge number of those have been done. People have been mixing and matching hard heads with soft liners — high-density polyethylene — for years with very good results,” Tucker said.

Stemmed, large head metal-on-metal (MoM) components are always harmful, whether they are from the same manufacturer or mixed-and-match, according to Tucker. There is also no evidence yet that ceramic-on-ceramic “mix and match” components for a THA result in problems for patients, he said.

Seek array of reliable implants

However, despite the commonality of mixing and matching THA components, not all surgeons do this.

Surgeons should never become so dependent on one type of component they have to use it in every primary THA procedure, Eleftherios Tsiridis, MD, PhD, FRCS, of Academic Orthopaedic Unit, PapaGeorgiou Teaching Hospital of Aristotle University Medical School of Thessaloniki, Greece, said.

“People get used to certain implants, which is a good thing. I support this. However, it does not mean that every shoe can fit every foot. You cannot use just one implant to do every case. An arthroplasty surgeon must have different kinds of implants in his or her armamentarium to fit different kinds of cases, so they do not have to mix and match,” Tsiridis told Orthopaedics Today Europe.

When surgeons have an array of cemented or uncemented implants available, it helps them to be more successful with hip replacement procedures. They are better versed and more proficient with a number of different components from different companies, as a result. Not only does this make them a better surgeon, but they are also less dependent on mixing and matching components, he said.

Increase the armamentarium

Tsiridis suggested surgeons familiarize themselves with several different implant designs and then choose a certain line of implant for each case type they see. This will at least limit the need to mix and match components from different manufacturers.

“It is not necessary mix and match components anymore and it is better to just keep things simple. Keep it simple to succeed. This is very sound advice,” he said.

Rob Nelissen, MD, PhD, of Leiden University Medical Center, in Leiden, The Netherlands, told Orthopaedics Today Europe he has never mixed and matched components from different manufacturers during primary THA.

If the tapers of the femoral stem and the head are slightly different from one company’s component to another, it can put patients at unnecessary risk, he said.

“The general message is do not mix and match different products from different companies. The companies have different quality controls and they may have different quality standards (i.e., tolerance levels of surface finishing),” Nelissen said.

However, according to Nelissen, mixing and matching components from different manufacturers is a generally accepted practice for revision THA.

Acceptable for revisions

During revisions, Nelissen said the surgeon always balances between more benefit for his or her patient and less risk for the patient, and will, in general, not remove a well-functioning implant (i.e., removal of loosened acetabulum, but not a well-fixed femoral stem).

However, “it will be problematic if the surgeon needs to revise an acetabular component that is 20 years old and the matching femoral head component is damaged, while the femoral stem is firmly fixed within the bone, but that femoral head is no longer on hand or available for purchase. For that matter, information on article codes of the primary implant will avoid surprises during surgery, thus underscoring the importance of registries, which should include this information,” he said.

Mixing and matching components is commonly done, Nelissen said in discussing the results of Tucker’s study. However, the trust of a surgeon in specifications of a company’s product can get them into trouble when they decide to mix and match components because the dimensions noted (i.e., taper 12/14 only tells something about the apex and base of the taper, but not its length, which will determine taper inclination) can be misleading, he said.

Dimensions are misleading

According to Nelissen, some of the issues concerning THA component dimensions may also stem from misunderstandings about what CE marking means. Some surgeons believe a product with the CE mark has good clinical evidence to support its use, but that is not true. It just means the product “is a look-alike of a former product or to put it bluntly: will not rust,” Nelissen said. Furthermore, in Europe, the mark means a product has been approved for sale by one of the notifying bodies, he said.

The same is true for the dimensions of products that are given a CE mark, Nelissen told Orthopaedics Today Europe.

“[Surgeons] do not think of the fact there are slight differences that you cannot see with your bare eye” when it comes to sizes of THA products from different companies marked on the packaging,” he said, noting dimensions printed on a box may read 28 mm or 30 mm for a femoral head, when in reality it measures 32.0001 mm. “When you have different companies, it can be 32.0004 mm, which might be a mismatch,” Nelissen said.

A study by Nelissen and colleagues in the Journal of BioMedical Materials in 2001 that examined component wear in hip replacement surgery showed components that do not fit perfectly together can cause surface damage. Secondly, they found mixing components from different companies may introduce slightly different chemical materials that can react negatively to one another and cause galvanic corrosion.

Measurements may be incorrect

Another possible problem is when manufacturers do not list the exact dimensions for their implants, according to Nelissen.

“Doctors should be aware of the fact that size on the box is without decimals. Surgeons should be aware of the fact that a 28-mm head — I am using that as an example because it is the most commonly used head size — it only says 28 mm, but could actually measure at 28.01 mm. When you mix a 28.01 mm component with a 28 mm diameter of a different company’s component (with different measurement tolerances), there will be a minimal mismatch. There are a certain number of surgeons who are not aware of that fact,” Nelissen said.

