MRI of Labral and Chondral Lesions

Transcription

1 Musculoskeletal Imaging Best Practices/Review Naraghi and White MRI of Labral and Chondral Lesions of the Hip Musculoskeletal Imaging Best Practices/Review FOCUS ON: Ali Naraghi 1 Lawrence M. White Naraghi A, White LM Keywords: acetabular labrum, cartilage, hip, MR arthrography, MRI, unenhanced MRI DOI: /AJR Received January 16, 2014; accepted after revision February 7, Both authors: Joint Department of Medical Imaging, University Health Network, Mount Sinai and Women s College Hospitals, University of Toronto, 585 University Ave, 1- PMB 284, Toronto, ON M5G 2N2, Canada. Address correspondence to L. M. White (lawrence.white@uhn.ca). This article is available for credit. AJR 2015; 205: X/15/ American Roentgen Ray Society MRI of Labral and Chondral Lesions of the Hip OBJECTIVE. Unenhanced MRI, indirect MR arthrography, and direct MR arthrography have been used in the radiologic evaluation of patients with suspected labral tears and chondral lesions of the hip. The purpose of this article is to examine the existing evidence for the use of these techniques in patients with hip pain and suspected labral or chondral abnormalities. CONCLUSION. Evidence from a review of the radiologic literature supports the use of direct MR arthrography over unenhanced MRI and indirect MR arthrography for the detection of labral and cartilage abnormalities in the hip. Although high-resolution unenhanced 3-T MRI appears promising, limited information in the literature supports its use in the detection and characterization of chondrolabral lesions. Clinical Vignettes and Images with pathologic conditions affecting the labrum and cartilage of the hip may present with a variety of symptoms, including hip pain typically localized to the groin, limitation of range of motion, and clicking. These symptoms may be aggravated by physical activity. Labral and chondral lesions may be seen in patients with femoroacetabular impingement (FAI), developmental dysplasia of the hip, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, iliopsoas impingement, repetitive or acute trauma, or osteoarthritis. Improvements in surgical techniques have meant that chondral lesions and labral tears are amenable to surgical intervention. However, because labral tears and chondral loss are among the many possible causes of hip pain [1, 2], diagnosis is based on a combination of clinical features and supportive imaging findings. As such, imaging is often undertaken to confirm the diagnosis and exclude other causes of hip pain [3]. Clinical vignettes and images are presented in Figures 1 5. All findings described were surgically proved at arthroscopy. The Imaging Question Despite advances in MRI hardware and acquisition pulse sequences that result in higher-resolution MR images with improved signal-to-noise ratios, imaging of the articular cartilage and the labrum in the hip remains challenging. A diagnostic challenge in evalua- tion of internal derangement of the hip is identifying an imaging technique that is reliable, accurate, and convenient. MRI techniques, including unenhanced MRI, direct MR arthrography, and indirect MR arthrography, have been used in the imaging evaluation of this patient population [4 10]. The goal of this review is to evaluate the most suitable technique for evaluation of patients with hip pain that has a suspected labral or chondral cause. Background and Importance The hip labrum plays an important role in hip function that includes hip stability, proprioception, distribution of forces in the hip, and joint lubrication [11, 12]. Although labral tears can have a variety of causes, there has been growing interest in the diagnosis and treatment of chondrolabral lesions, partly because of increasing interest in FAI. FAI, which results in abnormal contact and abutment between the femoral head and the acetabular rim, has been proposed as a cause of hip pain and a predisposing factor in the development of osteoarthritis of the hip [13 16]. FAI is thought to be caused by morphologic variations of the femoral head-neck junction, the acetabulum, or both [13]. These variations are characterized by anterolateral loss of the offset at the femoral head-neck junction, resulting in a cam type of deformity, or by acetabular morphologic changes, such as retroversion, focal or global overcoverage, or coxa profunda or protrusio acetabulum, resulting in AJR:205, September

