FAI: when the bones were fixed and the pain forgot to leave.

Pain catastrophizing and nervous-system sensitization predict hip pain after arthroscopy better than the scan does.

This page is about understanding the condition and the role the brain and nervous system can play in it. It is not a diagnosis. Your own clinicians know your case.

What femoroacetabular impingement is

Femoroacetabular impingement (FAI) describes a hip whose ball and socket do not fit together smoothly. In CAM-type impingement, there is extra bone on the head or neck of the femur (see our article on CAM morphology). In pincer-type impingement, the rim of the socket extends too far and over-covers the ball. Many people have both. During movements such as deep squatting, crossing the legs or rotating the hip inward, the irregular surfaces pinch the labrum (the cartilage ring around the socket) and the joint cartilage.

Typical symptoms are a deep groin ache, sometimes with pain at the side of the hip or buttock, stiffness, a catching or clicking feeling, and pain with prolonged sitting, sport or getting out of a car. The diagnosis of FAI syndrome requires three things together: symptoms, examination findings that reproduce the pain, and imaging that shows the bony shape. Any one alone is not enough, because the bony shape is common in people who have no pain at all.

The neuroplastic contribution

Neuroplastic symptoms are real symptoms produced by learned pathways in the brain and nervous system, a sensitized alarm system, rather than by ongoing damage in the body. They are not imaginary and not 'all in your head', and because the brain can change, they are reversible.

The ATNS Index of Neuroplastic Symptoms is clear that FAI is not caused by neuroplastic symptoms. The bony mismatch is real. But the index advises assessing for neuroplastic symptoms when the picture does not add up:

• Symptoms are not typical, for example pain at rest or at night, pain that spreads beyond the hip, or pain that does not follow the impingement positions.
• The course over time is not typical, for example pain that fluctuates with stress or mood rather than with activity.
• The response to treatment is not as expected, for example pain that persists or worsens after a technically successful operation.

This is not surprising. Years of groin pain, scans that use words like 'deformity', and advice to protect the hip all teach the nervous system to treat the joint as dangerous. Once that lesson is learned, correcting the bone does not automatically unlearn it. Our guide to hurt versus harm explains why a surgically repaired joint can still hurt.

What the research shows

Hip arthroscopy for FAI has given researchers a natural experiment: the structure is corrected, so what predicts who still hurts? A 2021 prospective study measured central sensitization (with the Central Sensitization Inventory) and pain catastrophizing before surgery. Both were associated with pain intensity at baseline and with hip pain three months after arthroscopy. In other words, how sensitized and fearful the nervous system was going in predicted the pain coming out.

A separate study looked at kinesiophobia (fear of movement) and pain catastrophizing in people having arthroscopy for FAI syndrome and found these psychological factors related to outcomes after surgery. Another study found that greater kinesiophobia correlated with greater pain in people with FAI syndrome, and that fear of movement, hip strength, self-efficacy and anxiety together explained a large share of the variation in reported function.

A study of preoperative temporal summation, a bedside measure of how the nervous system amplifies repeated stimuli, found that it was associated with impaired recovery after arthroscopy for FAI syndrome, suggesting it may help identify people at higher risk of a poor result. These cohorts are mostly small and observational, so they show association rather than cause, but together they support the index's advice: when FAI pain does not behave as expected, the nervous system is worth assessing.

Signs the brain may be part of the picture

• Pain continues or has worsened after an operation your surgeon considers successful.
• Pain is present at rest, at night or in positions that do not load the hip.
• Pain has spread to the back, thigh, pelvis or the other hip.
• You are afraid to squat, run or sit cross-legged even though you have been cleared to.
• Your pain rises with stress, poor sleep or emotional strain.
• Symptoms vary from day to day in ways activity does not explain.
• You have other sensitized-system conditions such as headaches, irritable bowel or widespread aches.

Fear of movement is a key driver, described in our guide to the fear-avoidance cycle.

A solution that addresses it

There is an approach that addresses the brain's contribution to hip pain: pain reprocessing. It combines education about neuroplastic symptoms, somatic tracking (attending to the sensation in the hip with curiosity rather than fear), reducing the threat attached to the joint, a graded return to walking, squatting and sport, emotional awareness and expression, and acceptance and commitment skills. Trained clinicians deliver it, and digital programs increasingly make it available at home. It works alongside, not instead of, physiotherapy and surgical follow-up.

Cindra is a daily AI companion built around these approaches, offering daily check-ins, short practices and plain-language lessons for people whose symptoms have a neuroplastic component. You can join the waitlist.

What to do next

Make sure the structural diagnosis is sound: symptoms, examination and imaging should all agree, and a specialist should have confirmed that the bony shape explains your pain. If you have had surgery, keep your follow-up appointments and complete rehabilitation. Seek prompt medical review for a hip that will not bear weight, locking, fever, calf swelling after surgery, or pain following a fall.

If the structural picture does not explain your pain, or treatment has not worked as expected, ask whether your symptoms fit a neuroplastic pattern. Then start learning and practising: read about central sensitization, use pacing to rebuild activity, and begin gently reclaiming the movements fear has taken away.

This article is for general education and is not medical advice, and it does not diagnose or treat any condition. Persistent symptoms deserve a proper medical assessment to rule out disease or injury before a neuroplastic explanation is considered. If your symptoms are new, changing, or come with red-flag signs such as fever, unexplained weight loss, numbness or weakness, chest pain, or loss of bladder or bowel control, see a clinician promptly.