Acetabular labrum: Pitfalls of MR imaging

Transcription

1 Acetabular labrum: Pitfalls of MR imaging Poster No.: C-2218 Congress: ECR 2010 Type: Educational Exhibit Topic: Musculoskeletal - Joints Authors: M. Castro, A. Almeida, N. P. Silva, R. H. Castro, A. Vieira; Porto/ PT Keywords: Acetabular labrum, Tears, MRI pitfalls Keywords: Musculoskeletal joint, Musculoskeletal system DOI: /ecr2010/C-2218 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 65

2 Learning objectives To understand and identify the different pitfalls that may reduce the specificity of the MR diagnosis of acetabular labral tears. Page 2 of 65

3 Images for this section: Fig. 0: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images show the normal labrum (circles) as a low signal triangular structure and the transverse ligament (arrows) connecting the anterior and posterior labrum. Page 3 of 65

4 Fig. 0: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material extending into the acetabular/labral interface, with a complete detachment of the labrum from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial pit is also seen in the anterior junction of the head and neck of the femur (circle). These finding is frequently associated with situations of femoro-acetabular impingement, one of the major causes of labral tears. Page 4 of 65

5 Fig. 0: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened labrum with increased interstitial signal. Page 5 of 65

6 Fig. 0: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the linear high signal under the base of the labrum (arrow) presenting with the same signal intensity of the contrast material. This is not cartilage undercutting the labrum, this is a labral tear. Page 6 of 65

7 Background As orthopedic surgeons become more comfortable performing arthroscopic surgery on the hip joint, labral abnormalities are more frequently being addressed by means of minimally invasive surgery. Accurate preoperative identification of labral tears by the radiologist has therefore become an area of increasing interest. Different authors reported sensitivity values of MR arthrograms from 66% to 100% and specificity values from 44% to 100%. Although it is obvious that some labral tears may not be visualized on MR arthrograms, it is less evident why false-positive MR arthrograms occur and what these findings actually represent. The presence of normal anatomic variants is the probable explanation for an important number of false-positive MR findings in some of the previous published studies. Page 7 of 65

8 Images for this section: Fig. 0: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are diagnostic for a labral tear. This patient also has signs of AVN of the femoral head. Page 8 of 65

9 Fig. 0: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow) crossing the anterior labrum (white arrow). Inbetween these two structures is a line of high signal that should not be mistaken by a labral tear. Page 9 of 65

10 Fig. 0: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal labroligamentous sulcus (arrow) at the junction of the anterior labrum with the transverse ligament. Page 10 of 65

11 Fig. 0: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of the posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral recess. Page 11 of 65

12 Imaging findings OR Procedure details Functions of the Acetabular Labrum Shock absorption Joint lubrication Pressure distribution Aiding in stability of the hip joint Etiology of the Labral Lesions The etiology of labral tears includes: Trauma Femoroacetabular impingement Capsular laxity/hip hypermobility Dysplasia Degeneration Importance of the Labral Lesions Previously thought to be a relatively uncommon injury, acetabular labral tears are becoming diagnosed with increasing frequency because of improvements in MRI and arthroscopic techniques. Prevalence of labral tears in patients with hip or groin pain has been reported to be 22-55%. Besides the symptomatic complaints due to labral tears, the importance of the pathology is its association with degenerative changes: % of patients with fraying or tearing of the acetabular labrum have chondral damage. The chondral damage is more severe in patients with labral lesions. In 94% of the patients, the articular damage occurs in the same zone of the acetabulum as the labral lesions. The relative risk of significant chondral erosion approximately doubles in the presence of a labral lesion. Acetabular Labrum Anatomy The acetabulum covers 170 of the femoral head. The acetabular labrum is a fibrocartilaginous structure that outlines the acetabular socket. It is a continuous, low signal, usually triangular structure that attaches to the rim of the acetabulum and is completed at the inferior portion by the transverse acetabular ligament over the acetabular notch (fig. 1). Page 12 of 65