A study published in 2015 in BioMed Research International analyzed the head-neck taper corrosion in THA implants. The researchers compared 12/14 tapers from two companies and found the components were a complete mismatch.

The 12/14 taper from company A (trunnion length, 11.8 mm; proximal cone diameter, 12.6 mm; distal cone diameter, 13.7 mm) was compared with a 12/14 taper from company B (trunnion length, 11.20 mm; proximal cone diameter, 12.60 mm; distal cone diameter, 13.65 mm). The cone angles of the two implants were 5°42´30´´ and 5°67´, respectively, which was a difference of 0.412°. This was five times more than the 0.075° threshold for mismatch, the researchers noted.

Those researchers also noted tapers should never be mismatched in a THA procedure, even if they are from the same company or are quoted as being the same size.

Excessive wear

Klaus-Peter Günther, MD, of Universitätsklinik Carl-Gustav Carus, in Dresden, Germany, who is an Orthopaedics Today Europe Editorial Board member, agreed with Nelissen. He said different manufacturers can have completely different taper geometries for their components.

“If a surgeon combines the taper from manufacturer A with the head from manufacturer B, it can theoretically cause problems. The same is true for a combination of a head or ball with an inlay from a different manufacturer. They can have different clearances, biomechanical properties, etc., and a combination of those different products can cause biomechanical problems in patients,” he said.

In Germany, there have been some problems with broken tapers or excessive wear when surgeons mixed and matched components, Günther said.

Risk of litigation

In addition, Günther said it is clear in Germany that when a surgeon decides to mix and match components for THAs, he or she is legally considered a “designer” of a new hip device.

“He is a producing a new implant, which is not legally provided by manufacturer A or B. As soon as he is leaving the recommendations of the manufacturer, who always recommend a combination of their own implants, he is making himself as a new producer,” Günther told Orthopaedics Today Europe.

This practice can certainly lead to litigation, which is now also a distinct possibility in the United Kingdom, Tucker said. There is now talk of potential litigation from patients in England against the manufacturers, hospitals and surgeons for complications from mixed-and-matched MoM components used in hip arthroplasty, he noted.

More than 2,100 MoM, mixed-and-matched THA procedures were performed between 2003 and 2013, according to data in Tucker’s study.

“Certainly, there is an indication there is going to be litigation against hospitals or surgeons where they have mixed and matched MoM components. Obviously, that is worrying for the surgeons and it is worrying for the hospitals and worrying for the insurers,” Tucker said.

A known problem?

In these instances, manufacturers of the implants are claiming surgeons are to blame for the problems because they went “off-label” and mixed and matched the components without the manufacturers’ consent.

However, Tucker said manufacturers knew for years the practice was occurring throughout the United Kingdom, and they even enabled it.

“Manufacturers were happy to sell 2,000 or 3,000 femoral components without any acetabular component,” he said. “If they are as diligent about patient safety as they say they are in their headlines, they could have been checking up on these hospitals that were buying hundreds of acetabular stems and different cups.”

The next step concerning research into the results with mixed-and-matched THA components is for different types of “off-label” implants to be studied in the lab and rigorously tested to determine their efficiencies and possible failure rates. When this is determined, according to Tucker, surgeons and implant manufacturers will have a better understanding of the dangers, and even benefits, of mixing and matching components from different manufacturers. – by Robert Linnehan

• References:
• Koerten HK, et al. J Biomed Mater Res. 2001;doi:10.1002/1097-4636(20010315)54:43.3.CO;2-1.
• Hussenbocus S, et al. Biomed Res Int. 2015;doi:10.1155/2015/758123.
• Tucker K, et al. Acta Orthop. 2015;doi:10.3109/17453674.2015.1074483.

• For more information:
• Klaus-Peter Günther, MD, can be reached at Fetscherstrasse 74, 01307 Dresden, Germany; email: klaus-peter.guenther@uniklinikum-dresden.de.
• Rob Nelissen, MD, PhD, can be reached at PO Box 9600 (J-11-R), 2300 RC Leiden, Netherlands; email: r.g.h.h.nelissen@lumc.nl.
• Eleftherios Tsiridis, MD, PhD, FRCS, can be reached at 54124 Thessaloniki, Greece; email: etsiridis@doctors.org.uk.
• Keith Tucker, MB, BS, FRCS, can be reached at Old Watton Rd., Norwich, Norfolk NR4 7TD, United Kingdom; email: ktucker77@aol.com.

Disclosures: Günther and Nelissen report no relevant financial disclosures. Tsiridis reports receiving grants from Stryker and DePuy Synthes and is secretary general of the European Hip Society. Tucker reports receiving revenues from a hip implant he designed, which goes into a research grant, and owns stock in Accenturs Medical.

