Introduction

Magnetic resonance (MR) imaging of the hip provides a platform to assess the osseous structures and surrounding soft tissues and is thus an invaluable tool in the assessment of both the hip joint and its associated structures. It is therefore important to develop a thorough grounding in the normal anatomical appearance of the pelvis and hip on MR imaging in order to thereafter appreciate the more common disorders that will regularly present in clinical practice.

Because a range of diagnostic modalities is available to the investigating clinician, it is also important that they have an understanding of the applications of each technique and its clinical appropriateness. Often, a patient’s principal presenting complaint will be that of low back pain, with associated symptomatology in the hip, groin or thigh.

Depending on the size of the field of view, the hips may be included on MR imaging of the lumbar spine; however, in order to explore the hip’s anatomy and pathoanatomy in detail, a focused MR imaging study, initially of both hips followed by a dedicated protocol of the hip in question should be performed, to optimize the detection of any pathology and to help direct the most appropriate clinical management of the patient.

History and examination

As with any patient examination, the eliciting of a detailed and accurate history is paramount and lays the foundation for the performance of an appropriate examination and establishment of a working diagnosis and differential. The most crucial element of the history in this area of the body is the precise localization of the area of pain: many patients who complain of ‘hip pain’ do not in fact have pain in their hip and, when questioned, will point to their buttock, gluteal fold or iliac crest; similarly, patients who do have hip pathology will often complain of symptoms in their groin, or the side or front of their thigh – not infrequently described as ‘sciatica’! The use of pain diagrams can help in this regard, but, at the very least, the patient should be asked to point to where they feel pain or discomfort.^1,2

The nature and precipitation of the pain can also give important clues as to the underlying cause of the patient’s complaint. Progressive, insidious pain and stiffness in the groin (often in association with a flexion contracture) and/or the buttock is indicative of arthritis; this will typically be made worse by walking and relieved by sitting. By contrast, a sacroiliac syndrome, which presents with buttock pain that may refer to the groin, will often be acute with an obvious precipitating cause and be relieved by walking and aggravated by sitting.

Sporting injuries often have very localized pain produced by highly specific activities: soccer players may complain of groin pain but only when passing the ball in certain directions; this can help differentiate injury to the adductor longus from rectus femoris or psoas. Increasing pain on repetitive activity is also typical of soft tissue injuries such as bursitis, which commonly affects the greater trochanteric area: often the patient will complain of being unable to sleep on the affected side.

With experience, the clinician will normally be able to recognize the atypical presentation of more unusual conditions such as osseous, intrapelvic and spinal lesions. These can, of course, mimic everyday injuries and the clinician should always be alert for an apparently benign condition that fails to respond to normally successful management protocols or is relentlessly progressive. Pain or clicking in the hip of a child is always a cause for concern and usually an indication for diagnostic imaging.³

Associated symptoms such as clicking or popping can also be associated with specific conditions⁴ and a familial history of pelvic conditions is often very revealing: many conditions such as degenerative coxarthrosis, inflammatory arthropathies, connective tissue disorders and dysplasia have familial tendencies.^5–9

Examination should commence with observation of the patient both stationary and walking. Obesity (a body mass index greater than 30) is a significant predisposing factor towards coxarthrosis,¹⁰ which will often be accompanied by an obvious flexion contraction causing an inability to stand with a straightened leg on the affected side; other forms of antalgia can also help identify the source of a patient’s pain both in posture and gait.

