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Paul Banaszkiewicz Paul Banaszkiewicz Segment Author

The number of patients identified with FAI has risen rapidly over the past 10 years.


Abnormal impingement of the femur against the acetabulum due to structural abnormalities of the femoral head–neck junction and/or acetabulum.
FAI is a dynamic process and occurs during joint motion.


  • Epidemiology and prevalence of FAI is unknown
  • Mostly affects people with a past history of athletic activities requiring extreme of hip flexion and rotation
  • Possible association with “subclinical SUFE” that causes impingement later in life
  • Siblings have a two to three times higher risk of having bony abnormalities causing FAI
  • 78% of patients with symptomatic Cam lesion have a similar lesion in the contralateral hip
  • Only 26% of the above patients have bilateral symptoms

Types of impingement lesions 

Impingement lesions exist as:

1.     Cam
2.     Pincer
3.     Mixed (cam + pincer)

1.Cam lesion

Proximal femoral deformity that causes impingement.
  • Aspherical femoral head
  • Femoral retroversion
  • Deficient head neck offset


  • Anterolateral (most common)
  • Anterior
  • Anteromedial
  • Posterolateral

Cam lesion causes cartilage damage deep inside the acetabulum.
With hip flexion, shearing force is applied to anterosuperior acetabular cartilage.
This results in:
Cartilage fissuring
Delamination from subchondral bone
Chondrolabral junctional tears

2 Pincer lesion

Acetabular deformity resulting in “over-coverage” and thus impingement.
Over-coverage can be:
1.     Focal
2.     Global

1.     Focal overcoverage pincer lesion:
Acetabular retroversion
Prominent anterior wall

2.     Global overcoverage pincer lesion:
Coxa profunda
Acetabular protrusion

Pincer lesion causes injury contained to the acetabular rim.
Pincer lesion impinges on the femoral neck resulting in direct labral damage.
This results in labral tears.


  • Activity-related groin pain
  • Pain may also be in the anterolateral proximal thigh
  • Usual complaint is “pain feels deep inside the hip joint”
  • Pain worse with hip flexion
  • Usually sharp stabbing in nature
  • Other activities that induce pain include:


  • Sitting for prolonged period such as:

Watching movie/TV

  • History of activities requiring supraphysiological movements such as sprinting, hurdling, dancing, athletics, etc.
  • History of mechanical symptoms:
Hip giving away

Mechanical symptoms point towards labral or chondrolabral tears.


Patient sits with hip relatively less flexed than normal side.

C-sign (grab sign) (Figure 3)

Patient localises their pain by holding onto their groin and anterolateral thigh with hand in cupping position.

Hip range of motion

  • Painful hip flexion (<100?)
  • Reduced internal rotation (<20–25?) with hip in 90? flexion

Impingement tests

  • 88% of patients have positive FADIR (flexion, adduction and internal rotation) test
  • Positive test causes pain deep inside the groin

Clicking may also be produced


Standard radiographic evaluation includes:

1.     Anteroposterior (AP) pelvis
2.     Horizontal beam lateral view (Figure 4)
3.     Dunn’s view

Radiographic features of pincer lesion

Signs of acetabular retroversion

Normal acetabulum is anteverted by ~15?.

The following three signs are all positive with retroverted acetabulum:

  • Cross-over sign
  • Ischial spine sign
  • Posterior wall sign

It is important to note that AP pelvic X-ray is not tilted or rotated before these three signs can be evaluated.

1.     Cross-over sign

  • Normally the lines representing the anterior and posterior acetabular rim join at the lateral edge of weight bearing acetabular roof called ‘sourcil’
  • With cross-over sign, the line of anterior acetabular rim overlaps that of the posterior acetabular rim
  • Positive sign is observed with:

o   Acetabular retroversion or
o   Anterior over-coverage

Ischial spine sign

  • Prominent ischial spine on AP view
  • Represents acetabular retroversion

2.     Posterior wall sign

  • Normally centre of femoral head is medial or just at the posterior acetabular rim line
  • In retroverted acetabulum, centre of the femoral head centre is lateral to the posterior acetabular

Radiographic features of pincer lesion

Signs of global over-coverage

Normally, the femoral head and acetabular floor are lateral to ilioischial line (Kohler’s line).

Coxa profunda

  • Medial lip of tear drop (acetabular floor) is medial to the ilioischial line
  • Femoral head, however, remains lateral to the ilioischial line

Acetabular protrusion

  • Both the acetabular floor and femoral head are medial to the ilioischial line


This can be used for those patients who have primary lesion of FAI but have not yet developed any labral tear or chondral damage.

Activity modification

Reducing their activities that aggravate pain such as running, hurdling, etc. can help reduce inflammation.

NSAIDS (non-steroidal anti-inflammatory drugs)


Cartilage damage can occur if activity is recommenced as primary lesion of FAI is not treated.


  • Arthroscopy
  • Surgical hip dislocation
  • Periacetabular osteotomy


Hip arthroscopy can be used both diagnostic and therapeutic.

Can be used therapeutically to:

  • Excise the cam lesion (osteochondroplasty)
  • Excise pincer lesion
  • Labral repair


Difficult to perform osteochondroplasty in the posterior aspect of the hip


  • Nerve injury
  • Iatrogenic hip dislocation (one reported case so far1)
  • Avascular necrosis (AVN)
  • Fracture neck of femur
  • DVT/PE (0.08%)

Surgical hip dislocation 

  • Pioneered by Ganz and involves dislocating hip joint
  • Allows direct visualisation of impingement lesion with excision and repair
  • One can also dynamically assess the adequacy of impingement lesion by moving the hip joint


  • Trochanteric non-union 1–2%
  • Neuropraxia (sciatic nerve)
  • Heterotopic ossification 37%
  • AVN (no case of AVN was reported in the series by Ganz et al.2)

Peri-acetabular osteotomy 

This is essentially a “re-orientation osteotomy”
Patients with acetabular dysplasia ? acetabular retroversion

Patients who already have developed moderate to high grade osteoarthritis

Osteotomy involves ischium, pubis and ilium
Acetabulum is osteotomised leaving posterior column intact
Acetabulum is then re-oriented to:
  • Improve femoral head coverage
  • Antervert a retroverted acetabulum


  • Nerve injury
  • (Most common lateral femoral cutaneous nerve of the thigh)
  • May render an asymptomatic FAI lesion to start impinging after PAO
  • Iatrogenic damage to posterior column
  • Non-union of osteotomy


  • 1. Matsuda DK. Acute iatrogenic dislocation following hip impingement arthroscopic surgery. Arthroscopy 2009;25(4):400–4
  • 2. Ganz R et al. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulkum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83(8):1119–24