1. Femuru acetabular impimgment
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
Fig. 7 —Schematic (left) and radiographic (right) presentations of coxa profunda (detailed view of anteroposterior pelvic radiograph) in 29-year-old woman. Acetabular fossa (F) is touching or overlapping ilioischial line (IIL). Femoral head (H) is more covered, resulting in decreased femoral head extrusion index (E / [A + E]), neutral acetabular index (AI'), and increased lateral center edge (LCE') angle. A' = covered portion of the femoral head, E' = uncovered portion of the femoral head.
Fig. 6 —Schematic (left) and radiographic (right) appearances of normal hip (detailed view of anteroposterior pelvic radiograph) in 35-year-old man. Acetabular fossa (F) is lateral to ilioischial line (IIL). Acetabular index (AI) is positive, and femoral head (H) is not entirely covered by acetabulum (E). Projected anterior wall (AW) lies medially to posterior wall (PW), which typically runs more or less through center of femoral head. Extrusion index (E / [A + E]) is approximately 25%. Lateral center edge (LCE) angle is 25–39°. Epiphyseal scar lies in femoral head circle (arrows). A = covered portion of femoral head, E = uncovered portion of femoral head.
Normal

3. Protrusio acetabuli
Protrusio acetabuli – occurs when the femoral head overlaps the ilioischial line medially
Pincer type FAI
Creates deep acetabulum
Fig. 8 —Schematic (left) and radiographic (right) presentations of protrusio acetabuli (detailed view of anteroposterior pelvic radiograph) in 42-year-old woman. Femoral head line (H) is crossing ilioischial line (IIL). As a consequence, femoral head extrusion index (E / [A + E]) is zero or even negative, acetabular index (AI") is negative, and lateral center edge (LCE") angle increases. F = acetabular fossa. A" = covered portion of femoral head, E" = uncovered portion of femoral head.
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.”
Fig. 7 —Schematic (left) and radiographic (right) presentations of coxa profunda (detailed view of anteroposterior pelvic radiograph) in 29-year-old woman. Acetabular fossa (F) is touching or overlapping ilioischial line (IIL). Femoral head (H) is more covered, resulting in decreased femoral head extrusion index (E / [A + E]), neutral acetabular index (AI'), and increased lateral center edge (LCE') angle. A' = covered portion of the femoral head, E' = uncovered portion of the femoral head.

8. ((abnormal < 10 degrees Tonnis 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
Fig. 10 —Schematic (left) and radiographic (right) presentations of focal anterior overcoverage of hip in 29-year-old woman. Acetabular retroversion is defined as anterior wall (AW) being more lateral than posterior wall (PW), whereas in normal hip anterior wall lies more medially. This cranial acetabular retroversion can also be described by figure-8 configuration.

11. Acetabular index Acetabular index – pincer type FAI Should be positive
Becomes negative as acetabulum “deepens”
Positive AI
Negative AI in protrusio acetabuli
Fig. 8 —Schematic (left) and radiographic (right) presentations of protrusio acetabuli (detailed view of anteroposterior pelvic radiograph) in 42-year-old woman. Femoral head line (H) is crossing ilioischial line (IIL). As a consequence, femoral head extrusion index (E / [A + E]) is zero or even negative, acetabular index (AI") is negative, and lateral center edge (LCE") angle increases. F = acetabular fossa. A" = covered portion of femoral head, E" = uncovered portion of femoral head.

12. Alpha angle

13. Alpha angle Normal Abnormal 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
Fig. 2  Prominence of the femoral head-neck junction in the anterior/anterosuperior portion of the proximal femur (white arrows) is known as the pistol grip deformity due to its similarities with the smooth hand grip of many pistols

16. Posterior wall sign Posterior wall sign – pincer type FAI
PW line should descend through center of femoral head
Medial – deficient
Lateral – prominent
Fig. 11 —Schematic (left) and radiographic (right) presentations of too-prominent posterior wall (PW) show posterior wall line running laterally to femoral head center in 30-year-old man.

17. Linear indentation sign
Linear indentation sign – pincer type FAI
Occurs due to mechanical injury and reactive change
Fig. 17A —Pincer hips in 37-year-old woman. In pincer hips, corresponding linear indentation often occurs on femoral side (black arrows) with reactive cortical thickening (white arrows), which can be seen on conventional radiograph (A) and on MR arthrogram with intraarticular contrast agent (B).
Fig. 17B —Pincer hips in 37-year-old woman. In pincer hips, corresponding linear indentation often occurs on femoral side (black arrows) with reactive cortical thickening (white arrows), which can be seen on conventional radiograph (A) and on MR arthrogram with intraarticular contrast agent (B).

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
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
Figure 5: Sagittal water excitation three-dimensional double-echo steady-state MR image (24.0/6.5, 25° flip angle) in a patient with pincer FAI. Note cartilage damage (arrowheads) at the posteroinferior aspect of the acetabulum.

23. Secondary MR signs Secondary MR findings in cam type FAI
Superolateral changes
Figure 4: Consecutive sagittal water excitation three-dimensional double-echo steady-state MR images (24.0/6.5, 25° flip angle) moving from medial (left) to lateral (right) in a patient with cam FAI. Note advanced acetabular cartilage damage at the anterior aspect of the acetabulum (white arrowheads). The cartilage is normal at the posterior aspect of the acetabulum (black arrowheads). An os acetabuli (curved arrow) is present at the anterosuperior aspect of the acetabular rim. Note the herniation pit (straight arrow) at the anterior femoral head-neck junction.
Figure 6: Labral tear (arrow) in a patient with cam FAI (transverse oblique section, water excitation three-dimensional double-echo steady-state MR sequence, 24.0/11.8, 25° flip angle) obtained through the center of the femoral neck. Note the osseous bump (arrowheads) at the anterior aspect of the femoral head.

24. What you want to prevent