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Acetabular Labrum: Abnormal Findings at MR Imaging in Asymptomatic Hips¹

¹ From the Department of Orthopaedic Surgery (I.A., Y.H., K.O., K.K., H.M.) and the Division of Radiology (H.K., F.M.), Chiba University, 1-8-1 Inohana Chuo-ku, Chiba City, Chiba 260-8677, Japan. Received March 4, 1999; revision requested April 8; final revision received October 28; accepted November 22. Address correspondence to I.A. (e-mail: abe@cc.rim.or.jp).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To determine the prevalence of abnormalities of the acetabular labrum in asymptomatic hips by means of magnetic resonance (MR) imaging and to correlate such abnormalities with age and the portion of the labrum.

MATERIALS AND METHODS: MR imaging was performed in 71 asymptomatic hips that were radially sectioned perpendicular to the acetabular labrum at 30° intervals.

RESULTS: The shape of the labrum was triangular in 80% (304 of 382) of the labral segments, round in 13% (49 of 382), irregular in 7% (27 of 382), and not identified in 1% (two of 382). A homogeneous low signal intensity was observed in 56% (212 of 382). The frequencies of labral irregularity or its absence and of high signal intensity increased both with subject age and with a more anterior anatomic labral location.

CONCLUSION: In asymptomatic hips, abnormal findings regarding the shape and signal intensity of the acetabular labrum can be detected by means of MR imaging. The fact that the findings vary according to age and labral portion should be considered in interpreting MR images in patients suspected of having a labral lesion.

Index terms: Acetabulum, 442.159 • Hip, abnormalities, 442.159 • Hip, anatomy, 442.92 • Hip, MR, 442.121411, 442.121412, 442.121413

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The acetabular labral lesion has been indicated in several reports (1–11) to be a cause of hip joint pain, and various surgical treatments thus have been suggested. A precise preoperative diagnosis of the location and severity of the lesion is a clinical necessity.

Magnetic resonance (MR) imaging of the whole acetabular labrum is difficult owing to its anatomically complicated location and to its narrowness and thinness, which are easily affected by a partial volume effect in the conventional setting of parallel sections. To solve this problem, radial-sequence MR imaging, designed to obtain sections constantly perpendicular to the acetabular labrum, and a high spatial resolution MR imaging technique with a surface coil were used. The use of radial-sequence MR imaging, which allows continuous depiction of the acetabular labrum, was reported by Kubo et al in 1996 (12). In this study, this method was modified by simplifying the procedures to enhance image reproducibility and by using a surface coil to obtain higher spatial resolution images with modified parameters to obtain continuous and constantly clear labral images.

Proper assessment of the importance of the abnormal labral MR findings is clinically relevant. For this reason, we performed detailed evaluations of labral shape and signal intensity on MR images according to asymptomatic volunteer age by using this modified radial-sequence MR imaging technique.

MR imaging of the acetabular labrum has been reported to produce high visibility; however, to our knowledge, most reports (13–15) are related to the usefulness of MR arthrography in the diagnosis of suspected labral lesions, and only two reports (16,17) concerning asymptomatic hips exist.

The purpose of our study was to determine the prevalence of abnormalities of the acetabular labrum in asymptomatic hips by means of MR imaging and to correlate such abnormalities with age and the portion of the labrum in detail.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Seventy-one hip joints in 71 asymptomatic volunteers (41 female, 30 male; age range, 13–65 years) with no history of hip joint treatment were examined by means of MR imaging. Institutional approval for this study was obtained by the ethics committee of Chiba University. The informed consent of all volunteers was obtained before commencement of this study. The purpose of this study was fully explained to these volunteers, and after obtaining their approval, we performed the MR examination. The study population was divided into 10-year age groups as follows: 14 subjects who were 10–19 years old; 15, 20–29 years old; 12, 30–39 years old; 16, 40–49 years old; and 14, 50 years or older.