2 TABLE 1: Studies Evaluating the and of MR Arthrography in the Detection of Hip Labral and Chondral Lesions Labrum Cartilage Pulse Sequence In-Plane (mm) c Slice Thickness (mm) (cm 2 ) Field Strength (T) Coil No of Chondral Lesion Labral Tear Reference a Standard b Authors Year (27) Open (27) NA 9 NA NA NA NA NA NA NA NA Anderson et al. [35] T A 69, F 46 A 88, F A 16, F Torso, body Aprato et al. [36] Open (21), arthroscopy (20) Conventional, 84; IDEAL, T2 FS NA NA Conventional, 70; IDEAL, Arthroscopy (67) NA NA 3 Surface Blankenbaker et al. [37] Arthroscopy (40) Torso NA NA NA NA Byrd and Jones [38] Chan et al. [39] Arthroscopy (17) 16 NA 1.5 NA D-FLASH NA NA Surface GRE NA NA 20 NA 1.0 (17), 0.5 (40) Czerny et al. [40] (57) Surgery not otherwise specified (22) Naraghi and White Surface GRE NA NA Czerny et al. [41] Open (40) 34 NA 0.5 (24), 1.0 (16) NA NA NA Arthroscopy (24) 23 NA 1.5 Torso Freedman et al. [43] NA NA NA NA James et al. [44] Arthroscopy (46) NA Surface Keeney et al. [45] (102) Arthroscopy (102) 93 A 46, F Phased NA NA NA NA Knuesel et al. [46] (50) Open (21) NA A 20, F Surface DESS NA NA Leunig et al. [47] Open, arthroscopy 17 NA 1.5 Surface 20 NA T1, T2, FLASH NA NA (23) Nishii et al. [49] (20) Arthroscopy (20) NA A 20, F Surface D-fast spoiled GRE NA NA Park et al. [50] (47) Arthroscopy (47) 46 NA 3 Torso, cardiac D intermediateweighted NA NA FSE NA NA 1.5 Surface T1 FS (14) Open, arthroscopy (14) Perdikakis et al. [51] 8 NA 1.5 Helmholtz T1 FS NA NA Open, arthroscopy (10) Petersilge et al. [52] NA NA Pfirrman et al. [9] Open (44) NA Surface D water excitation DESS Reurink et al. [53] (95) Arthroscopy (95) 91 NA 1.5 NA NA NA NA NA A 73 86, F Schmid et al. [6] (42) Open (42) NA Surface T1 FS and T1 FLASH NA NA A 48 84, F NA NA 44 NA 1.5 Body D Water excitation DESS Studler et al. [7] Open, arthroscopy (57) (Table 1 continues on next page) 480 AJR:205, September 2015

3 TABLE 1: Studies Evaluating the and of MR Arthrography in the Detection of Hip Labral and Chondral Lesions (continued) Labrum Cartilage Pulse Sequence In-Plane (mm) c Slice Thickness (mm) (cm 2 ) Field Strength (T) Coil No of Chondral Lesion Labral Tear Reference a Standard b Authors Year T1 and T2 FS 80 NA NA NA Arthroscopy (5) 5 NA 1.5 Surface, torso Sundberg et al. [54] A , F A 71 92, F D water excitation DESS Sutter et al. [55] Arthroscopy (28) 26 A 25, F Surface Tian et al. [56] Arthroscopy (34) 59 NA 3 Surface T1 FS NA NA NA T1 FS, T2 FS NA NA Arthroscopy (30) 24 NA 1.5 Torso Toomayan et al. [57] pincer impingement. A variety of morphologic imaging signs have been MRI of Labral and Chondral Lesions of the Hip described for the relation between femur and acetabulum in patients with FAI, and these are covered in other review articles [3, 17, 18]. Although controversies persist regarding the clinical significance and treatment of patients with chondrolabral lesions and FAI [19], there has been an increase in incidence of surgical procedures to treat osseous, chondral, and labral abnormalities in such patients. Surgical techniques include débridement or repair of labral tears, microfracture of acetabular chondral lesions, resection of the acetabular rim, and femoral osteochondroplasty [20]. These procedures were once performed at open surgery but are more routinely performed arthroscopically or by miniarthrotomy with or without arthroscopic assistance [21 23]. As a result, hip arthroscopy has become one of the most rapidly growing areas in orthopedic surgery, and the annual number of hip arthroscopic procedures was expected to exceed 70,000 in 2013, compared with 30,000 in 2008 [24]. This increase in the incidence of surgical intervention has led to an increase in demand for imaging of patients with suspected labral and chondral injuries. The goals of imaging when labral or chondral injury is suspected are accurate identification of features that affect management by visualization of bony morphologic changes and detection and characterization of chondral and labral lesions [17]. Features deemed necessary for surgical decision making include acetabular version and coverage, morphologic changes in the femoral head-neck junction, presence and location of labral tears, and the size and depth of chondral lesions, including possible delaminating lesions of the acetabular chondral rim [25]. The presence of osteoarthritis should also be noted because this can preclude surgical treatment of the chondral and labral lesions and necessitate other surgical options, such as osteotomy or arthroplasty NA NA 97 NA NA NA Ziegert et al. [58] Arthroscopy (144) 144 NA 1.5 and 3 Surface Note NA = not available, A = acetabular, F= femoral head, T1 = T1-weighted, T2 = T2-weighted, FS = fat-suppressed, IDEAL = iterative decomposition