"Ceramic-on-ceramic resurfacing is the answer."

Ceramic-on-ceramic hip resurfacing will have a difficult time outperforming the current gold standard, uncemented metal-on-metal hip resurfacing which has a 99% 15-year implant survivorship. There are not yet any published data on the trials with ceramic-ceramic.

The main reason to pursue these new bearings is to take advantage of their superior wear characteristics. Ceramic-on-ceramic have the lowest benchtop laboratory wear rates, they are the only bearing better than metal-on-metal, the current gold standard. But metal-on-metal already has such a low wear rate that it can never wear out in anyone’s lifetime.

But metal-on-metal has an Achilles heel. If the socket is malpositioned in too steep or anteverted a position, a small percentage (5% of these) will suffer edge-loading mechanics and start releasing large amounts of metal debris. How often does this happen? I have published several papers on this topic. The first showed a 1% 10-year failure due to metallosis before the time we were aware of proper cup positioning. The second paper outlines a safe zone for socket positioning (RAIL: relative acetabular inclination limit) to avoid metallosis. In the third paper, we validate the safe zone. We evaluate a subsequent cohort of patients where we were able to place 100% of cups within the safe zone and experienced no cases with excessive ion levels or metallosis. I have not had a single case of metallosis in over 5000 cases since 2009.

The problem with metallosis has been solved in metal-on-metal bearings. The only remaining problem is one of perception and misinformation. The diagnosis of a metallosis failure is very straightforward. But many surgeons who do not perform hip resurfacing are quick to diagnose this problem without meeting the diagnostic criteria. The problem comes when a patient has residual unexplained pain. In a THR, where this occurs in 20% of cases, nobody suggests metal allergy as a cause, in hip resurfacing, where this occurs much less commonly, a presumptive diagnosis of metal allergy or excess ions is frequently made by uninformed surgeons evaluating an unhappy patient with hip resurfacing. A small residual fluid collection is seen in 30% of well-functioning THR and hip resurfacing cases. This is a normal postoperative finding. In a painful THR this may be misdiagnosed as a trunion failure, in a hip resurfacing it could erroneously be called a metallosis case.

Revision for unexplained pain carries a very low success rate. Far less than 50% of patients are satisfied. After all, if you don’t understand the problem, you can’t really expect to fix it, but sometimes you get lucky. I sometimes offer my own patients with unexplained pain a revision with this proviso, but I do not recommend it. I do not offer this option to others.

If we had a ceramic-on-ceramic hip resurfacing that otherwise worked as well as the current gold standard metal-on-metal variety, this problem with misdiagnosing unexplained pain would go away. It would be great to rid ourselves of this thorny problem.

But ceramic-on-ceramic may not be as good for several reasons. First, the early fracture/head collapse rate may be higher due to a smaller supporting stem. Second thin shells of ceramic (4mm) may fracture with repetitive high impact. Third, squeaking may be a problem. Finally, the porous titanium coating may detach from the ceramic cup after many years. I have published my experience with this problem with the Corin metal-on-metal system which had titanium coating that debonded from a cobalt substrate between 8-10 years postop. On the other hand, the ZB Magnum cup with the same type of coating that I have used for the last 17 years has not had that problem. Will titanium remain adhered to a ceramic shell over the long run in highly active patients? This is my main concern.

Having said this, I would welcome the opportunity to offer patients this option if they desired. I personally would have a metal-on-metal. Ceramic-on-ceramic is unlikely to beat 99% of 17-year KM implant survivorship in over 5000 cases.