We used 1.5-T systems (Signa Horizon 5.6 upgrade version from Signa Advantage, Signa Horizon 5.7; GE Medical Systems, Milwaukee, Wis) and a flex coil (GP Flex; GE Medical Systems). At the time of selection of the acetabular labrum radial-imaging sequence, the following sequences were tried in three hip joints of volunteers: fast spin echo (2,000/16 [repetition time msec/echo time msec]; echo train length, nine); spoiled gradient echo (52/10; flip angle, 60°); spoiled gradient echo (52/10; flip angle, 30°); short inversion time inversion recovery (2,000/30/100 [inversion time msec]). Of these sequences, the fast spin-echo sequence was selected for radial imaging of the acetabular labrum owing to its high spatial resolution and ability to help distinguish between cartilaginous tissue and joint fluid.

Detailed parameters of the fast spin-echo sequence were as follows: 2,000/16; echo train length, nine; 512 x 384 matrix; field of view, 20 x 20 cm; section thickness, 4 mm; and three signals acquired for scan times of 8 minutes 44 seconds (Signa Horizon 5.6 upgrade version from Signa Advantage) and 8 minutes 25 seconds (Signa Horizon 5.7). When the Signa Horizon 5.6 upgrade version was used for radial-sequence MR imaging, "Multi Slice Multi Angle," or MSMA, was selected, and when the Signa Horizon 5.7 was used, "Fast SE Excel," or FSE-XL, was selected.

The setting for the sections was as follows. The subjects were asked to lie down in the supine position with the hip joint in neutral rotation fixed with a band. First, the localizer image in the transverse plane through the center of bilateral femoral heads was obtained. By using this transverse localizer image, orientation of the sagittal oblique sections through the anterior and posterior edges of the acetabulum, parallel to the acetabular opening, was determined. For the oblique sagittal images, radially sectioned images passing through the center of the femoral head at every 30°, perpendicular to the acetabular labrum, were obtained (Figs 1, 2).

View larger version (33K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Schematic shows radial-sequence MR imaging of the left hip joint. On the plane at the acetabular opening, each section passes through the center of the acetabulum and is always perpendicular to the acetabular labrum. The lines indicate the direction of the radial-sequence images at every 30°.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. (a) Transverse fast multiplanar spoiled gradient-echo MR localizer image (51/5.5; flip angle, 60°; matrix, 256 x 160; 7-mm-thick sections; field of view, 35 cm; one signal acquired) through the center of the femoral head. The images obtained were oblique sagittal sections through the acetabular anterior and posterior margins. (b) Oblique sagittal fast multiplanar spoiled gradient-echo MR localizer image (51/5.7; flip angle, 60°; matrix, 256 x 160; 7-mm-thick sections; field of view, 24 cm; one signal acquired). Radial images through the center of the acetabulum were obtained every 30°. The lines indicate the direction of radial-sequence images at every 30° on the MR localizer image.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. (a) Transverse fast multiplanar spoiled gradient-echo MR localizer image (51/5.5; flip angle, 60°; matrix, 256 x 160; 7-mm-thick sections; field of view, 35 cm; one signal acquired) through the center of the femoral head. The images obtained were oblique sagittal sections through the acetabular anterior and posterior margins. (b) Oblique sagittal fast multiplanar spoiled gradient-echo MR localizer image (51/5.7; flip angle, 60°; matrix, 256 x 160; 7-mm-thick sections; field of view, 24 cm; one signal acquired). Radial images through the center of the acetabulum were obtained every 30°. The lines indicate the direction of radial-sequence images at every 30° on the MR localizer image.

The MR images were evaluated in a blinded fashion on a consensus basis by two experienced orthopedic surgeons (I.A., Y.H.) and an experienced musculoskeletal radiologist (H.K.). Six images of each subject’s acetabular labrum, which was scanned from 60° anterior to 90° posterior for a total of 426 images, were examined, and evaluation of the acetabular labral shape and changes in signal intensity were performed (Fig 3). Forty-four poor-quality images, which were deemed to be affected by motion artifact or influence of arterial flow, were considered inadequate for evaluation and were deleted from the study.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 3a. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 3b. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (128K): [in this window] [in a new window] [Download PPT slide]   Figure 3c. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 3d. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 3e. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 3f. Intermediate-weighted fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired) in the right hip joint in a 30-year-old woman. (a) Transverse oblique image through the labrum at 60° anterior. (b) Coronal oblique image through the labrum at 30° anterior. (c) Coronal oblique image through the labrum at 0°. (d) Coronal oblique image through the labrum at 30° posterior. (e) Transverse oblique image through the labrum at 60° posterior. (f) Transverse image through the labrum at 90° posterior. The band of low signal intensity that crosses each image is an artifact called saturation.

