Hip impingement (FAI)

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What is hip impingement (FAI)?

Hip impingement occurs when a problem inside the hip joint interferes with its smooth motion, preventing the ball from gliding smoothly inside the socket. Over time, the cartilage can become damaged, leading to hip (or femoro acetabular) impingement, which is a risk factor for early osteoarthritis of the hip.

What causes hip impingement?

There are two main conditions which cause hip impingement:

  • Cam impingement is a deformity in the ball at the top of the femur, causing it to jam in the socket when the hip is bent.
  • Pincer impingement is a deformity of the socket which can cause the ball of the femur to rub against the rim of the socket when the hip is bent.

Hip impingement can also be caused by other, less common medical conditions such as coxa vara, which causes the thigh bone and ball to grow at different rates in children, and Legg-Calve-Perthes disease, which results in the death of bone in the ball of the joint, due to insufficient blood supply.

What are the symptoms of hip impingement?

Hip impingement is often not painful in the early stages so you may not experience any symptoms at this point. However, as the damage to cartilage worsens you may start to experience:

  • Pain when walking or flexing the hip
  • Less flexibility in the hip
  • Pain at night or when walking on flat ground as osteoarthritis develops

How is hip impingement diagnosed?

A number of tests may be used to diagnose hip impingement, including:

  • X-rays to show irregularities in the ball or socket part of the joint or at the top of the femur
  • MRI scans which can reveal damage to the cartilage that lines the socket
  • CT scans which provide a detailed 3D image of the joint and can help to show the extent of any deformity and cartilage damage and help the consultant to decide whether surgery might be required

How is hip impingement treated?

The symptoms of mild hip impingement can be normally managed by taking anti-inflammatories, exercises recommended by a physiotherapist to increase hip flexibility and strength and resting the affected hip.

More severe hip impingement may require surgery. Common surgical procedures for hip impingement include:

  • Hip arthroscopy – this is a minimally invasive form of surgery, also called keyhole surgery. It involves making a small incision in the skin and inserting an arthroscope, which is a thin instrument with a camera at one end that enables the consultant to see inside your hip joint. Surgery for hip impingement is often performed arthroscopically, using tiny surgical instruments. The advantage of this type of surgery is that it is performed as an outpatient and recovery times are faster than with conventional surgery.
  • Hip replacement – this may be necessary if the damage to cartilage is severe. It involves replacing the hip joint with a prosthetic implant and generally achieves excellent results, relieving pain and improving movement and flexibility.