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

Ceramic-on-ceramic articulations in hip prostheses were once considered a promising alternative to other material combinations due to their high wear resistance and biocompatibility. However, with increasing experience and advancements in other materials, the disadvantages of this articulation often outweigh the benefits. Today, ceramic-on-highly cross-linked polyethylene is considered the gold standard - but why?

What is a ceramic-on-ceramic articulation?

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

Advantages of ceramic-on-ceramic bearings in hip prostheses

Before we address the disadvantages, it is important to understand the positive properties that make this bearing so attractive in the first place:

• Low wear: Ceramic is extremely wear-resistant, reducing the risk of particles entering the joint space and causing particle-induced aseptic loosening.
• Biocompatibility: Ceramic is a very well-tolerated material that hardly causes any allergic reactions or inflammation.
• Smooth surface: Ceramic surfaces are extremely smooth, minimizing friction in the joint and improving mobility.
• Longevity: Studies show that modern ceramic prostheses have a high service life – an important aspect, especially for younger, active patients.

Ceramic scores with its extreme hardness, high wear resistance, and good biocompatibility. These advantages led to ceramic-on-ceramic bearing pairs being considered ideal, especially for younger, active patients. Nevertheless, significant disadvantages have emerged over time.

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

1. Risk of fracture

Ceramic is a brittle material that can break under certain conditions, such as high stress or malpositioning. Despite modern manufacturing methods, this risk remains, especially in younger and physically active patients. In the past, the risk of fracture was even significantly higher – although it has become less common with improved manufacturing techniques and material compositions, it is by no means ruled out. A fracture of the ceramic components represents a serious complication and usually requires a complex revision surgery.

Why does ceramic break?

Ceramic is extremely hard, but also brittle. This means it withstands high compressive loads well, but reacts sensitively to shear forces and punctual loads. Even small malpositions of the prosthesis or uneven loading can cause micro-cracks, which can lead to fractures in the long term. In the event of a fall, the risk increases additionally.

2. Squeaking phenomenon

Another well-known problem is the occurrence of squeaking noises, also referred to as "Squeaking". These noises can significantly impair the quality of life of patients and occur more frequently with CoC articulations 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

• Malpositioning 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.
• Wear of the surface: Micro-cracks or unevenness due to stress can promote the development of noise.

3. High precision requirements

The tolerance of ceramic-on-ceramic articulations to deviations in the positioning of the head and cup is low. This requires very precise, preferably computer-assisted planning and implantation to achieve optimal results. Even the smallest malpositions can lead to increased wear, noise, or even fractures.

Technical Challenges

• Precise angular positioning: The acetabular angle and the alignment of the prosthesis shaft must be precisely matched.
• Soft tissue balancing: An uneven tension of the surrounding musculature and capsule structures can lead to incorrect loading.
• Surgical technique: Only experienced surgeons with modern techniques can ensure the precision required for this type of bearing pair.

4. Costs and Complexity

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

Alternative articulations for the artificial hip joint

Due to the mentioned disadvantages, the use of ceramic-on-ceramic articulations in hip arthroplasty is increasingly being questioned. There are some alternatives that offer similar benefits but are less prone to complications:

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

Why ceramic on highly cross-linked polyethylene is the current standard

In recent years, another material combination has proven to be superior: ceramic on highly cross-linked polyethylene. This bearing combines the advantages of ceramic 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 longer-lasting than earlier polyethylene variants. In addition, it remains elastic enough to better compensate for misalignments or small load deviations.

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 degradation due to particle reactions).
• No noise generation: Unlike ceramic-on-ceramic articulations, there is no squeaking.
• Higher fracture safety: Ceramic heads remain intact, but the polyethylene inlay provides additional cushioning, which significantly reduces the risk of fractures or splintering.
• Adaptability: Highly cross-linked polyethylene tolerates minor misalignments better and reduces the risk of edge loading.
• Cost efficiency: The combination is more cost-effective in production and application than pure ceramic-on-ceramic articulations.

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

Ceramic-on-ceramic bearings undoubtedly have their advantages in hip arthroplasty - especially with regard to abrasion resistance and biocompatibility. Nevertheless, the disadvantages outweigh: noise development, risk of fracture, and low fault tolerance make them a less ideal solution for many patients.

Modern bearing couples made of ceramic on highly cross-linked polyethylene offer a better balance of durability, resilience, and patient satisfaction in hip prostheses today. They minimize wear, are quieter, and less prone to fracture – properties that are particularly important for active patients. Therefore, patients who require a hip prosthesis should carefully weigh the advantages and disadvantages together with their treating physician – and keep an eye on newer, proven alternatives.