View larger version (35K): [in this window] [in a new window] [Download PPT slide]   Figure 4. Classification of the acetabular labra according to their shape on MR images and corresponding fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired). Acetabular labra were classified into four groups according to shape: triangular with a sharp edge of the labrum (arrow), round with a round edge (arrow), irregular (arrow) when they could not be classified into either of the first two categories, and absent when they could not be identified.

View larger version (37K): [in this window] [in a new window] [Download PPT slide]   Figure 5. Classification of the acetabular labra according to their signal intensity on MR images and corresponding fast spin-echo MR images (2,000/16; echo train length, nine; matrix, 512 x 384; 4-mm-thick sections; field of view, 20 cm; three signals acquired). Acetabular labra were classified into five grades: grade 1 included those having a homogeneous low signal intensity, grade 2A included those having an intralabral area of moderate signal intensity (arrow), grade 2B included those having an intralabral area of high signal intensity (arrow), grade 3A included those having an area of high signal intensity that communicated with the free surface (arrow), and grade 3B included those that appeared as a whole area of diffuse high signal intensity.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Shape
The shape of the labrum was triangular in 80% (304 of 382) of the labral segments, round in 13% (49 of 382), irregular in 7% (27 of 382), and not identified in 1% (two of 382). The triangular shape was by far the most common shape among all portions from 60° anterior to 90° posterior (Fig 6). Of the images at 60° anterior, the labrum was judged to be absent in 4% (two of 50), irregular in 20% (10 of 50), round in 14% (seven of 50), and triangular in 62% (31 of 50). As the sequence of images shifted posteriorly in the labrum, occurrence of the triangular shape increased significantly (P < .001). The labrum was triangular in 68% (48 of 71) of the subjects at 30° anterior, 72% (51 of 71) at 0°, 82% (58 of 71) at 30° posterior, 96% (65 of 68) at 60° posterior, and 100% (51 of 51) at 90° posterior.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 6. Bar graph shows the distribution of the acetabular labra according to their shape on sequential MR images. The black bar denotes triangular; the slant-shaded bar, round; the striped bar, irregular; and the white bar, absent. In the anterior portion, the frequency of appearance of absent, irregular, and round was high, and the frequency of triangular was low. As imaging of acetabular labra shifted to the posterior portion, the frequency of appearance of triangular became gradually higher.

View larger version (30K): [in this window] [in a new window] [Download PPT slide]   Figure 7. Bar graph shows changes in the shape of the acetabular labrum in all labral segments on MR images in relation to age. The black bar denotes triangular; the slant-shaded bar, round; the striped bar, irregular; and the white bar, absent. The labrum was triangular in young subjects and became gradually more rounded and irregular with age.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 8. Bar graph shows the distribution of the acetabular labra according to their signal intensity on sequential MR images. The black bar denotes grade 1; the gray bar, grade 2A; the slant-shaded bar, grade 2B; the striped bar, grade 3A; and the white bar, grade 3B. The labrum was of a higher signal intensity in the anterior portion compared with that in the posterior portion.

View larger version (30K): [in this window] [in a new window] [Download PPT slide]   Figure 9. Bar graph shows the distribution of the acetabular labrum in all labral segments according to the signal intensity on MR images and age. The black bar denotes grade 1; the gray bar, grade 2A; the slant-shaded bar, grade 2B; the striped bar, grade 3A; and the white bar, grade 3B. The signal intensity of the acetabular labrum increased with age.

View larger version (38K): [in this window] [in a new window] [Download PPT slide]   Figure 10. Bar graphs show the distribution of the acetabular labrum according to the signal intensity on sequential MR images and age. Changes of signal intensity of the acetabular labrum were observed in most age groups and ranged from the 90° posterior to the 60° anterior portion. The changes became more pronounced in the anterior portions and with age.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Understanding the normal variations of the labrum in shape and signal intensity in correlation with labral portion and age of asymptomatic subjects is vital for an accurate diagnosis of acetabular labral lesions by means of MR imaging.

