Knee Replacement

What is a total knee replacement?
A knee replacement involves replacing a worn out knee joint with a metal and plastic replacement. The femur (thigh bone) has its end resurfaced with metal and the tibia (shin bone) has its top end resurfaced with a flat metal tray. A plastic tray separates the two metal implants. Sometimes the metal tray is substituted for a thicker plastic insert. It is not usually necessary to resurface the patella (knee-cap), but any irregularities of bone are trimmed to make it smooth.

What are the metal and plastic components made of?
The metal components are made of cobalt chrome and the plastic of polyethylene.

I’ve heard of a new metal that lasts longer.
A new ‘ceramic-metal’ called zirconium is available for the femoral part of the joint. Its surface is an oxidised metal making it act like a ceramic. Theoretically, it has up to 80% less wear than conventional cobalt chrome implants, but no long term data is available as yet.

What happens during the operation?
A 10-15cm vertical cut is made just to the midline of your knee, and the bone is prepared to allow the knee replacement. The metal and plastic components are attached using ‘bone cement’ which is comparable to grout. Once the new knee is stabilised, it is then washed out and the wound stitched up and bandaged.

How long does it take?
Usually about an hour.

What happens after the operation?
Once you have woken up, you return to the ward. The next day you get out of bed and start physiotherapy to get your knee moving. Most people require five days in hospital before they are safe to go home, but it depends on the individual and often the time in hospital is as little as three days. If you are finding it difficult, you may require a special machine (CPM) to help you bend your knee. The physiotherapists will arrange further physiotherapy as an out-patient.

How long does it take to get over the procedure?
Everyone varies, but in general you should achieve a reasonable range of movement in about three months, but will continue to improve for over a year. You may feel tired for a number of months.

Are there any complications with surgery?
Unfortunately, there a number of potential complications:

(i)      Thrombosis are clots in the leg. These are quite common, but most patients are unaware of them and they cause no problems and resolve with no specific treatment. However, sometimes they can be large and cause considerable problems. If they break off and travel to the lungs they are called embolisms, and can be fatal to 3 in 1000 patients. We will give you specific treatment to try and prevent this.

1. Infection is a serious potential problem that occurs in about 1% of patients despite the use of antibiotics. If the metalwork gets infected, it is exceedingly difficult to eradicate the infection, and may require numerous operations, with no guarantee of success. We will give you antibiotics to try and prevent infection.

2. Aseptic loosening is a term used to describe the wearing out of a joint in time. Roughly 95% of total knee replacements last 10 years, but in certain people the lifetime of the joint may be a lot less. Many joints can last far longer, if the patients looks after his or her joint well.

(iv)    Persistent pain can occur even after an otherwise apparently successful knee replacement. The cause is often not evident and it may be impossible to eradicate it as re-doing the operation does not improve the symptoms.

(v)     Stiffness can occur after the operation. The operation is designed to eradicate arthritic pain, not to regain movement and in general the range of movement you had prior to the operation is the range you gain afterwards. However you may loose a few degrees movement and in a few cases the stiffness is severe leaving the patient with less than 90 degrees movement, which can make walking, and getting up from a seated position very difficult.

Although there sounds like there a lot of complications, the overall success rate is about 90%.

If the joint wears out in the future can it be replaced again?
Yes is can, but the success rate is not quite as good, surgery is more difficult, the complications are twice as likely and it takes more out of the patient, who is older and perhaps not quite as fit and he or she was the first time around.

Will all this be explained to be in clinic?
Yes, we will go through the operation in great detail and allow you to ask any questions you wish. 
 
Are there any alternatives to a knee replacement?

Yes there are and include adequate pain relief, knee braces, physiotherapy injections and washout of the knee. We will explore all these avenues before embarking on a knee replacement.