Hip Impingement

• Hip impingement is also called 'femoroacetabular impingement'
• It occurs when the edge of the ball of the hip joint rubs against the edge of the socket
• It causes pain in the hip, groin, thigh or even knee
• There may be sudden sharp pains or catching sensations
• If symptoms fail to settle with rest or physiotherapy then you need to see a surgeon
• An MRI scan with dye injected into the hip may be required
• Treatment can be performed with a hip arthroscopy (keyhole surgery of the hip)

Femoroacetabular Impingement (FAI) is a condition whereby the bone at the front of the ball part of the hip joint (the femoral head) rubs against the edge of the socket (the acetabulum) when the hip is flexed up (ie, when the knee is brought up towards the chest).

There are generally two types of FAI:-

Cam - this is where the femoral head is not entirely round, and the edge of the head is therefore prominent,

Pincer - this is where the edge of the hip socket develops spiky bits of bone (called osteophytes) that catch on the femoral head/neck, ie it makes the socket too deep.

A lot of the time, these two forms exist together.

Normal hip, seen from the top looking down towards the foot.	Cam-type FAI caused by bony 'bump' at front of femoral head/neck.	Pincer-type FAI caused by deep socket or spikes of bone (osteophytes) at front of socket.

What causes FAI?

It is not yet clear whether FAI is something that is congenital (people are born with it) or whether it is a degenerative condition (like arthritis) that develops from wear and tear. It is likely that it may well be a combination of the two.

What are the symptoms of FAI?

FAI typically causes pain in the hip joint that is often felt in the front of the groin or at the top of the thigh. The pain is particularly bad when the knee is brought up towards the chest and the hip is flexed, especially if the thigh is rolled inwards at the same time (flexion + internal rotation of the hip).

How is FAI investigated?

FAI can sometimes be seen quite clearly on simple X-rays, especially if there is a Cam shaped femoral head present. However, sometimes it is necessary to perform additional investigations such as MRI scans. In particular, MR-arthrograms have the advantage of showing up other pathologies within the hip joint, such as labral tears, which are often seen in conjunction with FAI.

What happens if FAI is left alone?

If FAI is left untreated then it may potentially get worse with time, and the pinching of the edge of the hip may cause acetabular labral tears (tears of the rim of cartilage around the hip socket), and it is possible that with time one may subsequently begin to develop increasing arthritis in the hip joint.

What are the treatments?

If the symptoms from FAI are mild, then conservative treatments may well suffice. These can include:-

• anti-inflammatories / painkillers
• physiotherapy /
• restriction of aggravating activities (rest)

For cases where the severity of the symptoms justifies intervention, then surgical treatment options include:- 

• Intra-articular injection of the hip joint with cortisone/steroid (in theatre under X-ray control)
• Hip arthroscopy

With hip arthroscopy, it is possible to shave down the excess bone at the front of the femoral head/neck, and to trim or repair any labral tears that might have developed.

Article written by
Mr Ian McDermott
Consultant Hip Surgeon and Knee Surgeon, London & Northwood
Last updated 13/01/10

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