Although there are myriad orthopaedic tests for the hips and sacroiliac joints, few have any proven validity.^11–14 Range of motion, however, often is enough to demonstrate hip pathology, particularly painful reduction of internal rotation. The Patrick/FABER test (external rotation of the hip with the leg in the ‘figure-4’ position: Flexion, Abduction and External Rotation) has been shown to have good reliability as has digital palpation in the identification of greater trochanteric bursitis – the same is also true of the many myofascial trigger points that frequently coexist with pelvic girdle dysfunction and with the posterior margin of the sacroiliac joint.^12,15,16

Identification of sacroiliac syndrome is more problematic; however, multiple positive provocation tests have been shown to have a measure of diagnostic reliability; these are detailed in Table 5.01^17–19 alongwith tests that the authors have also found useful when similarly used in combination. It is, however, important not to perform too many tests; if three or four have already proved positive, there is little to be gained from continuing and the patient may well have an adverse reaction – the tests are called provocative for a reason and can eventually aggravate the patient’s symptoms. It should also be kept in mind that the pelvis is a closed loop kinematic chain and that comorbidity with lumbosacral facet joint dysfunction is high.²⁰

Table 5.01 Suggested provocation tests for the sacroiliac joint
Provocative tests with evidence of diagnostic reliability

Differential diagnosis

Once the differentiation between intrapelvic conditions, hip pain and sacroiliac syndrome has been made, the diagnosis should be further refined. The main differential with sacroiliac syndrome is with myofascial syndromes in the muscles of the gluteal region and lumbosacral junction and with lumbar spine injury, which can often refer or radiate to the buttock. As these conditions are often comorbid, the clinical challenge is to ascertain the extent of the contribution from each.

Figure 5.01 • The thigh thrust sacroiliac joint provocation test.

(Reproduced from Manual Therapy¹⁷ with permission.)

Figure 5.02 • The compression sacroiliac joint provocation test.

(Reproduced from Manual Therapy¹⁷ with permission.)

When it comes to the hip joint, the main aim of the differential diagnosis is to distinguish between intra-articular pathology, extra-articular pathology, and those conditions that can mimic hip pain. These are summarized in Table 5.02.^3,21,22

Table 5.02 Causes of pain around the hip joint

The clinician should also be alert for paediatric cases presenting as knee pain without discernible cause. Two common hip conditions often present in this manner: slipped capital femoral epiphysis and Legg–Calvé–Perthes disease, and both have prognosis directly related to early detection.²³

Technique and protocols

During any MR imaging evaluation, patient co-operation is critical. For evaluation of the hip, the patient should lie supine with mild internal rotation of the feet. Symmetry of rotation of both feet is important when both joints are examined simultaneously, which they often are to compare the appearance of the trochanters and adjacent muscles.^24–26 Two types of images are available: a screening examination of both hips, or a higher-detail study of a single joint (Figure 5.03).

Figure 5.03 • MR imaging of the hip using two different protocols in paediatric patients. In (A), MR imaging of the left hip has been performed using a gradient-weighted sequence in the coronal plane. The specificity of the MR imaging to include just one hip joint allows for the close inspection of this region, particularly with respect to the labrum; however, in (B), an MR image of both hips in the coronal plane using a fluid-sensitive sequence allows for the comparative evaluation of both hips albeit with a reduction in the anatomical detail, but which remains a very useful technique to study the hips. Both techniques have advantages and disadvantages.

The study begins with a plan scan (or ‘scout’ view) through the level of the femoral head and will usually include axial and coronal views (Figure 5.04). T1-weighted and fluid-sensitive images will be obtained in multiple planes. Depending on the pathology suspected, sagittal views may also be acquired (Figure 5.05). Fat-suppression techniques are very commonly used in the hip and pelvis to show early changes in marrow signal.^24,25,27,28

Figure 5.04 • Three MR imaging scout views demonstrating planes of imaging for (A) axial pelvis (T1-weighted), (B) axial hip (T1-weighted in a paediatric patient), and (C) coronal pelvis gradient echo.

Figure 5.05 • MR imaging using T1-weighted, spin echo images of the hip in the sagittal plane. These sequences are useful in the evaluation of the subchondral bone, in conditions such as avascular necrosis, or in cases of acetabular labral tears. Figure (A) demonstrates the scout view for the resulting sagittal sections (B–D). Note that the anterior aspect of the patient is to the reading left in these figures, which progress from medial to lateral.

