Knee prosthesis loosening: information & specialists for knee prosthesis loosening

Most knee prostheses last at least 10 to 15 years. However, the prosthesis can loosen over time due to various factors. If the knee prosthesis is no longer firmly anchored to the bone, this is known as prosthesis loosening. Here you will find further information as well as selected specialists and centers for knee prosthesis loosening.

Definition

Around 190,000 artificial knee joints (also known as knee endoprostheses or knee TEP ) were implanted in Germany in 2019. Most artificial knee joints last at least ten to 15 years.

However, it can happen that the anchoring of individual components of a knee prosthesis in the bone weakens. This is known as knee prosthesis loosening.

Early loosening of the knee joint endoprosthesis is defined as loosening within the first two years after knee replacement surgery.

Twenty years ago, around eight percent of knee endoprostheses had to be replaced (revision surgery or replacement surgery). In 2017, it was still around six percent.

Knee endoprostheses highlighted in X-ray image © Joel bubble ben | AdobeStock

Types of knee prosthesis loosening

Knee prosthesis loosening can basically be divided into two forms.

• Septic knee prosthesis loosening: A bacterial infection (= septic, sepsis) in the area of the implant leads to loosening of the prosthesis.
• Aseptic knee prosthesis loosening: All forms of loosening that are not caused by a bacterial infection (= aseptic).

Septic knee prosthesis loosening mainly occurs in the weeks and months following implantation of the knee TEP. However, they can also occur years later. Aseptic loosening is particularly common in knee prostheses that have been in place for more than two years.

Symptoms of loosening of the knee endoprosthesis

Patients usually have little or no discomfort in the knee at the beginning of knee prosthesis loosening. Occasionally, however, the knee pain can start suddenly.

Over time, the pain, which is usually load-dependent, increases and the maximum walking distance decreases. The pain can also be triggered by a force acting on the knee, such as

• a twist in the knee or
• a blow or fall on the knee.

Some patients also feel localized pain at the point where the implant is attached to the bone. This is often on the shin below the knee, for example.

A swollen knee or an effusion in the knee joint can also occur.

Knee pain is a very common symptom of knee prosthesis loosening © Csaba Deli | AdobeStock

In the case of a septic cause, the knee may be reddened and overheated. Pus may ooze out of the scar, which may be separating. A fever with chills may also develop.

As the loosening and symptoms progress, mobility in the knee joint is reduced. The patient may limp and climbing stairs may be considerably more difficult.

In later stages, the pain also occurs at rest. The risk of bone fractures in the area of the prosthesis increases with pronounced loosening.

In addition, knee malalignment can occur(knock knees, bow legs).

Causes and risk factors

Possible causes of knee prosthesis loosening include, for example

• Bacterial infections that develop due to the introduction of bacteria.
• Knee endoprostheses are made of metal alloys and polyethylene. The abrasion of polyethylene can directly and indirectly dissolve the bone in the area of the prosthesis. This is also known as particle disease or abrasion-induced osteolysis
• Arthrofibrosis, i.e. excessive formation of connective tissue cells (scarring) in the knee joint after TEP surgery
• Misalignment or incorrect positioning of individual components of the prosthesis
• Loosening of the attachment of the prosthesis
• Unstable knee joint due to insufficient functionality of the extensor apparatus
• Periprosthetic fractures, i.e. bone fractures in the area of the prosthesis
• Damage or injuries to the patella or the patella replacement

Risk factors for septic knee prosthesis loosening

There are various circumstances in which the immune defense either no longer works properly or is suppressed. An inadequately functioning immune system can no longer fight off invading bacteria as well. The pathogens then find it easier to multiply and cause an infection on the prosthesis.

