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F.A.I.

F.A.I. Femuru acetabular impimgment. Coxa Profunda. Coxa profunda – floor of fossa acetabuli overlaps ilioischial line medially Pincer type FAI Creates deep acetabulu. Normal. Protrusio acetabuli. Protrusio acetabuli – occurs when the femoral head overlaps the ilioischial line medially

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F.A.I.

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  1. F.A.I. Femuru acetabular impimgment

  2. Coxa Profunda • Coxa profunda – floor of fossa acetabuli overlaps ilioischial line medially • Pincer type FAI • Creates deep acetabulu • Normal

  3. Protrusio acetabuli • Protrusio acetabuli – occurs when the femoral head overlaps the ilioischial line medially • Pincer type FAI • Creates deep acetabulum • Normal

  4. Lateral Center Edge Angle normal 25 -39 degrees

  5. 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

  6. Anterior Center Edge Angle Lequesne (abnormal < 25 degrees) .

  7. Decreased extrusion index • Decreased extrusion index – pincer type FAI • (E / [A + E]) • 25 % in normal subjects • Decreases as femoral head becomes “more covered.”

  8. ((abnormal < 10 degreesTonnis Angle

  9. Crossover Sign. • The crossover sign is a sensitive and specific indicator of native acetabular version.   On an AP pelvis radiograph, the outlines of the edges of the anterior and posterior walls of the acetabulum should meet superiorly and laterally.  In cases of acetabular retroversion, this crossover of the anterior and posterior acetabular wall outlines is more distal. Changes in the acetabular rim may also be noted.

  10. 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

  11. Acetabular index • Acetabular index – pincer type FAI • Should be positive • Becomes negative as acetabulum “deepens” Positive AI Negative AI in protrusio acetabuli

  12. Alpha angle

  13. 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

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

  15. 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

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

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

  18. 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 %

  19. 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

  20. 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

  21. Secondary radiographic signs • Secondary radiographic signs • Labral ossification • Synovial herniation pits • Premature degenerative changes

  22. Secondary MR signs • Classic MR findings in pincer FAI • Posteroinferior cartilage abnormality due to contracoup injury

  23. Secondary MR signs • Secondary MR findings in cam type FAI • Superolateral changes

  24. What you want to prevent

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