Current Concepts in the Imaging of Femoroacetabular Impingement Syndromes

Transcription

1 Current Concepts in the Imaging of Femoroacetabular Impingement Syndromes Poster No.: C-1840 Congress: ECR 2011 Type: Educational Exhibit Authors: A. ABDULLAH, J. Zeiss, H. Semaan, H. Semaan, H. Elsamaloty, T. Lewis, F. Ebrahim; TOLEDO, OH/US Keywords: Arthrography, MR, Digital radiography, CT, Musculoskeletal joint DOI: /ecr2011/C-1840 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 55

2 Learning objectives Emphasis will be placed on recognizing Femoroacetabular impingement (FAI) on conventional radiography as well MRI in appropriate clinical setting. The role of radial MR imaging around the femoral acetabulum or neck will be included. A brief discussion of the current imaging criteria will be provided. A gamut of potential pitfalls in the diagnosis of FAI will be discussed. Page 2 of 55

3 Background Femoroacetabular impingement (FAI) is an important cause of early osteoarthritis of the hip in young patients. FAI can potentially cause chronic symptoms of pain, joint locking, and reduced range of motion. Imaging plays a central role in the diagnosis of FAI. However, the diagnosis of FAI is strictly made in the presence of appropriate clinical history in conjunction with imaging findings. Fig.: Etiology of FAI References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US The structural abnormalities associated with femoroacetabular impingement were noted several decades ago, when abnormalities of the femoral head-neck contour were referred to as tilt or pistol grip deformities, which Ganz et al. classified as cam morphology. Page 3 of 55

4 Fig.: FAI References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US In cases of cam FAI, the non-spherical shape of the femoral head at the femoral headneck junction and reduced depth of the femoral waist leads to abutment of the femoral head neck junction against the acetabular rim. Page 4 of 55

5 Fig.: AP view of the pelvis demonstrating bilateral osseous bumps at the femoral head and neck junction. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 5 of 55

6 Fig.: AP view of right femur demonstrating physeal scar which projects lateral to a best fit circle of the femoral head also know as "horizontal growth plate sign" seen in Cam FAI. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 6 of 55

7 Fig.: Axial T1W fat suppressed MR arthrogram images demonstrate an alpha angle of approximately 62 degrees. A straight line (A) is drawn perpendicular to the the femoral neck at its narrowest point. A second line (B)is drawn perpendicular to line A. A best fit circle (dotted red) is drawn outlining the femoral head. Alpha angle is measured by drawing a line (C) from the center of femoral head on line B to where it protrudes anterior to the circle. An alpha angle of greater than 55 degrees is considered abnormal and is seen in cam FAI. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US In addition, Ganz et al. identified another mechanism of femoroacetabular impingement known as pincer which is secondary to acetabular overcoverage of the femoral head and is present in a third of the patients with a cam deformity. In cases of pincer FAI, acetabular overcoverage limits the range of motion and leads to a conflict between the acetabulum and the femur(fig. 6 and 7). Page 7 of 55

8 Fig.: Axial CT demonsrating retroversion of the rigt acetabulum. AP view of the right hip demonstrates lateral over-coverage with a lateral center edge angle greater than 40 degrees. AP view of the left femur deonstrats a crossover sign of the anterior wall lateral to the posterior wall consistent with acetabular retroversion. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 8 of 55

9 Fig.: AP view of the pelvis demonstrating posterior wall of the acteabulum (red line) oriented medial to the center of the femora head suggestive of deficient posterior wall. Posterior wall deficiency is seen in pincer-type FAI and is asscoiated with actabular retroversio. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 9 of 55

10 Fig.: AP view of the pelvis demonstrates the anterior rim line lying lateral to the posterior acetabular rim in the cranial part of the acetabulum and crosses medially in the inferior part making a figure 8 or crossover sign. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US It is radiologically prudent to identify the type of FAI because surgical management differs for each type. In cases of cam-type FAI, the surgical approach is to reshape the femoral waist and restore the spherical shape of the femoral head. In cases of pincer FAI, the surgical management is reduction of acetabular overcoverage by trimming the acetabular rim. Patients with FAI usually present wth clinical symptoms of groin pain, pain overlying the trochanters, pain with flexion and internal rotation, and may even have clinical symptoms after surgery. The symptoms of impingement are often unilateral but bilateral FAI can occur in individuals who have hip joint laxity such as that seen in patients with connective tissue disorders. Page 10 of 55

11 Physical examination in patients with FAI includes evaluation for loss of internal rotation out of proportion to the loss of range of movement at other positional extremes. Loss of internal rotation out of proportion with other motions typically favors FAI over osteoarthritis, which can produce a universal limited range of motion. In patients with FAI, a grinding and popping sensation can be felt when the femur is externally rotated during maximal abduction of the hip. Page 11 of 55

