Clinical comment

THA surgery is one of the most common procedures performed in orthopedic surgery. It is considered one of the most effective orthopedic procedures with excellent long‐term survival in the elderly.³ Metal‐on‐polyethylene (MoP) replacements are still the traditionally implanted bearings, used initially by Charnley in the 1960s, and still recommended by many today. Long‐term survival of this bearing combination is limited by polyethylene wear and related osteolysis.⁴ In the younger patient, with longer life expectancy and increased activity, there is an up to tenfold increase in the demands of any replacement bearing.⁵ Regarding this, there is an oft‐quoted, long‐term study of patients under the age of 51 which demonstrated a failure rate requiring revision arthroplasty of over 25% at 20 years and almost 50% at 27 years.⁶ Revision procedures are challenging, a risk to the patient, and of considerable cost to health service providers.⁷–¹⁰ Alternative bearings and joint replacements have therefore been developed and include ceramic bearings, metal‐on‐metal (MoM) resurfacings, and highly cross‐linked polyethylene, all aiming to prolong the survival of the prosthesis, and prevention of osteolysis and its consequences.

Available literature and quality of the evidence

Randomized controlled trials (RCTs) and meta‐analyses are available to answer this question.

Findings

A randomized controlled trial (RCT) comparing 31 ceramic‐on‐ceramic (CoC) THAs with 30 cobalt chrome on highly cross‐linked polyethylene (MoP) revealed no difference in outcome scores between the two groups looking at Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Form 36 (SF‐36) scores at a follow‐up of between 2 and 24 months.¹¹ Another compared 30 CoC replacements with 26 ceramic‐on‐plastic (CoP) replacements and reported no significant difference in joint specific outcome scores at a mean follow‐up of eight years.¹² A further RCT with a mean follow‐up of 35.2 months compared 346 CoC with 168 MoP replacements, and reported equivalent Harris Hip Scores (HHSs) and patient satisfaction.¹³ A five‐year RCT published in 2005 comparing 213 CoC with 101 MoP hips concluded that CoC articulations were at least equivalent in performance to the MoP design.¹⁴ HHSs were 96.6 in the ceramic and 97 for MoP. An extension of this series, assessing a titanium‐coated ceramic bearing, again identified no difference in HHS with a mean of 96.6 at 4.2 years’ follow‐up.¹⁵ A subsequent review of the same cohorts at a mean follow‐up of eight years again identified no difference in outcome scores.¹⁶ Finally, a minimum two‐year follow‐up RCT compared 250 CoC articulations with 250 CoP hips showed no difference in clinical outcome.¹⁷

Three meta‐analyses¹⁸–²⁰ all published in 2015 included in excess of 5000 patients and failed to show a significant clinical difference, be this CoC, CoP, or MoP.²⁰ The authors concluded that other factors, including cost, be considered rather than clinical outcomes. Furthermore, 10 RCTs, all published from 2005 to 2013, showed no statistical difference in survival or patient outcomes.¹²,¹⁷,²¹–²⁸ However, some of these trials did confirm radiographic changes with slight increased wear in the CoP compared to the CoC. A Canadian study identified this wear to be three times that of CoC,²¹ and one further study identified significant wear but no clinical sequelae in the CoP prosthesis at 10 years.¹²

Despite so much data suggesting no clinical difference but some radiographic deterioration, several papers deserve specific mention of practical significance to our patient. Petsatodis et al. undertook a study of 100 young patients (mean age 46) who had undergone a CoC THA and showed that at 10 and subsequently 20 years a very satisfactory result with only six requiring revision, these due to loose ceramic chips.²⁹ Another studied 100 patients (mean age 45), each of whom underwent CoC and CoP in bilateral replacements.²⁴ Patients were reviewed after 12.4 years (mean) with, in effect, each patient acting as their own control. There was no difference in clinical outcomes at their latest follow‐up. These data appear to support the view that there may be some deterioration on scientific review but no difference in patient satisfaction or clinical outcome.

Ceramics have continually improved over the years. First‐generation alumina ceramics (1974–1988) were characterized by low density, high porosity, and large grain size, and did not perform well with early series reporting high failure rates, but not directly due to the alumina itself. The main failures were aseptic loosening of the femoral stem³⁰,³¹ or of the monoblock acetabular system³² with reported fracture rates of 3–13%.³³

Second‐ and third‐generation alumina ceramics (1988–1994 and 1994–present, respectively) are characterized by a reduced grain size with increased alumina purity with the addition of calcium oxide (CaO) or magnesium oxide (MgO) materials.³⁴ With third‐generation ceramics there has been further improvements with hot isostatic pressing, laser etching (avoiding surface stress risers), and proof testing.³³ Prior to proof testing, ceramic components were subject to a finished product audit in which only a sample from each batch was subject to testing.

Despite these improvements there continues a search for a ceramic material to satisfy increasingly more challenging patient demands. These changes include smaller components, additional sizes, along with even greater reliability and longevity. Known as a fourth‐generation ceramic, BIOLOX delta (CeramTec AG, Plochingen, Germany) is a combination of both the major subsets of ceramic, an alumina matrix with zirconia particles homogeneously dispersed and encapsulated increasing the fracture toughness.³³

Ceramics may be used as an alternative to a metal head in a conventional hard‐on‐soft bearing against polyethylene. With a lower Ra (the mathematical average of all deviations from the mean line of the surface profile) and improved wettability, this combination has the potential to provide a low wear alternative to either stainless steel or cobalt chrome. Ceramic may also be used as a more modern hard‐on‐hard bearing against either a ceramic liner or, as a more recently introduced, ceramic‐on‐metal (CoM) bearing surface.³⁵–³⁷ Advantages with hard‐on‐hard bearings is the potential for fluid film lubrication, an exceptionally low wear rate, and avoiding osteolytic polyethylene debris. Using hard‐on‐hard bearings also allows the use of large heads, which if used with a conventional polyethylene option would create excessive volumetric wear. CoC options also avoid the production of metal ions, which are released and may complicate MoM and CoM alternatives.³⁵–³⁸

Using a MoP articulation also offers the surgeon access to multiple head sizes and modular neck lengths spanning 20 mm. On the acetabular side, in addition to multiple inner diameter options, there is also the availability of lateralized liners, elevated rims, and anteverted, eccentric, and constrained liners. In contrast most CoC systems have only one head size per cup diameter, with three or four head lengths spanning 10 mm or less. These alternatives for equalizing leg lengths and maximizing stability are two crucial goals of THA.⁸ Numerous liners and head options assist in achieving these goals. Any loss of these options may currently be the most substantial disadvantage of CoC THA.

Resolution of clinical scenario

• Overall, there is some evidence to suggest lower wear rates with ceramic‐bearing surfaces.
  
• There is little evidence to demonstrate clinical benefit in most patients, and cost is a major consideration.
  
• There is evidence to demonstrate excellent results with ceramic surfaces in young patients.