Magnetic Resonance Imaging of the Hip Joint

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CHAPTER 4 Magnetic Resonance Imaging of the Hip Joint

Stefan Werlen, Tallal Charles Mamisch, Reinhold Ganz, Michael Leunig

Introduction

For years, classic magnetic resonance imaging (MRI) has been performed in three planes to identify hip pathologies such as avascular necrosis, loose bodies, and labral pathologies. Recently, there has been a need for more information to help diagnose the early stages of osteoarthritis, which are not well visible on standard radiographs or with MRI. Magnetic resonance arthrography (MRA) of the hip has been used with increasing frequency to identify pathomorphologies of the hip such as femoroacetabular impingement (FAI) or developmental dysplasia of the hip (DDH). For these conditions, plain radiographs give insufficient information about cartilage, labral, and even osseous abnormalities. MRA has been used since 1992 at our institution for the visualization of the acetabular labrum and the articular cartilage, especially for patients with FAI and DDH. During the past decade, various modifications of our MRA technique have been implemented, and these have led to considerable improvements in our ability to visualize pathologic changes of the hip.

MRA is a minimally invasive method of assessing the extent of cartilage damage, which has numerous implications for both the surgeon and the patient. Knowing the extent of damage—particularly of the cartilage—is essential in helping the surgeon to determine the correct surgical strategy (i.e., to preserve or replace the joint). Moreover, it provides detailed preoperative information so that the surgeon can inform the patient about potential long-term outcomes of a surgical procedure. In this chapter, we explain our current technique of 1.5-T MRA of the hip, and we demonstrate some of the findings and their interpretations with regard to bone, cartilage, labral, and capsular tissue in patients with FAI. Given the fact that the current protocols of 1.5-T scanners have limitations, we will also present more recent technologic advances in MRI: 3 T16 and dGEMRIC biochemical imaging of the hip.

1 5-T Morphologic imaging

During the past 15 years, we examined approximately 3500 hips with the use of MRA. The MRA technique was constantly refined during this time. Our 1.5-T protocol is the result of a close collaboration between radiologists (SW) and surgeons (RG and ML).

Examination Protocol

All patients are examined with the use of a Siemens Vision and Avanto 1.5-T, or Trio 3T high-field scanner (Erlangen, Germany). A flexible surface coil is used exclusively for high spatial resolution and signal-to-noise ratio. Before the MRA examination, all patients receive an intra-articular injection of 10 mL to 20 mL of saline-diluted Gd-DOTA 0.0025 mmolGd/mL (ArtiremR, Guerbert AG, Paris) into the hip joint with the use of fluoroscopic guidance. Patients are positioned supine under a C-arm, and the hip is placed slightly in external rotation to relax the anterior capsule. After the disinfection and sterile draping of the injection site, the injection is performed with a 22-gauge, spinal, obtuse-cut–angle needle, which helps to prevent injection into the capsular tissue or any extravasation. Between the injection and MR examination, a maximum time allowance of 10 minutes is preferred. The patients are then positioned supine, and the lower extremities are fixed with 20 degrees of internal rotation to prevent motion during scanning, to generate a standard version of the femoral neck, and to control the position of the pelvis.

After a short localizer in three planes, the examination continues with an axial T1-weighted sequence (repetition time [TR] 650, echo time [TE] 20, 200 mm × 200 mm field of view, 224 × 512 matrix, 4-mm section thickness with a 0.2-mm section gap, 17 slices, 3 minutes and 44 seconds). The sequence is centered on the femoral head, and it covers the whole joint (Figure 4-1).

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Figure 4–1 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the transverse T1-weighted sequence. B, Transverse slice through the acetabulum just above the joint space. C, Transverse slice through the midsection of the joint. The white arrow shows the normal anterior joint capsule.

The second sequence is an axial FLASH sequence with a few thin slices that is centered on the upper joint space. This sequence is used to evaluate the version of the acetabulum, and it also helps with the assessment for subcortical hypersclerosis of the rim as well as for the presence of synovial cysts (TR 550, TE 10, flip angle of 90 degrees, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.1-mm section gap, 11 slices, 3 minutes and 6 seconds; Figure 4-2).

