Femoroacetabular Impingement (FAI) occurs when either the ball (femoral head/neck junction) or the socket (acetabulum) has a shape that causes abnormal contact.
The hip is a ball-and-socket joint formed by the femoral head (ball) and the acetabulum (socket). With FAI, the mismatched shapes can rub during movement and gradually irritate or damage important structures, including:
- Cartilage (articular cartilage/chondral surfaces)
- Labrum (labral tears)
- Ligamentum teres (tears/instability)
- and, over time, osteoarthritis of the hip
FAI morphology is common and is a frequent cause of hip arthritis and activity-related groin pain.
There are two main patterns:
- CAM impingement: extra bone on the femoral head/neck junction (the “ball” side).
- PINCER impingement: over-coverage or overhang of the acetabular rim (the “socket” side).
Symptoms of FAI
FAI usually causes deep groin pain that can radiate to the front of the hip, thigh, or occasionally the buttock or lower back. Early on, pain may occur only with sport; later it can appear with daily activities that bring your knee towards your chest.
- Sitting in low chairs, getting up from chairs
- Driving, prolonged sitting, or long flights
- Putting on socks/shoes
- Picking items up from the floor
- Climbing stairs or hills
- Twisting, pivoting, or deep squatting
Causes of FAI
FAI develops during adolescence while the hip is still maturing. It may relate to genetics, growth-plate development, and high load on the hip during rapid growth. Many people are unaware they have FAI morphology until it starts to irritate the joint.
If you have new or persistent groin/hip pain, see your doctor. A focused clinical assessment and appropriately positioned imaging can clarify the diagnosis.
Investigations for FAI
A trained clinician can often suspect FAI from your history and examination. Imaging refines the diagnosis and guides treatment:
- Specialised X-rays: targeted pelvic/hip views to assess head–neck offset and acetabular coverage (a standard single hip X-ray may miss subtle morphology).
- CT with 3D reconstruction: excellent for visualising the 3D bony anatomy and planning surgery (location and amount of bone to reshape).
- MRI: assesses the labrum and cartilage. If imaging is equivocal, an image-guided diagnostic injection can help confirm the hip joint as the pain source.
Treatment for FAI
Initial care usually includes activity modification, physiotherapy (gait/core/hip strengthening and movement retraining), and targeted pain strategies. If symptoms persist or imaging shows mechanical conflict, hip arthroscopy can address the underlying morphology and associated damage.
During arthroscopy, we can:
- Stabilise ligamentum teres tears and treat inflammation.
- Repair labral tears with suture anchors to restore the suction seal.
- Treat cartilage damage: remove unstable flaps; consider microfracture for focal full-thickness defects to stimulate fibrocartilage fill. (Fibrocartilage is not the same as native hyaline cartilage; there is currently no proven method to fully restore original cartilage.)
- Pincer impingement: carefully trim acetabular over-coverage.
- Cam impingement: reshape the femoral head–neck junction to restore clearance and reduce future wear.
- Remove femoral cysts/loose bodies when present.
Best outcomes are achieved when precise surgery is combined with high-quality rehabilitation, and when significant cartilage loss is not yet present. See also: evidence comparing surgery with physiotherapy.
Reducing Damage from FAI
Many athletes have FAI morphology yet never develop problems. Symptoms depend on how much the bony bump contacts the rim during motion.
Sports with frequent hip flexion, pivoting, and deep rotation may aggravate symptoms (e.g., AFL football, hockey, netball, athletics, dance, swimming, rugby). If you have groin pain with sport, seek assessment early.
- Run with your natural foot progression (some people are slightly in-toed or out-toed; forcing a change can irritate the hip).
- Strengthen hip and core; avoid rapid spikes in training load.
- Cycling: if your knees track outward naturally, be cautious with fixed-position cleats that force internal rotation.
Further Reading and References
- Tran P, Pritchard M, O’Donnell J. Outcome of arthroscopic treatment for cam type femoroacetabular impingement in adolescents. ANZ J Surg. 2013;83(5):382–386.
- Tan C, Tran P, Weinberg L, Howard W. Surgical predictors of acute postoperative pain after hip arthroscopy. BMC Anesthesiol. 2015;15:96.
- Buikstra JG, Fary C, Tran P. Hip pathology with normal imaging: arthroscopic findings. BMC Musculoskelet Disord. 2017;18(1):120
- The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): international consensus statement. Br J Sports Med. 2016;50(19):1169–1176.
- The Natural History of Femoroacetabular Impingement. Front Surg. 2015;2:58.
FAQs
Is FAI always symptomatic?
No. Some people have FAI morphology on imaging but no pain. Symptoms arise when shape and movement combine to irritate the labrum or cartilage.
Can FAI be managed without surgery?
Yes. Many improve with load modification, physiotherapy, and targeted injections. Surgery is considered when mechanical conflict persists.
What does surgery aim to achieve?
Restore clearance between the ball and socket, repair the labrum, and address cartilage problems—helping pain, function, and long-term joint protection.
