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Types of Joint Endoprosthetics

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Types of Joint Endoprosthetics

The methods used in joint replacement depend on the diagnosis and, therefore, on the causes for the disruption of musculoskeletal apparatus. Diagnostics include an X-ray and a computer tomography, which help to estimate the damage degree and determine what type of endoprosthetics is required for the patient: a partial or a full. The patient's general condition, their age, concomitant diseases are also taken into consideration when selecting the prosthesis size and type.

A joint replacement surgery is performed when traditional medication and physiotherapy were proven ineffective. The improvement of joint replacement methods has reached such a level that patients no longer need a special rehabilitation.

The orthopaedic clinics in Germany perform hip, elbow, knee, shoulder, and other joint replacements. The main task of these operations is to restore the normal functioning of the joint and to eliminate the pain.

The types of joint arthroplasty differ in the way the prosthetic is attached to the bone. The replacement operation with cemented fixation utilizes special glue. This technique is considered to be outdated because it does not provide a reliable connection.

Usually the uncemented fixation of endoprosthetics is used. The method is extremely reliable because of the porosity of the prosthetic material. Over time, the bone tissue grows into its pores and securely holds the endoprosthesis.

Given the degree of joint damage and the general clinical picture, the prosthetics of different configurations are used depending on the case. Among other things, one should take into account that any artificial joint has a certain lifespan, so over time it may need to be replaced. There are four main types of hip replacement operations.

  1. Partial prosthetics of the hip joint. During the operation part of the acetabular cup, the femoral neck and the femoral head are removed. In this type of surgical treatment the hip joint is completely replaced with a prosthetic. The acetabulum is usually reconstructed using ceramic and metal. The material is attached with special glue or screws. The femoral head prosthetic is attached to the femur using a special stem. This operation requires a fairly long rehabilitation period.
  2. Total joint endoprosthetics. This type of hip prosthesis is one of the most difficult because it involves a complete replacement of the hip joint. The total hip joint replacement is a necessary measure in the event, when during the course of the disease, the pelvic bone and the joint bed were completely destroyed, making it impossible to restore them. In addition, total endoprosthetics can be appointed when the patient is overweight and the partial replacement of the joint does not guarantee that the prosthetic can hold the load. Among other things, the total replacement of the hip joint can be assigned in the case of severe deformation of the femur and the acetabulum.
  3. Surgical replacement of the joint surfaces. In some cases, doctors may assign a light surgical correction of the damaged joint. Such operations are only possible if the erosive process affects only the surfaces of the acetabulum and the pelvic bone head. Such operations have minimal surgical impact and are aimed solely to strengthen the acetabulum and the surface of the femoral head with artificial materials.
  4. Revision hip joint replacement. Typically, this operation is assigned when the inserted prosthesis has reached the end of its service life and needs to be replaced. In some cases, the revision arthroplasty of the hip joint may be appointed before the artificial joint has reached its end of life in cases where the prosthesis ceases functioning due to unforeseen circumstances, for example damage to the prosthetic as a result of a fall. To perform the secondary hip arthroplasty the doctor needs to have a high level of professionalism, since replacing the old prosthetic is a rather painstaking work requiring extreme accuracy.

The stem of most hip endoprostheses is made of titanium alloys or cobalt and chromium based alloys. Prostheses stems have different shapes and are often covered with porous material allowing the bone tissue to grow into the endoprosthesis.

The endoprosthesis head is made of ceramic materials or cobalt or chromium based alloys. The head surface is thoroughly polished in order to achieve effortless sliding inside the cup component of the endoprosthesis. Metal, ultra high molecular weight polyethylene or reinforced by metallic elements polyethylene are used for the cup component. Depending on the required implant size, the total weight of all components of the endoprosthesis can be around 400-500 g (0.9-1.1 lbs).

All the materials have following common characteristics:

  • Biocompatibility with the tissues of the human body. They cause no rejection reactions from the body.
  • They are resistant to corrosion, deterioration and destruction. They retain their form and functionality for a long period of time. These properties are particularly important for normal joint operation.
  • The mechanical characteristics of the materials correspond to the biological structures they are replacing. Sufficient toughness of the endoprosthesis materials allow it to sustain the weight load, pressure resistance ensures the flexibility of the endoprosthesis. The ability of the components to slide relative to each other is created by their smooth surfaces.
  • The highest quality. Strict quality control and high standards are combined with affordable prices.

In order to be able to fully adapt the endoprosthesis to the body and weight of the patient, each endoprosthesis element is manufactured in different sizes.