13 Fig.: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images show the normal labrum (circles) as a low signal triangular structure and the transverse ligament (arrows) connecting the anterior and posterior labrum. References: Radiology, Hospital de São João - Porto/PT Labral Tears Diagnosis Labral tears present with anterior hip or groin pain, and less commonly buttock pain. Frequently, there are also mechanical symptoms including clicking, locking, and giving way. Most reported tears occur at the anterior portion of the labrum. In Japan the majority of tears occurs in the posterior aspect of the labrum, likely due to the frequent practice in that country of squatting or sitting on the ground or floor. Criteria for tears on MR arthrography (MRA) include (fig. 2, 3 and 4): Contrast extending into the labrum or acetabular/ labral interface Blunted appearance Displacement/detachment from underlying bone Presence of a paralabral cyst Page 13 of 65

14 Fig.: Fig. 2) Coronal T2 GRE- weighted image demonstrates the articular fluid extending into the acetabular/labral interface (arrow). The labrum is flattened and detached from the underlying bone. These findings are suggestive of a labral tear. References: Radiology, Hospital de São João - Porto/PT Page 14 of 65

15 Fig.: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material extending into the acetabular/labral interface, with a complete detachment of the labrum from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial pit is also seen in the anterior junction of the head and neck of the femur (circle). These finding is frequently associated with situations of femoro-acetabular impingement, one of the major causes of labral tears. References: Radiology, Hospital de São João - Porto/PT Page 15 of 65

16 Fig.: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are diagnostic for a labral tear. This patient also has signs of AVN of the femoral head. References: Radiology, Hospital de São João - Porto/PT Pitfalls in the Evaluation of the Labrum It was documented that patients visited, on the average, 3.3 health-care providers before being correctly diagnosed with a labral tear and more importantly, 33% received an alternate diagnosis prior to being diagnosed with a labral tear. Studies have compared MRA with surgical findings and have shown a range of sensitivity from 60% to 100% and that of specificity from 44% to 100% for acetabular labral pathology. Page 16 of 65

17 It is obvious that some labral tears may not be visualized on MRA, but it is less evident why false-positive MR arthrograms occur. The presence of normal anatomic variants is the probable explanation for an important number of false-positive MR findings in some of the previous published studies. 1. Variations in Labral Shape and Signal Intensity Asymptomatic subjects can present sometimes with variations from the triangular shaped and low signal intensity acetabular labrum resulting in a potential imaging pitfall of tear overdiagnosis. Round, irregular and flattened labrum has been reported in people without hip pain (fig. 5 and 6). Fig.: Fig. 5) Coronal STIR-weighted image demonstrates mild increase of the interstitial signal of the anterior labrum, without other signs that suggest the presence of a tear. References: Radiology, Hospital de São João - Porto/PT Page 17 of 65

18 Fig.: Fig. 6) Coronal T1-weighted MR arthrography image shows a rounded labrum, without signs of tear. References: Radiology, Hospital de São João - Porto/PT Focal intermediate to slightly high signal intensity may be seen inside the labrum (fig. 7) or at the labral base. Page 18 of 65

19 Fig.: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened labrum with increased interstitial signal. References: Radiology, Hospital de São João - Porto/PT These variations of the labral shape and signal intensity are more common in older patients and in the antero-superior labrum (weight-bearing area). 2. Acetabular Cartilage Undercutting the Labrum Cartilage undercutting the labrum can mimic high-intensity signal from a labral tear (fig. 8). Page 19 of 65

20 Fig.: Fig. 8) Coronal STIR-weighted image demonstrates a linear high signal under the base of the anterosuperior labrum (arrow). Is this a tear? Is this cartilage undercutting the labrum? Is not always easy to make this distinction without articular contrast. There is no labral tear in this patient. References: Radiology, Hospital de São João - Porto/PT Contrast material in the joint may avoid this pitfall because the contrast material and cartilage are of different signal intensities (fig. 9 and 10). Page 20 of 65

21 Fig.: Fig. 9) Coronal T1-weighted MR arthrography image where is easy to see that the linear high signal under the base of the labrum (arrow) is not as high as the signal of the contrast material. This is only cartilage undercutting the labrum. References: Radiology, Hospital de São João - Porto/PT Page 21 of 65

22 Fig.: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the linear high signal under the base of the labrum (arrow) presenting with the same signal intensity of the contrast material. This is not cartilage undercutting the labrum, this is a labral tear. References: Radiology, Hospital de São João - Porto/PT 3. Iliopsoas Tendon Crossing the Labrum The iliopsoas tendon crosses anterior to the anterior labrum. It is important to understand this relationship because the high signal between these two low signal structures may mimic a tear of the labrum (fig. 11). Page 22 of 65