Intravenous contrast is not routinely utilized but may be helpful to differentiate cystic from solid masses or early ischaemic changes and in the evaluation of labral pathologies that have proven inconclusive on normal MR protocols. In these situations, findings may be accentuated even more if paired with fat-suppression techniques.^25,27,29,30

Evaluation of the sacrum, sacroiliac joint and superior bony pelvis anatomy requires different positioning for the patient and should be ordered separately. The patient is often asked to lie supine with the knees slightly bent and hip joint mildly flexed; this position precludes good visualization of the iliofemoral joint. The planes of imaging for these areas is also different; in cases where sacroiliac arthropathy is suspected, images obtained in an oblique coronal plane parallel to the joint may be helpful (Figure 5.06). Intravenous administration of contrast can help identify early sacroiliitis. If pathology is suspected in the posterior soft tissues, imaging in the prone position may be also considered, to limit compression of the soft tissues.^{24,25,27,31,32}

Figure 5.06 • MR imaging depicting scout view of the sacrum. Particularly note the angulation of the plane of imaging which allows this plane to capture not only the sacrum but also a portion of the hip region which may reveal previously occult lesions.

Normal anatomy and common variants

MR imaging displays osseous and soft tissue structures with great clarity; the osseous anatomy is best evaluated on the T1-weighted sequences. The acetabular fossa is a deep pocket that covers approximately 40% of the surface of the femoral head. The thick fibrocartilaginous labrum and transverse acetabular ligament completely encircle the acetabulum. Both structures will be demonstrated as low intensity areas on most of the MR sequences.³³

The femoral head is generally spherical and covered by articular cartilage with the exception of the insertion point of the ligamentum teres: the fovea centralis. Covering the proximal femur is the articular capsule extending from the supra-acetabular region to the femoral neck.^34,35 It is a normal finding to see a small amount of fluid inside the joint space (Figure 5.07). Adjacent to the capsule is one of the largest synovial bursae of the body: the iliopsoas bursa. It is seen as a high intensity area on fluid-sensitive images, sandwiched between the muscle and the capsule. In a small percentage of the population, it may even communicate with the joint.³⁶ MR imaging allows for assessment of the major muscle groups surrounding the hip articulation: the external rotators inserting on the greater trochanter, and iliopsoas attaching to the lesser trochanter and the hip flexors crossing over the large joint (Figures 5.08, 5.09; Box 5.01).^22,33

Figure 5.07 • T2/proton-weighted axial MR images of both hips at the level of the femoral head and greater trochanter. Normal synovial fluid is present as a region of increased signal intensity in the right coxofemoral joint space (thin arrow). A mild joint effusion is seen in the left coxofemoral joint space (block arrow). No definitive measurement is accepted to determine the presence of effusion; however, it is generally accepted that only minimal fluid – a barely visible thin film of increased signal – should be seen in the joint space between the femur and acetabulum.

Figure 5.08 • MR imaging demonstrating coronal gradient echo images of the left hip of a 13-year-old girl (A–G). The images are displayed following the scout view (A), from anterior (B) to posterior (G) to depict various normal anatomical structures. Note the degree of detail attained on these images, including the individual muscle groups. The key to the images is detailed in Box 5.01.

Figure 5.09 • MR imaging demonstrating axial proton density images of the hips of a 13-year-old girl (A–I). The images are displayed from superior (A) to inferior (I) from the supra-acetabular ridge to the diaphysis of the femur. A variety of anatomical structures are depicted on the views. The key to the images is detailed in Box 5.01.