Commonly Used Prostheses

Here are some examples of the most commonly used hip prostheses:

  • Prosthesis with a metal ball and a plastic cup (liner). This type of prosthetics is being used since the early 1960s. Nowadays it is made up of the so-called cross-linked polyethylene, this type of plastic liners wears out less.
  • Prostheses with a ceramic ball and a plastic cup (liner). The ceramic head of the femoral component are harder and more resistant to scratches than those made of metal. Together with the plastic cup liner, they make the prosthetic much more resistant to fretting than the metal head prosthetics.
  • Metal-on-metal prostheses. Metal-on-metal prosthetics do not have a liner, and the femur head is much larger, making it possible to have a wider range of motion and less chances of hip dislocation. In addition, metal-on-metal prostheses are much more wear resistant than their plastic analogues and have a smaller percentage of inflammatory reactions. However, there is a constant debate that metal fragments that emerge as a result of metal over metal friction can be linked to the increased level of metallic ions in the blood. Whether it actually affects the patient's health or is yet unknown.
  • Prostheses with a ceramic ball and ceramic liner. This type of prostheses is considered to be one of the most reliable. Their longevity and endurance make the full ceramic prostheses suitable for younger patients. Since ceramics is the most durable material used for prostheses, it is characterized by very low wear: about 0.0001 mm per year. Ceramic surfaces are also very smooth, which also contributes to the decreased level of wear. However, long-term durability data is still limited as this type of endoprosthesis is relatively new.

There are many types of implants and the ways they are installed. What brands and designs will be used by your doctor depends on many factors, including:

  • patient’s needs: their diagnosis, coexisting diseases, anatomical features of the knee joint, as well as physiological age, weight, level of habitual activity;
  • experience level of the orthopaedic surgeon, their knowledge of a particular type of implant;
  • price and working lifespan of the implant.

The doctor must describe the type of the selected implant and prosthetic technology that will be used to replace the knee joint. You decide whether to accept it or not.

Most likely that one of the following procedures will be proposed:

  • partial prosthetics;
  • total prosthetics;
  • tibial osteotomy;
  • revision knee joint replacement.

Partial (Unicompartmental) Knee Endoprosthetics

This type of knee joint arthroplasty is widely used, as this low-invasive approach can significantly reduce the recovery period.

Advantages of the technology:

  • shorter hospital stay (2-3 days less compared with the traditional complete joint replacement);
  • short recovery period: 1-2 weeks after the operation many patients are already able to walk on their own, without assistance;
  • less blood loss compared to the full replacement: patients less often need a transfusion;
  • the postoperative period is less painful. Even patients who had surgery on both knees at once are able to walk without the help of a walker or a cane quite quickly.

Total Knee Joint Replacement

For a long time this procedure was considered a "golden standard" for the treatment of gonarthrosis and the knee joint replacement in older persons (60 years and older). It is also used to treat younger patients.

According to clinical studies, after the full knee joint replacement in patients up to 50 years, 9 out of 10 implants remain functional after a decade; for elderly patients (60 years and older), the probability is about 95%. 1-1.5% of all operations per year fail. So the probability that the implant will serve for a long time is quite high.

At the end of the rehabilitation course following the installation of the knee joint prosthetics, most patients cease to limp, feel stiffness, are able to walk for a long time and to have recreational activities (travel, swimming, cycling).

Tibial osteotomy

This surgery implies cutting one of the bones and the redistribution of the walking load on the parts of the knee unaffected by arthritis. This procedure allows to postpone the replacement arthroplasty, but it still will be needed in the future.

Osteotomy has a number of drawbacks:

  • the decrease in pain is less than in total or partial knee joint replacement;
  • you will probably need another operation in less than a decade. Only 60-65% of patients who underwent an osteotomy will not need to have another operation in 10 years;
  • it is not performed in the cases when the joint is largely affected by arthritis.

Methods of Implant Fixation

There are several methods to attach an endoprosthesis to bones:

  • cemented. The implant is held in place with the help of quick-hardening bone cement (polymethyl methacrylate). The total cemented endoprosthetics of the knee joint is used mainly in elderly patients;
  • cementless. Endoprosthesis is pressed together with the bone. This type of fixation relies on the ability of the bone tissue to grow. Simply put, it grows inside the implant, forming a strong connection with it. This method is considered to be the most progressive;
  • hybrid. The femur component is inserted without cement, and the elements of the tibia and kneecap are fixed using cement.

Posterior Stabilized Knee Endoprosthesis

This design of a knee joint endoprosthesis implies fitting of metallic components into plastic elements. This ensures smooth motions and minimizes wear.

The tibial component in these models has a raised surface where the internal pin sits. The pin is firmly placed in a special slot on the femur. To ensure that the endoprosthesis components are firmly fixed to the bone, the posterior cruciate ligament shall be removed.

The smooth co-operation of the components mimics the function of the removed posterior cruciate ligament: preventing the hip bone from sliding forward along the surface of the tibia bone while the knee is bent.