23 Fig.: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow) crossing the anterior labrum (white arrow). Inbetween these two structures is a line of high signal that should not be mistaken by a labral tear. References: Radiology, Hospital de São João - Porto/PT This pitfall can be easily avoided following the iliopsoas tendon proximally to the muscular component or distally to the insertion in the lesser trochanter (fig. 12). Page 23 of 65

24 Fig.: Fig. 12) Axial T2 GRE-weighted images, show the iliopsoas tendon (blue arrow) crossing the anterior labrum (white arrow) (a). It is easy to follow the iliopsoas tendon proximally to the muscular component (b) or distally to the insertion in the lesser trochanter (c). References: Radiology, Hospital de São João - Porto/PT 4. Labroligamentous Sulcus A normal cleft/sulcus is frequently observed at the junction of the anterior labrum with the transverse ligament (fig. 13 and 14. See also fig. 18). Page 24 of 65

25 Fig.: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level of transverse ligament and anterior labral junction shows the normal labroligamentous sulcus (arrow) that may be mistaken for a labral tear. References: Radiology, Hospital de São João - Porto/PT Page 25 of 65

26 Fig.: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal labroligamentous sulcus (arrow) at the junction of the anterior labrum with the transverse ligament. References: Radiology, Hospital de São João - Porto/PT The sulcus at the anterior labral-ligamentous junction is frequently accompanied by a periligamentous recess located anterior to the ligamentum teres and medial to the anterior portion of the transverse ligament (fig. 15). Page 26 of 65

27 Fig.: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess (arrow) inferiorly to the junction of the anterior labrum with the transverse ligament. References: Radiology, Hospital de São João - Porto/PT This normal finding is located more inferior than most anterior labral tears and should not be misinterpreted as a traumatic anteroinferior labral-ligamentous detachment. 5. Labrocapsular Recess The hip articular capsule inserts directly to the anterior and posterior labrum, but superiorly it inserts in the bony acetabulum creating a high signal labrocapsular recess that can be similar to a labral tear (fig. 16, 17 and 18). Page 27 of 65

28 Fig.: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light blue arrow) that should not be mistaken by a labral tear. References: Radiology, Hospital de São João - Porto/PT Page 28 of 65

29 Fig.: Fig. 17) Coronal T2 GRE-weighted image where is also possible to distinguish the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light blue arrow). References: Radiology, Hospital de São João - Porto/PT Page 29 of 65

30 Fig.: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow) and an antero-superior labral tear (white arrow). References: Radiology, Hospital de São João - Porto/PT Following the inferior and lateral extension of the capsule to the femur allow us to distinguish the superior capsule from a labral fragment, avoiding this pitfall. 6. Sublabral Recess A sublabral recess is a frequent finding that should be considered when we see partial separation of the labrum from the underlying cartilage (fig. 19, 20 and 21). As discussed previously this criteria is also used to diagnosis a labral tear. So, to avoid this major cause of pitfalls, we should be aware of some evidences: Page 30 of 65

31 Sublabral recesses have been described in the anterior and posterior labrum. However, outside the Japanese population, tears of the posterior labrum are very rare, and usually not seen unless there is a history of posterior hip dislocation. In view of this, the radiologist can consider a cleft in the posterior labrum as a sublabral sulcus in virtually all cases. In the anterior labrum, recesses are most commonly located anteroinferiorly in 8-o'clock position. Torn labrum is more frequently found at anterosuperior location in 10- and 11o'clock positions. Recesses do not extend into the substance of the labrum or through the full thickness of the labral base. Unlike the shoulder, where a normal sublabral foramen has been identified at the anterosuperior quadrant of the glenoid, a sublabral foramen has not been convincingly shown in the hip. Usually a recess is associated with linear sublabral contrast material interposition with a sharply defined labrum. To diagnosis a recess we should not see abnormal signal intensity of the labrum, cartilage lesions, osseous abnormalities or ganglion cysts. Page 31 of 65

32 Fig.: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of the posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral recess. References: Radiology, Hospital de São João - Porto/PT Page 32 of 65

33 Fig.: Fig. 20) Axial T1-weighted MR arthrography showing another sublabral recess (arrow) of the posterior labrum. References: Radiology, Hospital de São João - Porto/PT Page 33 of 65

