In modern endoprosthetics, various bearing surfaces are available for hip prostheses (total hip arthroplasty, artificial hip joint). One of these options is the ceramic-on-ceramic (CoC) bearing surface, in which both the femoral head and the acetabular cup are made of ceramic. Although this bearing surface is known for its high wear resistance and biocompatibility, there are specific disadvantages that should be considered when making a decision.

Ceramic-on-ceramic bearing surfaces in hip prostheses were long considered a promising alternative to other material combinations. They were valued for their high wear resistance and biocompatibility. However, with increasing experience and advances in other materials, it has become clear that the disadvantages of this bearing surface outweigh the advantages in many cases. Today, ceramic-on-highly cross-linked polyethylene is considered the gold standard – but why?

What is a ceramic-on-ceramic sliding pair?

The bearing surface in a hip prosthesis describes the materials that move against each other within the joint. In a ceramic-on-ceramic bearing surface of an artificial hip joint, both the femoral head and the acetabular cup are made of ceramic material – usually aluminum oxide or zirconium oxide ceramic. These materials are extremely hard and wear-resistant, making them particularly durable.

Advantages of ceramic-on-ceramic bearing surfaces in hip prostheses

Before we turn to the disadvantages, it is important to understand the positive properties that initially make this sliding pairing so attractive:

• Low abrasion: Ceramic is extremely wear-resistant. This reduces the risk of particles entering the joint space and causing so-called particle-induced aseptic loosening.
• Biocompatibility: Ceramic is a very well-tolerated material that rarely causes allergic reactions or inflammation.
• Smooth surface: Ceramic surfaces are extremely smooth, which minimizes friction in the joint and improves mobility.
• Longevity: Studies show that modern ceramic prostheses have a long lifespan – an important aspect, especially for younger, active patients.

Ceramics score points due to their extreme hardness, high wear resistance, and good biocompatibility. These advantages led to ceramic-on-ceramic bearing surfaces being considered ideal for a time, especially for younger, active patients. However, significant disadvantages have emerged over time.

Main disadvantages of ceramic-on-ceramic bearing surfaces in hip prostheses

1. Risk of breakage

Ceramic is a brittle material that can fracture under certain conditions, such as high stress or misalignment. Despite modern manufacturing methods, this risk remains, especially in younger and athletically active patients. Previously, the risk of fracture was considerably higher – although improved manufacturing techniques and material compositions have reduced it, they have by no means eliminated it. Fracture of the ceramic components represents a serious complication and usually requires complex revision surgery.

Why does ceramic break?

Ceramic is extremely hard, but also brittle. This means it withstands high pressure loads well, but is sensitive to shear forces and point loads. Even minor misalignments of the prosthesis or uneven stress can cause microcracks that can eventually lead to fracture. A fall further increases this risk.

2. Squeaking phenomenon

Another known problem is the occurrence of squeaking noises. These noises can significantly impair patients' quality of life and occur more frequently with ceramic-ceramic bearing surfaces than with other materials. Squeaking is caused by frictional vibrations between the ceramic surfaces and is particularly audible during certain movements, such as rapid rotations or large ranges of motion.

Causes of squeaking

• Misalignment of the implants: Even small deviations in the position of the components can increase the risk of noise development.
• Dry running: If the synovial fluid does not sufficiently reach between the sliding surfaces, dry friction can occur.
• Surface wear: Microcracks or unevenness caused by stress can promote the formation of noises.

3. High precision requirements

The tolerance of ceramic-on-ceramic bearing surfaces for deviations in the positioning of the head and socket is low. This necessitates very precise, ideally computer-aided, planning and implantation to achieve optimal results. Even the slightest misalignments can lead to increased wear, noise, or even fractures.

Technical challenges

• Precise angular positioning: The acetabular angle and the alignment of the prosthetic stem must be precisely coordinated.
• Soft tissue balancing: Uneven tension in the surrounding muscles and capsule structures can lead to incorrect loading.
• Surgical technique: Only experienced surgeons with modern technology can guarantee the precision necessary for this type of bearing pair.

4. Costs and complexity

Ceramic-on-ceramic prostheses are more expensive than other bearing surfaces such as ceramic-on-polyethylene or metal-on-polyethylene. The higher material quality and more complex manufacturing process are reflected in the price. Furthermore, implantation is technically more demanding, which can mean longer operating times and potentially higher complication rates.

Alternative bearing surfaces for the artificial hip joint

Due to the aforementioned disadvantages, the use of ceramic-on-ceramic bearing surfaces in hip arthroplasty is increasingly being questioned. Several alternatives offer similar advantages but are less prone to complications:

• Ceramic on highly cross-linked polyethylene (CoXPE): Offers a good combination of abrasion resistance and break resistance.
• Metal-on-polyethylene: Still a common choice, especially for older patients, but with higher abrasion.
• Metal-on-metal: Due to metal abrasion and potential metal ion release, it is now rarely used.

Why ceramic on highly cross-linked polyethylene is today's standard

In recent years, a different material combination has proven superior: ceramic on highly cross-linked polyethylene. This sliding pairing combines the advantages of ceramics with modern developments in the field of polyethylene inlays.

Highly cross-linked polyethylene – what makes it so special?

Highly cross-linked polyethylene undergoes a special manufacturing process in which the polymer chains are more strongly bonded together. The result is a material that is significantly more abrasion-resistant and durable than previous polyethylene variants. Furthermore, it remains elastic enough to better compensate for misalignments or minor load variations.

Advantages of ceramic-on-highly cross-linked polyethylene

• Reduced abrasion: Highly cross-linked polyethylene produces significantly fewer abrasion particles compared to conventional polyethylene, minimizing the risk of loosening and osteolysis (bone loss due to particle reactions).
• No noise generation: In contrast to ceramic-on-ceramic sliding pairings, there is no squeaking.
• Increased fracture resistance: While the ceramic heads remain, the polyethylene inlay provides additional cushioning, significantly reducing the risk of breakage or splintering.
• Adaptability: Highly cross-linked polyethylene tolerates minor misalignments better and reduces the risk of edge loading.
• Cost efficiency: The combination is cheaper to manufacture and use than pure ceramic-on-ceramic sliding pairs.

Conclusion: Why ceramic on highly cross-linked polyethylene is the safe choice

Ceramic-on-ceramic bearing surfaces undoubtedly have their advantages in hip arthroplasty – particularly regarding wear resistance and biocompatibility. Nevertheless, the disadvantages outweigh them: noise generation, risk of fracture, and low error tolerance make them a less than ideal solution for many patients.

Modern ceramic bearing surfaces on highly cross-linked polyethylene now offer a better balance of durability, resilience, and patient satisfaction in hip replacements. They minimize wear, are quieter, and less prone to fracture – qualities that are particularly important for active patients. Anyone needing a hip replacement should therefore carefully weigh the advantages and disadvantages with their doctor – and keep the newer, proven alternatives in mind.