Femoro-acetabular impingement (FAI)

 

  • Abnormal contact between the femur and acetabulum which leads to labral damage and various degrees of chondral injury

  • CAM vs Pincer Effect ( or both)

  • Clinical symptoms

    • activity related groin or hip pain, exacerbated by hip flexion

    • difficulty sitting

    • mechanical hip symptoms of clicking or popping

    • can present with gluteal or trochanteric pain

      • due to aberrant gait mechanics

    • limited hip flexion (<90 degrees), especially with internal rotation (<5 degrees)

    • Pain on FADIR maneouvre (flexion, adduction, internal rotation): Generally the affected limb is in externally rotation.

CAM impingement

  • occurs if femoral head/neck bone is too broad, mostly on the anterolateral neck

  • usually young athelete male

  • characterized by any of the following 

    • decreased head-to-neck ratio

    • aspherical femoral head

    • decreased femoral offset

    • femoral neck retroversion

  • causes shearing at the chondro-labral junction, leading to cartilage delamination and labral separation .

  • Chondral damage occurs more frequently on the anterior superior portion of the acetabulum.

FAI1.jpg
Grantham, W. J (2019).&nbsp;Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

Grantham, W. J (2019). Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

PINCER impingement

  • occurs if acetabular bone/labrum overhang is too broad, mostly at the anterosuperior quadrant 

    • antero superior acetabular rim overcoverage

    • acetabular retroversion

    • acetabular protrusio

    • coxa profunda

  • usually in active middle-aged women

  • the femoral neck impinges and crushes the labrum creating intra-substance tearing

  • this levers the femoral head into the postero-inferior acetabulum leading to a contrecoup cartilaginous injury

 
FAI2.jpg
Grantham, W. J (2019).&nbsp;Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

Grantham, W. J (2019). Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

FAI8.jpg
 
Repartition of cartilage damage in femoroacetabular impingementGrantham, W. J (2019).&nbsp;Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

Repartition of cartilage damage in femoroacetabular impingement

Grantham, W. J (2019). Etiology and Pathomechanics of Femoroacetabular Impingement. Current Reviews in Musculoskeletal Medicine.

Difference in labral lesions CAM vs PINCER Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967&nbsp;

Difference in labral lesions CAM vs PINCER

Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967 

 

Imaging:

  • Xrays : AP +L + Frog leg (for alpha angle measurement) + DUNN + Lequesne false profile

    • Must search for the following: Coxa profunda and coxa protrusio, Center-edge angle of Wiberg, Acetabular index, Crossover sign, Posterior wall sign, Ischial spine sign, femoral head sphericity on all views, osteoarthritis

  • CT scan: 3D is important for pre-operative assessment

  • MRI for labrum ad cartillage damage assessment.

    • Prefer Arthro MRI for accurate.

    • Ensure MRI is formatted to be in-line with femoral neck 

    • Findings: Labral fraying or frank tears, chondral damage, subchondral cyst formation

  • Arthroscan can replace MRI

DUNN lateral view

DUNN lateral view

False Profile Lequesne: to assess anterior coverage of the femoral head

False Profile Lequesne: to assess anterior coverage of the femoral head

False Profile Lequesne: to assess anterior coverage of the femoral head

False Profile Lequesne: to assess anterior coverage of the femoral head

 
Check the quality of the Xray before judging !!!

Check the quality of the Xray before judging !!!

FAI+pas+cam.jpg
Image1.jpg
 
Useful radiographic parameters Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967&nbsp;

Useful radiographic parameters

Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967 

Useful MRI parameters Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967&nbsp;

Useful MRI parameters

Seminars in Musculoskeletal Radiology, 23(03), 257–275. doi:10.1055/s-0039-1683967 

 
Image2.jpg
Image4.png



 

What we find in CAM imaging

CAM impingement

CAM impingement

Pistol- grip like deformity

Pistol- grip like deformity

Alpha angle: values of &gt;42° are suggestive of a head-neck offset deformity,&nbsp;&gt;50-55° indicates Cam deformityAssessed on frog-leg lateral radiograph

Alpha angle: values of >42° are suggestive of a head-neck offset deformity, >50-55° indicates Cam deformity

Assessed on frog-leg lateral radiograph

Alpha angle on MRI

Alpha angle on MRI

Omega angle

Omega angle

 
Femoral head neck offset : distance between line 2 (neck line) and 3femoral head line). If &lt;10 mm —&gt; CAM

Femoral head neck offset : distance between line 2 (neck line) and 3femoral head line). If <10 mm —> CAM

head neck offset ratio= FHNO/diameter of FH.If &lt;0.17—&gt;CAM

head neck offset ratio= FHNO/diameter of FH.

If <0.17—>CAM

 
 

What we find in PINCER imaging

Lateral center edge angle (or Wiberg angle). Normal between 25-40 degrees

Lateral center edge angle (or Wiberg angle). Normal between 25-40 degrees

Anterior center edge angleNormal &gt; 20

Anterior center edge angle

Normal > 20

Tonnis angle ( Normal above 0 degree)

Tonnis angle ( Normal above 0 degree)

Cross over sign

Cross over sign

Cross+over+sign.jpg
Pincer.png
 

Differential Diagnosis: Various pathologies will refer pain to the hip region

  • hip instability

  • iliopsoas pathology

  • Ischiofemoral impingment 

  • adductor strains and athletic pubalgia

  • lumbar radiculopathy

Treatment

  • Activity modification, Physical therapy, NSAID

  • Arthroscopic osteoplasty

  • Hip arthroplasty (if osteoarthritis)

Complications: heterotopic ossification, femoral neck fracture…