- Femoroacetabular impingement (FAI) is a hip condition where abnormal bone contact causes pain and restricted movement.
- FAI often develops during adolescence due to intense sports or specific pediatric hip conditions.
- Patients commonly experience deep groin pain, especially with prolonged sitting or hip flexion movements.
- Early recognition of FAI symptoms is vital to manage pain and prevent long-term hip joint damage.
Table of Contents
Femoroacetabular impingement
Femoroacetabular Impingement (FAI) is a condition in which an abnormal contact between the femoral head and the rim of the acetabulum causes pain, limited movement, and, over time, damage to the articular cartilage and the acetabular labrum of the hip. FAI is now recognized as one of the main causes of hip pain in young adults and as an important predisposing factor for the development of early hip osteoarthritis. The prevalence in the general population is estimated between 10% and 25%, with a higher frequency in male athletes.
Table of Contents
- Hip Anatomy and Impingement Mechanism
- Types of Impingement
- Causes and Risk Factors
- Symptoms
- Diagnosis
- Conservative Treatment
- Surgical Treatment
- Recovery Times
- Prevention
- Frequently Asked Questions (FAQ)
- Frequently Asked Questions
- Sources and Scientific References
Hip Anatomy and Impingement Mechanism
The hip joint (coxofemoral) is a ball-and-socket joint, meaning a spherical joint where the femoral head articulates with the acetabular cavity of the pelvis. Under normal conditions, the femoral head glides smoothly within the acetabulum, thanks to the articular cartilage and the acetabular labrum (a ring of fibrocartilage that deepens the acetabulum and seals the joint).
In FAI, morphological abnormalities of the femoral head and/or acetabulum create premature contact during movements, particularly hip flexion, internal rotation, and adduction.
Types of Impingement
CAM Type
A bony outgrowth (bump) on the femoral head-neck junction, often anterolateral, reduces the offset between the head and neck. During flexion, this protuberance abuts against the acetabular rim, causing cartilage damage by “outside-in” abrasion.
- More frequent in young, male athletes
- Often bilateral
- Alpha angle > 55° on X-ray or MRI
PINCER Type
The acetabulum is excessively deep or retroverted (coxa profunda, protrusio acetabuli, acetabular retroversion), causing premature contact of the acetabular rim with the femoral neck. The initial damage is to the acetabular labrum (compression and degeneration), with secondary cartilage damage.
- More frequent in middle-aged women
- Often associated with acetabular retroversion
MIXED Type
The combination of CAM and PINCER abnormalities is the most common form in clinical practice, present in approximately 70-80% of symptomatic patients.
Causes and Risk Factors
Origin of the Deformity
The morphological abnormality of FAI develops during skeletal growth:
- Intense sports activity in adolescence: high-impact sports during bone maturation (soccer, hockey, basketball) increase the risk of developing a CAM deformity
- Pediatric hip diseases: slipped capital femoral epiphysis, Legg-Calvé-Perthes disease
- Genetic factors: familial predisposition to CAM or PINCER morphology
Factors that Promote Symptoms
| Factor | FAI Type |
|---|---|
| Sports with deep flexion (soccer, martial arts, hockey) | CAM and mixed |
| Classical dance, yoga | PINCER |
| Male sex | CAM |
| Female sex | PINCER |
| High BMI | Both |
Symptoms
Pain
- Location: anterior groin region (the patient typically indicates the pain with a “C” hand shape around the groin — C-sign)
- Characteristics: deep, dull pain, gradually worsening
- Triggering factors: prolonged sitting, sports activity, hip flexion and rotation movements (crossing legs, getting in/out of a car, climbing stairs)
- Associated lateral pain (trochanteric region) due to biomechanical compensation
Restricted Movement
- Reduced flexion combined with internal rotation (positive impingement test)
- Progressive stiffness in deep flexion
- Difficulty with deep squatting
Mechanical Symptoms
- Joint clicking or locking (if labral tear is present)
- Feeling of instability or giving way
- Crepitus during movements
Functional Impact