of water and fat with echo asymmetry and least-squares estimation, GRE = gradient-recalled echo, DESS = dual-echo steady-state, FSE = fast spin-echo. a Values in parentheses are number of hips. b Reference standard is type of surgery (open vs arthroscopy). Numbers in parentheses are number of patients with surgical correlation. c In some cases a range of and matrix were provided. It was not possible to calculate the in-plane resolution in these cases. MRI of the hip poses challenges that affect image quality and diagnostic accuracy. The articular cartilage of the hip is relatively thin [26], the joint is obliquely oriented, and the articular surfaces are highly curved and closely opposed. Use of conventional imaging planes results in partial volume averaging due to the spheric shape of the hip joint. This is most striking in relation to the anterosuperior and posterosuperior aspects of the joint on coronal and axial images. In addition, within traditional closed-bore MRI systems, the hip is located off isocenter of the magnetic field, which can hamper image quality owing to gradient nonlinearities and inhomogeneities of the main magnetic field. There is also marked variability in the appearance of the acetabular labrum even in volunteer subjects without symptoms [27, 28]. In addition to larger- images, which are used to assess for extraarticular causes of pain, it is necessary to obtain dedicated focused images of the involved hip with a small (14 18 cm) imaging. Oblique axial images prescribed along the long axis of the femoral neck are used to supplement conventional triplanar orthogonal acquisitions and aid in evaluation of the femoral head-neck junction and acetabular overcoverage. These imaging planes may be supplemented by radial images of the hip obtained at prescribed angular intervals perpendicular to the surface of the hip joint with all resultant imaging planes intersecting through the center of the joint. Radial imaging provides for cross-sectional imaging depiction of the labrum and articular cartilage of the hip joint, negating the effects of volume averaging. Radial acquisitions also facilitate complete assessment of the femoral head-neck junction, including the anterosuperior quadrant, where the cam deformity is often most pronounced [29]. High-resolution unenhanced MRI of the hip is easily performed with optimized state-of-the-art techniques. Improvements in surface coil technology and the higher magnetic field strength associated with 3-T platforms deliver a higher signal-to-noise ratio, which can be used to achieve high spatial resolution with a reasonable acquisition time. AJR:205, September

4 Naraghi and White Imaging is best performed with a surface coil or a multichannel cardiac coil [30, 31]. Conventional MRI is an attractive option in comparison with MR arthrography given the improved patient throughput and the lack of gadolinium injection with its associated limitations, which include cost, need for fluoroscopy or ultrasound, patient discomfort, and risk of complications. Direct MR arthrography, which entails intraarticular injection of a dilute gadolinium mixture, has the advantages of distending the joint, improving contrast-to-noise ratio, and enabling acquisition of higher-resolution images [32, 33]. In addition, intraarticular administration of local anesthetic agents at arthrography can be a useful adjunct in localization and confirmation of an intraarticular source of hip pain [34]. Indirect MR arthrography, achieved by IV injection of gadolinium followed by exercise of the extremity of interest, has a similar effect with regard to contrast resolution but does not require intraarticular injection or imaging guidance to facilitate intraarticular contrast injection. One of the main limitations of indirect MR arthrography, however, is that it does not produce substantial joint distention. Synopsis and Synthesis of Evidence We performed a literature review using PubMed for English-language articles from 1990 to The search terms were MRI, MR arthrography, indirect MR arthrography, hip labrum, hip cartilage, and femoroacetabular impingement. A total of 678 articles were identified. All available abstracts were reviewed. Studies addressing the diagnostic accuracy of conventional MRI, direct MR arthrography, and indirect MR arthrography against a surgical reference standard were selected. Studies of pediatric populations, postoperative hips, and cadavers were excluded. The yield was 30 studies of the diagnostic utility of MRI of the hip labrum and cartilage [4, 6, 7, 9, 10, 35 58]. Tables 1 4 show the