The risk factors for septic knee prosthesis loosening include, for example

• Immunodeficiencies
• Diabetes mellitus - diabetics have a 10-fold higher risk of prosthesis infection than non-diabetics, overweight diabetics even have a 20-fold higher risk
• Rheumatoid arthritis
• Chronic inflammatory skin disease
• Cancer
• Coagulation disorders
• Taking cortisone or anticoagulants
• Advanced age
• Severe obesity
• Nicotine, alcohol and drug abuse

Risk factors for aseptic knee prosthesis loosening

• Advanced age
• Severe obesity
• Problems with the prosthesis material, the bone cement and the technique used to implant and secure the prosthesis. This can occur with both metal implants and those made of polyethylene
• Lack of experience on the part of the surgeon when inserting the artificial knee joint, for example by selecting an implant that is too large or too small, not setting the stability correctly or not cementing it properly
• Pre-damaged bone due to osteoporosis or bone necrosis
• Pre-existing conditions (diabetes, gout, rheumatism, osteoarthritis, etc.)
• Traumatic events, such as an accident or fall

Osteoporosis (low bone density, as seen on the right) can be the reason for a knee revision © crevis | AdobeStock

Examination and diagnosis

Sooner or later, knee pain leads people to see a doctor. Based on the symptoms, gait pattern and medical history, it is often suspected that the complaints are due to the knee prosthesis. The doctor will ask the patient, for example

• when the knee TEP operation took place,
• what previous illnesses exist and
• whether traumatic effects have occurred.

To rule out a septic cause, a small blood count is taken and the CRP value in the blood is determined. Fluid is removed from the joint by means of a joint puncture and examined in the laboratory. If necessary, a tissue sample from the area around the prosthesis provides further information.

The most important imaging procedure is an X-ray examination of the knee. When evaluating the X-ray image, the doctor looks for typical signs of loosening. In order to better recognize changes, images taken at different times are compared with each other.

Indications of a prosthesis loosening are, for example

• Cement fractures,
• Bone fractures,
• implant fractures,
• Changes in the position of the prosthesis,
• Bone changes,
• abrasion of the sliding partners and
• axial changes.

Computer tomography (CT) and skeletal scintigraphy can also provide important information about the cause of the complaints.

General information on treatment

If a knee endoprosthesis has become loose, a knee revision (knee prosthesis replacement operation) must be performed. This means that the prosthesis is removed and replaced with a new prosthesis (so-called revision endoprosthesis).

The removal (called explantation) of the old prosthesis and the insertion of the new prosthesis usually take place during a single surgical procedure. This is referred to as a one-stage replacement operation.

This is a complex operation. You should therefore only have the procedure performed by experts in orthopaedics and trauma surgery with extensive experience in knee arthroplasty.

The aim of a knee revision is to

• to restore stability,
• eliminate discomfort and
• regain full mobility in the knee joint.

However, if the cause of the loosening is a bacterial infection, the treatment is much more complex. In this case, one operation is often no longer sufficient; at least two surgical procedures are required. The procedure is therefore referred to as two-stage alternating surgery.

During the first operation

• The prosthesis is removed,
• the infected tissue is cleaned and removed if necessary and
• antibiotic therapy is started.

The new knee endoprosthesis can only be inserted once the infection has completely healed. The initial aim of the treatment is to eliminate the infection. The second step is to achieve stability, mobility and freedom from symptoms.

A doctor checks the function of the knee after knee prosthesis surgery © amazing studio | AdobeStock

Progression and prognosis

The insertion of a revision knee prosthesis after aseptic prosthesis loosening is more complex than the initial implantation of a knee TEP. In principle, however, the procedures are comparable, also with regard to the subsequent risk factors for renewed loosening (see above).

However, due to advances in prosthesis technology and material properties, it can be assumed that the artificial knee joint will last longer than in the past.

If the infection can be completely eliminated in the case of septic prosthesis loosening, the prognosis is also good.

However, if the infection flares up again and again, this can result in further surgical interventions. Amputation may also be necessary in individual cases to prevent the infection from spreading.

Prevention

Above all, it is important that you only have knee surgery performed by proven experts in knee arthroplasty. As the surgeon's and clinic's experience increases, the risk of knee prosthesis loosening later on decreases.

Otherwise, you should avoid activities that put strain on the knee or only do them after consulting your doctor.

As being very overweight is also a risk factor for prosthesis loosening, you should avoid being overweight.