Femoroacetabular impingement
Femoroacetabular impingement (FAI) is abnormal contact between the femoral head and the acetabulum caused by bony overgrowth, causing hip pain in young active adults and potentially leading to early hip arthritis.
📊 FAI morphology (cam and pincer deformities) is present in up to 25% of the general population but only a proportion develop symptomatic impingement. It is a leading cause of hip pain and labral tears in young adults.
What is femoroacetabular impingement?
Femoroacetabular impingement occurs when abnormal bony morphology of the femoral head or acetabulum causes abnormal contact (impingement) during hip movement. There are two main types: cam impingement, where an aspherical bump on the femoral head-neck junction (the cam deformity) jams against the acetabular rim during hip flexion; and pincer impingement, where over-coverage of the femoral head by the acetabulum (acetabular retroversion or deep acetabulum) causes the acetabular rim to impinge against the femoral neck. Mixed cam-pincer impingement is common.
The repeated abnormal contact damages the acetabular labrum (the fibrocartilaginous rim of the acetabulum) and the adjacent cartilage. A labral tear is the most common intra-articular pathology associated with FAI. Over years, progressive cartilage damage can lead to early-onset hip osteoarthritis, particularly in patients with cam-type morphology. Cam deformity is particularly common in high-level athletes, especially those who participate in high-impact sports during adolescence.
The Birmingham Hip Instability Score and the iHOT-33 (International Hip Outcome Tool) are validated patient-reported outcome measures used to assess hip function and the impact of treatment in FAI. The FemoroAcetabular Impingement Trial (FAIT, Lancet 2018) demonstrated that arthroscopic hip surgery produced significantly better outcomes than physiotherapy alone at 12 months for patients with symptomatic FAI and labral tears.
Common causes
- Cam deformity (aspherical femoral head-neck junction)
- Pincer deformity (acetabular over-coverage or retroversion)
- High-impact sport during adolescent growth (particularly associated with cam development)
- Previous Perthes disease or SCFE causing altered femoral head morphology
Who is at risk? Young male athletes (particularly football, hockey, martial arts) are at highest risk of cam FAI. Female patients are more commonly affected by pincer-type FAI. High-volume sport during adolescence is associated with cam deformity development.
Symptoms
Symptoms vary depending on the severity and duration of the condition. Common symptoms include:
- Deep groin pain in young active adults, worse with hip flexion activities (sitting, cycling, squatting)
- Pain at the end of range of movement
- A positive FADIR test (flexion, adduction, internal rotation of the hip reproduces pain)
- Clicking or locking of the hip in labral tear
- Reduced hip internal rotation and flexion
- Pain that limits sport, particularly twisting and turning activities
When to seek help: See your GP or a hip specialist if groin pain is persistent, limiting sport or daily activities, and is not responding to rest and simple analgesia. An X-ray is the first-line investigation to identify cam or pincer morphology.
How is it diagnosed?
Your surgeon will take a detailed history and examine the joint. The following investigations may be arranged to confirm the diagnosis:
- X-ray - AP pelvis and Dunn 45-degree view to assess cam morphology (alpha angle measurement); lateral views assess acetabular version
- CT scan with 3D reconstruction - precise measurement of cam morphology and acetabular version for surgical planning
- MRI arthrogram - gold standard for labral tear assessment and articular cartilage evaluation
- Clinical examination - FADIR and FABER tests
The diagnosis of symptomatic FAI requires the combination of: (1) symptoms (pain with hip flexion activities), (2) clinical signs (positive FADIR test), and (3) imaging (bony morphology on X-ray/CT, labral tear on MRI arthrogram). Bony morphology alone on imaging is not sufficient to diagnose symptomatic FAI.
Treatment pathway
Treatment is tailored to the severity of the condition, your age, activity level, and overall health. Most conditions are treated in a stepwise fashion, starting with the least invasive options.
Physiotherapy and activity modification
A structured physiotherapy programme targeting hip abductor and rotator strengthening, core stability, and movement pattern correction. Activity modification to avoid provocative positions. The FAIT trial demonstrated that even patients ultimately having surgery benefit from initial physiotherapy.
Hip arthroscopy (cam resection and labral repair)
Arthroscopic surgery to reshape the cam deformity (femoral osteoplasty), correct acetabular over-coverage (rim trimming), and repair or reconstruct the torn labrum. Performed through 2-3 small portals around the hip under general anaesthetic. The FAIT trial (Lancet 2018) demonstrated significantly better outcomes for surgery versus physiotherapy alone at 12 months.
Recovery
Recovery after hip arthroscopy for FAI requires a structured rehabilitation programme. Crutches are used for 2-4 weeks. Progressive loading of the repaired labrum begins from 6 weeks. Return to sport takes 4-6 months and should be guided by functional criteria rather than time alone.
