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The patello-femoral joint (PFJ)  or knee cap joint sits at the front of the main knee joint . It is essentially a complicated pulley which serves to increase the efficiency of the muscles which operate the knee joint. Although it is component of the whole of the knee joint, it often has its own set of problems which cause pain, instability swelling etc

Disorders of the patello-femoral joint are extremely common. They constitute up to a third of knee referrals for knee pain.

Unlike the hip joint, which is a ball and socket joint, the patello-femoral joint is very shallow and more like a cup and saucer than a ball and socket. As such, the patella (kneecap) is much less restrained, it is therefore more prone to direct injury and to dislocation or partial dislocation(subluxation). The articular cartilage behind the patella is the thickest in the body, even thicker than the hip joint! This is a reflection of the tremendous forces which can go through this particular joint.

Because of it’s lack of structural constraints,it is more dependent on the surrounding soft tissues to keep it in place. Any condition which weakens those soft tissues , therefore lead to less controlled movement of the patella and subsequently to pain. Thus problems are very common in people who tend to have lax joints. Similarly, any condition which weakens the muscles around the knee will also tend to destabilise the PFJ Joint.

This is why physiotherapy is often a mainstay treatment for these disorders but also in the event that surgery is needed, physiotherapy still remains very important to achieve full rehabilitation and recovery.

If the groove that the patella sits in is particularly shallow or if the knee sits rather high in the groove it is much more prone to these abnormal movements and so to dislocation.

Thus it seems that some people are built in a way that makes them prone to disorders of the knee cap.

Dislocation of the knee Where the patella moves completely out of its joint is a well recognised injury. It can often be extremely painful and the patient may have to be taken to hospital to have the patella put back in place. The knee will remain swollen and painful for some time afterwards, and as a result the muscles will weaken and in some cases the patella can then redislocate without much force being applied. See section on recurrent dislocation

Some patients present with knee without dislocation or subluxation, just with a painful knee. Typically this will occur on climbing up or down stairs, crouching and kneeling, or even keeping the knee in one place for a length of time.

Instability or giving way of the knee is a very common symptom in those who have unstable or painful knee caps and often leads to them seeking professional advice

Not all disorders of the knee Require surgery and in fact most of them do quite well with conservative treatment which will be discussed in some of the later sections

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