pertinent features of these studies, including magnetic field strength, coil used, in-plane resolution, slice thickness, and the sensitivities and specificities for detection of labral and chondral abnormalities. Assessment of Labral Tears Ten studies were identified in which the sensitivity and specificity of conventional MRI for detection of labral tears were measured (Table 2). There was significant variation in the diagnostic performance of unenhanced MRI for detection of hip labral tears; both sensitivity and specificity ranged from zero to 100%. Only three of these studies had a sensitivity greater than 90%, and four studies showed specificity greater than 80%. Two of the studies with lower sensitivities were performed in the mid 1990s, when the image quality and anatomic resolution of MRI systems were more limited than in later systems [40, 42]. Newer MRI systems, with a combination of higher magnetic field strength and, just as important, advances in coil technology can deliver high spatial resolution while maintaining a high signal-tonoise ratio and contrast resolution. Studies by Mintz et al. [4], Sutter et al. [55], and Zlatkin et al. [10] who used - coils, a small (12 17 cm), and high inplane resolution showed sensitivity of 77 97% for the detection of labral tears at 1.5 T. Three studies evaluated detection of labral tears at 3 T with variable results. In a small cohort, Sundberg et al. [54] found sensitivity of 100% in a cohort of five patients. Tian et al. [56] found sensitivity of 61 66% and specificity of 74 77% in a larger population. Interestingly, the in-plane resolution in both these studies was inferior to that in the studies by Mintz et al., Zlatkin et al., and Sutter et al., which were conducted with high-resolution technique at 1.5 T. Using high-resolution imaging at 3 T, White et al. [59] found sensitivity of 100% and specificity of 50% for the detection of labral tears. We found 19 studies evaluating the diagnostic accuracy of MR arthrography against a surgical reference standard in the assessment of labral tears (Table 1). The sensitivity for detection of labral tears ranged from 69% to 100% in these studies, most showing sensitivities greater than 90%. The variability in sensitivities of MR arthrography studies is less striking than that found in studies of conventional MRI. The specificity for detection of labral tears was far more variable in those studies, ranging from zero to 100%, most of the studies showing specificity less than 80%. There does not appear to be a clear relation between spatial resolution and the diagnostic accuracy of MR arthrography. This may be partly related to joint distention with imbibition of contrast material into the tear and to the improved signal-to-noise ratio afforded by use of intraarticular gadolinium and T1-weighted imaging. We found only two studies [10, 48] of the diagnostic accuracy of indirect MR arthrography of the hip in the assessment of labral tears (Table 3). The sensitivities of this technique were 82% and 100% and the specificities 100% and zero. Six studies directly compared the diagnostic accuracy of MRI with that of MR arthrography or indirect MR arthrography in the same patient population (Table 4). Apart from the study by Sundberg et al. [54], which included only five patients with arthroscopic correlation, all of the studies showed superior sensitivity of MR arthrography. Interestingly, there was little difference in specificity between the two imaging techniques in the studies directly comparing conventional MRI and MR arthrography. Smith et al. [60] performed a meta-analysis of the diagnostic accuracy of unenhanced conventional MRI and MR arthrography for the detection of labral tears. In a search of multiple databases, they identified 19 studies as of April 2010 that assessed the sensitivity and specificity of MRI and MR arthrography in the evaluation of hip labral tears. They found pooled sensitivity of 66% and specificity of 79% for conventional MRI and pooled sensitivity and specificity of 87% and 64% for MR arthrography. After analyzing ROC curves, those investigators concluded that MR arthrography is superior to conventional MRI for detection of labral tears. Results of more recent studies [36, 50, 51, 53, 55, 56] have been in keeping with their findings. Smith et al. did not specifically evaluate the influence of MRI pulse sequences, spatial resolution, or coils on diagnostic accuracy because it would be difficult to establish a trend given the marked variability in imaging techniques in a relatively small number of studies. Assessment of Chondral