In the pelvis and proximal femur, the composition of the bone marrow varies with age, skeletal maturity and health status, and the MR imaging appearance will change accordingly (Figure 5.10). In the adult, bone marrow throughout the pelvis and femoral head will demonstrate intermediate signal intensity, slightly more intense than the muscle, on T1-weighted images; the marrow in adults is generally composed of fatty components. The signal may however be heterogeneous and patchy, interrupted by low signal zones on T1 images, representing residual foci of haematopoietic (red) marrow. These are considered normal findings and are generally bilateral and symmetrical. Abnormality is represented by the persistence of red marrow in the epiphysis and should lead to further investigation. In children, the marrow patterns vary by region. The femoral head and greater trochanter will contain yellow marrow and the intertrochanteric or metaphyseal region will contain haematopoietic marrow (Figure 5.11).^24,28,29,37

Figure 5.10 • MR imaging of the pelvis performed in the coronal plane illustrating the differences in bone marrow patterns between patients of different ages. In (A), T2-weighted imaging with fat suppression of a 56-year-old man demonstrates a predominantly low signal intensity throughout the femoral heads, which is slightly more heterogeneous in the proximal femurs. In (B), T2-weighted imaging with fat suppression in a 13-year-old demonstrates the relatively higher signal intensity throughout the bony pelvis and proximal femoral shafts. In (C), a T1-weighted spin echo image in a 25-year-old woman shows a slightly heterogeneous signal intensity about the proximal femurs. In a younger patient of 13 years old (D), a T1-weighted image demonstrates the overall lower signal intensity seen in the pelvis and proximal femurs except at the level of the epiphyses.

Figure 5.11 • Sagittal, fast spin echo T1-weighted MR images of a 13-year-old girl (A–J). The images are displayed from lateral (A) to medial (J), beginning at the outer aspect of the greater trochanter and continuing medially to the ilium. In this young patient, the femoral head exhibits high signal intensity on the T1-weighted image since it contains yellow marrow and the intertrochanteric or metaphyseal region is of a lower signal intensity since it contains haematopoietic marrow. The key to the images is detailed in Box 5.01.

Other causes of marrow signal abnormalities include bone islands. They are easily recognized as decreased signal zones on all sequences and are frequently found in the proximal femur (Figure 5.12).^27,38 Obliquely oriented linear zones of decreased signal intensity in the femoral neck may also be seen and represent the bony weight-bearing trabecular groups. Well-defined areas of abnormal low T1-weighted and high T2-weighted signal intensity may be present in the anterior-lateral portion of the femoral neck. Synovial herniation pit defects are also common in this location and can be recognized by the presence of focal increased signal intensity on T2-weighted images, a sclerotic margin, focal central radiolucency and their characteristic location. Accurate identification is dependent on correlation with other studies such as plain film radiography.³⁹

Figure 5.12 • MR imaging: coronal, T1-weighted sequence with a slice taken through the femoral head and acetabulum demonstrating a focal round region of decreased signal intensity at the junction of the femoral head and neck. On T2-weighted imaging this region will normally appear as a region of low signal intensity. This is a small bone island (arrow), a normal variation.

Multiple acetabular labral shapes have been described; however, 66%–80% of normal acetabular labra are triangular other than in the posterosuperior portion, which is typically flat, a finding which is generalized in 9% of individuals. A round labrum appears to be a normal variant and is seen in 11%–13% of individuals, whilst up to 7% have irregular labra. The structure is absent in up to 14% of individuals. No correlation between labral shape and injury or degeneration has been established. The labrum will demonstrate low signal intensity on most MR imaging sequences.^40–43

Pathological findings

Avascular necrosis

One of the major indications for MR imaging of the pelvis and hip is to investigate the possibility of avascular necrosis (AVN) of the femoral head. MR imaging is very sensitive in the early detection of this condition.^24,25,27

The risk factors for AVN are multiple and include trauma, corticosteroids (endogenous or exogenous), haemoglobinopathies, alcoholism, pancreatitis, Gaucher’s disease, radiation treatment and dysbaric injury. The clinical presentation also varies greatly; however, when suspected, careful examination of both hips should be performed since bilateral presentation may be seen in up to 40% of patients (Figure 5.13).^44–46

Figure 5.13 • MR imaging of both hips performed in the coronal plane using a short tau inversion recovery (STIR) sequence, demonstrating a focal region of increased signal intensity about the right femoral head, in the subchondral bone, with a central region of decreased signal (arrow (A)). On the axial T2-weighted (B) and sagittal T1-weighted (C) sequences, a focal region of decreased signal intensity is again noted in the centre with associated collapse of the anterior portion of the femoral head, seen particularly well on the sagittal slices (arrow (C)) involving over one-third of the femoral head surface.

