A knee prosthesis, also known as a knee replacement prosthesis, is an artificial substitute for the knee joint and offers a solution for advanced joint damage, particularly for patients with osteoarthritis of the knee (gonarthrosis). However, the artificial knee joint is usually only used once other treatment options such as physiotherapy or medication therapy have been exhausted. Depending on the extent of the damage, a partial or total prosthesis is inserted.

Knieprothese - Arzt kontrolliert die Knieprothese

Overview of osteoarthritis of the knee

The knee joint is an extremely complex joint. The joint surfaces of the upper and lower leg bones do not match each other precisely, meaning that the menisci lie in between them. Their purpose is to stabilise the knee and ensure an even transmission of force. Damage to the menisci, chronic overloading of the knee or misalignment of the legs (bow-legs, knock knees) put the articular cartilage under increased strain and can cause osteoarthritis to develop. In osteoarthritis, not only is the articular cartilage worn out, but the bone close to the joint also changes and can become damaged. With this condition, inflammatory reactions additionally occur in the joint, often causing severe pain.

The treatment of osteoarthritis focuses on relieving pain and maintaining joint function for as long as possible. Depending on the severity and the individual case, treatment initially takes a conservative route, for example through physiotherapy or anti-inflammatory medication. In cases of advanced osteoarthritis, surgery such as a conversion osteotomy or a knee prosthesis may be considered.

Treatment goal

A knee prosthesis is primarily used to treat advanced osteoarthritis. Typical symptoms such as pain and loss of movement increase as osteoarthritis progresses. The main goal of a knee operation with a knee prosthesis is therefore to renew the knee’s natural mobility and to reduce pain long term. The knee prosthesis is used when conservative treatments are no longer enough to alleviate the symptoms.  Depending on the extent of the joint damage, either partial prostheses (hinge prostheses) or total prostheses (complete surface replacement) are used.

Surgical procedure

Surgical procedure for total knee replacement

Knee replacement surgery can be carried out under spinal anaesthesia or under general anaesthesia and takes about one to two hours.

First, the knee joint is opened up using a longitudinal incision along the kneecap, with the kneecap being carefully pushed to the side. The surgeon then removes the anterior cruciate ligament, whose function is later taken over by the implant. Depending on the type of prosthesis, the posterior cruciate ligament is sometimes also removed. A bone saw is then used to remove the damaged joint surfaces precisely, with computer-aided navigation systems often helping to optimise the alignment of the incisions.

First, a test joint is inserted to check the stability before the final artificial joint, consisting of metal or titanium components with plastic parts in between, is fixed in place. On the lower leg, the new knee joint is anchored with bone cement, while on the thigh it is often firmly clamped to the bone, eliminating the need for cementing. Before closing the surgical wound, a final check of the knee joint function is performed with the artificial joint.

Surgical procedure for partial prosthesis (hinge prosthesis)

Not all areas of the knee joint are affected by osteoarthritis. If only the area of the kneecap or the inner or outer part of the joint is worn out, a partial knee prosthesis, also known as a hinge prosthesis, may be a suitable solution. The key advantage of a partial prosthesis is that it only treats the damaged part. As a result, the intervention is more gentle on the patient and the recovery time is noticeably shortened.

Some basic steps of the procedure for a partial prosthesis (sled prosthesis) are similar to those for a full prosthesis. Both surgeries can be performed under spinal anaesthesia or general anaesthesia and include the opening of the knee joint and the precise removal of damaged joint surfaces. The procedure for partial prostheses also often uses a navigation system to precisely align the incisions.

However, the main difference lies in the target region and the size of the intervention. While the total prosthesis replaces all the joint surfaces of the knee, the use of a partial prosthesis is limited to the specifically affected area – either the inner or outer part of the knee joint or behind the kneecap. As a result, more of the natural joint structure is retained, which makes the intervention gentler and enables faster recovery. In addition, the anterior cruciate ligament is often retained, as the intervention only works on limited parts of the knee , further aiding with stability and functionality.

