Femoroacetabular Impingement (FAI): Cam vs Pincer Morphology and FADIR Deep Squat Care
In short
Anterior groin pain in young active adults is frequently driven by femoroacetabular impingement. Learn Cam vs Pincer bony morphology, the FADIR test, and movement modifications.
In this guide (5 sections)
Patho-Anatomy of Femoroacetabular Impingement (FAI)
Femoroacetabular Impingement (FAI) is a motion-dependent clinical disorder of the hip joint characterized by abnormal mechanical abutment between the femoral head-neck junction and the acetabular rim during terminal hip motion.
Repetitive high-energy impingement causes premature damage to the acetabular labrum and underlying articular cartilage, serving as a primary precursor for early-onset hip osteoarthritis in young active adults.
The Warwick Agreement established that diagnosis requires a triad of symptoms (anterior groin pain), clinical signs (positive impingement testing), and relevant radiological findings.
Cam vs Pincer Morphology
FAI is categorized radiologically into two distinct bony morphological variants, which frequently coexist as mixed impingement.
| Morphological Type | Anatomical Location & Bony Abnormality | Radiological Metric | Mechanism of Tissue Damage | |
|---|---|---|---|---|
| 1. Cam Morphology | Aspherical femoral head; loss of head-neck waistline ('pistol grip deformity') | Alpha Angle > 60 degrees on Dunn lateral view | The nonspherical bone 'bump' jams into the acetabulum during flexion, shearing cartilage off bone. | |
| 2. Pincer Morphology | Excessive acetabular coverage (acetabular retroversion, coxa profunda) | Center-Edge (CE) Angle > 40 degrees | Over-covering acetabular rim pinches the labrum like a nutcracker against the femoral neck. | |
| 3. Mixed Impingement | Combination of both Cam bone bump and Pincer acetabular over-coverage | Both elevated Alpha angle and high CE angle | Represents over 70% of all symptomatic clinical FAI presentations. |
Clinical Examination: The FADIR and FABER Tests
Physical examination reproduces the patient familiar groin pain by driving the hip into provocative impingement vectors.
- The FADIR Test (Flexion, Adduction, Internal Rotation): Supine; passively flex hip to 90 degrees, adduct across midline, and internally rotate. Sharp anterior groin or 'C-sign' pain has > 95 percent sensitivity for anterior FAI and labral tears.
- The FABER Test (Flexion, Abduction, External Rotation): Place foot on opposite knee; measure distance from lateral knee to couch. Anterior pain indicates intra-articular hip pathology; posterior pain indicates sacroiliac dysfunction.
- Iliopsoas Tendon Snapping Assessment: Passive extension from flexed abducted posture; audible deep groin snap indicates coexisting coxa saltans interna.
- Hip Internal Rotation Range Measurement: Patients with Cam morphology display marked loss of passive internal rotation (< 15 degrees) at 90 degrees hip flexion due to bony abutment.
Movement Modifications: The Safe Squatting Arc
In Indian cultural life, deep squatting (for Indian toilets or chores) forces hip flexion past 110 degrees with adduction, aggressively ramming the Cam bump into the acetabular rim.
Physiotherapists instruct patients to modify squats: widening stance width, angling toes outward 30 degrees (external rotation), and limiting squat depth to 90 degrees or using an elevated toilet seat.
Frequently Asked Questions
Does having a Cam or Pincer bump mean I need surgery?
No. Cam and Pincer morphologies are present in up to 30 percent of completely pain-free individuals. Surgery (hip arthroscopy) is only indicated if structural impingement causes persistent pain and labral damage that fails 3 to 6 months of specialized physiotherapy.
What is the C-sign in hip pain?
When asked to locate their pain, patients with FAI cup their hand in a 'C-shape' over the lateral hip and groin, placing their thumb on the posterior trochanter and index finger in the anterior groin crease.
What exercises should be avoided with FAI?
Avoid extreme deep squats below parallel, deep lunges, high-kick martial arts, and aggressive hip internal rotation stretches that forcefully compress the femoral head against the acetabular rim.
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