Ceramic hip replacements: how durable, fragile and expensive?

Ceramic hip replacements were first used in Europe in the 1980s, but they have only recently received approval for implantation in patients in the United States. Ceramic materials are a good alternative to various types of alloys. Ceramics have their own unique properties, which are especially valuable when creating prostheses, extending their service life and improving functional characteristics.

Minimally invasive endoprosthetics in the Czech Republic: doctors, rehabilitation, terms and prices.

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Types of ceramics

Different types of ceramics.

Types of joint body material:

• inert. Prevents bone tissue from growing in and retains its shape;
• bioactive. Assimilates with bone tissue, but the shape remains the same;
• biodegradable. Completely dissolves and is replaced.

Types of ceramics:

1. On oxides of aluminum, zinc and titanium. Such prostheses are classified as bioinert. They are durable and characterized by a high degree of biocompatibility. Usually ceramics-polyethylene and ceramics-ceramics are used in friction units.
2. Zirconium. Zirconium dioxide is not inferior to metal in strength. However, in the company of an admixture of yttrium, it is somewhat toxic to the body.
3. Carbon (C-Si, C). Bioinert material of increased strength with excellent biocompatibility. Often used in the manufacture of inserts for acetabular cups and implant rods.
4. Based on calcium phosphates and aluminates. Bioactive but non-degradable material. Products made from it can act as intermediaries between bone, implants and other biomaterials. They are also used as carriers of various active substances with rapid surface release.
5. Based on calcium sulfates, phosphates and aluminates. Biodegradable material. Can be a carrier of active substances with slow surface release.
6. Composite ceramic material BIOLOX delta. It is an innovative alloy of aluminum oxide (82%), zirconium dioxide (17%) and other elements. Aluminum oxide has a very high density due to the fine-grained structure of the matrix. The products are characterized by high biocompatibility, wear resistance, chemical and hydrothermal stability.

Clinical example No. 1.

Patient P., 64 years old, has been experiencing severe, gradually progressive pain in the area of ​​the right hip joint for 3 years. I contacted K+31 in May 2021, was examined by an orthopedist, and x-rays of the hip joints were taken. Coxarthrosis was diagnosed on the right, stage 3, on the left, stage 2. Surgical treatment is recommended - total endoprosthetics of the right hip joint.

Taking into account the age of the patient, it was decided to use a cementless fixation prosthesis from Zimmer, a ceramic/ceramic friction pair.

Preoperative planning was carried out, calculated dimensions: Avenir 6 stem, Trilogy 60 cup, ceramic liner with an internal diameter of 40 mm, ceramic head 40 mm.

In May 2021, surgery was performed, total arthroplasty of the right hip joint.

The patient was activated and erect on the day of surgery. (in popular language, 6 hours after the operation the patient was seated in bed and stood up with additional support on a walker).

The next day after surgery, the patient was trained to walk with additional support on a walker. The pain syndrome was minimal due to the use of narcotic and non-narcotic analgesics, as well as intraoperative injection of soft tissue in the intervention area with a long-acting analgesic. On the second day after surgery, the patient was trained to walk up the stairs with crutches. The patient was discharged on the 4th day after surgery for outpatient follow-up care.

Ceramic friction pair

The friction unit is formed by the head and the acetabular implant - a modular cup (acetabular component). The acetabular cup consists of a metal hemisphere, which is fixed with its convex part in the acetabulum (on cement or using the press-fit method), as well as a ceramic liner, which is attached inside the cup using a special locking mechanism (Morse taper). It is inside this stock that the head will slide when moving.

There are also monobloc acetabular cups in which the liner is initially secured at the factory. When installing such an implant, there is no risk of splitting the gasket.

Ceramic liners have very high strength, so they are much thinner than others. Can be paired with larger heads, which means increased joint stability.

Many Western surgeons agree that when implanting hip joints in patients under the age of 75, a monoceramic friction pair should be used. Since such compatibility is almost not subject to abrasion and the formation of debris, unlike metal, where particles entering the bloodstream can cause allergies and various kidney pathologies. Depending on the composition of the ceramics, the components of the prosthesis can be colored: if aluminum (Al2O3) ceramics are used, yellow, and if composite (a mixture of aluminum and zirconium) are used, pink.

ANATOMY OF THE HIP JOINT

The hip joint is spherical in structure, so movements in it are possible in many planes. The joint is formed by the acetabulum, forming a kind of deep bowl, and the head of the femur, which has the shape of a ball.