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Figure 4–2 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the transverse FLASH sequence. B, Transverse slice through the acetabulum just above the joint space. The white arrow points to the attachment of the rectus femoris tendon (pars recta) at the spina iliaca anterior inferior. C, Transverse slice through the uppermost part of the joint. The short white arrow points to the anterior acetabular rim; the long white arrow points to the posterior acetabular rim.

Next is a coronal–oblique proton-density l–weighted (PDW) thin-slice sequence (TR 3200, TE 15, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.1-mm section gap, 23 slices, 5 minutes). This sequence is aligned perpendicular to the femoral neck, and it is marked on the axial T1W sequence (Figure 4-3).

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Figure 4–3 A, Slice from the T1-weighted transverse sequence as a localizer for the coronal-oblique PDW sequence. The white lines overlying the joint represent the coronal-oblique PDW sequence. B, Coronal-oblique slice through the midsection of the joint. The white arrow points at a slightly enlarged, hypointense lateral labrum.

A second PDW sequence in the sagittal direction (TR 3200, TE 15, 120 mm × 120 mm field of view, 256 × 256 matrix, 2-mm section thickness with a 0.2-mm section gap, 23 slices, 5 minutes and 37 seconds) is applied as the next step (Figure 4-4).

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Figure 4–4 A, Coronal scout view showing the right hip joint. The white lines overlying the joint represent the slices of the sagittal PDW sequence. Sagittal slices through the hip joint showing B, a bony apposition at the femoral neck (white arrow), and C, a torn labrum (white arrow).

Finally, a radial PDW sequence (Figure 4-5) is used in which all slices are oriented basically orthogonal to the acetabular rim and labrum. This sequence is based on a sagittal oblique localizer, which is marked on the PDW coronal sequence, and it runs parallel with the sagittal oblique course of the acetabulum. The MRA imaging parameters are as follows: TR 2000, TE 15, 260 mm × 260 mm field of view, 266 × 512 matrix, 4-mm section thickness, 16 slices, 4 minutes and 43 seconds. In the center of the radial sequence, where the slices cross over, the signal wipes out. This produces a broad line without signal on the image, which affects the quality of the image. The more slices in a sequence, the broader the no-signal line gets. To reduce this artifact, this sequence is split into two sequences of eight slices each. The whole examination, including the hip injection, lasts about 50 to 60 minutes.

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Figure 4–5 A, Slice from the coronal-oblique sequence. The white lines overlying the femoral neck represent the slices of the radial scout view plane. B, Radial scout view with overlying slices of the radial PDW sequence. C, Slice from the radial PDW sequence showing a secondary metaphyseal bump at the femoral neck, characteristic for pincer impingement (white arrow).

Interpretation and Findings

There are numerous methods that address how best to interpret MR images of the hip. We prefer to look first at the bony structures, beginning with the acetabulum, and we then proceed to the soft-tissue structures.

Osseous structures

Normally, the acetabulum has an anteversion of between 14 and 26.5 degrees (men: 18.5 ± 4.5 degrees; women: 21.5 ± 5 degrees). To determine the version, we use the axial FLASH sequence with few but very thin (2-mm) slices. Because acetabular version in the cranial third of the acetabulum contributes to the development of osteoarthritis of the hip, we measure the version at the superior portion of the acetabulum and use the first slice, where the anterior rim can be differentiated from the posterior. When a retroversion is present (e.g., in a conventional radiograph of the pelvis), the posterior acetabular rim lies laterally to the anterior rim at the uppermost part of the hip.