12 Images for this section: Fig. 0: Etiology of FAI RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 12 of 55

13 Fig. 0: FAI RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 13 of 55

14 Fig. 0: AP view of the pelvis demonstrating bilateral osseous bumps at the femoral head and neck junction. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 14 of 55

15 Fig. 0: Axial T1W fat suppressed MR arthrogram images demonstrate an alpha angle of approximately 62 degrees. A straight line (A) is drawn perpendicular to the the femoral neck at its narrowest point. A second line (B)is drawn perpendicular to line A. A best fit circle (dotted red) is drawn outlining the femoral head. Alpha angle is measured by drawing a line (C) from the center of femoral head on line B to where it protrudes anterior to the circle. An alpha angle of greater than 55 degrees is considered abnormal and is seen in cam FAI. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 15 of 55

16 Fig. 0: AP view of right femur demonstrating physeal scar which projects lateral to a best fit circle of the femoral head also know as "horizontal growth plate sign" seen in Cam FAI. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 16 of 55

17 Fig. 0: Axial CT demonsrating retroversion of the rigt acetabulum. AP view of the right hip demonstrates lateral over-coverage with a lateral center edge angle greater than 40 degrees. AP view of the left femur deonstrats a crossover sign of the anterior wall lateral to the posterior wall consistent with acetabular retroversion. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 17 of 55

18 Fig. 0: AP view of the pelvis demonstrating posterior wall of the acteabulum (red line) oriented medial to the center of the femora head suggestive of deficient posterior wall. Posterior wall deficiency is seen in pincer-type FAI and is asscoiated with actabular retroversio. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 18 of 55

19 Fig. 0: AP view of the pelvis demonstrates the anterior rim line lying lateral to the posterior acetabular rim in the cranial part of the acetabulum and crosses medially in the inferior part making a figure 8 or crossover sign. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 19 of 55

20 Imaging findings OR Procedure details The role of imaging in femoroacetabular impingement is to evaluate the hip joint for abnormalities associated with impingement and to exclude arthritis, avascular necrosis, or other joint problems on radiographs. MR arthrography can be used to confirm or exclude labral tears, cartilage damage, and other pathologic signs of internal hip derangement if impingement is suspected. Alternatively, radiography is then usually followed by MRI for cartilage and labral disorders and a 3D understanding of the bone anatomy. Radiographic findings consistent with FAI include early onset of degenerative arthritis, acetabular retroversion, a decreased femoral head-neck junction, and evidence of impaction in regions of the anterosuperior acetabulum and anterior femoral neck. Computed tomography demonstrates the osseous abnormalities that may be seen in patients with FAI, including acetabular retroversion and prominent anterior femoral headneck junction osseous bump. MR imaging is not only effective at demonstrating the findings that may be seen with CT but is also capable of demonstrating articular cartilage damage and acetabular labral tears The alpha angle is greater in cam-type FAI at the anterior and anterosuperior locations. The acetabulum is deeper in patients with pincer-type FAI than in patients with camtype FAI. Cartilage lesions at the anterosuperior and superior positions are generally larger in patients with cam FAI than in patients with pincer FAI. Cartilage lesions at the posteroinferior position are larger and labral lesions at the posterior and posteroinferior positions are more conspicuous in patients with pincer FAI than in patients with cam FAI. We retrospectivey evaluated several cases of FAI at our institution using CT, MR, and radiography. The radiologic findings of these cases are described below: Case 1: Patient was a 33-year old who presented with left hip locking and pain. Page 20 of 55

21 Fig.: Axial and coronal fat suppressed T1W MR arthrogram and PD images demonstrate an osseous bump at the femoral/head neck junction (yellow arrows)with a anterior superior labral tear (red arrow). AP pelvis radiograph shows a non-ossifying fibroma involving the femoral neck (blue arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 2: Patient was a 31-year old male with right hip pain in the trochanteric region. Page 21 of 55

22 Fig.: Axial and coronal T1W MR arthrogram and PD fat suppressed images demonstrate a CAM bump at the femoral head and neck (blue arrows) junction with associated superior acetabular cartilage delamination (yellow arrow) along with a small anterosuperior labral tear (green arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 3: Patient was a 39 year-old previous atlete presented with right hip pain with internal rotation. Page 22 of 55

23 Fig.: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate femoral head/neck junction CAM bump (blue arrow) with subchondral cyst formation. A small accompanying acetabular labral (yellow arrow) tear is also visualzied. Axial CT images demostrate bilateral osseous bumps at the femoral head/neck junction. Patient was asymptomatic on the left side, however. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 4: Patient was a 29 year-old female with hip and groin pain. Page 23 of 55