The head of the femur is connected to the main part (the diaphysis) by a short section of bone called the femoral neck. Strong and thick muscles and tendons surround the joint.

The surfaces of the acetabulum and the head of the femur are covered with articular cartilage. The thickness of articular cartilage is about half a centimeter in large joints. Articular cartilage is a tough, smooth material that covers the bones in the joint area. Articular cartilage allows the bones it covers to glide smoothly past each other without being damaged. The color of articular cartilage is white and shiny.

The joint is surrounded by a dense, waterproof capsule, inside which a special fluid is produced that lubricates the articulating surfaces. The bones in the joint are held together by dense ligaments and muscles. The design of the hip joint allows for extremely high mobility while maintaining satisfactory stability.

Powerful muscles around the joint allow us to move in an upright position for a long time, and also, if necessary, to accelerate when running and jumping. There are also important nerves and blood vessels around the joint.

Disadvantages of ceramics

Biolox cup split.

• rigidity;
• sometimes during operation a characteristic creak appears;
• the possibility of destruction either due to incorrect installation technique, or itself due to impaired implant production technology;
• causticity (mainly in monoceramic pairs, but in the latest generation of materials it almost never happens);
• friction products (debris) further increase the wear rate of the prosthesis. Also, their presence can provoke the dissolution of bone tissue in the implant bed. During revision operations, it is quite difficult to completely remove all particles. Therefore, the use of bioactive types of ceramics in the manufacture of endoprostheses is controversial.

Examples of wear on ceramic heads.

Another disadvantage of ceramic endoprostheses is their high cost. However, the ceramic-polyethylene friction unit is not in many ways inferior to the monoceramic one, but the price is much lower.

Studies of 83 monometallic (46) and monoceramic (37) friction units for corrosion resistance showed that ceramic heads significantly reduce corrosion of the cone in which the leg is attached.

Purpose of bipolar implants

Bipolar prosthetics are indicated for medial femoral neck fractures and fracture dislocations in people over 70 years of age.

Until recently, the diagnosis of a “femoral neck fracture” in an elderly person practically meant a death sentence: slow decline due to lack of mobility and bedsores. Surgeries were decided infrequently, which is quite reasonable: in old age, anesthesia is very difficult to tolerate, cases of implant rejection are frequent, and the recovery period is very long.

Currently, the situation has changed with the advent of bipolar heads for hip endoprostheses on the orthopedic market. Prosthetics with a unipolar bipolar implant saves the lives of hundreds of elderly people.

There is one significant disadvantage - increased wear of the acetabulum's own cartilage due to friction of the prosthesis. Therefore, if serious pain symptoms appear, a revision operation is performed, in which the outer hemisphere of the prefabricated implant is removed and an artificial acetabulum is installed (as in total endoprosthetics).

Obviously, such a prosthesis is not entirely suitable for young and active people. But in the elderly, motor activity is much lower, so this type of prosthetics is quite acceptable for them and often serves for a long time and regularly without replacement.

Manufacturers of ceramic implants

The ceramic production technology itself is quite complex. For this reason, most manufacturers (Zimmer, Smith & Nephew, Biomet, Aesculap, B. Braun, DePuy, Stryker) purchase material from the one-of-a-kind plant of the German company CeramTec (producing ceramics since 1974, owns 93% of the market). Over the entire period of its existence, the company has changed 3 generations and currently specializes in the 4th generation of material - Biolox delta, from which all innovative series of implants are made.

Particular attention should be paid to the recent development of Russian scientists - nanoceramics. This is a unique analogue of Biolox delta, in no way inferior to it. Research in this area began in 2011 at NEVZ-ceramics JSC, and in 2015 the first nanoceramic hip prosthesis was implanted. The products have already been evaluated by such a large manufacturer as the Johnson & Johnson (DePuy) concern, offering joint participation in the project.

A nanoceramic product can last 20 years without replacement. It is characterized by high bioinertness and durability. Due to their relatively low price, these prostheses will soon be widely used in hip replacement surgeries as part of the government quota program.

PREPARATION FOR HIP ENDOPROSTHETICS

The decision about surgery is made by the doctor together with the patient. After determining the medical history, the doctor performs a thorough clinical examination to measure the patient's current range of motion, pain level, and functionality. During the examination of the patient, the surgeon examines radiographs, as well as CT and MRI data.

A thorough and complete medical examination before surgery will also be required. This is done in order to minimize the risk of complications during surgery. If a long surgery is expected or the patient's hemoglobin level is below normal, blood transfusions may be required after or during surgery. Prevention of thromboembolic complications is mandatory.

