9 Pelvis

9.1 Introduction

The pelvis is a closed ring of bone formed by the two innominate bones and the sacrum. The pelvis transmits the forces acting on the spinal column to the lower extremities and protects the pelvic organs. Parts of the proximal pelvic ring provide insertions for the musculature of the trunk, and parts of the hip and thigh musculature insert into its distal parts. Therefore, evaluation of any pelvic pathology should also include examination of the spine and lower extremities.

Degenerative changes lead to chronic irritation of the pubic symphysis and sacroiliac joints. Unbalanced stresses resulting from deficient posture can produce arthritic changes in the sacroiliac joint. Predisposing factors include scoliosis and leg-length difference.

Sacroiliac dysfunction is a disturbance of the motion at the sacroiliac joint.

The sacroiliac joint is also frequently involved in rheumatic disorders. Table 9.1 provides an overview of types of sacroiliac arthritis.

Pelvic trauma can involve soft-tissue damage or bone injuries. Bone injuries include pelvic rim fractures (such as an avulsion fracture of the anterior superior iliac spine), fractures of the pelvic ring, and acetabular fractures.

Pelvic ring fractures are divided into three categories according to the condition of the posterior segment of the ring, which is crucial for the biomechanical stability of the pelvis (Table 9.2):

• stable (type A injuries);

• rotationally unstable (type В injuries);

• rotationally and vertically unstable (type С injuries).

There is no universally accepted classification system for pelvic ring fractures. Table 9.2 shows the 1991 version ofthe AO/ASIF classification system as proposed by Pennal etal. (1980). Since then, the AO/ASIF system has undergone further revision. The 1995 version is a combined classification ofthe anterior and posterior pelvic ring. It is designed as an open system, which enables it to encompass a wide variety of pelvic ring injuries and permit precise scientific documentation. The classification of pelvic fractures is in evolution and the literature should be reviewed for more detailed information.

Table 9.1 Arthritis of the sacroiliac joint in rheumatic disorders

Table 9.2 AO/ASIF classification of pelvic ring fractures (1991)

An example of a rotationally unstable pelvic ring injury (i.e., unstable in the horizontal plane) is an isolated rupture of the pubic symphysis caused by an anteroposterior (AP) force in which the anterior ligaments of one or both sacroiliac joints are also torn. Vertical stability of the pelvis is not compromised because the crucial biomechanical posterior ligament connections remain intact. However, shear forces will produce a rotationally and vertically unstable injury (the classic Malgaigne fracture), such as can occur when landing on one leg after a fall from a height.

The system developed by Letournel and Judet (1993) has become the standard for classifying acetabular fractures. The acetabulum is divided into anterior (iliopubic) and posterior (ilioischial) columns. For each of these locally, basic forms of fractures (fracture ofthe acetabular rim, column fracture, and transverse fracture) are distinguished from combined fracture forms, such as a fracture of both columns. This classification was modified by the AO/ASIF according to Table 9.3.

The incidence of pelvic fractures varies between 3% and 10%, depending on the author and patient group. Automobile accidents are cited as the most frequent cause, accounting for 80-90% of all injuries. This is followed by falls from a great height and crush injuries. Injuries to the pelvis and hip represent a relatively insignificant number of athletic injuries, accounting for 2-3% of these injuries. Fatigue fractures in the hip and pelvis are also relatively rare; only about 3% of all fatigue fractures occur as the result of athletic activity.

Pelvic injuries can be categorized according to their cause as extrinsic (externally caused) and intrinsic injuries. The latter are due to forces acting within the body itself and include such injuries as avulsion fractures or muscle tears. In addition to the classic cases of sudden trauma, stress in the form of chronic improper use or overuse can also cause injuries. Examples of this are the rare stress fractures of the pubic bone that can occur in joggers.

Extrinsic soft-tissue injuries include skin abrasions (frequently superficial) and crush injuries at structures such as the iliac crest where the bone is only covered by a thin layer of soft tissue. Blunt trauma in the lateral and posterior pelvis can result in extensive compression ofthe surrounding muscle layers. These injuries may present as broad hematomas (Table 9.4).

Table 9.3 AO/ASIF classification of acetabular fractures (1991)

Table 9.4 soft-tissue injuries in the pelvis

Intrinsic soft-tissue injuries include the numerous types of muscle pulls and tears. Injuries to the adductors are common. Injuries to the proximal portion of the rectus femoris are also observed. In rare cases, tears in the insertions of the iliopsoas can also occur. Minor tears can also occur in the abdominal oblique muscles at the iliac crest, and in the rectus abdominis in the region of the pubic bone (Table 9.4).

The group of extrinsic bone injuries includes traumatic damage to the pubic bone, ischium, sacrum, or coccyx. Extreme trauma can also disrupt the pelvic ring. These injuries are often complicated by associated injuries to neurovascular structures, the urethra, or the bowels (complex pelvic trauma). Less severe injuries of this type include fractures of the coccyx (Table 9.5).

Intrinsic bone injuries (avulsion fractures) are caused by muscular traction on the origin of the apophysis. They frequently occur in teenagers and young adults and primarily involve the anterior superior and anterior inferior iliac spines, the pubic bone, and, rarely, the iliac crest and ischial tuberosity (Table 9.5).

Overuse fractures can also be included among the intrinsic bone injuries. Sites include the pubic bone and, rarely, the ischium and sacrum.

The pelvis may be involved in systemic disorders. These include disturbed calcium and phosphate metabolism that may result from vitamin D deficiency, primary hyperparathyroidism, or renal dysfunction, which itself can lead to secondary hyperparathyroidism. Sequelae of these metabolic changes observed in the pelvic bones include osteomalacia with softening of the bone and structural insufficiency. In children for example, chronic vitamin D deficiency leads to flattening of the pelvis typical of rickets.

Table 9.5 Bone injuries in the pelvis

Another systemic skeletal disorder primarily affecting the pelvis in older patients is Paget disease (osteitis deformans). The cause of this disorder is unclear. Symptoms include “rheumatic” symptoms, spontaneous fractures, and skeletal deformations.

Finally, there are inflammatory disorders (such as osteomyelitis) and tumors. Tumors are often metastatic in origin. Osteoblastic metastases proceed from prostate and breast carcinomas. Osteolytic metastases generally stem from bronchial, thyroid, and kidney carcinomas, occasionally from breast carcinomas. Primary tumors in the pelvic region include chondrosarcomas and Ewing sarcomas.

9.2 Clinical Standard Examination

The tentative diagnosis reached on the basis of clinical examination can be verified or modified by subsequent diagnostic imaging studies (Table 9.6).