New treatment option – Mako robot-assisted knee prosthesis

Hirslanden Klinik Permanence and Salem-Spital are the first hospitals in Switzerland to use the Mako robotic arm-assisted surgical technique. This procedure is a new treatment option for knee joint replacement designed to increase the precision of the implant of a total or partial prosthesis using a robot arm. You can find more information here.

Preparation and precautions

Choosing the artificial knee joint

Before the surgery, the knee joint is thoroughly analysed as part of a comprehensive process. X-ray images and, if necessary, MRI scans are taken to determine the extent of the damage in detail. Based on these images, precise measurements are carried out and then provide the basis for precise planning of the surgery. With the help of an advanced computer simulation, the prosthesis can be individually adapted and the subsequent positioning prepared as realistically as possible. This ensures that the implant is matches the anatomical conditions as best as possible, resulting in a better fit and long-term stability.

Choosing a suitable knee prosthesis also requires close collaboration between doctor and patient. Different types of prostheses offer individual benefits, depending on the condition of the affected knee joint. The personal needs and lifestyles of patients play an important role when it comes to deciding on the right artificial joint.

Preparing for the intervention

Patients are usually admitted to the hospital on the day of the procedure. Any anti-bloodclotting medications are paused a few days beforehand. Before the surgery, blood tests, possible allergy clarifications and an electrocardiogram or blood pressure test are routinely carried out. In addition, patients should refrain from eating for at least 6 hours before the intervention and from drinking for about 2 hours before the procedure in order to avoid complications during the anaesthesia.

Aftercare and recovery

After the surgery, the patient is first monitored in the recovery room for a few hours. After they have been transferred to the hospital room, they can take their first steps under the guidance of a physiotherapist. From the first day, physiotherapy and a special kinetic splint promote the mobility of the artificial knee joint. Patients usually stay in hospital for four to six days, during which time the fit of the prosthesis is checked using X-rays.

Placing complete strain on the joint is allowed at home. Initially, however, the use of walking sticks is advised to minimise the risk of falling until full safety is restored when walking. A check-up is performed after about eight weeks. Many patients can return to light sports that are gentle on the joints, such as cycling or Nordic walking, after three to six months. The duration of incapacity for work depends on the patient’s job: around six weeks in the case of office work and up to three months in the case of heavy physical exertion.

After the knee prosthesis is inserted, rehabilitation is a crucial step towards restoring full mobility. Physiotherapists work closely with patients to gradually improve the mobility of the artificial joint. It is important to strengthen the surrounding muscles in order to support the strain on the new joint and thus ensure the long-term durability of the artificial knee.

Long-term prospects of success

A knee prosthesis is unable to fully restore the functionality of a natural joint. Minor residual symptoms or functional restrictions often persist, especially in everyday life or during sports activities. For this reason, a knee prosthesis is usually only inserted if it promises a noticeable improvement in quality of life compared to a worn joint.

The average durability of an artificial knee joint is about 15 years and can vary depending on the strain. Various factors can limit the service life of a knee prosthesis, including mechanical stress, such as sports that are heavy on the joints, and immunological reactions, such as infections and allergies. These influences can cause the implant to loosen over time, which can often lead to increased pain during exercise and unsteadiness when walking.

Potential complications

Despite good planning and preventive measures, the insertion of an artificial knee joint is also associated with certain risks. As with all surgeries, occasional infections, nerve injuries, bleeding or blood clots may occur. In rare cases, excessive scarring can occur, which restricts the mobility of the joint.

In other rare cases, it is possible for the knee prosthesis to detach from its anchorage in the bone prematurely. The cause of this loosening may either be septic (infection-related) or aseptic osteolysis (non-infection-related bone-degrading reaction). In these cases, the existing prosthesis is removed and replaced with a new implant as part of a revision operation.

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