Femoroacetabular Impingement (FAI)
What is Femoroacetabular Impingement?
The hip is a ball-and-socket joint made up of:
- The femoral head (ball)
- The acetabulum (socket)
FAI occurs when there is reduced space between these structures, causing the surrounding soft tissues to become compressed during movement.
Over time this can lead to pain, inflammation and reduced hip function.
Common Symptoms
Symptoms may develop gradually or follow a sporting injury or trauma.
Common symptoms include:
- Groin pain
- Pain on the outside of the hip or pelvis
- A dull ache in the hip
- Sharp or catching pain during certain movements
- Hip stiffness
- Reduced range of movement
Symptoms are often aggravated by activities such as:
- Sitting in a low chair
- Putting on shoes or socks
- Getting in and out of a car
- Twisting on the affected leg
- Changing direction quickly during sport
- Squatting or deep bending
What Causes FAI?
There are several reasons why FAI may occur, and many people have more than one contributing factor.
Muscle Imbalance
Weak or poorly coordinated muscles can alter the way the hip moves.
Instead of sitting centrally within the socket, the ball of the hip may move forwards, reducing the available space inside the joint.
Labral Tear
The hip socket is surrounded by a ring of cartilage called the labrum.
A twisting injury while weight-bearing can tear the labrum, causing pain, catching sensations and instability.
CAM Impingement
In CAM impingement, the femoral head or neck has an irregular shape.
As the hip bends, the abnormal bone comes into contact with the socket sooner than normal, causing pinching.
Pincer Impingement
Pincer impingement occurs when extra bone develops around the edge of the hip socket.
This reduces the available joint space and increases contact between the socket and the femoral head during movement.
How is FAI Diagnosed?
Diagnosis usually involves three stages.
Medical History
Your clinician will ask about:
- Where your pain is located
- Activities that aggravate symptoms
- Previous injuries
- How your symptoms affect daily life
Physical Examination
Your hip will be assessed for:
- Movement
- Strength
- Flexibility
- Pain during specific positions
Certain clinical tests help identify movements that reproduce your symptoms.
Imaging
Imaging may be used to confirm the diagnosis.
This may include:
- X-ray – useful for identifying CAM or pincer impingement
- MRI scan – may identify labral tears
- MR Arthrogram (MRA) – an MRI performed after injecting dye into the hip joint to better visualise cartilage injuries
Your clinician will advise which investigation is most appropriate.
Treatment Options
For most people, physiotherapy is the first-line treatment.
Many people with CAM or pincer changes seen on X-ray never develop symptoms, so improving how the hip moves is often more important than the shape of the bones themselves.
Physiotherapy
The main goals of physiotherapy are to:
- Improve hip movement
- Correct muscle imbalance
- Increase strength
- Improve flexibility
- Reduce pressure within the hip joint
- Improve everyday function
Most rehabilitation is completed through a structured home exercise programme.
Although some exercises may initially increase discomfort, this is usually temporary as strength and movement improve.
Pain Relief
Pain relief may help you participate more comfortably in rehabilitation.
Options may include:
- Paracetamol
- Non-steroidal anti-inflammatory drugs (NSAIDs), such as Ibuprofen
- Weak opioid medication (when appropriate)
Always follow medical advice and medication instructions.
Hip Joint Injection
If pain is preventing rehabilitation, your clinician may recommend a corticosteroid injection.
These injections:
- Can reduce inflammation
- May provide pain relief for several months
- Are performed under imaging guidance (fluoroscopy)
As with any invasive procedure, injections carry risks and may not be suitable for everyone. Your clinician will discuss the benefits and potential risks before treatment.
Surgery
Surgery is generally only considered if:
- Symptoms continue after at least three months of physiotherapy
- Imaging confirms FAI
- Conservative treatments have not improved symptoms
If surgery is appropriate, you will be referred to an orthopaedic specialist to discuss the available options.
Key Rehabilitation Exercises
These exercises may help improve hip strength and flexibility while you wait for physiotherapy. Your physiotherapist may adapt your programme depending on your individual assessment.
Exercise 1 – Bridge
Lie on your back with:
- Knees bent to approximately 90°
- Feet flat on the floor
- Feet shoulder-width apart
Tighten your stomach muscles and slowly lift your hips until your body forms a straight line from your shoulders to your knees.
Slowly lower back down.
Repeat: 10 repetitions
Exercise 2 – Hip Flexor Stretch
Adopt a half-kneeling position.
Keeping your back upright:
- Gently push your pelvis forwards.
- You should feel a stretch at the front of your hip.
Hold: 10–20 seconds
Repeat: 5 times
What if My Symptoms Do Not Improve?
If your symptoms continue despite completing a minimum of three months of physiotherapy and conservative management, your clinician may discuss further treatment options.
If appropriate, you may be referred to an orthopaedic surgeon for further assessment.
You can usually choose the hospital or specialist you would like to see through the NHS e-Referral Service.
When Should You Seek Medical Advice?
Arrange an assessment if you experience:
- Persistent groin pain
- Pain that limits daily activities
- Hip locking or catching
- Reduced hip movement
- Symptoms that continue despite rehabilitation
- Pain affecting sport or work
Early assessment can help identify the cause of your symptoms and guide the most appropriate treatment.
Key Points
- Femoroacetabular impingement (FAI) occurs when the hip joint becomes pinched during movement.
- Groin pain and pain during twisting or deep bending are common symptoms.
- Physiotherapy is the first-line treatment for most people.
- Exercises focus on improving hip strength, movement and muscle balance.
- Surgery is usually only considered after at least three months of unsuccessful conservative treatment.