34 Fig.: Fig. 21) Axial T1-weighted MR arthrography reveals a sublabral recess (arrow) of the posterior labrum that is deeper than the previous ones, but still not extending into the substance of the labrum or through the full thickness of the labral base. References: Radiology, Hospital de São João - Porto/PT Page 34 of 65

35 Images for this section: Fig. 0: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images show the normal labrum (circles) as a low signal triangular structure and the transverse ligament (arrows) connecting the anterior and posterior labrum. Page 35 of 65

36 Fig. 0: Fig. 2) Coronal T2 GRE- weighted image demonstrates the articular fluid extending into the acetabular/labral interface (arrow). The labrum is flattened and detached from the underlying bone. These findings are suggestive of a labral tear. Page 36 of 65

37 Fig. 0: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material extending into the acetabular/labral interface, with a complete detachment of the labrum from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial pit is also seen in the anterior junction of the head and neck of the femur (circle). These finding is frequently associated with situations of femoro-acetabular impingement, one of the major causes of labral tears. Page 37 of 65

38 Fig. 0: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are diagnostic for a labral tear. This patient also has signs of AVN of the femoral head. Page 38 of 65

39 Fig. 0: Fig. 5) Coronal STIR-weighted image demonstrates mild increase of the interstitial signal of the anterior labrum, without other signs that suggest the presence of a tear. Page 39 of 65

40 Fig. 0: Fig. 6) Coronal T1-weighted MR arthrography image shows a rounded labrum, without signs of tear. Page 40 of 65

41 Fig. 0: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened labrum with increased interstitial signal. Page 41 of 65

42 Fig. 0: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of the posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral recess. Page 42 of 65

43 Fig. 0: Fig. 20) Axial T1-weighted MR arthrography showing another sublabral recess (arrow) of the posterior labrum. Page 43 of 65

44 Fig. 0: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow) and an antero-superior labral tear (white arrow). Page 44 of 65

45 Fig. 0: Fig. 17) Coronal T2 GRE-weighted image where is also possible to distinguish the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light blue arrow). Page 45 of 65

46 Fig. 0: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light blue arrow) that should not be mistaken by a labral tear. Page 46 of 65

47 Fig. 0: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess (arrow) inferiorly to the junction of the anterior labrum with the transverse ligament. Page 47 of 65

48 Fig. 0: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal labroligamentous sulcus (arrow) at the junction of the anterior labrum with the transverse ligament. Page 48 of 65

49 Fig. 0: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level of transverse ligament and anterior labral junction shows the normal labroligamentous sulcus (arrow) that may be mistaken for a labral tear. Page 49 of 65

50 Fig. 0: Fig. 12) Axial T2 GRE-weighted images, show the iliopsoas tendon (blue arrow) crossing the anterior labrum (white arrow) (a). It is easy to follow the iliopsoas tendon proximally to the muscular component (b) or distally to the insertion in the lesser trochanter (c). Page 50 of 65

51 Fig. 0: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow) crossing the anterior labrum (white arrow). Inbetween these two structures is a line of high signal that should not be mistaken by a labral tear. Page 51 of 65

52 Fig. 0: Fig. 8) Coronal STIR-weighted image demonstrates a linear high signal under the base of the anterosuperior labrum (arrow). Is this a tear? Is this cartilage undercutting the labrum? Is not always easy to make this distinction without articular contrast. There is no labral tear in this patient. Page 52 of 65

53 Fig. 0: Fig. 9) Coronal T1-weighted MR arthrography image where is easy to see that the linear high signal under the base of the labrum (arrow) is not as high as the signal of the contrast material. This is only cartilage undercutting the labrum. Page 53 of 65

54 Fig. 0: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the linear high signal under the base of the labrum (arrow) presenting with the same signal intensity of the contrast material. This is not cartilage undercutting the labrum, this is a labral tear. Page 54 of 65

55 Fig. 0: Fig. 21) Axial T1-weighted MR arthrography reveals a sublabral recess (arrow) of the posterior labrum that is deeper than the previous ones, but still not extending into the substance of the labrum or through the full thickness of the labral base. Page 55 of 65

56 Conclusion The knowledge of the pitfalls of the MR imaging in the evaluation of the acetabular labrum are the main way to increase the specificity of the diagnosis of labral tears. Page 56 of 65