Table 9.6 Standard examination procedure

Patient History

Interpreting information from the history is difficult in the presence of pelvic symptoms, particularly where there are atypical chronic symptoms such as groin pain or “diffuse” pelvic pain. The patient should be routinely asked the following questions:

• How long have the symptoms been present and under what conditions did they first occur?

Sudden symptoms in the sacroiliac region that occur with body motion are a sign of sacroiliac joint dysfunction.

• Does the pain occur at rest or during exercise?

What stresses is the patient subjected to?

Irritation of the adductors and iliopsoas in particular can decrease or disappear during exercise. Frequently it can reappear with increased intensity after exercise. Persistent groin pain radiating into the buttocks or thigh can occur following strenuous exertion, for example in distance runners. Groin pain can be a sign of a stress fracture of the ischium, pubic bone, or proximal femur. These fractures are most often encountered in female runners; the history should always include sports activities.

• Does the pain occur independently of exercise?

Does it disturb the patient’s sleep?

Pain occurring independently of exercise or which disturbs the patient’s sleep always suggest a disorder other than trauma or overuse, such as appendicitis, prostatitis, urinary tract infection, kidney disorders, gynecologic disorders, osteomyelitis, or tumors in the pelvis or groin region.

• What is the nature of the pain?

Intermittent episodes of dull pain in the sacrum or lower lumbar region occurring primarily in the morning suggest rheumatic disorders, primarily anky losing spondylitis. If the patient reports these symptoms, you should inquire about pain in other parts of the body, particularly in the joints.

• Where is the pain localized? To where does it radiate?

It is important to determine whether referred pain can be linked to a certain dermatome or area of distribution of a peripheral nerve. The differential diagnosis should consider pathology in the lumbar spine. Nerve roots L1 through S5 are responsible for the sensory supply of the lower extremities, buttocks, and genitals (see Fig.8.40b, p. 311).

Obtaining a history with acute injuries to the pelvis is usually easier. Pelvic injury in an accident usually requires trauma involving significant kinetic energy. The patient will often have multiple trauma so that reconstructing the mechanism of injury will require information from other sources. The patient’s age is significant because the same pelvic injuries may require far less trauma in older patients than in younger patients because of osteoporosis. The risk of associated pelvic and extrapelvic injuries in older patients is higher. Ask patients who are conscious and responsive about blood in the urine or perianal bleeding. These can be important signs of associated injuries to the urogenital system or the bowel. Always inquire about disturbed sensation and/or paralysis in the lower extremities. This can be a sign of injury to the femoral, sciatic, or obturator nerves, or the lumbosacral nerve plexus.

Describing the mechanism of injury (crush injury, fall, or automobile accident) including the direction of forces acting on the pelvis is important for diagnosing acute injuries of soft tissue and bone. In adductor tears or avulsions in the region of the pubic bone, the patient will feel a stabbing pain in the groin at the moment of injury. Adducting the legs will be painful. Adductor tears typically occur with abrupt excessive abduction. Sports such as soccer, ice hockey, skiing, and hurdle events entail an increased risk of these injuries. Such injuries can occur in everyday situations where the patient attempts to avoid a fall. Less frequent causes of avulsion fractures include electrical accidents and tetanus.

The abdominal muscles that insert into the pelvis on the pubic bone (especially the rectus abdominis) are especially prone to tear in overuse injuries from weight lifting, gymnastics, crew, and wrestling.

Physical examination

Observation

Observation of the pelvis begins when the patient enters the examining room. Gait irregularities may be due to:

— pain (Duchenne gait);

— muscular weakness (Trendelenburg sign);

— leg shortening (compensatory limp);

— arthrodesis of the hip (compensation for a fused joint).

In the antalgic gait (Duchenne’s gait), the patient attempts to reduce stress on the painful hip by reducing the stance phase of the affected leg in a typically truncated gait, or by shifting the upper body, and thus the body’s center of gravity, over the affectedjoint in the stance phase.

In the Trendelenburg gait, weakness of the hip abductors causes the pelvis to dip toward the unaffected side in the stance phase, and the patient shifts the upper body over the affected side (see Figs.8.19a, b, p. 302). The stance phase is not as sharply truncated as in an antalgic gait. Bilateral insufficiency of the gluteal musculature produces a typical waddling gait.

In a compensatory limp with leg shortening, the upper body is shifted slightly over the leg in the stance phase. Otherwise, the gait is relatively smooth.

In a gait that attempts to compensate for hip fusion, the increased tilt of the pelvis in the sagittal plane, as it moves from hyperlordosis into lumbar kyphosis, produces femoral anteversion in the swing phase.

For a complete examination, the patient should undress completely (seriously injured patients should be undressed). You should observe the undressing as closely as possible because it can provide important information about possible limited motion in the lumbar and sacral spine and/or painful motion, for example in hip flexion. Evaluate the gait again after the patient has undressed.

Document any skin changes such as external signs of injury (scrapes, contusions, or hematomas), discoloration (for example erythema as a sign of inflammation), congenital skin changes, swelling, penetration, and the position of skin folds. The patient’s underwear may contain residual secretions indicative of associated injuries with pelvic fractures, such is bleeding from the anus and/or urethra.

When inspecting the patient from the front, note the position ofthe anterior iliac spines. Normally they should be at the same level. Deviation can be a sign of pelvic obliquity or a difference in leg length.

Observing the pelvis from the side will give you an impression ofthe inclination ofthe pelvis. Lack of normal lumbar lordosis can be a sign of a spasm in the paravertebral musculature. Hyperlordosis or increased anterior pelvic version can be a sign of insufficiency of the abdominal musculature, of a weakness in the extensors, or of a flexion contracture in the hips.

Observe the contour of the musculature of the buttocks on the posterior aspect ofthe pelvis. Asymmetry in the marginal skin folds can be due to diseases of the hip (developmentally dislocated hip), neuromuscular diseases, or leg-length differences. Patients who are not excessively obese will have two small depressions (“sacral dimples”) superior to the posterior iliac spines (Fig. 8.7, p. 297). Deviation of one of these depressions from horizontal is a sign of pelvic obliquity.

A leg-length difference in trauma patients can be a sign of an unstable injury of the pelvic ring with superior displacement of one hemipelvis, or an ace-tabular fracture with central dislocation ofthe hip.

Palpation and Examination

Palpation may be performed with the patient standing or supine. This will depend on the pattern of injury and the degree to which the patient is impaired.

Both sides should be palpated simultaneously if possible. This provides information about differences in skin temperature or unilateral swelling.

• Examination with the patient standing

When examining the patient from the front, rest both hands on the patient’s waist with your thumbs on the patient’s iliac spines. Place your fingers on the anterior iliac crest. Compare both sides, and note any pelvic obliquity (Fig. 9.1).

Fig. 9.1 Observation and palpation of the position of the anterior pelvis with the patient standing.

