painful knee

What is a total knee replacement?

A knee replacement is when an artificial joint is inserted, most often in the scenario of osteoarthritis.

Osteoarthritis itself is the degeneration or wearing out of the joint surface of a joint that moves. In the case of a knee, it involves the knee surfaces. The most common areas affected are the area between the main thigh and calf bone (femur and tibia) or between the patella and the femur (kneecap and thigh bone). Arthritis is very common, and can develop due to wear and tear (degeneration) or family history. Factors that hasten its development are smoking, some medical conditions and previous injuries such as cartilage tears or fractures (break of the bone) around the joint.

How is knee pain and arthritis treated?

Treatment of arthritis, in general, is the treatment of the symptoms (namely pain). Options of treatment start with simple measures such as regular analgesics such as Panadol or stronger versions such as Panadeine or Panadeine Forte progressing up to more heavy medications such as Endone (which is used sparingly) as well as anti-inflammatory medications such as Voltaren. Other options include physiotherapy and hydrotherapy. 

Physical measures to take stress off the knee are important, such as weight reduction and use of a walking stick to take stress off the painful knee when lifting the good leg off the ground. If all of these measures fail, then in an appropriate patient, a knee replacement is considered.

A knee replacement is undertaken through an incision through the front of the knee, and the thigh bone and leg bones are cut (shaped) to fit metal plates onto the ends of the bones. These are inserted with or without the use of a bone cement and are separated from each other by a plastic liner. A second plastic liner is placed behind the patellar (knee cap). 

This leads to a protective covering over the ends of the bones, with a plastic liner. This lubricates the two joints and has the advantage of re-aligning the leg into more normal alignment, as often in arthritis the knee falls into knock kneed or bow legged (valgus or varus) positioning. Surgery is a very common procedure, but one needs to be aware that knee replacements do not last forever.

How does a knee replacement wear out, and how long does it last?

A knee replacement wears out with the bearing surfaces abrading with use, and this leads to small microscopic fragments of either metal or plastic floating off around the knee. This then lodges around the knee replacement and is considered a foreign body. The body tries to get rid of the small fragments of plastic or metal by attempting to destroy it and in doing so, releases enzymes which do not affect the fragments but damages the bone around it, leading to the knee replacement becoming loose in time.

In general, a knee replacement should last between 15 to 25 years but they can wear out abnormally quickly, particularly when extra stress is placed through the knee or if infection develops. Extra stress is placed on the knee by weight bearing in a patient who is carrying excessive weight. As such, weight reduction prior to surgery is important both to help reduce symptoms, reduce the speed at which knee arthritis develops and also protect the knee replacement when it is undertaken.  

In considering a knee replacement, it is important to know how long knee replacements last for, and therefore the Australian Orthopaedic Association introduced an arthroplasty registrar which keeps track of all of the joint replacements undertaken in Australia.

As such we refer to this registry at Glenelg Orthopaedics and choose a knee replacement based upon this. 

What is the advantage of a knee replacement?

After a knee replacement is undertaken, the patient will often have significantly less pain, with the ability to walk longer and feel more comfortable. Full range of motion does not always occur and the knee will always be more swollen but over 90% of patients are very satisfied with the procedure.

What are the risks of a knee replacement?

The risks of a knee replacement need to be considered carefully. The primary risk is the risk of the anaesthetic, which carries the risk of chest infections, cardiac distress or heart attacks, and anaesthetic complications such as CVA (stroke). These are extremely rare but patients who are at higher risk will be assessed prior to surgery by the anaesthetist to minimise such risks. Other risks include risks of clots (Deep vein thrombosis, also known as DVT) which can form in the legs and travel to the lungs with serious consequences. Such risk is reduced by early mobilisation and moving the leg in the post-operative period, as well as the use of blood thinners. Most patients will have an area of numbness on the lateral aspect (outside of the knee) which will feel a little unusual. This usually improves with time but may not fully recover. Finally, there is a risk of infection. This is thought to occur 0.5% of cases but is very serious and may require further surgery to attempt to clear the infection.

In general, a knee replacement can improve quality of life significantly, but does have risks which need to be considered carefully. At Glenelg Orthopaedics we can explain in a clear and concise fashion the advantages and risks of such procedures and you can be reassured we can provide advice and let you make up your mind, without pressure.

For any further information please feel free to make an appointment to see Dr Nimon or one of the specialists at Glenelg Orthopaedics.