Femoroacetabular%20 impingement[1]
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This document discusses femoroacetabular impingement (FAI), a condition causing hip pain in young patients due to abnormal contact between the femoral head and acetabular rim. There are two main types: pincer FAI from acetabular overcoverage, and cam FAI from aspherical femoral head morphology. Clinical features include groin pain worsened by flexion and internal rotation. Radiographs and MRI can identify abnormalities like a pistol grip deformity, increased alpha angle, or acetabular retroversion. Treatment involves surgery to address bony abnormalities and prevent early osteoarthritis.
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Femoroacetabular%20 impingement[1]
- 2. •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 %
- 3. •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
- 4. •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
- 5. •Pincer type of FAI •Middle to older aged women (40) •Seen in ballet dancers •Close approximation of acetabular rim and femoral Normal 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 Pincer •Posterior wall sign •Posterior inferior cartilage abrasion due to contracoup injury
- 6. •Coxa profunda – floor of fossa acetabuli overlaps ilioischial line medially •Pincer type FAI •Creates deep acetabulum •General overcoverage •Normal
- 7. •Protrusio acetabuli – occurs when the femoral head overlaps the ilioischial line medially •Pincer type FAI •Creates deep acetabulum •General overcoverage •Normal
- 8. •Lateral center edge angle – pincer type FAI •Normal is between 25 and 39 degrees •Increases with deeper acetabulum and more overcoverage Protrusio acetabuli
- 9. •Decreased extrusion index – pincer type FAI •(E / [A + E]) •25 % in normal subjects •Decreases as femoral head becomes “more covered.”
- 10. •Acetabular index – pincer type FAI •Should be positive •Becomes negative as acetabulum “deepens” Positive AI Negative AI in protrusio acetabuli
- 11. •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
- 12. •Posterior wall sign – pincer type FAI •PW line should descend through center of femoral head •Medial – deficient •Lateral – prominent
- 13. •Linear indentation sign – pincer type FAI •Occurs due to mechanical injury and reactive change
- 14. •Associated with pincer type •Os acetabuli
- 15. •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
- 16. •Pistol grip deformity - Cam type FAI •Loss of normal concavity •Etiology •Growth abnormality of the capital femoral epiphysis •SCFE •LCPD •Fracture healing
- 17. •Horizontal growth plate sign - Cam type FAI
- 18. •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
- 19. •Femoral head-neck offset (OS) – Cam type FAI •Abnormal if less than 10 mm
- 20. •Femoral retrotorsion – Cam type FAI •Congenital or post traumatic •Calc by CT •Normal torsion •Retrotorsion
- 21. •Coxa vara - Cam type FAI •Abnormally located femoral neck •Decreased caput collum diaphysis (CCD) angle •Normal is 125 to 135
- 22. •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
- 23. •Secondary radiographic signs •Labral ossification •Bony impaction changes •Synovial herniation pits •Premature degenerative changes
- 24. •Secondary MR findings in cam FAI •Superolateral changes
- 25. •Classic MR findings in pincer FAI •Posteroinferior cartilage abnormality due to contracoup injury
- 27. •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
- 28. 1. Tannast M, Siebenrock K, Anderson S. Femoroacetabular impingement: radiographic diagnosis-- what the radiologist should know. AJR Am J Roentgenol. 2007 Jun;188(6):1540-52. 2. 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. 3. 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
Editor's Notes
- 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.
- 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.
- 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. 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.
- 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.
- 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.
- 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 ).
- Fig. 8 Coronal T1-weighted MR image of the right hip shows a small accessory ossicle at the lateral margin of the acetabulum ( white arrow ). These accessory ossicles are known as os acetabuli
- 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
- Fig. 6 Anteroposterior radiograph of the pelvis shows coxa vara deformity on the right ( white arrow ) and a normal caput collum diaphysis angle on the left. The result of the coxa vara deformity is that the femoral neck is situated more superiorly than normal given the decreased caput collum diaphysis angle (angle as measured is 117°; normal angles range from 120° to 135°). Additionally, this image shows coxa magna, acetabular dysplasia, and a prominent superolateral femoral head that likely impinges upon the lateral acetabulum when the child s hip is abducted. The left hip proximal femur and acetabulum are normal
- Fig. 12 Oblique axial CT image shows an increased alpha angle (normal is less than 50°) and prominence of the anterior femoral head-neck junction ( arrowheads ). The angle is obtained by placing a circle around the oblique axial circumference of the femoral head, placing a line in the center of the femoral neck along its longitudinal axis, and placing a second line that extends from the intersection of the first line and the center of the femoral head to the point where the osseous anterior femoral head intersects the circle
- 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.
- 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.