Fig. 9.2 Observation and palpation of the position of the posterior pelvis with the patient standing.

To evaluate the position of the pelvis from behind with the patient standing, place your thumbs on the patient’s posterior superior iliac spines. Move your index finger from lateral across the iliac crests (see p. 301). This may be difficult in obese patients. Normally the anterior and posterior iliac spines and the iliac crests will be at the same level (Fig. 9.2).

Figs.9.3a-c
(a) Tensor fasciae latae and iliotibial tract.
(b) Sartorius in relation to the rectus femoris.
(c) Psoas major and iliacus, which together form the iliopsoas.

Painful neuromas may be found in the region of the iliac crests following removal of bone graft since the cluneal nerves can be injured in this procedure.

• Examination with the patient supine

Muscular insertions can be palpated with the patient supine. The tensor fasciae latae is located lateral to the anterior superior iliac spine (Fig.9.3a). The origin of the sartorius is palpable anteriorly (Fig.9.3b). Tenderness to palpation in these regions suggests tenosynovitis at the muscular insertions or an avulsion fracture. The iliopsoas, consisting of the iliacus andpsoas, is located medially. (Fig. 9.3c). The iliacus is palpable in the lateral inguinal canal; the psoas can be palpated through the abdominal wall next to the rectus abdominis. Have the patient flex his or her legs to relax the abdominal wall. This will make it easier to palpate the psoas. Overexertion from lifting weights with simultaneous deep knee bends or intensive kicking practice in football or soccer can produce irritation of the psoas that presents as tenderness to palpation. A tear or bursitis of the insertion of the iliopsoas produces tenderness to palpation at its insertion on the lesser trochanter. The anterior inferior iliac spine lies inferior to the anterior superior iliac spine. This is where the rectus femoris has its origin (Fig. 9.3b). It can also be irritated by overuse (for example in kicking practice, frequent sprinter starts, or weight training), torn, or even injured in an apophyseal fracture or avulsion fracture. Apophyseal fractures most frequently occur in adolescent athletes. An unrecognized fracture or malunion can result in thickened callus that can simulate a tumor. In relatively rare cases, this in turn can produce local pain or compressive neuropathy in what is referred to as entrapment syndrome.

Fig. 9.4 Position of the hip in relation to the most important neurovascular structures in the groin.

The hip lies at the intersection of the inguinal ligament and the femoral artery (Fig. 9.4). It is not directly accessible to palpation. Tenderness in this region may be regarded as a sign of hip pathology. Swelling proximal to the inguinal ligament suggests an inguinal hernia; swelling distal to it may be a sign of a femoral hernia. Examination of the hernial orifices (Fig. 9.5a) and palpation of the inguinal canal (Fig.9.5b) with the patient standing or supine is indicated whenever swelling is present. The differential diagnosis should exclude swelling of an inguinal lymph node. Exploration of the inguinal region includes palpation of the femoral artery. Its pulse is normally palpable midway between the anterior superior iliac spine and the pubic tubercle. A weakened pulse in trauma patients can be a sign of vascular injury.

Figs.9.5a, b
(a) Location of the three different hernial orifices in the right groin.
(b) Palpation of the inguinal canal with the patient standing or supine. Instruct the patient to bear down or cough after you insert your finger.

Fig. 9.6 Palpation of the pubic symphysis and the pubic tubercle with the patient standing.

Fig. 9.7 Positions of the various hip adductors relative to each other.

The pubic symphysis or the pubic tubercle can be palpated anteriorly at the level of the trochanters with the patient supine or standing (Fig. 9.6). Note whether the two pubic tubercles are level with each other. Displacement can occur in a rupture of the pubic symphysis. Physiologic painful loosening occurs during pregnancy. Since the rectus abdominis also inserts here, the area will be tender to palpation when the muscle is irritated. Another cause of pain can be inflammation of the pubic symphysis. This is most often due to overuse, but can also be caused by infection. The pectineus inserts lateral to the pubic tubercle; the adductor longus and brevis insert infe-riorto it (Fig. 9.7). Tears in these muscles produce significant swelling inferior to the pubic bone from the contracted muscle belly and often a hematoma; they also leave a depression at the pubic bone.

Important examination sites on the posterior pelvis in the lateral position and prone position include the ischial tuberosity, sacroiliac joint, posterior hip musculature, sacrum, and coccyx.

The ischial tuberosity is located approximately at the level of the gluteal folds. It is the origin of the hamstrings, which include the semitendinosus, semimembranosus, and long head of the biceps femoris (Fig. 9.8). Since it is difficult to palpate with the hip in extension when the patient is standing, this part of the examination is best performed with the patient in a lateral position with the hip flexed (Fig. 9.9). Here too, tenderness to palpation suggests a tendon disorder, bursitis, or an apophyseal avulsion fracture.

The sciatic nerve lies midway between the ischial tuberosity and the greater trochanter. It is palpable with the patient prone or in the lateral position. It may also be palpable when the hip is flexed since this moves the gluteal musculature superiorly (Fig. 9.10). Irritation of the nerve such as can occur with a prolapsed intervertebral disk or as a direct sequela of trauma can produce extreme tenderness to palpation at Valleix’s points (see p. 306). It is important to differentiate the sciatic nerve from the ischial tuberosity, since bursitis there can produce similar pain which can lead to misdiagnosis.

Arthritic, inflammatory, or traumatic changes in the sacroiliac joints can manifest themselves in local tenderness to palpation. Palpate the prone patient with both hands. Move your thumbs from lateral across the posterior iliac spine to the midline in the depression between the iliac spine and the median sacral crest. Palpate the entire length of the joint on both sides for comparison.

There are a number of tests to further evaluate sacroiliac joint dysfunction (see section 8.3). These can be performed with the patient standing, supine, or prone and include:

•  Standing :

Test for pathologic anterior movement of the posterior iliac spines when the patient bends over Spine test

•  Prone :

Mennell’s first sign

Three-step test

Shaking test

•  Supine:

Patrick’s four-point sign

Mennell’s second sign

Elasticity test

Leg-length changes.

The greater part of the outer contour of the posterior pelvis is defined by the gluteus maximus (Fig. 9.8). This is best palpated with the patient prone. Instruct the patient to press the buttocks together. Palpate with both hands, noting tone, size, and form. Palpating the muscles while they are tensed and relaxed will reveal hematomas or abscesses (for example from intramuscular injections). These pathologic changes are often not visible in their initial stages.