Avascular necrosis can be classified using clinical, radiographic or MR criteria (Table 5.03). The changes seen in stage 1, which is almost invariably latent on plain films, represent the hypovascular area surrounding the necrosis. The shape of the femoral head and integrity of the joint space remain intact until stage 3. Although, at this stage, plain films are sufficient to detect AVN, the degree of bone marrow oedema demonstrated on MR images correlates quite strongly to the levels of reported pain.^47–49 Even though specific measurements are not available, it is important to realize that the normal amount of fluid in the capsule is generally not sufficient to generate signal changes on T2-weighted images, making any high signal intensity area in the joint clinically suspicious.^25,29,50

Table 5.03 Classification of avascular necrosis

Trauma

Dislocations of the hip joint usually only occur following severe trauma and are associated with lesions of the femoral head, labrum and acetabulum. Bone bruises on either the femoral head/neck or acetabulum may be visualized as areas of decreased T1-weighted and increased T2-weighted signal zones adjacent to the area of impact (Figures 5.14, 5.15).^24,25,27

Figure 5.14 • Plain film hip radiographs of a gentleman who sustained a rally car accident involving several rolls of the car. The initial imaging demonstrates dislocation of the right hip (A and B). The patient was recommended to remain immobile for 2 months before resuming normal activities having had the articulation relocated; however, he was still limited by hip pain which was worsening. Follow-up imaging was performed (C and D), which demonstrated an irregularity and deformity about the lateral aspect of the femoral head as well as joint effusion (note the displaced gluteus medius fascial plane). Owing to the previous trauma and the imaging and examination findings, MR imaging was ordered (Figure 5.15).

(This case is reproduced courtesy of Vincent Klingelschmitt DC, France.)

Figure 5.15 • MR imaging of both hips, using coronal T1-weighted (A) and STIR (B) sequences. The T1-weighted sequences demonstrate the large region of decreased signal intensity about the right hip, extending throughout the femoral head to the femoral neck (A). In (B), a large region of increased signal intensity is noted about the right hip extending from the head to the proximal femoral shaft, corresponding to the decreased signal intensity noted on the T1-weighted images and which represents bone marrow oedema which is likely post-traumatic in origin associated with the osteochondral lesion and avascular necrosis of the femoral head. In addition, a large joint effusion is noted about the right hip as well as deformation of the acetabular labrum superolaterally (oval).

Injuries to the fibrocartilaginous labrum may occur with dislocations or be associated with degenerative processes. They can be difficult to identify on non-contrasted sequences or to differentiate from benign individual variation. Tears may appear as irregularities in the surface as well as focal increases in signal intensities; they may also be associated with cysts. Clicking, snapping, decreased ranges of motion and deep hip pain, aggravated by hip rotation and flexion, are the most common clinical symptoms (Figure 5.16).^51–53

Figure 5.16 • Multiplanar MR imaging of the right hip: a STIR sequence demonstrating the coronal slices (A–C), a sagittal slice (D) and one slice in the axial plane (E). In (A)–(D), the anterosuperolateral labrum, which normally demonstrates a low signal and has a triangular appearance, has a thin high signal intensity line traversing it with a slight deformation of the triangular shape of the labrum; this indicates a small tear, a common injury to sustain during sports activities and which can produce significant clinical symptoms for the patient.