Posterior Cruciate Retaining Total Knee Arthroplasty

With this implant it is possible to save the posterior cruciate ligament of the knee. Such endoprostheses have no central pin on the tibial component and its corresponding slot on the femur. Such implants are suitable for patients whose posterior cruciate ligament is in satisfactory condition, able to provide sufficient stabilization of the knee joint.

Partial (Unicompartmental) Knee Replacement

In case of a total knee joint replacement, massive implants are used to replace the ends of the femur and tibia bones. If only one part of the knee joint is damaged, small implants (partial, or unicompartmental implants) that replace the damaged area can be used.

Mobile-Bearing Knee Joint Implants

Mobile-bearing (rotating platform) knee joint implants consist of three components. This allows the endoprosthesis to simulate a real joint function. The presence of a rotating platform gives the plastic element inside the metal liner of the tibial component some rotation possibility. This design allows patients to rotate their knee inwards and outwards.

In comparison to other endoprostheses, implants with a rotating platform require more support from the soft tissue (ligamentous apparatus of the knee joint). Often, when the soft tissue is underdeveloped or weak displacement of the endoprosthesis occurs. Endoprostheses with a rotating platform usually cost more than other types of implants.

The results of clinical studies do not clearly reveal that the implants with a rotating platform serve longer, more effectively reduce pain, or improve the function of the knee joint.

Fixed-bearing Knee Joint Implants

Most patients receive an endoprosthesis with a fixed bearing. This type of implants have the polyethylene element of the tibial component firmly attached to the metal liner beneath it. The femoral component glides along the cushioning surface.

If the patient is too active, or suffers from obesity, the endoprosthesis with a fixed bearing wears out faster. This process is accompanied by endoprosthesis loosening and joint pain.

Endoprosthesis loosening is the main reason for artificial joints failure. For young and active patients and for obese and overweight patients, doctors recommend the knee joint implants with a mobile bearing or a rotating platform. Such implants serve longer and wear out slower.

The elbow joint replacement is performed quite rarely. Due to the complexity of its structure it is difficult to select a prosthetic that would fully mimic its function.

There are total and unicompartmental or partial elbow prostheses. A total joint replacement is more advantageous for older patients. Partial replacement of only the head of the ulna can be performed in younger patients.

Constructively there are two types of artificial elbow joints:

  1. Unlinked/Uncoupled Implants
  2. Linked/Coupled Implants

There are some other constructive options, such as partially or fully coupled systems.

The systems can also be divided into partial and total (TER) implants.

Though the need for a full elbow prosthetic is very rare. A more sparing option is a partial prosthetics, placed directly on the affected joint area. Because the elbow is a "coupling" consisting of several simple joints, only one of them usually gets replaced, most often the humeroulnar joint.

The choice between the coupled and the uncoupled systems depends not only on the degree of joint damage, but also on the condition of the ligamentous apparatus. If the ligaments are also affected, a special prosthetic stabilization is required, so the linked system is implanted. The patient's age, his or her general condition and, above all, the state of the bone tissue are also taken into account.

Unlinked/Uncoupled Elbow Joint Implants

In this case it means resurfacing prosthetics: the damaged sections of the cartilage layer are covered by a protective shell, that duplicates the shape of the corresponding joint element.

Usually the humerus joint head (the epiphysis at its lower end) or the ulna upper epiphysis are replaced this way. If both of them are affected the bilateral prosthetics of both joint elements is carried out. An uncoupled bilateral prosthetic is stabilized by elbow's ligaments, if they are healthy and functional.

Main indications for this type of prosthetics are severe secondary phase of arthrosis, unresponsive to conservative treatment, accompanied by severe pains. It is often the result of progressive rheumatoid arthritis in the elbow. We shall not exclude another underlying cause: consequences of a long-standing, incorrectly cured fracture of elbow bones.

The essential condition to install this system are healthy elbow ligaments.

This prosthetics scheme is especially suitable to young, physically active patients. The resurfacing prostheses better preserve the bone tissue of the joint. It allows the joint to serve for a long time after the surgery.

Linked/Coupled Elbow Joint Implants

Such systems are used for bilateral prosthetics (of both the upper and lower part of the elbow joint), if the ligaments are also damaged. An uncoupled implant would be unstable in this case.

There are two degrees of articulation: partial and complete.

Semiconstrained coupled models have movable, hinged connection between the upper and lower prosthetic parts.

A completely coupled joint prosthesis has a rigid connection. This is a particularly stable system. An additional stability factor is the axial locking of both linked parts. They are fixed with long pins inserted into tubular bone cavities along their longitudinal axes. It is possible to make a prosthesis for all three joints that make up the elbow, which are particularly complex systems used if the whole elbow is damaged.

However, the patient should be aware that with such a complex device, the lifetime of a completely linked joint implants is not as long as it of the uncoupled systems. Therefore, this prosthetics scheme is optimal for older patients (65 years or more), leading not to a very active lifestyle.