• Examination of the injured patient

Some of the examination procedures described above are very specific and time consuming. The preliminary examination following severe trauma with suspected pelvic fracture must be performed quickly. The purpose of this examination is to establish the severity of pelvic instability (Figs. 9.11 a, b). Examine the patient with both hands, applying lateral compression to the iliac wings and anterolateral or AP compression to reveal any abnormal mobility of the two halves of the pelvis. Palpate the injured hemipelvis while carefully applying traction or compression to the ipsilateral leg to determine vertical instability. Comparative palpation of the posterior iliac spines will reveal posterior instability of one hemipelvis. A palpable gap in the pubic synthesis may be seen if it is ruptured and the patient is not overly obese. Pain to compression of the hip can be a sign of an acetabular fracture. Avoid abrupt manipulation, particularly if the patient is conscious.

Fig. 9.8 Diagram of the hamstrings in relation to the gluteus maximus.

Rectal and vaginal examination must be performed. This can reveal injuries of the rectum or urogenital system. Perforation of the vaginal or rectal wall is a sign of an open fracture of the pelvic ring. Lack of blood on the palpating finger means that injury to the lower rectum or vagina can be largely excluded. Vaginal injury must not be confused with menstrual bleeding. Evaluate sphincter tone during the rectal examination. Sphincter dysfunction or caudal symptoms suggest a sacrum fracture. Rectal examination should also be performed for direct trauma such as a fall on the buttocks to exclude deformities in the coccygeal region (Fig. 9.12).

Fig. 9.9 Palpation of the right ischial tuberosity with the patient in a left lateral position with the ipsilateral hip flexed.

Fig. 9.10 Palpation of the sciatic nerve with the patient in a left lateral position. The sciatic nerve can occasionally be palpated midway between the ischial tuberosity and the greater trochanter when the hip is flexed.

Figs. 9.11 a, b Lateral (a) and anterior to posterior (b) compression is applied to provoke pain in the supine patient with a pelvic fracture.

Fig. 9.12 Rectal examination of the coccyx and sacrococ-cygeal joint with the patient in a lateral position.

Urethral tears in males are characterized by abnormal mobility or superior displacement of the prostate. In the examination, the prostate or its tip will be palpable in the middle of a “rubbery” hema-toma displaced toward the abdominal cavity. Frequently cited in the literature, this sign of a superiorly displaced prostate may be difficult to ascertain, especially in young patients due to the small size of the prostate. Often the nature of the injury will prevent optimum positioning for rectal palpation with the hip flexed. Blood at the urethral meatus or an abnormal prostate examination dictate that a retrograde urethrogram has to be performed before the urethra is instrumented with a catheter.

Functional Examination

Aside from the hips, there are no true joints in the pelvis. The sacroiliac joints and the pubic symphysis are articulations with limited motion.

However, there are a few functional tests that provide information about injuries to the pelvis and the musculature inserting into it.

Painful limitation of adduction against resistance with the legs extended or complete loss of adduction are signs of irritation or a tear in the muscles responsible for this motion. Flexing the hip against resistance is painful if the iliopsoas or the adjacent bursa is injured. If extending the knee also produces groin pain, this can be a sign of a proximal injury to the rec-tus femoris. Pain or limited motion experienced when raising the upper body from a supine position with the hips in 90° flexion combined with pain in the pubic bone suggests an abdominal muscle tear.

The nature and diagnosis of sacroiliac joint dysfunction has been discussed in the section Palpation and Examination.

Neurovascular Examination

As already mentioned, pelvic injuries, tumors, and inflammation can cause nerve irritation or injury. For this reason, examination of the pelvis should also include preliminary neurologic examination as discussed in Chapter 8, p. 309. This examination is of little use in patients with an endotracheal tube in place.

Always palpate the peripheral pulses. Lack of a peripheral pulse in the legs can be a sign of vascular injury as a result of pelvic trauma, for example injury to the iliac or femoral artery.

9.3 Radiology

Indications, Diagnostic Value, and Clinical Relevance

Radiographs of the pelvis are mandatory diagnostic imaging studies. The plain pelvic radiograph is the starting point for diagnostic evaluation. It provides an overview of the entire pelvis and provides a basis for any subsequent special views that may be required.

Figs.9.13a,b Plain pelvic radiograph with the patient standing (a) and supine (b). When positioned supine, the patient is disrobed with the knees extended and the feet internally rotated about 15°. The central ray is aimed directly at the center of the pelvis.

Fig. 9.14 Schematic diagram of the bony structures in the region of the acetabulum in the plain AP pelvic radiograph. 1 iliopectinal line, 2 ilioischial line, 3 Kohlerös teardrop figure, 4 acetabular roof, 5 anterior rim of the acetabulum, 6 posterior rim of the acetabulum.

Fig. 9.15 Ferguson view of the pelvis. The patient is positioned supine and disrobed with the knees extended and the feet internally rotated 15°. The central ray is aimed directly at the center of the pelvis, and the X-ray tube is tilted cranially 30°-35°.

Standard Views

AP plain pelvic radiograph: The patient is undressed and stands with his or her back to the film cassette. The knees are extended, and the feet are internally rotated about 15°. Any leg-length difference should be compensated. The central ray is aimed at the middle of the pelvis; gonad protection should be used if possible (Fig. 9.13a). This examination may also be performed with the patient supine (Fig. 9.13b); this will often be necessary in trauma patients. The plain pelvis radiograph visualizes both ilia, the sacrum, pubic bone, coccyx, and the proximal femur. It provides information on fractures of the pelvis, proximal femur, femoral neck, and trochanteric region. It also reveals signs of inflammatory processes and osteo-lytic or osteoplastic changes. The AP pelvic radiograph is not always sufficient for evaluating the entire sacrum, sacroiliac joints, and acetabulum (Fig. 9.14). Often either a PA view (with or without tilting of the X-ray to 3 0 °-3 5 ° caudally) or a Ferguson view will be required.

Ferguson view: For this view, the patient is positioned supine as for the plain AP radiograph of the pelvis. The difference is that the X-ray tube is inclined cranially 30°-35°. The central ray is aimed at the center of the pelvis (Fig. 9.15). This technique provides the examiner with a tangential view of the sacroiliac joints and the sacrum, and it visualizes the pubic bone and coccyx.

Fig. 9.16 Plain pelvis radiograph showing bilateral anterior fractures of the pelvic ring and a sacroiliac fracture dislocation on the left.

Fig. 9.17 Plain pelvic radiograph showing a left acetabular fracture (central hip dislocation).

Fig. 9.18 Plain pelvic radiograph showing rupture of the pubic symphysis and the right sacroiliac joint (Type C1.2 according to the AO/ASIF classification, corresponding to the CT scan in Fig. 9.48, p. 442).

Fig. 9.19 Plain pelvic radiograph. The fracture of the anterior roof of the acetabulum is only clearly discernible in the CT scan (Fig. 9.47), but not in the plain pelvic radiograph, the iliac wing view (Fig.9.36a), or the obturator view (Fig.9.34a).