Lesions Direct comparison between studies evaluating chondral abnormalities is difficult because some authors report the accuracy of MRI in the detection of chondral lesions, whereas others assess the accuracy of grading chondral abnormalities of the hips or evaluated specific types of chondral lesions. In general, sensitivity of MRI and MR arthrography is limited in the evaluation of cartilage abnormalities of the hip, but specificity is typically high. Six studies examined the diagnostic performance of conventional MRI in identification of chondral lesions of the hip (Table 2). of conventional MRI for chondral lesions was 0 93%. ranged from 50% to 100%. In four of the studies, the accuracies of MRI in the detection of femoral 482 AJR:205, September 2015

5 MRI of Labral and Chondral Lesions of the Hip TABLE 2: Studies Evaluating the and of Conventional Unenhanced MRI in the Detection of Hip Labral and Chondral Lesions Authors Year Reference a Standard b Labral Tear No of Chondral Lesion Field Strength (T) c Coil (cm 2 ) Slice Thickness (mm) In-Plane (mm) d Pulse Sequence Labrum Cartilage Byrd and Jones [38] Czerny et al. [40] Edwards et al. [42] Arthroscopy (40) Torso NA NA NA NA (57) Surgery not otherwise specified (22) 20 NA 1.0 (17), 0.5 (40) Surface GRE NA NA Arthroscopy (23) 1 NA 1.5 NA NA NA NA NA 0 95 A 0 67, F Mintz et al. [4] Arthroscopy (92) 89 A 44, F Surface Sundberg et al. [54] Sutter et al. [55] Arthroscopy (5) 5 NA 3 Body multichannel Arthroscopy (28) 26 A 25, F Surface Intermediateweighted A 91 93, F A , F A 75 85, F D DESS 100 NA NA NA D water excitation DESS Tian et al. [56] Arthroscopy (90) 59 NA 3 Surface Intermediateweighted FS, T2 FS Toomayan et al. [57] White et al. [59] Zlatkin et al. [10] Large, 7 small Arthroscopy (21) 12 Large, 4 small NA 1.5 Body, torso 30 38; NA , Arthroscopy (42) 41 A 36, F 11 3 NA Intermediateweighted Arthroscopy (14) Body, spinal T1, T2 Large, 8; small, A 58 83, F A , F NA NA Large, 100; small, 100 NA NA A 94, F 94 A 67, F PD, PD FS, T2 FS NA Note NA = not available, GRE = gradient-recalled echo, A = acetabular, F= femoral head, DESS = dual-echo steady-state, FS = fat-suppressed, FS = fat-suppressed, T2 = T2-weighted, T1 = T1-weighted, PD = proton density weighted. a Values in parentheses are number of hips. b Reference standard is type of surgery (open vs arthroscopy). Numbers in parentheses are number of patients with surgical correlation. c Values in parentheses are number of patients. d In some cases a range of and matrix were provided. It was not possible to calculate the in-plane resolution in these cases. AJR:205, September

6 Naraghi and White TABLE 3: Studies Evaluating the and of Indirect MR Arthrography in Detection of Hip Labral and Chondral Lesions Authors Year Reference Standard b Labral Tear No of Chondral Lesion Field Strength (T) Coil (cm 2 ) Slice Thickness (mm) In-Plane (mm) c Pulse Sequence Labrum Cartilage Nishii et al. [48] Arthroscopy (19) 11 NA 1.5 Surface T NA NA T1 FS NA Zlatkin et al. [10] Arthroscopy (14) Body, spinal Note NA = not available, T1 = T1-weighted, FS = fat-suppressed. a Reference standard is type of surgery (open vs arthroscopy). Numbers in parentheses are number of patients with surgical correlation. b In some cases a range of and matrix were provided. It was not possible to calculate the in-plane resolution in these cases. TABLE 4: Studies Directly Comparing and of Unenhanced MRI and MR Arthrographic Techniques in Detection of Hip Labral and Chondral Lesions Author Year MRI Type Reference a Standard b Labral Tear No of Chondral Lesion Field Strength (T) Coil (cm 2 ) Slice Thickness (mm) In-Plane (mm) c Pulse Sequence Labrum Cartilage Byrd et al. [38] 2004 MRI 40 Arthroscopy (40) Torso NA NA NA NA Byrd et al. [38] 2004 MRA 40 Arthroscopy (40) Torso NA NA NA NA Surface GRE NA NA Czerny et al. [40] Czerny et al. [40] Sundberg et al. [54] Sundberg et al. [54] Sutter et al. [55] Sutter et al. [55] 1996 MRI 56 (57) Surgery not otherwise specified (22) 1996 MRA 56 (57) Surgery not otherwise specified (22) 20 NA 1.0 (17), 0.5 (40) 20 NA 1.0 (17), 0.5 (40) 2006 MRI 8 Arthroscopy (5) 5 NA 3 Body multichannel 2006 MRA 8 Arthroscopy (5) 5 NA 1.5 Surface, torso 2014 MRI 28 Arthroscopy (28) 26 A 25, F Surface 2014 MRA 28 Arthroscopy (28) 26 A 25, F Surface Surface GRE NA NA D DESS 100 NA NA NA T1 FS, T2 FS 80 NA NA NA D water excitation DESS D Water excitation DESS Tian et al. [56] 2014 MRI 90 Arthroscopy (90) 59 NA 3 Surface Intermediateweighted FS, T2 FS A 58 83, F A 71 92, F A , F A , F NA NA (Table 4 continues on next page) 484 AJR:205, September 2015