  • With resurfacing endoprosthetics of the shoulder joint (resurfacing arthroplasty) only the joint surface (more often the head of the humerus) are changed. The main feature of the resurfacing endoprosthetics is that the damaged parts of the joint cartilage surface are removed without osteotomy. An artificial component of the endoprosthesis is installed on the peeled section of the shoulder bone.
  • Unicompartmental endoprosthetics (hemiarthroplasty). In the case of unicompartmental prosthesis, one of the two shoulder joint parts is changed (either the head of the humerus or the glenoid cavity of the scapula).
  • Total shoulder joint replacement, with a complete replacement of the adjoining surfaces (both the head of the humerus, and the glenoid cavity of the scapula). There are two types of total shoulder joint replacement: the replacement of only joint surfaces (Partial Resurfacing Arthroplasty - PRA) and the use of prostheses on a stem (Total Shoulder Arthroplasty - TSA).
  • Revision shoulder joint arthroplasty is an operation performed to replace the existing endoprosthesis or its component.

There are two types of endoprostheses on a stem:

Anatomical Total Endoprosthesis

This endoprosthesis copies the natural shape, build, and biomechanics of the shoulder joint. The affected joint surfaces are replaced with similar artificial components. A sine qua non for anatomical endoprosthesis is the preservation of the elements of the rotational cuff, which stabilizes the joint pushing the prosthetic head into the glenoid cavity of the scapula, because the surface of the artificial shoulder joint is less than the size of the adjoining surface of the prosthetic head, which, on the one hand, increases the possible amount of motion in the joint and, on the other hand, increases the risk of dislocation of the endoprosthesis head.

Reverse Total Endoprosthesis

The philosophy of this endoprosthesis is in the opposite location of its components. It means that the blade component has a hemispheric form (similar to the humeral head), and the shoulder component has a concave shape. In the case of degenerative changes of the shoulder rotator cuff, its thinning or rupture, gradually progressing arthrosis of the shoulder joint occurs, the shoulder bone gets cranially displaced (upwards, under the acromion) and the joint becomes unstable. This is when this kind of total endoprosthesis is needed.

The stem of the endoprosthesis can be fixed without cement (using the press-fit method, i.e. firm impaction) and with cement (the components are fixed to bone with bone cement). The choice of fixation type depends on a number of factors, such as the quality of the bone, the patient's age, the concurrent conditions, the anticipated activity after the operation and many others, and is made in each case individually.

Ankle joint prosthesis system does not have such a broad constructive diversity as, for example, artificial knee or hip joints. Due to the extremely complex "design" of the ankle joint its partial and multifarious prosthetics are impossible. In Germany, the only option available is total prosthetics.

Accordingly, all applicable systems are based on a single design decision: upper and lower protection for intra-articular surfaces and a "cushion" in-between serving for their soft interaction. Hence their general name: total ankle joint endoprosthesis.

All models of artificial ankle joints consist of three main parts:

  1. A round metal plate that closes the top bulging contact surface of the foot hucklebone;
  2. A metal plate closing the bottom contact surface of tibia;
  3. A movable polyethylene core in-between.

While it is a total prosthesis, the method used is generally sparing, conserving a lot of bone tissue. There is no need to use long pins to stabilize the prosthetic parts. The protective plate on the hucklebone is secured with small pins. The basic fastening principle is a firm, anatomically calibrated clasping of the bone surface by a plate and special properties of the adjacent surface ensuring that it is covered by the bone tissue. Same principle is used on the top plate. The only fastener is the central pin (which is also short). Plus the effect of surface intergrowth.

The polyethylene core is not fixed. It glides freely between the plates, thus facilitating their mutual functional mobility relative to each other. However, the plastic part cannot slip from the clamp, and it is hampered by the stabilizer on the edge of the top plate. Thus, the solid parts of the prosthesis have an everlasting (in principle) liner: its surface properties are very close to the properties of a healthy joint cartilage.

The precise fitting of polyethylene and metal surfaces provides a reliable guarantee against the material attrition, improves the durability of the artificial joint. In addition, the polyethylene core optimizes the load distribution in the prosthetic zone, which also contributes to longevity. And allows the recipient of the prosthetic to walk, run, and even jump without hindrance.

GermanMedicalGroup + 49 (7221) 39-65-785 Flugstrasse 8a 76532 Baden-Baden Germany The methods used in joint replacement depend on the diagnosis and, therefore, on the causes for the disruption of musculoskeletal apparatus. The methods used in joint replacement depend on the diagnosis and, therefore, on the causes for the disruption of musculoskeletal apparatus. 2017-11-13 The methods used in joint replacement depend on the diagnosis and, therefore, on the causes for the disruption of musculoskeletal apparatus.

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