The goal of this technique is to provide better information on possible injuries to the sacrum, pubic bone, and coccyx.

Abnormal Findings

• Changes due to trauma

The plain pelvis radiograph provides a good overview where there are multiple fractures of the pelvis (Fig. 9.16). However, it does not reliably image injuries of the acetabular region (Fig. 9.17) or the sacroiliac joint (Fig. 9.18). With acetabular fractures (Fig. 9.19), one is often surprised by the extent of the injury. Special views, and CT scans in particular, are mandatory in such cases (see section Special Views and Computed Tomography).

• Tumors

A chondrosarcoma is defined as a malignant neoplasm derived from cartilage cells. It can develop on an existing endochondroma or a cartilaginous exosto-sis. A primary form also exists. When the tumor develops from the center of a bone, it is known as a central chondrosarcoma. Tumors that spread from the surface of a bone are referred to as periosteal chondrosarcomas. These must be distinguished from periosteal osteosarcomas. Fifty percent of chondrosarcomas discovered are found in the pelvis and proximal femur. Men are affected by the primary form twice as often as women. The disorder most often occurs above the age of 30.

Fig. 9.20 Partial plain pelvic radiograph. The lateral aspect of the left iliac wing shows an irregularly demarcated dense bony deposit. A calcified structure is also discernible lateral to the acetabular convexity, which at least in the plain film is not in direct contact with the pelvic bone. This was diagnosed as a chondrosarcoma.

In the radiograph, the chondrosarcoma typically appears as an osteolytic tumor with cortical destruction and varying degrees of matrix ossification (Fig. 9.20).

Fig. 9.21 Plain pelvic radiograph showing bone destruction with a moth-eaten appearance at the sacroiliac joint involving the adjacent portion of the sacrum. This was diagnosed as a Ewing sarcoma.

Fig. 9.22 Partial plain pelvic radiograph. The bone structure of the right acetabulum and the ilium largely shows pathologic changes; the normal bone structure is no longer present. “Cloudy” areas of sclerosis are present. This was diagnosed as an osteosarcoma.

Ewing sarcoma occurs primarily in children and adolescents. It is highly malignant. Ewing’s sarcoma is thought to proceed from bone marrow cells. One of the most frequent sites is the pelvis. In radiographs, it can appear as moth-eaten destruction of bone with an associated periosteal reaction and a large soft-tissue mass. This soft-tissue mass may be the main characteristic (Fig. 9.21).

Osteosarcoma represents one of the most frequently encountered primary bone tumors. All types are characterized by malignant cells that form osteoid and bone matrix. This tumor most frequently develops between the ages of 10 and 20 (as a primary osteosarcoma). Men are affected slightly more often than women. This tumor can occur in different forms : as an osteolytic osteosarcoma, an osteoblastic osteosarcoma, or as a combined form. Its radiographic appearance varies. The classic appearance is moth-eaten areas of osteolysis with islands of osteosclerotic foci. The demarcation of tumor from healthy surrounding tissue is ill-defined. Periosteal reactions such as formation of spicules or layered bone remodeling are frequent associated findings (Fig. 9.22).

Giant-cell tumors are locally aggressive bony changes containing histologic osteoclastic giant cells. Occurrence in the pelvis is atypical. Women between the ages of 20 and 40 are most frequently affected; the ratio of women to men is 2: 1. These tumors appear in radiographs as purely osteolytic areas without a sclerotic halo (Fig. 9.23).

An aneurysmatic bone cyst in the pelvis is rare. It can develop on a chondroblastoma, osteoblastoma, giant-cell tumor, or in fibrous dysplasia, or it can appear in the absence of existing changes. Most often these cysts occur before the age of 20. Usually several cysts will be found together. The tumor tends to expand (Fig. 9.24).

Fig. 9.23 Partial plain pelvic radiograph. A typical sharply delineated area of osteolysis without a sclerotic halo in the right ilium adjacent to the sacroiliac joint. This was diagnosed as giant-cell tumor.

There are many tumors that can metastasize into the skeleton. These include lung, breast, prostate, and kidney cancer. Several of these tumors produce both osteoblastic and osteolytic metastases (Figs. 9.25-9.28).

Fig. 9.24 Partial plain pelvic radiograph. Extensive polycystic lesions with destruction of the right iliac wing. Secondary findings include multiple vascular clips in situ following a kidney transplant. This was diagnosed as aneurysmatic bone cysts (corresponds to Figs. 9.51 a, b, p. 443).

Fig. 9.25 Plain pelvic radiograph showing diffuse bony metastases of a breast carcinoma of mixed osteolyticosteoblastic type (corresponds to Figs. 8.139a, b, p. 353).

Fig. 9.26 Plain pelvic radiograph showing multiple irregular areas of increased bone density, some extensive, throughout the entire visualized portion of the pelvic including both proximal femurs and the sacrum. This was diagnosed as osteoblastic metastases of a breast carcinoma.

Fig. 9.27 Plain pelvic radiograph showing decreased bone density superior to the left acetabulum in the lateral ilium without sharp demarcation. This was diagnosed as osteolytic metastases of an adenocarcinoma (prior to chemotherapy).

Fig. 9.28 Plain pelvic radiograph. In contrast to the image in Fig. 9.27, the previously osteolytic areas appear as sclerotic areas of dense bone after chemotherapy.

Fig. 9.29 Plain pelvic radiograph in a 26-year-old female patient. Extensive dense or sclerotic area extending to the acetabulum is visible in the left iliac wing. This was diagnosed as chronic osteomyelitis, although neoplasms can have the same radiographic appearance.

Fig. 9.30 Plain pelvic radiograph showing ankylosis of both sacroiliac joints, traction osteophytes at muscle insertions, and osteoarthritis of the right hip. This was diagnosed as ankylosing spondylitis.

• Other changes

Osteomyelitis. The signs of acute osteomyelitis in plain radiographs include destruction of cortical bone and bone marrow, periosteal reactions, and the presence of bone sequestrae. Chronic osteomyelitis is discernible as an area of dense bone (Fig. 9.29).

Ankylosing spondylitis. Typical changes in the pelvis in ankylosing spondylitis (Bechterew disease) include ankylosis of both sacroiliac joints and traction osteophytes at the muscular insertions. Chronic osteoarthritis of the hip can develop when the large joints are involved (Fig. 9.30).

Fibrous dysplasia. This disorder involves fibrotic changes in bone that belong to the group of developmental dysplasia disorders. The monostotic form most frequently occurs in the femur, followed by the tibia and ribs. It develops in the center of the bone and then spreads to the marrow. The higher the proportion of fiber in the bony changes, the more radiolucent they will appear. In contrast to the polyostotic form, this form of the disorder is often an incidental finding.