24 Fig.: Axial and coronal T1W MR athrogram imags demostrate a subtle CAM bump at the femoral head/neck junction (blue arrows) along with a superior and posterior labral tear (yellow arrows). The osseous bump was not well seen on AP Pelvis radiograph. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 5: Patient was a 27 year-old male with left hip locking and groin pain. Page 24 of 55

25 Fig.: Axial and coronal T1W fat suppressed MR arthrogram demonstrate an anterosuperior left acetabular labral tear (blue arrows) with an accompanying femoral CAM bump (red arrow). AP radiograph redemonstrate the osseous bump at the femoral head and neck junction also known as "pistol grip deformity". References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 6: Patient was a 34 year-old male with left hip joint pain and locking. Page 25 of 55

26 Fig.: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate an osseous bump at the femoral head and neck junction (solid blue arrow) with acetabular cartilage delamination (solid red arrow) along with a small labral tear (yellow arrow). A loose body (dotted blue arrow) was identified in the iliopsoas bursa which communicated with the hip joint (dotted red arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 7: Patient was a 29 year-old female with longstanding worsening hip pain. Page 26 of 55

27 Fig.: Coronal T1W fat suppressed MR arthrogram images demonstrate an area of avascular necrosis invovling the femoral head (red arrow). An incidental osseous bump is also noted at the femoral head and neck junction (blue arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 8: Patient was a 27 year-old male with complaints of left sided hip pain. Page 27 of 55

28 Fig.: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate a mixed CAM (blue arrows) and subtle Pincer-type (red arrow) FAI with a small accompanying acetabular labral tear (yellow arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 9: Patient was a 31 year-old who presented with hip pain who was initially diagnosed wth Cam impingement which prompted a labral repair and femoral resurfacing procedure. Three months later patient presented with new onset pain. Subsequent imaging demonstrated a retear of the acetabular labrum. Page 28 of 55

29 Fig.: Coronal T1W pre-surgical MR arthrogram images demonstrate a CAM bump (solid blue arrow) with a small acetabular labral tear (solid red arrow). Post surgical images demonstrate a resurfacing femoral defect (dotted blue arrow) and a retear of the acetabular labrum (dotted red arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 10: Patient was a 28 year-old with right hip pain. Page 29 of 55

30 Fig.: Axial PD MR image demonstrates a retroverted appearenece of the left acetabulum (yellow arrow). AP radiograph demonstrate a postive posterior wall sign. Findings were consitent with pincer-type FAI. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 11: Patient was a 42 year old male who presented with right hip locking and decrease range of motion with certain positioning of the hip. Page 30 of 55

31 Fig.: Radiogrphic analysis revealed an osseous bump at the femoral head/neck juntion (blue arrows). Axial and coronal CT images further confirmed this finding along with a small sublabral cyst (yellow arrow). References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Case 12: Patient was a 41 year-old female who presented with right hip pain and locking sensation. Page 31 of 55

32 Fig.: AP radiograph of the right hip demonstrate an osseous bump at the femoral head and neck junction (dotted blue arrow) with adjacent lucency (solid blue arrow). Coronal STIR and axial PD MR images demonstrate a CAM bump (yellow arrow) with an adjacent area of bone edema (red arrow). An intrarticular loose body was also seen. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 32 of 55

33 Images for this section: Fig. 0: Axial and coronal fat suppressed T1W MR arthrogram and PD images demonstrate an osseous bump at the femoral/head neck junction (yellow arrows)with a anterior superior labral tear (red arrow). AP pelvis radiograph shows a non-ossifying fibroma involving the femoral neck (blue arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 33 of 55

34 Fig. 0: Axial and coronal T1W MR arthrogram and PD fat suppressed images demonstrate a CAM bump at the femoral head and neck (blue arrows) junction with associated superior acetabular cartilage delamination (yellow arrow) along with a small anterosuperior labral tear (green arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 34 of 55

35 Fig. 0: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate femoral head/neck junction CAM bump (blue arrow) with subchondral cyst formation. A small accompanying acetabular labral (yellow arrow) tear is also visualzied. Axial CT images demostrate bilateral osseous bumps at the femoral head/neck junction. Patient was asymptomatic on the left side, however. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 35 of 55

36 Fig. 0: Axial and coronal T1W MR athrogram imags demostrate a subtle CAM bump at the femoral head/neck junction (blue arrows) along with a superior and posterior labral tear (yellow arrows). The osseous bump was not well seen on AP Pelvis radiograph. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 36 of 55

37 Fig. 0: Axial and coronal T1W fat suppressed MR arthrogram demonstrate an anterosuperior left acetabular labral tear (blue arrows) with an accompanying femoral CAM bump (red arrow). AP radiograph redemonstrate the osseous bump at the femoral head and neck junction also known as "pistol grip deformity". RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 37 of 55