7 MRI of Labral and Chondral Lesions of the Hip TABLE 4: Studies Directly Comparing and of Unenhanced MRI and MR Arthrographic Techniques in Detection of Hip Labral and Chondral Lesions (continued) Labrum Cartilage Pulse Sequence In-Plane (mm) c Slice Thickness (mm) (cm 2 ) Field Strength (T) Coil No of Chondral Lesion Labral Tear Reference a Standard b MRI Type Author Year Tian et al. [56] 2014 MRA 34 Arthroscopy (34) 59 NA 3 Surface T1 FS NA NA NA NA 100 Large, 100 small T1, T2 8 Large, 25 small NA ; ; NA 1.5 Body, torso Arthroscopy (21) 12 Large, 4 small 2006 MRI 14 Large, 7 small Toomayan et al. [57] NA T1 FS, T2 FS NA NA 2006 MRA 30 Arthroscopy (30) 24 NA 1.5 Torso Toomayan et al. [57] NA PD, PD FS, T2 FS 14 Arthroscopy (14) Body, spinal 2009 Indirect MRA Zlatkin et al. [10] T1 FS NA 14 Arthroscopy (14) Body, spinal 2009 Indirect MRA Zlatkin et al. [10] Note NA = not available, MRA = MR angiography, GRE = gradient-recalled echo, DESS = dual-echo steady-state, T1 = T1-weighted, FS = fat-suppressed, T2 = T2-weighted, A = acetabular, F= femoral head, PD = proton density weighted. a Values in parentheses are number of hips. b Reference standard is type of surgery (open vs arthroscopy). Numbers in parentheses are number of patients with surgical correlation. c In some cases a range of and matrix were provided. It was not possible to calculate the in-plane resolution in these cases. head and of acetabular chondral lesions were reported separately. Of the conventional MRI studies, the study by Edwards et al. [42] dates from 1995 and yielded the lowest sensitivity. Only one group of investigators [59] reported the accuracy of 3-T conventional MRI in the detection of chondral lesions of the hip; they found sensitivity of 94% and specificity of 67% for the acetabulum and 100% for the femur. Twelve studies measured the accuracy of MR arthrography in assessing chondral lesions of the hip (Table 1). There was a wide range in sensitivity (22 92%) and specificity (25 100%). The two studies with the lowest sensitivities [9, 35] only evaluated the accuracy of MR arthrography in the detection of delaminating chondral lesions. Three studies [6, 36, 55] evaluated the performance of MR arthrography separately for femoral head and acetabular chondral lesions. These showed lower sensitivity of MR arthrography for the detection of femoral head chondral lesions. Only one study of indirect MR arthrography of chondral changes [10] showed sensitivity of 82% (Table 3). The specificity was not reported. Two studies evaluated the performance of conventional MRI and MR arthrography in the same patient population for detection of chondral abnormalities (Table 4). Byrd and Jones [38] found higher sensitivity and lower specificity of MR arthrography. In the study by Sutter et al. [55], sensitivity for acetabular chondral lesions was improved with the use of MR arthrography for both readers, but specificity was poorer with MR arthrography for one reader. For femoral lesions, there was no difference in sensitivity, but specificity was poorer with MR arthrography. Smith et al. [61] performed a meta-analysis of the diagnostic accuracy of MRI and MR arthrography in the assessment of hip chondral lesions using a method similar to the one they used in their meta-analysis of hip labral lesions. They identified 16 MRI studies of the diagnostic accuracy of MRI or MR arthrography in the detection of chondral lesions of the hip. They calculated pooled sensitivity and specificity of 59% and 94% for MRI and pooled sensitivity and specificity of 62% and 86% for MR arthrography in overall detection of chondral lesions. The pooled sensitivity and specificity for conventional MRI for femoral head lesions were 63% and 95% versus 79% and 97% for acetabular lesions. They identified only one MR arthrography study showing accuracy of detection of femoral head chondral lesions. The pooled sensitivity and specificity of MR arthrography for acetabular lesions were 76% and 92%. After analyzing ROC curves, Smith et al. concluded that the diagnostic accuracy of MRI is superior to that of MR arthrography in the detection of chondral lesions. Evidence-Based Guidelines Current evidence supports the use of MR arthrography in the evaluation of labral tears of the hip. This evidence comes from pooled analysis of the available literature and from studies directly comparing conventional MRI and MR arthrography in the same patient population. Most studies related to unenhanced MRI of the hip for evaluation of intraarticular abnormalities have been conducted with MRI performed on a 1.5-T platform, and the imaging spatial resolution in some of the older studies does not compare to the high-resolution imaging achievable later. Although the current evidence favors the use of MR arthrography, AJR:205, September