The polyostotic form is a significantly more aggressive disorder. It primarily involves the pelvis, followed by the long cortical bones, skull, and ribs. The disease is progressive until the skeleton matures. Foci usually increase in size and number. In 95% of all cases, these foci do not change after growth has ceased. The typical complication is a pathologic fracture. It is often combined with skin changes, particularly cafe-au-lait spots. The radiographic appearance of fibrous dysplastic foci depends on the relationship and distribution between the connective-tissue and bony components. Bubble-like honeycomb cystic patterns can appear. These are usually sharply demarcated from the surrounding bone by a sclerotic halo. The bone can be greatly distended with thinning of the cortex, particularly in the polyostotic form of the disorder (Fig. 9.31).

Fig. 9.31 Partial plain pelvic radiograph showing areas with loss of trabecular structure in the cancellous bone. The lesions have a “ground glass” appearance. Areas of increased sclerosis are also seen. This was diagnosed as fibrous dysplasia.

Paget disease. This is a chronic progressive dysfunction of bone homeostasis where osteoclastic and oste-oblastic functions become uncoupled. Its precise cause is not known. Usually the disease occurs between the ages of 45 and 55. Men are most often affected; the ratio of men to women is 3: 2. The pelvis is most frequently involved, followed by the femur, skull, tibia, vertebrae, clavicle, humerus, and ribs. Three radiographic phases are differentiated (Fig. 9.32):

1. Osteolytic or hot phase: This involves bone resorption in the form of a radiolucent wedge, which is also referred to as a “candle flame” because of its shape.

Fig. 9.32 Plain pelvic radiograph showing diffuse increase in bone density in the right hip. This was diagnosed as Paget disease. Incidental findings included a radiodense metallic structure projected on the right sacrum, consistent with a projectile (such as a pistol bullet).

2. Intermediate phase: In addition to bone destruction, the onset of bone remodeling is also discernible. This appears on the radiograph as a widening of the cortex. The cancellous bone shows a course trabecular pattern.

3. Cold phase: The bone now shows a diffuse increase in density. It also appears widened and enlarged; the cortex and the border between cortex and cancellous bone is indistinct.

Deformation of the bone can also occur. Complications of Paget disease include secondary osteosarco-mas and high-output cardiac failure.

Special Views

These studies provide imaging of those areas that are not well visualized on standard views. The advent of CT scanning has lessened the utility of some of these studies.

Judet Views (Obturator and Iliac Wing Views)

The extent of an acetabulum fracture is often underestimated on the plain pelvis radiograph. Overlapping shadows of bone structures make it very difficult to imagine the three-dimensional structure of a fracture. These two perpendicular oblique views of the hip permit better orientation in determining the course of a fracture.

Anterior (internally rotated) view or obturator view. The patient is positioned supine with the body rotated 45° toward the contralateral side. A wedgeshaped cushion is usually placed under the side of interest to stabilize the patient in this position. The central ray is aimed at the affected hip (Figs. 9.33a–c).

This exposes the obturator foramen. Fractures of the anterior (iliopubic) column of the hip and the posterior rim of the acetabulum can be demonstrated in this view (Figs. 9.34a, b).

Figs. 9.33a-c Judet view (anterior oblique view or obturator view). Patient positioning:
(a) oblique supine position.
(b) The patient is turned 45° to the contralateral (unaffected) side. A wedge-shaped cushion is usually placed under the affected side to stabilize the patient in this position.
(a, c) The central ray is aimed at the affected hip.

Posterior (externally rotated) view or iliac wing view. In contrast to the anterior view, the patient is rotated 45° toward the affected side, and the contra-lateral side is supported with a wedge-shaped cushion. The central ray is again aimed at the affected hip (Figs.9.35a-c).

Figs. 9.34a, b Judet view (anterior oblique view or obturator view). Patient positioning:
(a) Plain radiograph corresponding to Figs. 9.19, 9.36a, and 9.47.
(b) Schematic diagram of the obturator view: 1 anterior column, 2 posterior column.

The full width of the iliac wing is visualized. The posterior (ilioischial) column of the hip and the anterior acetabular margin, projected far laterally, are clearly visible (Figs. 9.36a, b).

Figs.9.35a–c Judet view (posterior oblique view or iliac wing view). Patient positioning:
(a) Oblique supine position.
(b) The patient is turned 45° onto the affected side. A wedge-shaped cushion is usually placed under the affected side to stabilize the patient in this position.
(a, c) The central ray is aimed at the affected hip.

Inlet and Outlet Views According to Pennal and Tile

Inlet and outlet views of the pelvis described by Pennal and Tile provide information in injuries to the pelvic ring. These two projections are approximately perpendicular to each other.

Figs. 9.36a, b Judet view (posterior oblique view or iliac wing view).
(a) Plain radiograph corresponding to Figs. 9.19, 9.34a, and 9.47.
(b) Schematic diagram of the iliac wing view: 1 posterior column, 2 anterior acetabular rim.

Inlet view. The patient is supine with the central ray aimed caudad at the middle of the pelvis at an angle of approximately 45° to the film cassette. In this position, the central ray is approximately perpendicular to the pelvic inlet and parallel to the plane of the sacrum (Fig. 9.37). This view best demonstrates the ring configuration of the pelvis; any narrowing or widening of the diameter of the pelvic ring will immediately be apparent. The inlet projection is also the best projection for visualizing posterior dislocation of one hemipelvis (Figs.9.38a, b). Internal or external rotation of one hemipelvis will be readily visible.

Outlet view. With the patient positioned supine, the central ray is angled cephalad 45° to the film cassette and aimed at the pubic symphysis, perpendicular to the plane of the sacrum (Fig. 9.39). The full length of the sacrum is visible, as are the sacral foramina. The anterior pelvic ring is superimposed over the posterior pelvic ring in this tangential view. This projection demonstrates superior or inferior dislocations (Figs.9.40a,b).

Fig. 9.37 Inlet view of the pelvis. The patient is supine with the central ray aimed caudad at the pelvis at an angle of approximately 45° to horizontal.

Figs. 9.38a, b Inlet view of the pelvis.

Fig. 9.39 Outlet view of the pelvis. The patient is supine with the central ray aimed cephalad at the pelvis (pubic symphysis) at an angle of approximately 45° to horizontal.

Figs.9.40a, b, Outlet view of the pelvis.
(a) Dislocation fracture through the left ilium (sacroiliac fracture dislocation). The posterior displacement of the left hemipelvis is readily visible.
(b) Schematic diagram of an inlet view of the pelvis in a fracture of the left sacrum.