38 Fig. 0: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate an osseous bump at the femoral head and neck junction (solid blue arrow) with acetabular cartilage delamination (solid red arrow) along with a small labral tear (yellow arrow). A loose body (dotted blue arrow) was identified in the iliopsoas bursa which communicated with the hip joint (dotted red arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 38 of 55

39 Fig. 0: Coronal T1W fat suppressed MR arthrogram images demonstrate an area of avascular necrosis invovling the femoral head (red arrow). An incidental osseous bump is also noted at the femoral head and neck junction (blue arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 39 of 55

40 Fig. 0: Axial and coronal T1W fat suppressed MR arthrogram images demonstrate a mixed CAM (blue arrows) and subtle Pincer-type (red arrow) FAI with a small accompanying acetabular labral tear (yellow arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 40 of 55

41 Fig. 0: Coronal T1W pre-surgical MR arthrogram images demonstrate a CAM bump (solid blue arrow) with a small acetabular labral tear (solid red arrow). Post surgical images demonstrate a resurfacing femoral defect (dotted blue arrow) and a retear of the acetabular labrum (dotted red arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 41 of 55

42 Fig. 0: Axial PD MR image demonstrates a retroverted appearenece of the left acetabulum (yellow arrow). AP radiograph demonstrate a postive posterior wall sign. Findings were consitent with pincer-type FAI. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 42 of 55

43 Fig. 0: Radiogrphic analysis revealed an osseous bump at the femoral head/neck juntion (blue arrows). Axial and coronal CT images further confirmed this finding along with a small sublabral cyst (yellow arrow). RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 43 of 55

44 Fig. 0: AP radiograph of the right hip demonstrate an osseous bump at the femoral head and neck junction (dotted blue arrow) with adjacent lucency (solid blue arrow). Coronal STIR and axial PD MR images demonstrate a CAM bump (yellow arrow) with an adjacent area of bone edema (red arrow). An intrarticular loose body was also seen. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 44 of 55

45 Fig. 0: AP view of the pelvis demonstrating bilateral osseous bumps at the femoral head and neck junction. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 45 of 55

46 Conclusion Conventional radiography can be used to analyze the morphology of hip joint and evaluate eventual osteoarthritis. CT-based methods are extremely beneficial in preoperative assessment and surgical planning. MR arthrography is considered the gold standard and clearly depicts the main diagnostic imaging features of FAI, acetabular cartilage, and labral pathology. Fig.: Schematics of FAI References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 46 of 55

47 Fig.: Axial CT images through the cranial acetabulam on the the first axial image that includes the femoral head demonstrate the anterior rim of the acetabulum lying lateral to the posterior rim (blue line) consistent with acetabular retroversion. The red line demonstrate the normal anteverted acetabulum. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 47 of 55

48 Fig.: Three-dimensinal computed tomography images demonstrate posterior acetabular wall deficiency. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 48 of 55

49 Fig. References: RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER TOLEDO/US Page 49 of 55

50 Images for this section: Fig. 0: Schematics of FAI RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 50 of 55

51 Fig. 0 RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 51 of 55

52 Fig. 0: Axial CT images through the cranial acetabulam on the the first axial image that includes the femoral head demonstrate the anterior rim of the acetabulum lying lateral to the posterior rim (blue line) consistent with acetabular retroversion. The red line demonstrate the normal anteverted acetabulum. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 52 of 55

53 Fig. 0: Three-dimensinal computed tomography images demonstrate posterior acetabular wall deficiency. RADIOLOGY, UTMC, UNIVERSITY OF TOLEDO MEDICAL CENTER - TOLEDO/US Page 53 of 55

54 Personal Information Page 54 of 55

55 References Beall D,Sweet C, Martin H, Lastine C, Grayson D, Ly J, Fish J. Imaging findings of femoroacetabular impingement syndrome. Skeletal Radiol (2005) 34: Crawford JR, Villar RN. Current concepts in the management of femoroacetabular impingement. J Bone Joint Surg [Br] 2005;87-B: Hack K, Di Primio G, Rakhra K,. Beaul e P. Prevalence of Cam-Type Femoroacetabular Impingement Morphology in Asymptomatic Volunteers. J Bone Joint Surg Am. 2010;92: Nouh M, Schweitzer M, Rybak L, Cohen J. Femoroacetabular Impingement: Can the Alpha Angle Be Estimated? AJR 2008; 190: Palmer WE. Femoroacetabular Impingement: Caution Is Warranted in Making Imagingbased Assumptions and Diagnoses. Radiology 2010; 257:4-7. Parvizi J, MD, Leunig M, Ganz R, MD. Femoroacetabular Impingement. J Am Acad Orthop Surg 2007;15: Tannast M, Siebenrock K, and Anderson S. Femoroacetabular Impingement: Radiographic Diagnosis-What the Radiologist Should Know. AJR 2007; 188: Page 55 of 55