Knee prosthesis

Need for a knee prosthesis often first arises later on in advanced osteoarthritis of the knee (gonarthrosis). In most cases, however, other treatment options are exhausted before an artificial knee joint is implanted.  A partial or full knee replacement is implanted depending on the extent of damage.

The knee joint is extremely complex. As the joint surfaces of the bones of the upper and lower leg do not fit exactly together, the menisci lie between them. They function to improve stability and ensure uniform load transmission. If damaged, the load on the joint cartilage is increased and osteoarthritis may develop. Otherwise, the most common causes of damage to the knee joint are chronic overloading of the knee and a deformity of the legs (knock knees or bow legs).

Typical symptoms such as pain and loss of mobility increase as the osteoarthritis progresses. A knee prosthesis is only implanted when the symptoms can no longer be satisfactorily alleviated otherwise. A partial or full knee replacement is implanted depending on the extent of damage to the knee joint.

What preparations are carried out before the procedure?

Prior to the procedure, the degree of osteoarthritis of the knee joint is determined based on x-ray images and, where applicable, MRI scans. The precise dimensions of the knee joint are measured so that the prosthesis can be sized accordingly in a computer simulation.

As a rule, you are admitted to the hospital on the day of the operation. Agents used to arrest bleeding are discontinued a few days prior to the procedure. As is usual prior to surgery, blood and allergy tests may be carried out as required, and an ECG is performed or blood pressure taken.

How is the operation performed?

Knee replacement surgery is performed under either local anaesthesia of the spinal cord (spinal anaesthesia) or under general anaesthesia. Which anaesthesia is used depends on each patient’s individual situation.

The knee joint is first exposed with an incision along the kneecap and the kneecap moved to one side. The anterior cruciate ligament is then removed, as the artificial joint later acts as a replacement. The posterior cruciate ligament may also be removed depending on the prosthesis used. The damaged joint surfaces on the upper and lower leg bones are excised with a bone saw. For greater precision, sawing is often computer-guided. A test joint is then first implanted to check joint stability. The definitive artificial joint is implanted afterwards. The prostheses are made of metal or titanium parts with plastic parts in between.  The artificial joint is anchored on the lower leg with bone cement. With the upper leg, the prosthesis is usually so firmly jammed with the bone that no cementing in place is required.

Before the surgical wound is closed, there is a final check of knee joint function with the artificial joint in place. The entire procedure lasts approximately two hours.

What is the success rate of this procedure?

No knee prosthesis can fully replicate the function of the natural knee joint. There are often residual symptoms with certain functional deficits in daily and sporting activities. The decision to replace the knee with an artificial joint is therefore only taken if improvement can be achieved with the knee replacement compared to the situation with the damaged joint. An artificial joint also does not last for ever. It will need to be replaced after around 15 years.

What are the possible complications and risks of this procedure?

Like any other operation, there are certain risks attached to knee replacement surgery.  As with all surgery, the operation may occasionally lead to infections, nerve damage, post-operative haemorrhaging or blood clots. In rare cases, excessive scar tissue may form, reducing joint mobility.

What happens after the operation?

After the operation, you will spend a few hours in the recovery room. You will then be taken to your hospital room, where a physiotherapist will help you take your first steps. You will exercise the knee joint from the very first day using a special device (knee CPM). You will stay in the hospital for around five days. During your hospital stay, the fit of the prosthesis is checked again using x-ray images and you will be instructed about exercises to regain mobility.

Once home, you can put your full weight on the joint. However, to avoid falls, you should first use a walking stick until you are confident again about walking.

There will be a follow-up after around eight weeks. Depending on your job, you will be unable to return to work from six weeks (office work) to three months (heavy physical work).

 

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