Risser View

This view is used to visualize the iliac crests to determine skeletal age (Fig. 8.165 [see p. 368] and Table 9.7). The patient is supine with the hips and knees flexed to reduce the lumbar lordosis. Gonad protection should be used. The cassette is placed beneath the iliac crests, and the ray is aimed at them (Figs. 9.41).

Figs. 9.41 Risser view of the pelvis. The patient is supine with the hips and knees flexed. The central ray is aimed at the iliac crests.

Fig. 9.42 PA symphysis view. The patient stands facing the film cassette with the pubic symphysis against its surface. The central ray is aimed at the pubic symphysis.

Table 9.7 Risser stages (see Fig.8.165, p. 368)

Symphysis Views

PA symphysis view. The patient stands facing the film cassette with the symphysis against its surface. The symphysis is palpated and marked posteriorly. The ray is aimed at the pubic symphysis (Fig. 9.42).

Craniocaudal symphysis view. The patient leans back from a sitting position on the table and with the legs extended and the arms supporting the upper body. The film cassette is beneath the symphysis, and the central ray is aimed at the palpable aspect of the symphysis. The patient exhales and holds his or her breath as the image is taken (Fig. 9.43).

Symphysis stress view. The patient stands on one leg facing the film cassette with the pubic symphysis in contact with the film cassette. Instability will create a step-off in this view that must be compared with the normal PA view (Figs. 9.44, 9.45a, b).

Similarly, chronic posttraumatic pelvic instability can be revealed in plain pelvic radiographs as abnormal mobility of one hemipelvis as the patient stands alternately on each leg.

Fig. 9.43 Craniocaudal symphysis view. The patient sits on the table and leans back with the legs extended and the arms supporting the upper body. The image is obtained after the patient exhales. The central ray is aimed at the pubic symphysis.

Tomography

Tomographie images are helpful in evaluating the extent of the fracture line and the position of the fragments in a trauma setting. They are also suitable for demonstrating the size and proliferation of masses or inflammatory processes. The projection used depends on the region of interest.

Conventional tomography has largely been replaced by the use of CT scans.

Angiography

Conventional angiography or digital subtraction angiography (DSA) can be useful, particularly in the evaluation of tumors. The main vessel supplying the region of interest is catheterized, and the catheter is advanced under fluoroscopic control. Contrast medium is injected when it reaches the affected area. This permits precise evaluation of the vascular regions supplying the area. DSA uses special algorithms to remove superfluous visual information from digital images to obtain more precise or isolated visualization of the vascular structures. In orthopedies, this technique is used primarily in tumor surgery (Fig. 9.46). In a trauma setting, it can provide important information about possible associated vascular injuries. In pelvis fractures, it can also be used for selective embolization of injured vascular structures, such as the branches of the internal iliac artery.

Fig. 9.44 Stress view of the pubic symphysis. The patient stands alternately on the left and right leg while facing the film cassette with the pubic symphysis against the surface of the cassette. The central ray is aimed at the pubic symphysis.

Figs. 9.45a, b Stress view of the pubic symphysis in a 51-year-old female patient with osteomyelitis of the left sacroiliac joint. Instability in the left sacroiliac joint resulted after extensive surgical excision. This is demonstrated in the stress views (left and right single-leg stance), which show motion at the symphysis.

Fig. 9.46 An angiogram demonstrating the vascular supply to an osteosarcoma in the right iliac wing. Notable findings include an extensive irregular vascular network with abrupt changes in vascular diameter.

Retrograde Urethrocystography

In pelvic trauma, the urethra and bladder can be visualized with a water-soluble contrast medium in retrograde Urethrocystography, permitting diagnosis and evaluation of injuries to the urethra and/or bladder. Contrast-medium leakage will be seen in injuries. A bladder tear will appear as a more or less diffuse leakage of contrast medium into the peritoneum or pre-peritoneal space depending on the severity of the injury. In an extraperitoneal tear, this will typically appear as a “teardrop bladder.” In a pelvic fracture, the teardrop form of the bladder in a cystogram can also be due to extravasated blood and/or urine (urinoma) and is not necessarily a characteristic sign of an extraperitoneal tear. In a tear, contrast medium will also leak from the bladder; otherwise the teardrop shape will be formed by the surrounding hematoma. A complete periprostatic tear of the intrapelvic urethra with superior displacement of the bladder will produce a high-riding bladder syndrome.

9.4 Ultrasound

Indications, Diagnostic Value, and Clinical Relevance

Ultrasonography of the pelvis is of limited importance. Soft-tissue injuries can be diagnosed. These include hematomas or inflammatory masses, such as an abscess from an injection. Ultrasound may conceivably be used to diagnose muscle tears in the adductors, or for diagnosing instability of the pubic symphysis.

Ultrasound studies of the abdomen can be performed on trauma patients with pelvic fractures to diagnose associated injuries, particularly ruptures of the spleen or liver (abdominal and pelvic trauma).

9.5 Nuclear Medicine Studies

Nuclear medicine studies of the pelvis are discussed in conjunction with nuclear medicine studies of the spine in Chapter 8, p. 380.

9.6 Computed Tomography

Indications, Diagnostic Value, and Clinical Relevance

Computed tomography (CT) is the preferred diagnostic imaging modality after plain radiography in the diagnosis of fractures or tumors. Compared to conventional radiographs, CT permits detailed, unobstructed visualization of deeper-lying bone structures such as the sacrum or sacroiliac joints. Superimposed intestinal gas, which can greatly complicate the interpretation of conventional radiographs, does not influence CT imaging. Physicians can obtain three-dimensional reconstruction from the CT images. This representation of the fracture or tumor may then be used for preoperative planning. These reconstructions allow the surgeon to verify the involvement of ace-tabulum and femoral head, the position of the fragments, or the presence of intra-articular loose bodies or fragments following acetabular fractures or hip dislocations. CT is especially useful after trauma to the sacrum or sacroiliac joints. The sensitivity of CT lies between 85% and 100% for evaluating the sacrum and sacroiliac joint, ilium, roof of the acetabulum, posterior rim of the acetabulum, pubic rami, or intra-articular loose bodies, depending on slice thickness. Its specificity is 100%o in all of these cases.

Technique, Instrumentation, and Examination Procedure

The patient is symmetrically positioned on the CT examining table to permit accurate comparison of both sides in the slice images. A preliminary scan is obtained to aid in selecting the area of interest. Next the CT slice images are obtained. A slice thickness of 5-10 mm is adequate for many tumors or fractures. Acetabular fractures are an exception since they may involve intra-articular loose bodies. In this case and with smaller bone or soft-tissue tumors, one should select a slice thickness not greater than 3-5 mm. If two-dimensional or three-dimensional reconstruction is planned, the slices should be 1-2 mm thick. Slice thicknesses of 2 mm are preferred in these cases to protect the patient against excessive radiation exposure.