In a study of the normal variations of the glenoid labrum, Neumann et al (19) reported that the labral-capsular complex varies in shape. Kornick et al (20) reported that in asymptomatic volunteers, the signal intensity of the knee meniscus increased with age, and change in signal intensity was observed more frequently at the posterior horn of the medial meniscus. MR findings in the acetabular labrum of asymptomatic volunteers were investigated in 200 hip joints by Lecouvet et al (16) and in 52 hip joints by Cotten et al (17); however, the difference in occurrences of abnormal MR findings in various portions of the labrum and in different age groups were not investigated in detail.

In our study, radial-sequence MR imaging was used to examine continuous changes in signal intensity and variations in the shape of the whole labrum in asymptomatic volunteers. Since 10 or more subjects per age group were examined, the sample size was considered representative of the normal population and, therefore, should contribute to the interpretation of MR findings in symptomatic patients.

The shape of the acetabular labrum was triangular in most subjects. The round shape was observed in all age groups but showed a tendency to increase with age. These findings indicate the possibility that round labra are a normal variation of the labrum and that the shape tends to change from triangular to round with age. The possibility of a triangular or round labrum changing to an irregular one owing to aging tends to be high, since the irregular shape was observed only in subjects 40 years or older. The fact that the labrum was absent in some subjects 50 years or older reveals that the labrum may disappear owing to aging.

As for variations of the acetabular labrum in shape at different portions, the frequency of changes in shape to round, irregular, and absent increased with anterior anatomic labral locations, which may be attributed to aging. In a three-dimensional dynamic analysis of hip joint loading reported by Oneda et al (21), distribution of stress at walking was reported to be concentrated in the anterolateral portion of the acetabulum, which may explain the changes in labral shape of the anterior portion.

Hodler et al (22) observed a correlation between MR findings and histologic findings in 12 cadaveric hip joints. According to Hodler et al, various types of tissue degeneration were observed within the labrum, where fibrocartilaginous tissue normally is present; moreover, high signal intensities were observed to reflect these degenerative changes and detachments.

Hodler et al (23) and Stoller et al (24) also found a correlation between MR findings and histologic findings in the meniscus in cadaveric knee joints, where areas of high signal intensity within the meniscus were consistent with various types of degeneration. They found that areas of high signal intensity that communicate with the surface reflect macroscopically distinguishable tears with a high probability. In a study of MR findings in the menisci, Munk et al (25) reported that increased intensity within the meniscus was observed in young subjects and was possibly attributable to increased vascularity.

With reference to the preceding studies, the following classification of signal intensity of the acetabular labrum is hypothesized: grade 1, no findings of degeneration within the labrum; grades 2A and 2B, presence of various types of degenerative changes or of the small fibrovascular bundles within the labrum; grade 3A, degenerative changes that nearly reach the labral surface, or progression of tears or detachments from the labral surface; and grade 3B, severe degeneration in which the fibrocartilaginous tissue of the labrum has almost disappeared. Since grade 2A was distributed more widely in each age group compared with the distribution of grade 2B, the following also is hypothesized: Grade 2A signal intensity may reflect the presence of a fibrovascular bundle that reportedly has been observed in normal tissue rather than in degenerative tissue, and grade 2B may reflect the presence of various types of degenerative changes within the labrum (22).

If we interpret our results on the basis of this hypothesis, degenerative changes, tears, or detachment of the labrum are observed in asymptomatic hips even in subjects 10–19 years old, although such changes are assumed to be limited to the anterior anatomic labral location in this age group. The frequency of macroscopic abnormal findings, thought to spread from anterior to posterior areas, probably would increase with subject age.

In a study of 45 hip joints of cadavers with no abnormal findings in the hip joints on radiographs, Azuma and Tanabe (26) observed changes in acetabular la-bral shape according to age. Accordingly, degeneration of the acetabular labrum was observed in the anterosuperior portion in subjects as young as 10–19 years of age and increased with age. In contrast, findings indicative of degenerative changes associated with age were not marked in the posterior labrum. The results of our study with MR imaging were completely consistent with those of Azuma and Tanabe (26).