Further caudally, all acetabuli have an anteversion. The angle of version is measured and mentioned in the report. We then look for signs of hypersclerosis of the subchondral bone in the FLASH sequence but also in all other sequences as a very hypointense subcortical signal. If this is present, it is a sign of overload. We also note whether ganglia are present at the subchondral bone; this is also a sign of overload. These cyst formations are of various diameters, from a few millimeters to several centimeters. Because they contain fluid or synovia, they have a bright signal intensity in the FLASH and PDW sequences, and they are hypointense in the T1W sequence. They are mostly located at the superomedial area and next to the rim of the acetabulum. Occasionally, one can see a tiny channel of connection with the joint.

For patients with a local or global overcoverage, one can observe a bone apposition at the rim, often anterolaterally but also posteriorly, where impingement takes place. We believe that this is a bony reaction to repetitive microtrauma, and it can be seen on a standard radiograph as a double line. This “osteophyte” is obtuse or sharp at the edge, and it is broad based. The labrum becomes thinned in this area, and, in some cases, it fully disappears. The latter observation gives the false interpretation of an ossification of the labrum.

At the femoral head and neck, we first look at the shape of the neck and femoral head and also at the transition zone between head and neck. A normal femoral head is spherical in shape, and the neck is waisted or concave. In hips with cam FAI, several differently shaped femoral necks can be encountered. In some cases, there is an isolated bump that is localized to the anterolateral face of femoral neck, whereas other necks are circumferentially thicker throughout; in some cases, there is the pistol grip deformity as a result of a more laterally located lesion. In hips with pincer FAI, there is often concavity in the contour of the femoral neck, followed by a distal osseous bump. This is a reaction that is mostly located on the anterolateral cortex of the femoral neck.

Impingement cysts of the head–neck junction are closely related to site of maximal impingement. They are usually located anterior on the femoral neck, and they vary in size from 3 mm to more than 12 mm in length. Mostly they are seen as bright, fluid-filled, spheric lesions, but sometimes they are composed of fibrous tissue. In this case, they are hypointense in all sequences. In most cases, there is a hypersclerotic rim around the cyst.

Cartilage

The zone of maximum acetabular articular damage is located at the anterosuperior rim near the labral attachment to the acetabular rim. In most cases of cam FAI, there is a small cartilage flap along the outer rim of the acetabulum. When these flap tears progress, the damage can be illustrated when contrast material gets between the acetabular cartilage and the subchondral bone. In advanced cases, the cartilage thins to the point of full-thickness ulceration, and this can extend toward the center of the acetabulum. With pincer FAI, there is also a cartilage abrasion posteroinferiorly; this is explained as a contrecoup lesion related to the leverage of the femoral head in that direction.

As the disease progresses, the cartilage of the femoral head becomes thin at the analogous site of impingement. The head then migrates into the acetabular defect. Later, the femoral disease progresses to the center of the head, near the fovea, with further flap tears of the femoral cartilage. These flap tears extend into sheets of cartilage that are separated from the bone and that can fill with contrast medium between the bone and the flap tear. Cartilage, which is separated from its bony base, will undergo malacic change and therefore change intensity to a brighter signal, whereas fresh flaps are hardly visible when the flap is reduced and pressed against the subchondral bone.

Labrum

A normal labrum appears as a triangular structure with a low signal intensity. It attaches with a broad base to the acetabular rim and cartilage, and the border is distinct on all sides. At the incisura acetabuli, the ligamentum transversum replaces the rim. In patients with FAI, there are signal-intensity changes, with the labrum having higher intensity as a result of excessive edema. In a patients with cam impingement, an undersurface separation of the base of the labrum is commonly seen as a bright linear structure between the acetabular cartilage and the base. This is not really a labral tear but rather a rupture of the cartilage from the labrum. This tear pattern is partial thickness at this stage. Later, as the disease progresses, the tear may propagate to the bony rim, thus creating a full-thickness tear. This is typically seen in hips with DDH and FAI, although in cases of DDH the labrum is bigger than normal. The tear can also extend toward the tip of the labrum as a longitudinal tear, which is seen as a bright linear lesion from the base to the tip. Alternatively, with long-standing pincer FAI, the labrum is thinned from the base to the tip by bony apposition of the acetabular rim; this is seen as the signal intensity changes into bone marrow intensity, and it can be localized (anterior overcoverage) or generalized (coxa profunda).