- Limitation in sports activity (often the first sign)
- Difficulty with prolonged sitting (cinema, car, desk)
- Limping after prolonged activity
- Reduced athletic performance
Diagnosis
Clinical Examination
- Anterior impingement test (FADIR test): 90° flexion, adduction, and passive internal rotation of the hip — positive if it reproduces groin pain. Very high sensitivity (>90%), limited specificity
- FABER test: flexion, abduction, and external rotation of the hip — may cause groin or sacroiliac pain
- Joint ROM: measurement of internal rotation (typically reduced), flexion, and abduction
- Muscle tests: assessment of hip stabilizer muscle strength
Instrumental Examinations
Pelvis and Hip X-ray:
- Antero-posterior view: evaluates head-neck offset, acetabular depth, retroversion (cross-over sign, posterior wall sign)
- Lateral view (Dunn 45° or 90°): measures the alpha angle (> 55° suggestive of CAM)
Magnetic Resonance Imaging with Arthro-MRI:
- Gold standard for evaluating the acetabular labrum and cartilage
- Highlights labral tears, cartilage damage, bone edema
- Better definition with intra-articular gadolinium injection
CT Scan with 3D Reconstruction:
- Useful for surgical planning
- Precise definition of bone morphology
Conservative Treatment
Conservative treatment is the first choice, particularly in patients with mild-to-moderate symptoms and in the absence of significant structural lesions.
Activity Modifications
- Temporarily avoid movements that cause impingement (deep flexion + internal rotation)
- Modify sports activity: reduce risky movements, avoid deep squats
- Ergonomics: chair with forward-sloping seat, avoid low seating
Medications
- Oral or topical NSAIDs during flare-ups
- Intra-articular cortisone injection: temporary relief, also useful as a diagnostic test
- Hyaluronic acid injection: variable results
Physiotherapy
Phase 1 — Pain Management and Protection (weeks 1-4):
- Education: avoid impingement positions and movements
- Manual therapy: axial hip traction, gentle mobilization in flexion and external rotation
- Release of hypertonic muscles: iliopsoas, adductors, piriformis, TFL
- Mobility exercises in a protected range (avoid flexion >90° with internal rotation)
Phase 2 — Strengthening and Stabilization (weeks 4-12):
Core and Pelvic Stabilization:
- Front and side planks (gradual progression)
- Single-leg glute bridge
- Bird-dog with pelvic control
- Dead bug with focus on lumbopelvic stability
Hip Muscle Strengthening:
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- Hip abduction with resistance band (clamshell and variations)
- Controlled lunges (limited range initially)
- Step-ups on a low step (15-20 cm)
- Hip extension in prone position (gluteus maximus)
- External rotator strengthening with resistance band
Flexibility:
- Psoas-iliacus stretch in kneeling lunge position
- Adductor stretch
- Piriformis and external rotator stretch
Phase 3 — Return to Sports Activity (from 3 months onwards):
- Progressive reintroduction of specific athletic movements
- Functional strengthening with sport-specific exercises
- Proprioceptive and plyometric work
- Maintenance of the stabilization program
Efficacy of Conservative Treatment
Structured physiotherapy produces significant improvement in 60-70% of patients with symptomatic FAI. Factors predicting a good conservative response include: mild-to-moderate symptoms, absence of significant cartilage damage, good compliance with the rehabilitation program.
Surgical Treatment
Indications
- Failure of conservative treatment after 3-6 months
- Persistent pain limiting daily or sports activities
- Significant acetabular labral tear on MRI
- Initial cartilage damage (before it progresses to osteoarthritis)
- Young and active patient with significant deformity
Hip Arthroscopy
Arthroscopy is the most commonly used technique and allows for:
- Femoral osteoplasty: reshaping of the CAM bump to restore head-neck offset
- Acetabular rim resection (rim trimming): in PINCER deformity
- Acetabular labral repair: suturing or reconstruction of the torn labrum
- Treatment of cartilage lesions: microfractures, debridement
Open Surgery
Indicated in complex cases with severe deformity or the need for acetabular osteotomy.
