Clinical Faceoff: Ceramic-on-Ceramic THA: Do the Advantages Outweigh the Limitations?

The revolutionary work in the early 1970s by France’s Pierre Boutin and Germany’s Heinz Mittelmeier helped build the foundation for what ultimately became the modern day use of alumina (and more recently, composite) ceramics. Today, alumina ceramics are considered an effective alternative to metal-on-polyethylene (MoP) for patients requiring THA. Alumina ceramic THA showed high rates of mechanical failure during early clinical work, particularly in terms of cup loosening and fracture of the femoral head [4]. Also, the use of zirconia ceramic caused high rates of failure in the late 1990s, and was eventually withdrawn from the market. However, mechanical and tribological properties of modern alumina and composite ceramics showed higher resistance to fracture, lower wear properties, and wear particles with reduced soft tissue bioreactivity [10]. The design rationale of these bearings is to provide low wear rates and substantial reduction of osteolytic changes even in active, young patients. The current risk of fracture is estimated between 0.02% and 0.1% [4] depending on implant design and positioning. Is it all really as good as it sounds?

I have invited two experts on this topic to debate the pros and cons of ceramic THA. Professor Laurent Sedel MD is a world-renowned hip surgeon from Paris, France who has extensive experience with ceramic-on-ceramic (CoC) bearings. He performed his first alumina-on-alumina THA more than 35 years ago. The considerable record of his peer-reviewed publications on this topic reflects the quality of his work.

William L. Walter MBBS, FRACS(Orth), PhD is an arthroplasty surgeon from Sydney, Australia. He is widely regarded as an expert in the field of hard-hard pairings in THA. In particular, his far-reaching work on ceramic tribology had relevant implications in the clinical practice and is highly regarded by his peers.

Dr. Pitto:I would like to start the debate with a trendy theme. Can you comment on what we know about noise generation using novel CoCimplants? What do you tell patients, and what should surgeons know about the current state-of-the-art on this topic?

Prof. Laurent Sedel: A CoC implant with an ill-fitting cup position or design may lead to noise generation [9]. Noises generated by dry contact (a condition caused by absence of lubricating film in the CoC articulation) may increase due to interposed metallic foreign bodies. We must always keep in mind that severe squeaking can be related to component fracture. Stem vibration (a physical phenomenon of acoustic resonation, with the implant generating a sound like a tuning fork) may also play a role. Some noise could be related to metal-on-metal (MoM) impingement (cup margin versus stem neck), especially when rising from a chair or bending forward. The only revision we have performed for noise was related to hip subluxation secondary to excessive anteversion of the socket and posterior impingement against the femoral neck.

In our 2011 study [1], we performed 284 CoC hips for 238 patients. All of the patients received the same prosthesis with alumina bearing components. According to the results of our study, 20% of the patients experienced some sporadic noise. Of those 20%, only 1% reported a recurring squeaking noise, and no one has been revised thus far [1]. It is important to consider positioning accuracy and the quality of implant design, and not all systems behave similarly in this regard [9]. Our patients are informed about the possible rare occurrence of joint noises. We tell them that this will have no consequence on their hip survival or functional performance. We believe that the noise problem is largely counterbalanced by the long-term, superior performance of ceramic.

Dr. William L. Walter: I agree with Prof. Sedel’s comments. In our patients, dry contact is usually due to posterior edge loading with bending. Metallic foreign body as a cause is rare in our patients. Cup malposition can contribute to risk and severity of edge loading. Anterosuperior edge loading causing problematic squeaking with every step of walking is usually due to excessive anteversion and inclination. Stem resonance is the noise amplifier, and some stems are more susceptible due to greater flexibility in the sagittal plane. Benign bending squeaks account for the majority of squeaking in our patients. I am not concerned about this, and once I reassure my patients, they are not concerned either. It is the trade-off for extremely low wear performance.

Dr. Pitto:It seems like most of the noises generated by the ceramic THA are related to implant design and positioning. What do we know about the relationship between joint noises (like squeaking) and the risks of accelerated wear and fracture?

Dr. Walter: Ceramic bearings revised for squeaking have higher wear than silent hips revised for other reasons [11]. These represent the worst cases, with severe edge loading producing noise during every step of walking. Milder problems with noise usually are of no clinical significance, and seldom come to revision. Noise and edge loading occurs less frequently in these cases. We do not know the wear rate in these hips because it cannot be measured on plain radiographs. We presume wear rate is higher than silent hips, but still low enough that it is not clinically important.

Prof. Sedel: In the past, we assessed and retrieved ceramic bearings showing edge loading and strip wear, and we interpreted this phenomenon as abnormal heavy wear after secondary tilting of the socket following aseptic loosening. Severe ceramic wear was not the initial cause of failure [10]. Hips revised for reasons other than cup loosening did not show heavy wear. We found also a statistical correlation between the depth of these stripes and the age of ceramics: Heads and liners of the early generations showed the worse wear. This problem in modern ceramics is uncommon.

Dr. Pitto:Clearly, at this stage we know that patients requiring revision for constant hip joint noise frequently show severe edge loading with high wear of the ceramic bearings. We should move now to a more traditional topic. What do you see as the ideal head size and liner thickness, and what are the trade-offs as you think about the options for bearing sizes?