Because of the high pressure in the joint as compared with the periarticular soft tissues, synovial fluid can be forced out through these tears, thus creating soft-tissue ganglia. In cases that involve longitudinal intralabral tears, intralabral ganglia can also occur.

Joint capsule

In FAI cases that involve advanced involvement of the joint capsule, the capsule can be thickened with higher signal intensity. This process is felt to be the result of direct trauma from impingement between the acetabular rim and the femoral neck. Another cause may be an arthritic microenvironment in which tissue factors are released and contribute to capsular alterations. After the surgical treatment of FAI, scarring of the capsule to the anterolateral femoral neck has been observed; these adhesions may be a cause of continued symptoms. The adhesions are seen as string-like hypodense structures that are located between the capsule and the anterior femoral neck. These adhesions can best be seen after the administration of intra-articular contrast.

Periarticular soft tissues

A bursa is commonly encountered around the iliopsoas tendon. In such cases, a connection between the joint and the iliopectineal bursa must be postulated. The bursal tissue is smooth and thin walled, and the cavity may fill with medium. In some cases, the thin bursal tissue bursts during the intra-articular injection of contrast medium. When this happens, most of the gadolinium flows out in the surrounding tissues. The bursae vary in extent from very small to very large; they can reach the extraperitoneal space in the pelvis.

3-T Morphologic imaging

In addition to novel MR sequences, imaging quality can also be improved with the use of higher field strengths, because they provide a higher intrinsic signal-to-noise ratio, which is critical for high-resolution imaging. Two preliminary studies have been published about the use of 3-T imaging of the hip, which may help to improve the MR diagnostic accuracy of diagnosis with the use of high-resolution imaging. In addition, 3-T imaging may obviate the need for a contrast medium (Figure 4-6). The visualization of acetabular and femoral cartilage separation and the assessment of the acetabular labrum and adjacent cartilage—both of which are essential for an accurate diagnosis of FAI—can be improved with the use of high-resolution techniques. These advantages can also improve the usefulness of postoperative MR by monitoring cartilage integrity, which is a useful measure for evaluating surgical outcomes (Figure 4-7).

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Figure 4–6 A, Proton-density turbo spin-echo oblique coronal view. Note the separation of the femoral and acetabular cartilage (noncontrast) and the clear assessment of the acetabular labrum and the adjacent cartilage, represented by the thin black line between the two cartilage (gray) layers (white arrows). B, magnification of A rotated 90 degrees counterclockwise.

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Figure 4–7 Proton-density turbo spin-echo radial view of a patient with persisting hip pain 6 months after an arthroscopic labrum resection. Note the signal alteration within the acetabular cartilage (white arrow) showing a cartilage defect as a result of the insufficient correction of the femoroacetabular impingement.

3-T Isotropic imaging

Isotropic three-dimensional sequences may provide for the diagnosis and characterization of acetabular and femoral cartilage on the basis of their anatomic correlation with the acetabular version or the femoral head–neck offset. A more precise overview of the different 3-T techniques is described in the review article by Philipp Lang, Farimah Noorbakhsh, Hiroshi Yoshioka. Figure 4-8 is an image from a patient with a cam-type impingement and cartilage degeneration with multiplanar reconstruction around the femoral neck that was obtained with the use of a three-dimensional true fast imaging with steady precession (FISP) sequence.

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Figure 4–8 Isotropic three-dimensional true-fast imaging with steady-state precession (0.53 mm × 0.53 mm × 0.53 mm voxel size; TA (acquisition time), 7:32 minutes) of a patient with A, localizer slice perpendicular to the long femoral neck axis, showing the radial slice plan. B, C, and D are radial slices in different positions. Radial reconstruction was performed around the femoral neck to assess the femoral metaphysis morphology and the cartilage and labrum degeneration.