MR imaging has largely replaced bone scintigraphy as the most effective tool for detecting stress or insufficiency injuries; it can detect changes 24 to 48 hours prior to any other type of imaging modality.^25,54 Insufficiency fractures from biomechanical stresses on weakened bone are common and often radiographically occult. A painful hip in a patient at risk for osteoporosis should always raise clinical suspicion of fracture, even if the patient remains weight-bearing and has no significant history of trauma. In these cases, a limited MR examination may be requested. Coronal and axial T1-weighted and T2-weighted fat-suppressed images of the entire pelvis may show the fracture site as a linear low signal area with surrounding bone marrow oedema. Careful evaluation of the entire pelvis is essential to eliminate concurrent sacral or ischiopubic fractures (Figures 5.17, 5.18).^{24,25,27,54–56}

Figure 5.17 • Plain film anteroposterior (AP) spot view of the right hip (A) showing an apparent increase in the trabecular pattern in the medial femoral neck and discontinuity of the trabeculae about this region in a patient with general osteopenia, likely due to osteoporosis. On T1-weighted MR imaging, the coronal sequence (B) shows a large region of decreased signal intensity in the right femoral neck corresponding to a fracture (arrow). In the follow-up, postsurgical views, the AP radiograph (C) demonstrates the presence of two surgical pins fixing the femoral neck fracture. The same MR protocol as previously (D) is included to demonstrate that, despite newer surgical materials designed to be compatible with MR units, a large amount of artifact may still be created resulting in a region which is very low signal intensity due to the presence of the surgical pins. This can provide difficulty in the interpretation of such an image, but by manipulating the images, it is possible to evaluate for lesions, such as those affecting the labrum.

Figure 5.18 • MR imaging using a coronal oblique STIR sequence of the sacrum demonstrating the presence of increased signal intensity about the left sacral ala with a region of irregular low signal intensity within (arrow). This represents an insufficiency fracture in a patient with previously diagnosed osteoporosis (detected using DEXA scanning).

Stress fractures from increased or abnormal stress on normal bone may also be assessed with MR imaging before findings are visible on radiographs. A linear, hypointense zone will be surrounded by a hyperintense bone marrow oedema on T2-weighted images as a response to the stress. Bone marrow oedema and articular irregularities along the pubic symphysis may indicate increased stress in this region; this condition is seen in athletes. It is often referred to as osteitis pubis and will present clinically as groin pain (Figure 5.19).^25,57,58

Figure 5.19 • MR imaging, T2-weighted sequences of the pelvis and hips in the axial plane demonstrating a diffuse region of bilaterally increased signal intensity about the pubic symphysis (arrows (A) and (B)). This corresponds to bone marrow oedema in the pubic bone bilaterally due to chronic osteitis, which may be caused by repetitive microtrauma such as sustained in sports injuries, especially in soccer players, or, in rarer cases, local bone infection.

Synovial herniation pits

Pit herniation defects (also known as synovial herniation pits or Pitt’s pits) represent a well-rounded abnormality in the cortex of the femoral neck in the upper, outer quadrant and are filled with fibrous and cartilaginous elements. On plain film, their appearance will be of a small, radiolucent lesion with a well-defined sclerotic rim; on MR imaging, a low focus on T1-weighted and high focal signal intensity on T2-weighted images will be seen.^24,25,27,59

These lesions were thought to be clinically silent and stable; however, there are now multiple reports of expanding, painful lesions and, indeed, synovial herniation pits are now known to be associated with femoroacetabular impingement syndrome (Figure 5.20). Clinically, this entity may mimic a labral injury: clicking and pain during normal range of motion, and may predispose to early degenerative changes.⁶⁰ Femoroacetabular impingement can be seen in patients with a history of acetabular deformity: developmental dysplasia (Figure 5.21); femoral defects, such as AVN; and slipped capital femoral epiphysis, or in patients with activities involving repetitive hip flexion, rotation and abduction.^61–65 Accessory ossicles such as os acetabulae are also known associated imaging findings (Figure 5.22).⁶⁶

Figure 5.20 • A focal region of decreased density is noted on the anteroposterior (AP) spot radiograph of the right hip (A) corresponding to a synovial herniation pit (Pitt’s pit). On the corresponding coronal plane STIR sequence of the right hip (B), a focal region of increased signal intensity is noted; this represents bone marrow oedema in the vicinity of the synovial herniation pit which may be symptomatic.

