Femoroacetabular Impingement

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Femoroacetabular Impingement

• Ryan Tompkins M.D.
• University of Florida
• Department of MSK Radiology

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Femoroacetabular Impingement

• Femoroacetabular Impingement (FAI)
• Acetabular rim syndrome
• Cervicoacetabular impingement
• Young patients with chronic pain
• Reduced ROM in flexion and internal rotation
• Repetitive microtrauma
• Increased incidence of premature degenerative
  arthritis
• Etiology
• Abnormal acetabulum
• Abnormal femur
• Increased stress
• Two types
• Pincer (acetabular)
• Cam (femoral)
• Mixed 86

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Clinical

• Clinical symptoms
• Groin pain
• Pain over trochanters
• Pain with flexion and internal rotation
• Usually unilateral
• Starts after mild trauma
• Younger patients than typical
• Maneuver
• Flex hip 90 degrees, adduct, and internally
  rotate
• Should compress labrum and cause pain

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Predisposing factors

• Some predisposing factors to FAI
• Legg-Calve-Perthes disease
• Congenital hip dysplasia
• Slipped capital femoral ephiphysis
• Avascular necrosis
• Malunited fractures
• Acetabular protrusion
• Elliptical femoral head
• Retroverted acetabulum
• Prominent femoral head-neck junction
• Proposed etiologies
• Abnormal anatomy
• Prominent femoral head neck junction
• Acetabular overcoverage
• Unusual stesses
• Carpet layers repeated flexion, adduction,
  internal rotation

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Pincer type FAI

• Pincer type of FAI
• Middle to older aged women (40)
• Seen in ballet dancers
• Close approximation of acetabular rim and femoral
  neck acetabular abnormality
• Acetabular overcoverage
• Focal articular damage
• Acetabular damage can propagate
• Primary radiographic signs
• Coxa profunda
• Protrusio acetabuli
• Acetabular retroversion
• Decreased extrusion index
• Neutral acetabular index
• Posterior wall sign
• Posterior inferior cartilage abrasion due to
  contracoup injury

Normal
Pincer
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Coxa Profunda

• Coxa profunda floor of fossa acetabuli overlaps
  ilioischial line medially
• Pincer type FAI
• Creates deep acetabulum
• General overcoverage

• Normal

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Protrusio acetabuli

• Protrusio acetabuli occurs when the femoral
  head overlaps the ilioischial line medially
• Pincer type FAI
• Creates deep acetabulum
• General overcoverage

• Normal

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Lateral center edge angle

• Lateral center edge angle pincer type FAI
• Normal is between 25 and 39 degrees
• Increases with deeper acetabulum and more
  overcoverage

Protrusio acetabuli
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Decreased extrusion index

• Decreased extrusion index pincer type FAI
• (E / A E)
• 25 in normal subjects
• Decreases as femoral head becomes more covered.

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Acetabular index

• Acetabular index pincer type FAI
• Should be positive
• Becomes negative as acetabulum deepens

Positive AI
Negative AI in protrusio acetabuli
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Acetabular Retroversion

• Acetabular retroversion pincer type FAI
• Cross over sign
• Focal acetabular overcoverage
• Cranial anterior wall line projects laterally
• Anterior/anterolateral labrum is obstacle to
  flexion and internal rotation
• Distinguish from deficient posterior wall

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Posterior wall sign

• Posterior wall sign pincer type FAI
• PW line should descend through center of femoral
  head
• Medial deficient
• Lateral prominent

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Linear indentation sign

• Linear indentation sign pincer type FAI
• Occurs due to mechanical injury and reactive
  change

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Os acetabuli

• Associated with pincer type
• Os acetabuli

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Cam type FAI

• Cam type of FAI
• Young males (32 years)
• Primary femoral abnormality
• Aspherical femoral head
• Femoral head jams into acetabular rim
• Shear forces on labrum and cartilage
• Diffuse articular damage
• Primary radiographic signs
• Pistol grip deformity
• CCD angle less than 125 degrees
• Horizontal growth plate sign
• Alpha angle greater than 50 degrees
• Femoral head-neck offset less than 8 mm
• Femoral retrotorsion

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Pistol grip deformity

• Pistol grip deformity - Cam type FAI
• Loss of normal concavity
• Etiology
• Growth abnormality of the capital femoral
  epiphysis
• SCFE
• LCPD
• Fracture healing

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Horizontal growth plate sign

• Horizontal growth plate sign - Cam type FAI

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Alpha angle

• Alpha angle Cam type FAI
• Used as an objective representation of the
  prominence of the anterior femoral head-neck
  junction.
• Abnormal is greater than 50 degrees

Normal
Abnormal
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Femoral head-neck offset

• Femoral head-neck offset (OS) Cam type FAI
• Abnormal if less than 10 mm

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Femoral retrotorsion

• Femoral retrotorsion Cam type FAI
• Congenital or post traumatic
• Calc by CT

• Normal torsion

• Retrotorsion

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Coxa vara

• Coxa vara - Cam type FAI
• Abnormally located femoral neck
• Decreased caput collum diaphysis (CCD) angle
• Normal is 125 to 135

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General radiographic signs

• Conventional radiographic findings
• Pincer
• Deep acetabulum
• Focal acetabular retroversion or posterior wall
  sign
• Cam
• Pistol grip deformity
• Coxa vara deformity
• Misshapen femoral head
• Prior trauma or deformity
• Secondary degenerative changes
• MR imaging
• Labral damage with corresponding damage to
  femoral head/neck junction
• Chondromalacia
• Superolateral in cam type
• Posteroinferior in pincer type
• CT imaging
• Similar to radiographic findings

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Secondary radiographic signs

• Secondary radiographic signs
• Labral ossification
• Bony impaction changes
• Synovial herniation pits
• Premature degenerative changes

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Secondary MR signs

• Secondary MR findings in cam FAI
• Superolateral changes

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Secondary MR signs

• Classic MR findings in pincer FAI
• Posteroinferior cartilage abnormality due to
  contracoup injury

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What you want to prevent
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Treatment

• Treatment
• Intertrochanteric flexion-valgus osteotomy
• Arthroscopic debridement
• Remove any nonspherical portion of femoral head
• Reduce size of acetabular rim in pincer type
• Total arthroplasy in end stage disease

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References

• Tannast M, Siebenrock K, Anderson S.
  Femoroacetabular impingement radiographic
  diagnosis--what the radiologist should know. AJR
  Am J Roentgenol. 2007 Jun188(6)1540-52.
• Pfirrman CW, Mengiardi B, Dora C, Kalberer F,
  Zanetti M, Hodler J. Cam and Pincer
  Femoroacetabular Impingement Characteristic MR
  Athrographic Findings in 50 Patients. Radiology
  2006 Sep 240(3)778-85. Epub 2006 Jul 20.
• Beall DP, Sweet CF, Martin HD, Lastine CL,
  Grayson DE, Ly JQ, Fish JR. Imaging findings of
  femoroacetabular impingement syndrome. Skeletal
  Radiol (2005) 34 691 701