3-T Biochemical imaging

Another promising new technique is contrast-enhanced MRI, which is referred to as dGEMRIC or delayed gadolinium-enhanced MRI of cartilage. This technique is based on findings that glycosaminoglycans (GAGs) contribute a strong negative charge to the cartilage matrix. Therefore, if a negatively charged contrast agent (e.g., gadolinium–diethylenetriamine penta-acetic acid 2) is given time to distribute in the cartilage, it will distribute in inverse proportion to the GAG content. By means of gadolinium enhancement within the cartilage and subsequent T1 quantification, the T1 value can be used as an index for GAG concentration within the cartilage. Because GAG seems to be lost early during cartilage degeneration, this technique may improve osteoarthritis diagnosis during the early stages. Despite promising results in patients with hip dysplasia, the described method is limited in the hip in terms of reproducibility and imaging planes, and it is additionally hindered by the requirement of additional sequences for the assessment of the acetabular labrum and the femoral head–neck junction morphology.

T2 mapping for biochemical imaging may be an alternative to the use of a contrast agent. T2 techniques make use of the T2 relaxation constant, which is affected by water–collagen interactions and, therefore, by water concentration, collagen concentration, and collagen alignment. In normal hyaline cartilage, there is a spatial variation of T2 with increasing values from the deep aspect to the superficial layer that are based on cartilage composition and structure within each layer. The influence of cartilage degeneration or alteration (e.g., cartilage repair tissue on the spatial T2 variation) has been investigated. The advantage of T2 mapping is that it does not require the use of a contrast agent. The drawbacks, however, are the nonspecificity of T2, as described previously, and the relatively long acquisition times required for the long echo trains needed for accurate T2 decay assessment (Figure 4-9).

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Figure 4–9 Color-coded T2 relaxation times in the acetabular cartilage based on a three-dimensional gradient-recalled echo sequence with different echoes. Note the altered T2 values in the anterosuperior (A)and the anterior acetabulum (B, cartilage damage more extensive) in the expected area of femoroacetabular impingement.

Conclusion

It has been shown that plain films are not as accurate as MR to assess the extent of intra-articular damage in patients with FAI. MRI can provide views of osseous and soft-tissue anatomy. Presently, MRI is the best available imaging tool for hip evaluation; however, it still has limitations for the diagnosis of cartilage and labrum lesions during the early stages of disease. In these cases, the relative thin cartilage, the spherical joint shape, and the narrowness of tissue structures pose logistical difficulties and demand high MR technology standards. So far, MR arthrography in combination with radially reconstructed planes is the method of choice for the assessment of FAI as a result of the improved detection of labral lesions. As compared with MR arthrography, the results of noncontrast techniques are less promising. In terms of cartilage evaluation, study results are still moderate, and the detection of cartilage delamination remains difficult. Recent developments in high-resolution isotropic imaging, cartilage-specific MR sequences, local gradient and radiofrequency coils, and high-field MR systems will improve diagnostic capabilities in terms of signal-to-noise ratio, contrast-to-noise ratio (CNR), shorter acquisition times, three-dimensional imaging, and the reduction of the need for a contrast agent. In addition to morphologic MRI, biochemical MR (i.e., dGEMRIC and T2 mapping) approaches that characterize cartilage microstructure and biochemical content will contribute to a better understanding of cartilage degeneration.

Annotated references and suggested readings

Ganz R., Beck M., Leunig M., Nötzli H., Siebenrock H. Femoro-acetabuläres impingement. In: Wirth C.J., Zichner L., editors. Handbuch der Orthopädie. Stuttgart, New York: Thieme, 2003.

This is a complete review of the work on FAI from the Bern group, which summarized different articles. This article very well summarizes the image findings that occur with FAI on x-ray and MRI..

Ganz R., Parvizi J., Beck M., Leunig M., Nötzli H., Siebenrock K.A. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. (417); 2003:112-120.

This is the first overview manuscript by Ganz and colleagues about femoroacetabular impingement as a disease, and the significant image findings are described. This is a basic article to read to understand FAI in the context of our chapter..