 

Is it acceptable practice to mix and match different manufacturers’ components for primary total hip arthroplasty?

Avoid in primary arthroplasty

The data from the 2014 report of the National Joint Registry of England and Wales seem to reassure surgeons who indulge in this practice. But why do they do it when most manufacturers now provide a full range of carefully matched products for primary hip arthroplasty? The main driver has not been cost, but the search for new materials to reduce the incidence of aseptic loosening attributed to the excessive production of wear particles. This was particularly the case when the “new” acetabular cups were introduced using highly cross-linked polyethylene sterilized by gamma radiation. Initially, not all manufacturers were able to offer this improved material with its reduced wear rates and so “mixing” began. The improved results achieved with these hard-on-soft implant combinations justified the confidence surgeons placed in the tolerances achieved by manufacturers using standard designs.

Many more potential problems emerge when the concept is extended to more complex combinations using harder materials, such as metal-on-metal prostheses and femoral head and stem junctions. Here, slight variations in design can significantly alter the taper, or bearing surface characteristics, resulting in corrosion and fretting with the production of osteolytic wear products.

The risk may be justified in revision surgery, but the practice should be avoided in primary arthroplasty. Should failure occur, it seems probable the surgeon would be judged at fault, even if the quality of one or both implants was found to be deficient.

David L. Hamblen, PhD, FRCS, is an Emeritus Professor of Orthopaedic Surgery at the University of Glasgow, Glasgow, Scotland, and an Orthopaedics Today Europe Editorial Board member.
Disclosure: Hamblen reports no relevant financial disclosures.

Regulatory bodies should allow effective combinations

Although most manufacturers state that in primary total hip arthroplasty (THA) components of the same manufacturer should be used, many surgeons mix and match components of different manufacturers. Because of minor design or material differences, this could create unexpected problems and lead to higher revision rates. The practice of mixing and matching seems to be more commonly used with cemented stems (23% in all-cemented and 41% in hybrid THA) compared with uncemented THA (8%), according to Tucker and colleagues.

In my practice, in principle, components from the same manufacturer are implanted in primary THA. Only in exceptional circumstances, for example when there is insufficient press-fit of an uncemented cup, a cup from a different manufacturer than the stem and head is used.

There is a big difference in types of mix and matching: 1) different stem and head; 2) different head and cup in metal-on-metal (MoM) THA; 3) different head and cup in ceramic-on-ceramic (CoC) THA; and 4) different head and cup in metal-on-polyethylene (MoP) THA.

Despite the proximal and distal diameter being similar, there exist considerable variation regarding the exact dimensions of the trunnion because of differences in taper length, taper angle, manufacturing tolerances and surface finish. (Rajpura and colleagues). Because of this geometric incompatibility between different manufacturers, Tucker’s study showed head and stem components should not be mixed and matched as this results in a significantly higher failure rate (P < .001).

In MoM THA, 99.7% of surgeons use matched components and therefore, the data is too limited to make any conclusions. Because of the high degree of attention on MoM THA in the media and the higher risk of litigation, it is probably better to not mix and match until better evidence is available.

Almost all currently used ceramic bearings are manufactured by the same manufacturer. Therefore, the outer diameter of the femoral head and the inner diameter of the liner of the cup have the same dimensions and mixing and matching could probably be safely done (Tucker and colleagues).

When using a hard-on-soft bearing, implant survivorship is not signicantly lower between the matched cases and the mixed cases where only the cup manufacturer was different regardless of whether a cemented or uncemented stem was used. In fact, in all-cemented THA the overall implant survivorship was better in the mixed group than in the matched group (P = .001) (Tucker and colleagues).

From my point of view, mixing and matching combining a stem and a femoral head from a different manufacturer should not be done because of the significantly higher failure rate. Nowadays, combining a femoral head and cup of different manufacturers also is discouraged and surgeons implanting not approved mixed and matched combinations do so under their own liability, but there is good evidence this can be done safely, especially in CoC and MoP bearing. Some mixed combinations used in high numbers outperform matched combinations and regulatory bodies should definitely allow these combinations in future guidelines to make sure we can offer the best available combination to our patients, even if this means mixing and matching a cup from manufacturer A and a stem-head combination from manufacturer B.

Geert Meermans, MD, is from the Department of Orthopaedics at Bravis Hospital, Bergen op Zoom & Roosendaal, The Netherlands.
Disclosure: Meermans reports he is a consultant to DePuy Synthes.

• References:
• Rajpura A, et al. Hip Int. 2015;doi:10.5301/hipint.5000213.
• Tucker K, et al. Acta Orthop. 2015;doi:10.3109/17453674.2015.1074483.