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Benefits of large-head ceramic-on-ceramic THA depend on indications, implant design, implantation
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Data in a few recent international joint replacement registers show an increase in the use of large-head ceramic-on-ceramic total hip arthroplasty, a trend orthopaedic surgeons worldwide are noticing and discussing.
However, orthopaedic surgeons have different definitions of large-head ceramic-on-ceramic (CoC) hip articulations. They have also raised questions about the indications for the procedure, the effect of larger head size on hip dislocation and risk of material fracture, and whether the post-implantation noise and squeaking that is sometimes associated with ceramic hip prostheses are resolved when a prosthesis with a larger femoral head is used.
Claus Varnum, MD, PhD, of Vejle, Denmark, has no personal experience with CoC total hip arthroplasty (THA) done with very large ceramic heads, but has recently noticed more, large heads are being used.
“I have looked into, for instance, the Australian registry and it is clear that, within the last 5 years, it seems there is use of lots of ceramic heads and bearings and these heads are larger, up to 40 mm in diameter,” Varnum told Orthopaedics Today Europe.
The definition of large-head CoC THA is straightforward, according to Stephen E. Graves, MD, of Adelaide, Australia.
“With metal-on-metal (MoM) large head was defined as 36 mm or greater. The same approach applies to head sizes with any other bearing,” he told Orthopaedics Today Europe.
Liner size affected by head size
For the past 40 years, Laurent Sedel, MD, of Paris, a pioneer in CoC THA, has used 32-mm ceramic heads as his hip articulation of choice.
“If you go further, then you have to take into account the size of the liner, because if you enlarge the head, the liner will be thinner and thinner. Then, the problem might come from the liner,” he said.
He told Orthopaedics Today Europe 34-mm or 36-mm diameter heads are large, in his estimation.
However, Sedel is aware of surgeons today who use 40-mm ceramic femoral heads that articulate on ceramic liners in their patients, but said that is a rare practice.
“At the moment, I understand the people who use a larger head use it to avoid dislocation of the hip, to prevent dislocation. But, doing that might increase the risk of liner fracture,” Sedel said.
Ceramic materials used
CoC THA outcomes depend on the ceramic materials used. In Australia, mixed ceramic is now used in CoC THA performed there. It has lower revision rates than either the alumina or zirconia materials used in THA, according to Graves.
With mixed ceramics, “the revision rate for all cause revision for the 36-mm [head] is the same as 32 mm. The revision rate for all-cause revision is less when a 40-mm head is used, but the follow-up in the Australian Orthopaedic Association National Joint Replacement Registry is only 5 years for this head size. Revision for squeaking is rare, as is breakage. There is some evidence to suggest the revision for infection is slightly reduced when a CoC bearing is used compared to crosslinked [XL] polyethylene,” Graves said.
Definitions of large ceramic heads
Eduardo García-Rey, MD, who presented on large-head CoC hips at the EFORT meeting in Geneva, said he and the other orthopaedic surgeons in his unit at Hospital La Paz, in Madrid, never use a ceramic femoral head larger than 32 mm. However, they consider that a large ceramic head compared to a 22-mm or 28-mm head.
García-Rey told Orthopaedics Today Europe about one-third of his patients, who are mostly younger patients or are short or have a small acetabulum, will receive a 28-mm femoral head.
On the other hand, it is an exception for him to use a head larger than 32 mm. Even in a large patient or someone at-risk for hip instability, García-Rey said he would still not select a femoral head size of 36 mm or 40 mm, for example.
“I think the best thing when we use ceramics is the low wear rates,” he said.
Furthermore, osteolysis is practically nonexistent with CoC articulations of any kind, Garcia-Rey noted.
“The new ceramics [available] since the late 1990s have improved all characteristics and the rates of fracture are low, and they are bioinert and tribologically good, regardless of the size [of head used],” García-Rey said.
Revision risk
A study in Lancet in 2012 compared survivorship and revision incidence for MoM hip bearings to other bearing types, such as CoC. Results showed CoC articulations in which larger head sizes were used were associated with improved survival. The investigators, for example, reported 2% and 3.3% 5-year revision rates with 40-mm CoC heads and 28-mm CoC heads, respectively, in men aged 60 years.
Varnum noted that although that study provides some evidence for the use of 40 mm CoC femoral heads, this was not the main focus of the study.
Furthermore, “it was only 1,354 patients with CoC bearings with that large femoral head size, so the number was small,” he said. It may, therefore, be too small from which to draw a conclusion, Varnum said.
Head size based on anatomy
For the CoC THA, Varnum determines the size of femoral head he will implant — 28 mm, 32 mm or 36 mm) based on the patient’s anatomy.
Sedel, who prefers not to use large ceramic heads, said, “I recognized that for a large person with a large acetabulum anatomically, we could go from 32 [mm] to 36 [mm], for example. That is okay because we have still a thick liner so there is not risk of fracture and you retain the advantages of CoC in this configuration.”
