Part Knee Replacement

What is a partial knee replacement?
As I have mentioned above, a total knee replacement involves replacing a worn out knee joint with a metal and plastic replacement. This involves replacing all of the femoral (thigh bone) surface and all of the tibial (shin bone) surface. This is an excellent operation for treating painful arthritic knees but in some patients, especially those who only have part of the joint worn out, they may feel that after the knee has been replaced, it is not quite ‘normal’ in feel.

In these patients it is possible to replace only the worn part and leave the non-worn part of the knee, resulting in not only a pain free knee but also one that feels more ‘normal.’

What bits can be replaced?
Basically we can replace any bit that is worn out. The most common pattern of wear occurs on the inside of medial part of the knee. Replacing this part only is called a ‘uni-compartmental’ knee replacement. It is similar to a total knee with metal and plastic components but smaller and covering only the inner (medial) part of the knee. Less commonly the outer or lateral part is worn in isolation and can be replaced in a similar way.

Sometimes it is only the knee cap or patella that is worn along with the underlying cartilage in the centre of the knee called the trochlea. This can be replaced with what is known as a patello-femoral joint replacement. In this case, the trochlea is replaced with metal and the patella with a plastic button.

Some patients have arthritis is two areas, most commonly in the medial compartment and patella/trochlea area. These can be replaced individually with two separate partial replacements or with one component that covers both areas, a so called ‘bi-compartmental’ knee replacement.
   
Can that new metal, zirconium, be used in partial knee replacements?
Yes, the ‘ceramic-metal’ called zirconium is available for the femoral part of the joint in both inner (medial) and outer (lateral) compartment replacements as well as the trochlea part in a patello-femoral replacement. It is also available for the bi-compartmental replacement.  

Can anyone have a partial knee replacement?
Any patient can have one but what is more important is whether your pattern of arthritis is appropriate. If the arthritis is limited to one compartment, inner, outer or patella, then you may be a candidate. However there are a number of requirements such as the knee not having a fixed flexion deformity which is a medical term for being able to straighten your leg fully. Similarly the knee cannot be too angulated in any direction and also the anterior cruciate ligament, the main internal ligament in the knee, needs to be functioning. This will be determined during the clinical examination, although you may need a scan to assess whether your knee is suitable.

What happens during the operation?
A small vertical cut is made over your knee depending on which bit has worn out. The bone is prepared to allow the partial knee replacement and 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 – about the same as a full replacement, although usually a slightly shorter time.

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. If you feel up to it you can start that day! Most people require a maximum of five days in hospital before they are safe to go home, but it depends on the individual – many are home in a couple of days.

How long does it take to get over the procedure?
Everyone varies, but in general you should achieve a full 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 and these are the same as a full knee replacement.

(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.

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.

Aseptic loosening is a term used to describe the wearing out of a joint in time. Roughly 95% of partial 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.

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.

Further wear can occur in the remainder of the joint, the part that wasn’t replaced. This may require that part to be replaced in the future. Therer is, however, some evidence, that inn the case of a medial (inner) sided replacement that the wear on the lateral or outer part is slowed down. So you may never require further surgery to the rest of the knee.

Although there sounds like there a lot of complications, the overall success rate is about 90 - 95%.

If the joint wears out in the future can it be replaced again?
Yes is can, but you would require a full knee replacement the second 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.