Post-Arthroscopy Rehabilitation
- Weeks 0-2: partial weight-bearing with crutches, assisted passive movements
- Weeks 2-6: progressive weight-bearing, hydrotherapy, stationary bike without resistance
- Weeks 6-12: progressive strengthening, recovery of full mobility
- Months 3-6: gradual return to sport
- Return to competitive sport: 6-9 months
Recovery Times
| Treatment | Improvement |
|---|---|
| Conservative (physiotherapy) | 2-4 months |
| Post-arthroscopy (daily activities) | 6-8 weeks |
| Post-arthroscopy (sports) | 4-9 months |
| Post-open surgery | 6-12 months |
Prevention
- Youth sports: avoid early specialization and excessive training volume during skeletal growth
- Adequate warm-up: before activities requiring deep hip flexion
- Muscle strengthening: keep hip stabilizing muscles strong (glutes, core)
- Flexibility: regular stretching of the psoas and adductors
- Correct sports technique: in sports like soccer, martial arts, dance
Frequently Asked Questions (FAQ)
No, not everyone with FAI morphology will develop osteoarthritis. Many people have morphological abnormalities without ever experiencing symptoms. However, untreated symptomatic FAI is a significant risk factor for early hip osteoarthritis, especially in the presence of documented cartilage damage.
In the acute phase, it is advisable to reduce activities that cause pain. After an adequate rehabilitation program or after arthroscopy, most patients return to their previous sports level. It is important to modify sports technique to reduce impingement movements.
Hip arthroscopy is a minimally invasive procedure with a generally good safety profile. Complications are rare and include temporary nerve damage (pudendal nerve neuropraxia due to traction), infection, and thrombosis. The success rate is high, with 80-90% of patients reporting significant improvement.
Symptoms typically appear between 20 and 40 years of age, often coinciding with the start or intensification of sports activity. The morphological abnormality develops during adolescence but can remain asymptomatic for years.
Yes, CAM morphology is bilateral in 60-70% of cases. However, not all patients with bilateral FAI develop symptoms on both sides. Clinical and instrumental evaluation of both hips is recommended.
Frequently Asked Questions
What are the typical symptoms of femoroacetabular impingement?
FAI commonly presents with deep groin pain, which may worsen with prolonged sitting, walking, or specific hip movements like flexion and internal rotation. Individuals might also experience a sensation of clicking, catching, or stiffness in the hip joint.
How is femoroacetabular impingement diagnosed?
Diagnosis typically involves a thorough clinical examination, assessing hip range of motion and specific impingement tests. Imaging studies, such as X-rays, MRI, or CT scans, are then used to confirm the presence of abnormal bone morphology and assess any associated soft tissue damage.
What non-surgical treatments are available for FAI?
Conservative management often includes activity modification to reduce aggravating movements and a targeted physical therapy program. Medications may be prescribed to help manage pain and inflammation.
What is the role of a physical therapist in managing FAI?
A physical therapist plays a crucial role in FAI management by developing individualized exercise programs to improve hip strength, flexibility, and movement patterns. They also provide education on activity modification and may guide rehabilitation following surgical intervention.
Sources and Scientific References
- Palmer AJR et al. (2019). Arthroscopic hip surgery compared with physiotherapy and activity modification for the treatment of symptomatic femoroacetabular impingement: multicentre randomised controlled trial. BMJ. 364:l185. DOI | PubMed
- Trigg SD et al. (2020). Femoroacetabular Impingement Syndrome. Curr Sports Med Rep. 19:360-366. DOI | PubMed
- Hoit G et al. (2020). Physiotherapy as an Initial Treatment Option for Femoroacetabular Impingement: A Systematic Review of the Literature and Meta-analysis of 5 Randomized Controlled Trials. Am J Sports Med. 48:2042-2050. DOI | PubMed
- Griffin DR et al. (2016). The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): an international consensus statement. Br J Sports Med. 50:1169-76. DOI | PubMed
- Terrell SL et al. (2021). Therapeutic Exercise Approaches to Nonoperative and Postoperative Management of Femoroacetabular Impingement Syndrome. J Athl Train. 56:31-45. DOI | PubMed