Ito K., Minka M.A.2nd, Leunig M., Werlen S., Ganz R. Femoroacetabular impingement and the cam-effect. A MRI-based quantitative anatomical study of the femoral head-neck offset. J Bone Joint Surg Br.. 2001;83(2):171-176.

Ito and colleagues assessed morphologic changes seen on MRI from patients with CAM impingement. They described the measurement of the head–neck offset at different positions on the MRI and compared these measurements with those of volunteers. This is one method that was used with MRI for the diagnosis of FAI as described in our chapter..

Jager M., Wild A., Westhoff B., Krauspe R. Femoroacetabular impingement caused by a femoral osseous head-neck bump deformity: clinical, radiological, and experimental results. J Orthop Sci.. 2004;9(0):256-263.

Jager and colleagues compared radiographic image findings before and after therapy with patient outcomes. This is one clinical study that addressed the value of image findings for patients with FAI..

Kim Y.J., Jaramillo D., Millis M.B., Gray M.L., Burstein D. Assessment of early osteoarthritis in hip dysplasia with delayed gadolinium-enhanced magnetic resonance imaging of cartilage. J Bone Joint Surg Am.. 2003;85-A(10):1987-1992.

This article was the first to describe the use of dGEMRIC for the assessment of early cartilage lesions of the hip joint. On the basis of these findings, the technique was found to be transferrable for clinical use for patients with FAI..

Leunig M., Beck M., Kalhor M., Kim J., Werlen S., Ganz R. Fibrocystic changes at the anterosuperior femoral neck: prevalence in hips with femoroacetabular impingement. Radiology.. 2005;236(1):237-246.

Leunig and colleagues described the diagnosis of cystic formation in the femoral neck in patients with FAI. This added an additional factor to the MRI assessment of FAI, and it is therefore described in our chapter..

Leunig M., Podeszwa D., Beck M., Werlen S., Ganz R. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement. Clin Orthop Relat Res. (418); 2004:74-80.

This is the first clinical article about the value of MRA as a standard technique for the assessment of labrum morphology in patients with hip impingement. This is basic information for understanding the techniques that we describe in this chapter..

Leunig M., Werlen S., Ungersbock A., Ito K., Ganz R. Evaluation of the acetabular labrum by MR arthrography. J Bone Joint Surg Br.. 1997;79(2):230-234.

This article is important for understanding the value of MRA for imaging of the hip. It also provides a detailed description of the technique of MRA..

Locher S., Werlen S., Leunig M., Ganz R. [Inadequate detectability of early stages of coxarthrosis with conventional roentgen images]. Z Orthop Ihre Grenzgeb.. 2001;139(1):70-74.

Locher S., Werlen S., Leunig M., Ganz R. [MR-Arthrography with radial sequences for visualization of early hip pathology not visible on plain radiographs]. Z Orthop Ihre Grenzgeb.. 2002;140(1):52-57.

These two articles by Locher and colleagues describe in two consecutive steps the limitations of plain radiography for assessing hip-joint degeneration and the value of radial imaging of the hip joint with the use of MRI. Radial MRI is one of the most important parts of the Bern hip protocol described in this chapter..

Murphy S., Tannast M., Kim Y.J., Buly R., Millis M.B. Debridement of the adult hip for femoroacetabular impingement: indications and preliminary clinical results. Clin Orthop Relat Res. (429); 2004:178-181.

This articles describes FAI and summarizes the results of therapy. It demonstrates the value of the imaging methods described within this chapter..

Philipp Lang., Farimah Noorbakhsh., Hiroshi Yoshioka M.R. Imaging of Articular Cartilage: Current State and Recent Developments. Radiol Clin N Am. 2005;43:629-639.

Recht M.P., Goodwin D.W., Winalski C.S., White L.M. MRI of articular cartilage: revisiting current status and future directions. AJR Am J Roentgenol.. 2005;185(4):899-914.

This is an overview of all of the current techniques that are used for cartilage imaging. This gives the reader a better understanding of the different techniques described in the chapter, and it also discusses possible future techniques..