Prolongation of T2 by means of the "magic angle" phenomenon may have a tendency to affect MR images by producing changes in signal intensity at a constant point in all acetabular labra, regardless of age (27–31). However, in our study, the frequency of the changes in signal intensity in the anterior acetabular labrum on MR images was low in the young, and thus the possibility that the "magic angle" phenomenon was the cause of the anterior changes in signal intensity can be denied.

In conclusion, our study revealed that the labrum undergoes changes in shape and signal intensity on MR images even in asymptomatic subjects. The occurrence of these changes in shape and signal intensity was related closely to the age of the subject and the portion of the labrum examined. These findings should be an asset in interpreting MR findings in patients suspected of having labral lesions.

	FOOTNOTES

 
Author contributions: Guarantors of integrity of entire study, H.M., H.K.; study concepts, I.A., Y.H.; study design, I.A., Y.H., F.M.; definition of intellectual content, I.A., Y.H.; literature research, I.A.; clinical studies, I.A., Y.H., K.O., K.K.; experimental studies, I.A., Y.H., F.M.; data acquisition, I.A., Y.H., K.O., K.K.; data analysis, I.A., Y.H., H.K.; statistical analysis, I.A.; manuscript preparation, I.A.; manuscript editing, I.A., Y.H.; manuscript review, Y.H., H.K., H.M.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Suzuki S, Awaya G, Okada Y, Maekawa M, Ikeda T, Tada H. Arthroscopic diagnosis of ruptured acetabular labrum. Acta Orthop Scand 1986; 57:513-515.[Medline]
2. Fitzgerald RH. Acetabular labrum tears: diagnosis and treatment. Clin Orthop 1995; 311:60-68.
3. Klaue K, Durnin CW, Ganz R. The acetabular rim syndrome: a clinical presentation of dysplasia of the hip. J Bone Joint Surg Br 1991; 73:423-429.
4. Dorrell JH, Catterall A. The torn acetabular labrum. J Bone Joint Surg Br 1986; 68:400-403.
5. Dameron TB. Bucket-handle tear of acetabular labrum accompanying posterior dislocation of the hip. J Bone Joint Surg Am 1959; 41:131-134.[Abstract/Free Full Text]
6. Shea KP, Kalamchi A, Thompson GH. Acetabular epiphysis-labrum entrapment following traumatic dislocation of the hip in children. J Pediatr Orthop 1986; 6:215-219.[Medline]
7. Ueo T, Suzuki S, Iwasaki R, Yosikawa J. Rupture of the labra acetabularis as a cause of hip pain detected arthroscopically, and partial limbectomy for successful pain relief. Arthroscopy 1990; 6:48-51.[Medline]
8. Ikeda T, Awaya G, Suzuki S, Okada Y, Tada H. Torn acetabular labrum in young patients: arthroscopic diagnosis and management. J Bone Joint Surg Br 1988; 70:13-16.
9. Ide T, Akamatsu N, Nakajima I. Arthroscopic surgery of the hip joint. Arthroscopy 1991; 7:204-211.[Medline]
10. McCarthy JC, Busconi B. The role of hip arthroscopy in the diagnosis and treatment of hip disease. Orthopedics 1995; 18:753-756.[Medline]
11. McCarthy JC, Day B, Busconi B. Hip arthroscopy: applications and technique. J Am Acad Orthop Surg 1995; 3:115-122.[Abstract]
12. Kubo T, Horii M, Hirasawa Y. Magnetic resonance imaging of rheumatic disease (abstr) In: XXX World Congress of the International College of Surgeons. Bologna, Italy: Monduzzi Editori, 1996; 1315-1319.
13. Czerny C, Hofmann S, Neuhold A, et al. Lesions of the acetabular labrum: accuracy of MR imaging and MR arthrography in detection and staging. Radiology 1996; 200:225-230.[Abstract/Free Full Text]
14. Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R. Acetabular labral tears: evaluation with MR arthrography. Radiology 1996; 200:231-235.[Abstract/Free Full Text]
15. Leunig M, Werlen S, Ungersböck A, Ito K, Ganz R. Evaluation of the acetabular labrum by MR arthrography. J Bone Joint Surg Br 1997; 79:230-234.
16. Lecouvet FE, Berg BCV, Malghem J, et al. MR imaging of the acetabular labrum: variations in 200 asymptomatic hips. AJR Am J Roentgenol 1996; 167:1025-1028.[Abstract/Free Full Text]
17. Cotten A, Boutry N, Demondion X, et al. Acetabular labrum: MRI in asymptomatic volunteers. J Comput Assist Tomogr 1998; 22:1-7.[Medline]
18. Armitage P, Berry G. Trends in proportions. In: Armitage P, Berry G, eds. Statistical methods in medical research. 3rd ed. London, Pa: Blackwell Scientific, 1994; 403-407.
19. Neumann CH, Petersen SA, Jahnke AH. MR imaging of the labral-capsular complex: normal variations. AJR Am J Roentgenol 1991; 157:1015-1021.[Abstract/Free Full Text]
20. Kornick J, Trefelner E, McCarthy S, Lange R, Lynch K, Jokl P. Meniscal abnormalities in the asymptomatic population at MR imaging. Radiology 1990; 177:463-465.[Abstract/Free Full Text]
21. Oneda Y, Tamai A, Masuda Y, Ishibashi O, Sakurai G, Masuhara K. Three dimensional analysis of stress distribution in the hip joint. Hip Joint 1986; 12:56-61[Japanese].
22. 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 in cadavers. AJR Am J Roentgenol 1995; 165:887-891.[Abstract/Free Full Text]
23. Hodler J, Haghighi P, Pathria MN, Trudell D, Resnick D. Meniscal changes in the elderly: correlation of MR imaging and histologic findings. Radiology 1992; 184:221-225.[Abstract/Free Full Text]
24. Stoller DW, Martin C, Crues JV, III, Kaplan L, Mink JH. Meniscal tears: pathologic correlation with MR imaging. Radiology 1987; 163:731-735.[Abstract/Free Full Text]
25. Munk PL, Helms CA, Vellet AD. The menisci. In: Munk PL, Helms CA, eds. MRI of the knee. Gaithersburg, Md: Aspen, 1992; 57-76.
26. Azuma H, Tanabe H. Morphology and aging process of acetabular labrum. J Joint Surg 1994; 13:307-315[Japanese].
27. Peterfy CG, Janzen DL, Tirman PF, van Dijke CF, Pollack M, Genant HK. "Magic-angle" phenomenon: a cause of increased signal in the normal lateral meniscus on short-TE MR images of the knee. AJR Am J Roentgenol 1994; 163:149-154.[Abstract/Free Full Text]
28. Erickson SJ, Prost RW, Timins ME. The "magic angle" effect: background physics and clinical relevance. Radiology 1993; 188:23-25.[Free Full Text]
29. Erickson SJ, Cox IH, Hyde JS, Carrera GF, Strandt JA, Estkowski LD. Effect of tendon orientation on MR imaging signal intensity: a manifestation of the "magic angle" phenomenon. Radiology 1991; 181:389-392.[Abstract/Free Full Text]
30. Fullerton GD, Cameron IL, Ord VA. Orientation of tendons in the magnetic field and its effect on T2 relaxation times. Radiology 1985; 155:433-435.[Abstract/Free Full Text]
31. Rubenstein JD, Kim JK, Morava-Protzner I, Stanchev PL, Henkelman RM. Effects of collagen orientation on MR imaging characteristics of bovine articular cartilage. Radiology 1993; 188:219-226.[Abstract/Free Full Text]

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				P. A. Dinauer, K. P. Murphy, and J. F. Carroll Sublabral Sulcus at the Posteroinferior Acetabulum: A Potential Pitfall in MR Arthrography Diagnosis of Acetabular Labral Tears Am. J. Roentgenol., December 1, 2004; 183(6): 1745 - 1753. [Abstract] [Full Text] [PDF]

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