Service life of endoprostheses

The service life is affected not only by the material of manufacture and the skill of the doctor, but also by various diseases such as chronic polyarthritis, as well as the level of physical activity, the condition of the bone tissue and the weight of the patient. The average lifespan for a hip implant is 10-25 years. But this is only an estimated time.

Metal heads paired with polyethylene wear out after about 10 years, while ceramic heads last much longer. Ceramic hip replacements are the most durable, with an ultra-low wear rate (0.0001 mm per year). Under favorable conditions they can last for decades.

But most revision surgeries are performed not because of wear, but because of loosening of the structure and destabilization of the joint.

Advantages and contraindications

Advantages of bipolar endoprosthetics:

• surgical time and blood loss are reduced. Duration about half an hour;
• the fastest possible rehabilitation;
• Technically it is easier to perform than prosthetics with other types of implants, the cost of manipulation is lower;
• most manufacturers offer prostheses with removable heads, which simplifies the task of selecting an implant for each individual patient, and also simplifies the task of revision surgery;
• longer service life of the prosthesis (depending on how accurately the outer hemisphere is selected to the size of the acetabulum, as well as on the strength of the stem and the reliability of its fixation in the bone).

Contraindications to installation of a bipolar prosthesis:

• fracture of the acetabulum or its dysplasia;
• fracture of the femur with dislocation and subsequent impression of the socket;
• oblique line of the roof of the acetabulum, leading to imbalance of the joint.

What not to do after surgery

The postoperative period plays a key role for the service life of the hip joint prosthesis. It is very important to constantly monitor the operated hip, maintaining its correct position:

• sleep for the first days only on your back, keeping your legs in a semi-abducted position;
• You can turn on your healthy side, but only by slightly abducting your prosthetic leg. For insurance, it is better to place a cushion or pillow under it;
• It is permissible to constantly sleep on the healthy side no earlier than after 2 weeks;
• for the first week, do not move the sore hip with a large amplitude, do not make sudden and rotational movements;
• Under no circumstances should the hip flex less than 90 degrees (chairs should be high or supported by a cushion);
• You cannot cross your legs or lay one on top of the other;
• It is very important to regularly perform special exercises.

After three months, the doctor will evaluate the condition of the joint using an x-ray.

Osteoporosis as a cause of unreliable fixation of the prosthesis

The service life of the endoprosthesis is largely determined by the strength of its fixation in the bone cavity.
This requires dense bone tissue, which most patients have problems with due to various diseases such as osteoporosis. Osteoporosis is a loss of mechanical strength and a breakdown of the structure of the entire bone tissue due to an imbalance in the process of cell renewal. Due to the increased fragility of bones in osteoporosis, fractures are common, including at the femoral neck.

Normally, in a person aged 30-50 years, the number of destroyed bone cells is replaced by an equal volume of new ones. After age 50, approximately 1% of bone cells are lost per year. After 65, senile osteoporosis occurs, associated with the natural weakening and wear of the skeleton.

It is especially difficult for women - in the first year after the onset of menopause, the loss is 10%, then 2-3%. This is due to changes in hormonal levels, which is why hormone replacement therapy is popular in some countries to avoid loss of muscle and bone mass.

But the disease can begin to develop long before the due date for the following reasons:

• smoking;
• abuse of coffee and alcohol;
• predominance of meat in the diet;
• lack of calcium and vitamin D3;
• against the background of rheumatoid arthritis;
• sedentary lifestyle.

Why does a femoral neck fracture occur?

Bone loss as a result of age-related and hormonal changes often leads to a significant decrease in its strength and sometimes inability to withstand even physiological loads.
This circumstance quite often leads to a fracture of the most loaded parts of the bone skeleton; most often the neck of the femur is susceptible to disaster. This short section of the thigh is a weak point in the supporting structure from the back of the head to the heels, and a violation of its integrity makes it impossible to support the leg. A fracture often occurs due to a minor injury, such as a fall on the hip joint, although there are scientific studies indicating that the fracture occurs first, and then a fall on the side of the injury. As a rule, such an injury is the lot of elderly or senile people who have already accumulated many health problems: hypertension, coronary heart disease and other related diseases.

A fracture of the femoral neck immobilizes a person, depriving him of the ability to rise and lean on his leg. Once in a hospital bed, the patient finds himself in a plaster cast or skeletal traction. In the absence of physical activity, side health problems grow like a snowball - among them, insufficiency of the function of internal organs, bedsores, congestive pneumonia: problems that are easily acquired and extremely difficult to resolve.