He considers someone with a socket larger than 56 mm or 58 mm as large.
“But if you do not have this large acetabulum, then there is no need to go to a larger head. And, I have another argument. That is, with CoC, the couple develops a special fibrous tissue which is dense and this is different from any couple of metal with polyethylene,” Sedel said.
Capsular tissue
Sedel is not alone in his thinking that the lower risk of revision associated with all types of CoC hips is due to the strong fibrous tissue that develops in the area of the hip capsule. He and García-Rey said this tissue is not present immediately after implantation, but some months later.
García-Rey noted more of that fibrous tissue layer is present in patients with CoC THA than in patients with a metal-on-polyethylene THA.
With CoC THA, “the tissue and the capsule around it, after 2 [years] or 3 years, become thicker; thicker than with metal-on-poly. Our dislocations are low,” he said.
Concerns about squeaking
According to Varnum, to date, the rates of CoC THA revision due to squeaking or other noise are low and not a real concern about this type of hip articulation.
Before greater adoption of CoC THA can occur, any concern about squeaking must be addressed, particularly in the U.S. market where it is a major problem, according to Graves.
“A major potential impediment to use is cost,” he said, noting studies must be done into the cost-benefit of CoC bearings compared to other quality bearings that are available.
“The outcome of CoC bearings is excellent but at this point, it is not possible to say that it is better in the long term than ceramic-on-crosslinked polyethylene or metal-on-crosslinked polyethylene,” Graves said.
Dislocations may be avoided
Some orthopaedic surgeons interviewed for this Cover Story said the greatest benefit of large-head CoC THA is it helps mitigate dislocations and may improve the stability of a patient’s hip. According to Varnum, results of a 2013 study by Kostensalo and colleagues suggest risk of revision due to dislocation is similar for femoral head sizes of 32 mm and 36 mm.
Among more than 42,000 patients with different types of bearing, “compared to a 28-mm head, there is no difference in risk for revision due to dislocation between 32 [mm] and 36 mm. So, in relation to dislocation, there should be no difference in these two femoral head sizes,” Varnum said.
According to Graves, “There is increasing stability with increasing head size, however most of that benefit is achieved with a 32-mm head. There may be a further small benefit for some patients by increasing to 36 mm, particularly when a patient has an increased risk of dislocation.”
He noted, however, that at the moment there is little evidence that suggests any further increase in head size beyond 36 mm is associated with further improvement in stability.
Material fracture
Evidence shows there is little increased risk of more fractures with larger CoC heads vs. smaller ones, which is borne out in the literature. Varnum studied survival of CoC THA bearings in the Danish Hip Arthroplasty Registry for his PhD. For CoC vs. metal-on-polyethylene articulations, “we found similar frequency of different revision causes between the two types of bearings, except for component failure where we found that patients with CoC bearings had a greater proportion of revisions due to component failure because there were a few cases of ceramic fracture,” he said.
The general indications of large-head CoC THA are a patient with a large socket or a young, active man.
“I will not recommend a CoC bearing in patients older than 65 years old,” Varnum said.
The indications for using a head size larger than 32 mm or 36 mm are not yet apparent, Graves noted.
“The early outcome of 40-mm heads looks promising. But this is only to 5 years and it is still possible problems may emerge as time progresses,” he said. “With wider use, these problems may emerge and potentially include increasing rate of breakage, increased incidence of groin pain, the development of trunnion problems and possibly third-body wear.” – by Susan M. Rapp
- References:
- Kostensalo I, et al. Acta Orthopaedica 2013; doi:10.3109/17453674.2013.810518.
- Owen DH, et al. Bone Joint J. 2014; doi:10.1302/0301-620X.96B2.32784.
- Pitto RP, et al. Clin Orthop Relat Res. 2016;doi:10.1007/s11999-016-4916-y.
- Pitto RP, et al. Clin Orthop Relat Res. 2015;doi:10.1007/s11999-015-4395-6.
- Smith AJ, et al. Lancet. 2012;doi.org/10.1016/S0140-6736(12)60353-5.
- Varnum C, et al. Acta Orthopaedica. 2015; doi:10.3109/17453674.2015.1012975.
- For more information:
- Eduardo García-Rey, MD, PhD, EBOT, can be reached at Orthopaedics Department Hospital La Paz, Madrid, Spain; email: edugrey@yahoo.es.
- Stephen E. Graves, MD, can be reached at AOA National Joint Replacement Registry, SAHMRI, North Terrace, Adelaide SA5000, Australia; email: segraves@aoanjrr.org.au.
- Laurent Sedel, MD, can be reached at Hopital Lariboisiere, University Denis Diderot, Paris, France; email: laurent.sedel@aphp.fr.
- Claus Varnum, MD, PhD, can be reached at Vejle Hospital, Kabbeltoft 25, 7100 Vejle, Denmark; email: claus.varnum@rsyd.dk.
Disclosures: García-Rey, Graves, Sedel and Varnum report no relevant financial disclosures.