What is femoral acetabular impingement (FAI)?
Femoral acetabular impingement (FAI) is a condition of hip joint where the bones are abnormally shaped, they pinch each other on the covering cartilages when the joint is in motion and cause damages.
The hip joint is a ball-and-socket joint (Fig. 1). The femoral head (the ball) fits into the acetabulum (the socket). The femoral head is covered with articular cartilage, the acetabulum has a ring of cartilage around its rim called the labrum. In FAI, there are abnormal bone growths (spurs) on the ball or the socket or both (Fig. 2). The ball can no longer move smoothly inside the socket. They rub onto each other and pinch on the covering cartilages causing damages.
Fig. 1 : Anatomy of the hip joint. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
Types of FAI
Pincer – Bone spurs on the acetabulum, commonly on the upper edge (Fig. 2 ). This situation is also described as over-coverage of the socket over the ball.
Cam – Bones spurs on the femoral head and neck making the neck less prominent and the head not completely round.
Combined – both cam and pincer are present, this is a very common situation.
Fig. 2 : Types of FAI. Bones spurs are colored in red. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
What damages can it make?
Impingement results in cartilage breakdown on the femoral head and labral tears on the rim of the acetabulum. FAI is also the cause of premature hip osteoarthritis in young adults.
Causes and risk factors
The bone spurs are the result of abnormal bone growth during childhood development. The reasons why this happens are unclear.
FAI is more common in young athletes, dancers who practice a larger range of motions of the hip, and in active individuals.
Symptoms
Some of the symptoms may include:
– Pain at the groin area or inner hip is more common although the pain may be felt at the side of the hip.
– Pain after sitting for a long period of time.
– Stabbing pain when sitting down or standing up.
Treatment
Treatments range from lifestyle changes, physical therapies to surgeries.
Lifestyle changes usually involve being less active. Physical therapy helps to increase hip strength but stretching should be avoided.
Arthroscopic surgeries are commonly performed to remove damaged tissues, repair the labrum and stimulate cartilage growth by microfractures. Removal of abnormal bony structures are also recommended to prevent future damages to the joint.