57 Images for this section: Fig. 0: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light blue arrow) that should not be mistaken by a labral tear. Page 57 of 65

58 Fig. 0: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened labrum with increased interstitial signal. Page 58 of 65

59 Fig. 0: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level of transverse ligament and anterior labral junction shows the normal labroligamentous sulcus (arrow) that may be mistaken for a labral tear. Page 59 of 65

60 Fig. 0: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess (arrow) inferiorly to the junction of the anterior labrum with the transverse ligament. Page 60 of 65

61 Personal Information Miguel Henriques Castro Radiology Department / Hospital de São João / Oporto Medical School / Portugal Department Director: Prof. Isabel Ramos miguelhcastro@gmail.com Page 61 of 65

62 Images for this section: Fig. 0: Porto Page 62 of 65

63 References Beaulé PE, O'Neill M, and Rakhr K. Acetabular Labral Tears. J. Bone Joint Surg. Am., Mar 2009; 91: Petersilge C. Imaging of the acetabular labrum. Magn Reson Imaging Clin N Am. 2005;13(4): Chan YS, Lien LC, Hsu HL, Wan YL, Lee MS, Hsu KY, et al. Evaluating hip labral tears using magnetic resonance arthrography: a prospective study comparing hip arthroscopy and magnetic resonance arthrography diagnosis. Arthroscopy. 2005;21(10):1250. Toomayan GA, Holman WR, Major NM, Kozlowicz SM, Vail TP. Sensitivity of MR arthrography in the evaluation of acetabular labral tears. Am J Roentgenol. 2006;186: Byrd JWT, Jones K. Diagnostic accuracy of clinical assessment, magnetic resonance imaging, magnetic resonance arthrography, and intra-articular injection in hip arthroscopy patients. Am J Sports Med. 2004;32(7): Hodler J, Yu JS, Goodwin D, Haghighi P, Trudell D, Resnick D. MR arthrography of the hip: improved imaging of the acetabular labrum with histologic correlation. Am J Roentgenol. 1995;165: Groh MM, Herrera J. A comprehensive review of hip labral tears. Curr Rev Musculoskelet Med. 2009; 2: Czerny C, Hofmann S, Urban M, et al. MR arthrography of the adult acetabular capsular-labral complex: correlation with surgery and anatomy. AJR Am J Roetgenol. 1999;173: Abe I, Haranda Y, Oinuma K, et al. Acetabular labrum: abnormal findings at MR imaging in asymptomatic hips. Radiology. 2000;216(2): Lecouvet FE, Vande Berg BC, Malghem J, Lebon CJ, Moysan P, Jamart J, et al. MR imaging of the acetabular labrum: variations in 200 asymptomatic hips. Am J Roentgenol. 1996;167: Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R. Acetabular labral tears: evaluation with MR arthrography. Radiology. 1996;200(1): Mintz DN, Hooper T, Connell D, Buly R, Padgett DE, Potter HG. Magnetic resonance imaging of the hip: detection of labral and chondral abnormalities using noncontrast imaging. Arthroscopy. 2005;21: Czerny C, Hoffman S, Neuhold A, et al. Lesions of the acetabular labrum: accuracy of MR imaging and MR arthrography in detection and staging. Radiology. 1996;200: Studler U, Kalberer F, Leunig M, Zanetti M, Hodler J, Dora C, et al. MR Arthrography of the Hip: Differentiation between an Anterior Sublabral Recess as a Normal Variant and a Labral Tear. Radiology. 2008;249(3): Dinauer PA, Murphy KP, Carroll JF. Sublabral sulcus at the posteroinferior acetabulum: a potential pitfall in MR arthrography diagnosis of acetabular labral tears. Am J Roentgenol. 2004;183: Page 63 of 65

64 Saddik D, Troupis J, Tirman P, O'Donnell J, Howells R. Prevalence and location of acetabular sublabral sulci at hip arthroscopy with retrospective MRI review. AJR Am J Roentgenol 2006;187:W507-W511. Plotz GM, Brossmann J, Schunke M, Heller M, Kurz B, Hassenpflug J. Magnetic resonance arthrography of the acetabular labrum: macroscopic and histological correlation in 20 cadavers. J Bone Joint Surg Br 2000;82: Page 64 of 65

65 Images for this section: Fig. 0: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow) and an antero-superior labral tear (white arrow). Page 65 of 65