Hip Impingement

What is Hip Impingement?

Hip impingement, also known as femoroacetabular impingement (FAI) happens when the ball and socket joint between the pelvis and femur bone are not functioning properly. Specifically, when the smooth glide between the ball (femoral head) and rim of the socket (acetabulum) is impeded, it can create hip impingement. FAI is believed to be one of the leading factors of developing osteoarthritis of the hip for people under the age of 40.

The impingement may cause little to no pain at first and then gradually worsen over time. A person may start to notice pain when doing activities that flex the hips, such as sitting for an extended amount of time, tying your shoes, riding a bike, walking, running, etc. Typical symptoms of FAI are discomfort, stiffness or pain around the groin and top of the thigh. Some people may not experience pain or discomfort. 

Types of FAI

There are two types of hip impingement. They include:

  • Cam impingement. This occurs when the ball (femoral head) is misshapen, more like an oval than a circle, making it more likely to get pinched between the hip and socket. This type of impingement can also cause friction between the ball and rim of the socket. 
  • Pincer impingement. This occurs when the cup or rim of the socket (acetabulum) is misshapen and creates friction between the rim and the head or neck of the femur bone. This can happen during normal flexion movement, such as when riding a bike, walking, or sitting. 

Signs and symptoms

Signs and symptoms of hip impingement may vary. Often, symptoms aren’t noticed until later in life and may gradually worsen over time. The most common symptoms of FAI include:

  • Stiffness or pain in the groin or top of thigh
  • Pain during flexion or bending of the hip or waist 
  • Pain that radiates into the side of the leg(s) or buttocks
  • The pain can be stabbing or a dull ache
  • Limping

People who are extremely active can exhibit symptoms that become aggravated by repeated movements over a long period of time. Hip impingement is one of the leading contributors to osteoarthritis of the hip in people under 40. Over time, the wearing down of the hip joint caused by friction and impingement leads to symptoms of FAI.


Hip impingement is caused by deformities in the ball and socket of the hip joint. The deformities occur when the hip bone does not develop appropriately during childhood growing years. The deformities can create friction and impingement that cause wear and tear on the hip joint and may lead to the pain and discomfort. The specific deformities are cam impingement, pincer impingement, or a combination of both. Other causes include:

  • Legg-Calve-Perthes disease is a disease where the femoral head (the ball) of the hip joint does not get enough blood and will cause the bone to die.
  • Slipped capital femoral epiphysis can happen in adolescents and it is when the ball separates from the thigh bone at the upper growth plate. The disease is more common in children who are obese.
  • Coxa vara is a condition in children where the femoral head (ball) and thigh bone do not develop at the same rate, causing deformities of the hip joint.

Risk Factors

Hip deformities are typically thought to be present since birth, but some deformities develop over time, specifically in young athletes who do activities that require significant amounts of twisting or squatting. Other conditions that are risk factors for developing deformities are slipped capital femoral epiphysis, coxa vara, and Legg-Calve-Perthes disease. 


A doctor can make a diagnosis for femoroacetabular impingement (FAI) through a physical exam, gathering a symptom history, and by using imaging tests. The imaging tests may include 1 or more of the following:

  • X-rays. The electromagnetic wave passes through tissues and materials in the body and creates a digital image of the internal structures of bones, exposing any bone deformities of the hip joint area. 
  • Magnetic resonance imaging (MRI). This uses magnets and radio waves to produce an image of the tissues around the hip joint, showing any fraying or tearing of the cartilage.
  • Computerized tomography (CT). This scan uses x-ray technology and computer processing to take cross-section images of bones, soft tissues, and blood vessels inside the body.


There are several treatment options for people who are diagnosed with femoroacetabular impingement (FAI). Treatment options include both nonsurgical and surgical options. Those options include:

Nonsurgical treatments

  • Activity modification. A doctor may recommend changing activities that could be aggravating or worsening the hip impingement. It may also be recommended to rest your hip, or to stop certain activities to allow time for the hip to heal.
  • Anti-inflammatory medications. Anti-inflammatory medications may be prescribed to help reduce pain and inflammation around the hip joint.
  • Physical therapy. Certain exercises can help increase range of motion in the hip, as well as work to build strength around the hip joint. Additionally, physical therapy can help to reduce stress on the damaged cartilage or surrounding tissue in the hip joint.

Surgical treatments

  • Arthroscopy. Arthroscopic surgery is performed with small incisions and thin instruments. A doctor inserts an instrument with a camera into the hip area and is able to cut away or repair damaged cartilage or labrum.
  • Hip replacement. If the damage to the hip is too severe, and no nonsurgical treatments or arthroscopy have been unsuccessful, a full hip replacement may be recommended.
  • Experimental treatments. There have been some promising experimental treatments, using the patient’s own blood and injecting it into the hip joint to stimulate cartilage growth.

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