Prof. Sedel: Sir John Charnley advocated for the 22-mm head diameter for THA. It was the best engineering option for MoP bearings. Ceramic bearings are different; the tribological properties improve in larger diameters, mainly because of the phenomenon of boundary lubrication. Ceramic fracturing of the head is another concern. Larger ceramic heads reduce fracture and dislocation risk, while increasing ROM. In 1975, the German orthopaedic surgeon, Peter Griss used a 26-mm ceramic head diameter and experienced numerous fractures. That is why more than 30 years ago we selected the 32-mm head size as ideal for these bearing couples, as long as the outer diameter of the cup is sufficiently large to accommodate a head of this size without needing to use an unreasonably thin liner. The 32-mm head is large enough to protect against breakage risk if the trunnion design is optimal. The use of a 12/14 stem taper design with adequate roughness has resulted in no fracture in patients followed for more than 15 years in our institution. The problem is more crucial on the cup liner side. Increasing head size requires decreasing liner thickness. Liner thickness of 6-mm is the minimum recommended. That is why we use a 28-mm head diameter for sockets smaller than 48-mm. If the overall size of the socket is larger than 56-mm, it is possible to use a 36-mm head size. Does it provide any advantage? The Finnish registry [7] compared revision rates for dislocation versus femoral head size. There was a 40% reduction of revision with 32-mm compared to 28-mm head diameter. However, increasing the head size to 36-mm did not show any improvement.

Dr. Walter: Bigger heads are more stable. Heads as large as 36-mm provide a benefit due to improved head neck-ratio. Beyond 36-mm, there is no further benefit for head-neck ratio, but there is still further benefit from increased jump distance. Bigger heads also have greater mass and greater radius, and are more likely to squeak if put on the same stem. Bigger heads produce greater frictional torque, and would likely require a stronger taper and stiffer stem.

Dr. Pitto:If we want to use bigger femoral heads, we need stems with adequate design. Recent research [8] shows that trunnion diameter and engagement length are important factors to consider when improving taper-trunnion junction technology. What are the major issues in trunnion design as we think about ceramic heads? I note that they often are used to “salvage” revisions carried out for MoM adverse soft tissue reactions. Are there any possible unintended consequences we should be aware of here?

Dr. Walter: Ceramic heads perform well on trunnions. Our experience includes inserting more than 4500 CoC bearings, and in that time, we have never seen trunnionosis with a ceramic head [5]. There is an increased incidence of head fracture when placing a ceramic head on an undamaged but used trunnion. However, the risk of fracture is low with modern ceramics like Biolox^® delta (DePuy, Warsaw, IN, USA), especially if a metal-sleeved head is used. A ceramic head should not be placed on a trunnion if there is visible damage.

Prof. Sedel: I agree with Dr. Walter regarding the absence of trunnionosis with ceramic. I disagree partially regarding the risk of placing a new ceramic head on a used trunnion. Theoretically, Dr. Walter is correct, but in practice we did that many times and observed no fracture of the ceramic head [3]. If the cone appeared badly damaged at revision, we exchanged the stem; if the cone showed only minor damage, we inserted a new ceramic head. I note we always used 32-mm heads. At the moment, we often prefer to retain the same head at revision because the original head and cone provide the best mating, and therefore, the best warranty of success.

Dr. Pitto:Interesting, quite a different approach to the problem of ceramic THA revision retaining the femoral component. I would like to address now a relevant issue of the healthcare economy. In an era where our implant choices will be increasingly scrutinized, how can we justify the more expensive CoC couples when survivorship is so high with metal on crosslinked polyethylene THA bearings?

Prof. Sedel: The price of an implant is related to many different aspects; CoC is more expensive because of the complex manufacturing technology. But costs also depend on local market features. In the United States, costs are mostly related to insurance fees related to fracture fear. In many countries, excess cost for ceramic THA is no more than 30%. In my opinion, it is not difficult to negotiate the increased cost if you look at the potential benefits: Ideal for high-functional demand patients, no osteolysis, long-term durability, and low revision rates. The costs are even more sustainable if patients are young and active. Regarding the success of highly crosslinked polyethylene, we must remind ourselves that this material has been on the market for less than 15 years. The data thus far derive from in-vitro studies, or from radiological studies that showed the reduction in head penetration. Will this reduce revision burden? It is far from certain. Biological factors represented by reaction to smaller foreign body particles could explain why in a recent prospective randomized study [6], the authors found no reduction in aseptic loosening with highly cross-linked polyethylene versus regular polyethylene. At our institution, we select bearings based on the patient’s age and activity. For patients 75 years of age and older, we utilize a full polyethylene cemented socket with either a metallic or a ceramic femoral head. In more active or young patients, we prefer CoC bearings. At this stage, we have found no indication for improved polyethylene.

Dr. Walter: Ceramic bearings are not significantly more expensive in my hospital environment. The involved higher cost of ceramic components is insignificant compared to potential expenses if a revision is required.

Dr. Pitto:Regrettably, in many countries, elevated costs are still the main reason for restricted use of ceramic components. How do alumina-on-alumina bearings differ from other available options in terms of periprosthetic tissue response?

Dr. Walter: First, alumina-on-alumina bearings have lower wear than any other bearing, so there is less periprosthetic debris. Second, ceramic debris is more inert than other debris [2]. Metal debris causes necrosis, polyethylene debris causes osteolysis, and ceramic debris causes very little reaction. Paradoxically, if there is particle disease with a ceramic THA it may be due to titanium debris generated by cup and neck rim impingement (component malposition) and not due to ceramic debris.

Prof. Sedel: I am in agreement with Dr. Walter. Particulate debris in ceramic THA could also be due to cement fragments, or to excessive local stresses related to tilting of the socket or inappropriate material quality. With modern generation ceramic bearings, material quality is not an issue. The premium advantage of CoC is the absence of periprosthetic foreign body reaction. We can add that the strong periprosthetic fibrous tissue reaction observed at revision of ceramic THA could also play a role in stabilizing the joint and preventing late dislocation.