Reynolds D., Lucas J., Klaue K. Retroversion of the acetabulum. A cause of hip pain. J Bone Joint Surg Br.. 1999;81(2):281-288.

This article describes the role of retroversion. The MR assessment of retroversion is described within our chapter, and this article provides a good overview of the subject..

Schmid M.R., Notzli H.P., Zanetti M., Wyss T.F., Hodler J. Cartilage lesions in the hip: diagnostic effectiveness of MR arthrography. Radiology.. 2003;226(2):382-386.

This article describes the limited value of standard MRA for assessing early lesions of the cartilage in the hip. These findings led to the need for advanced imaging techniques, as described in this chapter..

Siebenrock K.A., Wahab K.H., Werlen S., Kalhor M., Leunig M., Ganz R. Abnormal extension of the femoral head epiphysis as a cause of cam impingement. Clin Orthop Relat Res. (418); 2004:54-60.

This article shows the value of measurements of the femoral epiphysis in patients with FAI. As the development of FAI becomes increasingly important, these measurements are needed to demonstrate the impact of epiphyseal development for patients with FAI..

Smith H.E., Mosher T.J., Dardzinski B.J., et al. Spatial variation in cartilage T2 of the knee. J Magn Reson Imaging.. 2001;14(1):50-55.

This is an article about the use of T2 for the assessment of cartilage. T2 mapping is a commonly used method for diagnosing cartilage issues of the knee, and it is currently being looked at for the diagnosis of hip cartilage problems. This article provides a background and better understanding of T2..

Sundberg T.P., Toomayan G.A., Major N.M. Evaluation of the acetabular labrum at 3.0-T MR imaging compared with 1.5-T MR arthrography: preliminary experience. Radiology.. 2006;238(2):706-711.

This article provides initial results of a comparison of high-field imaging with standard MRA. This is a future direction for the imaging of FAI, and 3-T imaging is discussed in this chapter. This article gives the reader some background information about high-field imaging..

Tanzer M., Noiseux N. Osseous abnormalities and early osteoarthritis: the role of hip impingement. Clin Orthop Relat Res. (429); 2004:170-177.

This article describes the osseous abnormalities and image findings in clients with FAI with hip pain and labral damages in three different patient groups. It gives the reader an overview of the clinical findings of hip arthroscopy as compared with the image findings described in this chapter..

Trattnig S., Marlovits S., Gebetsroither S., et al. Three dimensional delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) for in vivo evaluation of reparative cartilage after matrix-associated autologous chondrocyte transplantation at 3.0T: preliminary results. J Magn Reson Imaging.. 2007;26(4):974-982.

This article describes the three-dimensional dGEMRIC technique for the assessment of cartilage. This new technique enables the radial use of dGEMRIC in the hip joint to assess the cartilage damage pattern found in patients with FAI..

Wagner S., Hofstetter W., Chiquet M., et al. Early osteoarthritic changes of human femoral head cartilage subsequent to femoro-acetabular impingement. Osteoarthritis Cartilage.. 2003;11(7):508-518.

This work correlates the imaging findings of the femoral head–neck offset with histologic findings. It also helps to identify the background of the femoral–head–neck abnormalities and therefore their signal presence on MRI..

Welsch T.C., Mamisch G.H., Domayer S.E., et al. Cartilage T2 assessment at 3-T MR imaging: in vivo differentiation of normal hyaline cartilage from reparative tissue after two cartilage repair procedures—initial experience. Radiology.. 2008;247(1):154-161.

This article describes the initial results of the use of biochemical imaging techniques and T2 mapping for the comparison of different surgical therapy concepts of cartilage repair. These techniques could potentially also be used for therapy assessment among patients with FAI, and early image examples are shown..

Xia Y. Magic-angle effect in magnetic resonance imaging of articular cartilage: a review. Invest Radiol.. 2000;35(10):602-621.

This article describes the limitations of the use of T2 mapping in the hip joint as a result of the magic-angle effect..

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