- Physiotherapy: 3-6 months (first line)
- After hip arthroscopy: crutches: 2-4 weeks
- Return to low-impact activity: 6-8 weeks
- Return to sport: 4-6 months
- Full recovery: 6-9 months
What results can I expect?
Hip arthroscopy for FAI achieves significant pain relief and functional improvement in 80-85% of patients. Better outcomes are associated with minimal pre-existing arthritis (Tonnis grade 0-1). Patients with advanced cartilage damage have less predictable outcomes and may progress to early hip replacement.
Femoroacetabular impingement - hip arthroscopy explained
In numbers
Typical activity timelines for this condition. These are approximate and vary considerably between patients. Always follow the specific guidance given by your surgeon and physiotherapist.
| Activity | Typical timeline | Notes |
|---|---|---|
| Try physiotherapy | At least 3 months | A structured physiotherapy programme is the appropriate first step in most cases.[2] |
| Modify activity | During treatment | Reduce deep hip flexion activities (deep squats, cycling in low position, prolonged sitting) while symptoms settle.[1] |
| Drive after arthroscopy | 3-4 weeks | When off crutches and able to control the car and perform an emergency stop. Inform your insurer.[4] |
| Return to work | 2-8 weeks after arthroscopy | Desk work usually 2 weeks. Manual work 6-8 weeks or longer.[1] |
| Return to straight-line running | 3-4 months after arthroscopy | Once strength and range of motion have returned and rehab milestones are met.[1] |
| Return to pivoting sport | 4-6 months after arthroscopy | Cutting and pivoting sport requires more rehab; guided by functional testing.[1] |
| Full strength and confidence | 6-12 months | Final outcome can take up to a year, especially in higher-level sport.[1] |
Common concerns from patients with this condition or recovering from treatment, and whether they are expected or worth mentioning to your team.
Your questions, answered
Plain-English answers to the things people most often ask, grounded in UK clinical guidance. Tap a question to open it.
About thisWhat is femoroacetabular impingement?
Femoroacetabular impingement, or FAI, is where extra bone on the ball or the rim of the hip socket causes the two to bump together during movement. This abnormal contact can pinch the soft tissues inside the joint and cause pain, especially with deep bending of the hip.
SymptomsWhat does FAI feel like?
The classic symptom is groin pain brought on by activity, prolonged sitting, or movements that bend the hip up, such as getting in and out of a car. Many people cup the side of the hip with a C-shape of the hand to show where it hurts, and some notice clicking or catching.
TreatmentDo I need surgery for it?
Not always. A good number of people improve with physiotherapy that retrains hip and core control, activity modification and pain relief. Keyhole surgery to reshape the bone and repair any torn cartilage is considered when symptoms persist despite a proper trial of non-surgical care.
RecoveryWhat is recovery like after keyhole surgery?
After hip arthroscopy you use crutches for a few weeks and follow a structured physiotherapy programme. Light daily activities return over the first month or two, with sport and heavier activity usually taking several months. Recovery is gradual and rehabilitation is key to the result.
OutlookWill FAI lead to arthritis?
FAI is associated with hip arthritis over the long term in some people, particularly when the abnormal contact is significant. Treating troublesome symptoms and keeping the hip strong and mobile is sensible, although surgery is offered to relieve symptoms rather than as a guaranteed way to prevent arthritis.
When to worryWhen should I get it checked sooner?
See someone promptly if the hip locks, gives way, or becomes suddenly much more painful, or if pain is waking you at night and not settling. Difficulty bearing weight after an injury should also be assessed.
- 1.British Hip Society: Patient information
- 2.Chartered Society of Physiotherapy: Patient information
- 3.BMJ: Femoroacetabular impingement, evidence summary
- 4.Royal College of Surgeons of England: Recovering from surgery, driving guidance
References are to UK clinical guidance and patient information from recognised organisations. This page is for general information and does not replace personalised advice from your own clinical team.
Preparing for surgery?
Read our step-by-step guide - what to expect before, during, and after your procedure.
How is it diagnosed?
- ✓X-ray - AP pelvis and Dunn 45-degree view to assess cam morphology (alpha angle measurement); lateral views assess acetabular version
- ✓CT scan with 3D reconstruction - precise measurement of cam morphology and acetabular version for surgical planning
- ✓MRI arthrogram - gold standard for labral tear assessment and articular cartilage evaluation
- ✓Clinical examination - FADIR and FABER tests
Recovery milestones
- ●Physiotherapy: 3-6 months (first line)
- ●After hip arthroscopy: crutches: 2-4 weeks
- ●Return to low-impact activity: 6-8 weeks
- ●Return to sport: 4-6 months
- ●Full recovery: 6-9 months