8 Naraghi and White we have found that optimized high-resolution nonarthrographic 3-T MRI of the hip can be highly accurate in detection of chondral and labral abnormalities of the hip. Sundberg et al. [54] and White et al. [59] found that 3-T conventional MRI may be a suitable alternative, but there are insufficient data about whether high-resolution unenhanced MRI performed at 3 T with modern multichannel surface coil technology can replace MR arthrography in the accurate diagnosis of labral abnormalities of the hip. There does not appear to be a clear relation between in-plane resolution and diagnostic accuracy for labral tears, likely because of the influence of other factors, such as signal-to-noise ratio and contrast resolution, related to the pulse sequences used. Current findings in the literature suggest that although imaging with a large encompassing the whole pelvis is beneficial for detection of extraarticular causes of hip pain, it has low accuracy in the evaluation of the hip labrum. regard to evaluation of hip articular cartilage, there appears to be less discrepancy between conventional MRI and MR arthrography. of both techniques is limited, but specificity is relatively high, particularly for conventional MRI. The foregoing guidelines are in accordance with the American College of Radiology appropriateness criteria, which give a rating of 9 for the use of MR arthrography in the evaluation of individuals with chronic hip pain with suspected labral tear with or without findings suggestive of FAI [62]. This compares to a rating of 6 for unenhanced MRI and a rating of 7 for CT arthrography. However, it is noted within the criteria that use of high-resolution 3-T MRI may obviate contrast administration in the future. As such, if unenhanced MRI is undertaken, protocol optimization to yield high spatial resolution and high contrast resolution is critical. Protocol parameters similar to those published by Mintz et al. [4] and Potter and Schachar [31] entailing fast spin-echo proton density weighted or intermediate-weighted pulse sequences, a small (< 18 cm), and small acquisition voxels are important factors in optimizing image resolution and overall image quality in MRI evaluation of the hip. Such unenhanced imaging should ideally be performed at 3 T with local multichannel surface coils. Another factor that has to be taken into consideration in the diagnostic evaluation of patients with hip-related pain and possible FAI is identification of the source of the patient s symptoms. Labral and even chondral abnormalities may be seen in many individuals who do not have symptoms. Therefore, the presence of such intraarticular abnormalities does not necessarily mean that these lesions are the cause of symptoms or that arthroscopic treatment would result in their alleviation [63]. Periarticular causes of hip pain can result in groin pain and produce symptoms similar to those in individuals with intraarticular abnormalities. Some orthopedic surgeons use the response to intraarticular injection of local anesthetic agents, performed in conjunction with intraarticular injection of contrast medium at MR arthrography, as part of their decisionmaking algorithm [34, 38, 64]. In this situation, even if unenhanced MRI is performed, the patient may still need an intraarticular injection as part of the treatment algorithm. Outstanding Issues That Warrant Research Few studies have directly compared higher-resolution unenhanced MRI directly with MR arthrography. Only three studies have evaluated the utility of 3-T MRI in the assessment of labral or chondral abnormalities of the hip, and the numbers of patients in these studies is small. Studies on the accuracy of unenhanced 3-T MRI in comparison with arthroscopy that have larger series of patients and reproducible results are lacking and would be needed to establish the accuracy of this technique. Direct comparative studies between high-resolution unenhanced 3-T MRI and MR arthrography in a larger group of patients with arthroscopic correlation would be ideal. The accuracy of newer 3D fast spin-echo pulse sequences has been assessed in the knee and shoulder [65 74]. We found no such studies in the hip, and the usefulness of the newer 3D pulse sequences remains unproven. The focus of this article has been on morphologic imaging of the labrum and cartilage. However, chondral pathologic