Figure 5.21 • MR imaging of both hips, performed in the coronal plane using T1-weighting. In this patient with bilateral developmental dysplasia of the hips, the sequences were used to study the shape of the hip joint as well as determine associated pathologies such as labral tears, commonly located in the anterosuperior aspect of the labrum. Note the unusual form of the femoral heads bilaterally and the lack of coverage of the femoral heads by the corresponding acetabulum. There is also irregularity noted about the acetabula, particularly on the right (white oval). In addition, there is a list of the lumbar spine to the left, although this may have been due to a positioning error.

Figure 5.22 • This 37-year-old male presented with a long-standing history of progressive hip pain, worse on the right. On the anteroposterior (AP) radiograph of the right hip (A), an os acetabulum is present with slight remodelling of the lateral femoral neck/head junction (oval), findings associated with femoroacetabular impingement syndrome (FAIS). MR imaging of the hips in FAIS is performed to determine the presence of associated pathologies such as labral tears. Coronal images were performed through both hips, using T1-weighted (B) and T2-weighted (C) sequences. The os acetabulum can be noted in both images (black circles), as well as the alteration in the appearance of the femoral head/neck, noted bilaterally but greater on the right. In addition, an acetabular tear is noted outlined in the white oval on the left side. Three-dimensional CT reconstructions (D–F) were performed to appreciate more fully the change in the junction of the femoral neck and head; this study is normally reserved for those preparing for surgical intervention. The os acetabulum is well defined, as is the unusual shape of the junction (black oval (D)).

Tumours

The pelvis and proximal femur are common locations for musculoskeletal tumours in patients of any age; these entities can also alter signal patterns. Neoplasms can present as a decreased T1-weighted and increased T2-weighted signal. This represents an inflammatory response but does not differentiate between benign or malignant; primary or secondary. It is generally accepted that the greater value of MR imaging is in the staging of tumours as opposed to their diagnosis, which often can be better accomplished with conventional radiographs. Common tumour or tumour-like conditions in the pelvis include many conditions such as metastatic disease, osteochondroma, fibrous dysplasia, Paget’s disease and osteoid osteoma (Figure 5.23).^24,25,27

Figure 5.23 • MR imaging, T2-weighted sagittal sequence (A) demonstrating a region of increased signal intensity in the anterior acetabulum, bone marrow oedema (white oval). The corresponding CT sagittal reconstruction image performed, bone window (B), demonstrates a focal region of increased density surrounded by a very small region of radiolucency or nidus (white circle) which is further surrounded by a region of less well defined increase in density that represents reactive sclerosis, the region on the MR image (A) which is affected by the bone marrow oedema.

Obstetrics

In recent years, applications for obstetrical imaging have been developed. Although ultrasonography remains the imaging modality of choice during pregnancy, MRI provides excellent resolution and tissue contrast for evaluation of both mother and fetus without the use of ionizing radiation (Figure 5.24). The first trimester remains a relative contraindication for MR imaging owing to the lack of information regarding the long-term effects.^67,68

Figure 5.24 • MR imaging of the lumbar spine in a 23-year-old female patient, with low back pain following a road traffic accident. Both images are performed in the sagittal plane, T1 in figure A and T2 in figure B. In both images, it is noted that the uterus (oval) is enlarged and that there is a small focus of altered signal, in figure A intermediate and in B decreased signal intensity. This represents a foetus in a patient who did not know that they were pregnant at the time of the imaging study.

Clinical pearls

• Avascular necrosis of the hip is a relatively common disease process with multiple associated risk factors. It may present as deep joint pain or even pain referred to the knee.

• Avascular necrosis is bilateral in approximately 40% of cases.

• Acute onset of hip pain in a patient at risk for osteoporosis should prompt rapid and thorough evaluation to exclude femoral neck fractures.

• Groin pain is one of the most difficult presentations to evaluate and treat. In athletes, osteitis pubis or other stress reactions should be considered as a possible diagnosis.