features may also be discerned by probing the biochemical environment using techniques such as delayed gadolinium-enhanced MRI of cartilage, T2 mapping, and T1-ρ imaging. These techniques are predominantly research tools, but several articles [75 80] describe the feasibility of using these techniques in the hip. The details of such techniques are beyond the scope of this article but have been covered in other reviews [81, 82]. Their place in the imaging assessment of articular cartilage in the hip requires further validation. The prognostic utility of MRI in the evaluation of patients with labral and chondral lesions is not well established and would be an important factor to determine as we continue to image more patients with these lesions. Summary Recommendations for Best Practices MR arthrography is the current standard technique of advanced imaging for the evaluation of patients with suspected labral tears and chondral lesions. Limited data suggest that high-resolution unenhanced MRI, particularly performed at 3 T, may be as accurate as MR arthrography in the detection of labral and chondral tears. Large- unenhanced MRI is far inferior to both MR arthrography and high-resolution unenhanced MRI in the detection of labral and chondral abnormalities of the hip. Recommendations for Future Research Data regarding the use of high-resolution unenhanced 3-T MRI of the hip are limited. Larger-scale studies comparing 3-T MRI and MR arthrography would be a major requirement for validating the use of unenhanced 3-T MRI. Additional studies on the validity and reliability of biochemical imaging techniques for articular cartilage would also be required to determine whether they could be applied in routine clinical practice. References 1. Bedi A, Kelly BT. Femoroacetabular impingement. J Bone Joint Surg Am 2013; 95: Pateder DB, Hungerford MW. 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11 Fig year-old man with 1-year history of MRI of Labral and Chondral Lesions of the Hip mechanical hip pain. A, Sagittal T1-weighted fat-suppressed 3-T MR arthrogram (TR/TE, 630/8.6) shows extension of gadolinium (arrowhead) into labrum. Finding is consistent with labral tear. B, Axial oblique T1-weighted fat-suppressed 3-T MR arthrogram (TR/TE, 630/8.6) shows labral tear (arrowhead) involving base of labrum and extending into substance of labrum. A A A B B B Fig year-old male soccer player with acute twisting injury of hip. A, Axial oblique T1-weighted fat-suppressed 1.5-T MR arthrogram (TR/TE, 620/12) shows full-thickness chondral defect of femoral head (arrowhead) and tear of anterosuperior labrum (arrow). B, Coronal T2-weighted fat-suppressed MR arthrogram (TR/TE, 4350/82) shows delaminating nature of chondral lesion (arrowhead). Fig year-old male varsity athlete with chronic anterior hip pain. A and B, Coronal unenhanced 3-T intermediateweighted fat-suppressed (TR/TE, 4460/28) (A) and proton density weighted radial (TR/TE, 1990/21) (B) images of left hip show tear of superior labrum (arrow) that extends into anterosuperior labrum (not shown). Full-thickness chondral defect (small arrowhead) is present at chondrolabral junction. Small subarticular cyst (large arrowhead, A) is evident on coronal image. AJR:205, September

12 Naraghi and White FOR YOUR INFORMATION A A B B Fig year-old woman with intermittent groin pain and occasional feeling of clicking in hip. A, Coronal unenhanced 3-T intermediate-weighted (TR/TE, 4430/26) MR image shows somewhat hypertrophic labrum with tear cleft and detachment through base of labrum (arrow). Focal chondral fissures (arrowheads) are present in superior aspect of acetabular cartilage. B, Sagittal proton density weighted fat-suppressed MR image (TR/TE, 1980/22) shows area of delamination (arrow) involving acetabular cartilage and chondral fissuring (arrowhead). Fig year-old woman with ill-defined hip pain exacerbated by exercise with feeling of catching and instability in hip. A and B, Sagittal unenhanced 3-T fat-suppressed proton density weighted (TR/TE, 2000/24) (A) and coronal intermediate-weighted fat-suppressed (TR/TE, 4450/27) (B) images show anterosuperiorsuperior labral tear (arrow). Delaminating chondral lesion (arrowhead, A) is present in anterosuperior aspect. Partial tear of ligamentum teres (arrowhead, B) also is present. This article is available for CME and Self-Assessment (SA-CME) credit that satisfies Part II requirements for maintenance of certification (MOC). To access the examination for this article, follow the prompts associated with the online version of the article. 490 AJR:205, September 2015