Intravenous contrast medium can be used to obtain information about the vascularization of neoplasms. Decisions about slice thickness, reconstructions, and contrast must be discussed with the consulting radiologist.

Abnormal Findings

Changes Due to Trauma

CT of the pelvis provides more precise information about the presence, location, and relationship of fragments to each other than can conventional radiography (Fig. 9.47). Injuries of the sacroiliac joints are often difficult to determine on plain radiographs. CT permits detection of even minor injuries or diastasis. Contralateral comparison in axial images is especially helpful (Fig. 9.48). Plaster casts do not degrade images. A further advantage is that CT examinations require only minimal movement of trauma patients.

Three-dimensional reconstruction permits precise visualization of fracture fragments. This is important for proper treatment of the fracture (Figs.9.49a–c).

Even chronic injuries to the pelvis can be visualized in CT scans. The additional information provided by the CT examination can be clearly seen in an avulsion fracture of the anterior superior iliac spine (Figs.9.50a, b). A plain pelvis radiograph would not have been sufficient to evaluate the shape and extent of bony structures at the anterior superior iliac spine following an avulsion fracture.

Tumors

The advantages of CT apply to diagnosing tumors. In addition to providing unobstructed visualization, CT scans also make it easier to diagnose discrete cortical destruction, endosteal changes, and minor matrix calcifications. This provides more information about the size of the tumor, and it also helps to identify the type of tumor. The use of intravenous contrast permits limited evaluation of tumor components extending beyond the bone, and it can demonstrate the size of necrotic areas and the relationship of the tumor to vascular structures.

Fig. 9.47 CT of the pelvis in the transverse plane. The fracture fragment is only clearly identifiable in the CT scan (corresponding to Figs. 9.19, 9.34a, 9.36a).

Fig. 9.48 Axial CT of the pelvis showing disruption of the right sacroiliac joint (corresponding to Fig. 9.18, p. 430).

Figs. 9.49a-c Plain pelvic radiograph and CT reconstruction.
(a) Radiograph showing fracture of the left pelvis involving the acetabulum.
(b, c) Three-dimensional CT reconstruction of the same fracture.

The advantages of CT over conventional radiography in diagnosing are seen in Figures 9.51 a and b, which show an aneurysmal bone cyst. The CT slices of the pelvis were obtained from the same patient as the plain pelvic radiographs in Figure 9.24. This patient had received a renal transplant 8 years prior to the occurrence of the tumor. In addition to showing the topographic relationship of the tumor to the organs, the CT demonstrates the typical tumor structure (i.e., polycystic andproliferative).

Figs. 9.50a, b
(a) Partial plain pelvic radiograph.
(b) Axial CT scan of the pelvis in a 16-year-old patient showing a chronic avulsion of the anterior superior iliac spine. Bone remodeling has produced a mass that could be confused with a tumor if the history or initial films were unknown. This can produce symptoms by irritating adjacent neurovascular structures. In contrast to plain radiography, the CT image precisely demonstrates the shape and size of the mass.

Figs. 9.51 a, b Axial CT scan of the pelvis. The images show an extensive, relatively sharply demarcated mass in the left ilium that anteriorly displaces the pelvic organs and soft tissue. The slices show the relationship of the tumor to adjacent structures and demonstrate its polycystic structure. This was diagnosed as an aneurysmai bone cyst (corresponding to Fig. 9.24, p. 432).

9.7 Magnetic Resonance Imaging

Indications, Diagnostic Value, and Clinical Relevance

Magnetic resonance imaging (MRI) has become an important modality for the evaluation of soft-tissue and bony structures in the pelvis in recent years. Its particular advantage lies in its ability to detect inflammatory changes and tumors at an early stage. It is the only method aside from nuclear medicine studies that can detect occult fractures.

Technique, Instrumentation, and Examination Procedure

Since the pelvis is a large region of the body, a body coil is frequently used. However, surface coils may be used under certain circumstances to image smaller areas. The coil images major vascular structures including the aorta, common iliac artery, internal and external iliac arteries, inguinal artery, and femoral artery. Pulsatile motion of these vascular structures can produce ghosting. Other motion artifacts may be caused by breathing or intestinal motion and can interfere with the image similarly to pulsatile ghosting.

Enteral administration of contrast media is helpful for distinguishing the bowel from other softtissue structures. Intravenous administration of gadolinium-DTPA is particularly useful in demonstrating and identifying tumors as benign or malignant, but it can also be helpful in evaluating infiltra-tive processes such as the spread of a prostate carcinoma to the wall of the bladder.

The slice thickness depends on the required degree of detail. Differentiating postoperative conditions, residual tumor tissue, and recurrent tumors is a particular problem. As with other diagnostic imaging modalities, regular follow-up examinations are frequently necessary. The imaging plane should also be chosen according to the pathology and anatomy. Coronal oblique imaging planes in addition to oblique transverse planes are needed for evaluating sacral processes. Processes in the inguinal canal frequently require an oblique sagittal imaging plane.

Abnormal Findings

Occult Fractures and Changes Due to Trauma

Common pelvic fractures are easily visualized using radiographic methods, i.e., plain radiography or CT. With the introduction of MR1, bone changes that escape detection in radiographic studies were described. These are referred to as occult fractures (Figs. 9.52a, b). In addition to cancellous fractures due to metabolic dysfunction, these findings can theoretically include changes in bone metabolism resulting from impaired perfusion or remodeling processes due to biomechanical dysfunction. These changes are visible especially in fat-suppressing pulse sequences. These findings may be diffuse. There is never a visible cortical lesion with these changes.

Figs. 9.52a, b MR images of the pelvis.
(a) SE 500/20 in the coronal plane showing reduced signal intensity in the right side of the sacrum.
(b) STIR 1900/125 in the coronal plane showing increased signal intensity in the sacrum. The change does not extend beyond the margins of the bone. Signal intensity is also slightly increased lateral to the right foramen between S1 and S2. This was diagnosed as a contusion of the right side of the sacrum following a fall. The corresponding plain pelvic radiograph was normal.

Tumors

Differentiating between benign and malignant bone tumors is difficult in MR images. Characteristics such as sharp demarcation, a purely tissue-displacing pattern of growth, and homogeneous signal behavior suggest a benign tumor, although some malignant tumors such as the chondrosarcoma behave similarly (Figs.9.53a–c). Biopsy is indicated to evaluate any bone tumors in the pelvis. Depending on the type of the tumor, Tl or T2-weighted images will provide the best contrast between the tumor and adjacent tissue. A fat-suppressing sequence (Figs.9.54a, b) has the highest sensitivity in detecting tumors since the pathophysiologic changes always include a locally enlarged extracellular space. T1-weighted images with gadolinium-DTPA are indicated to demonstrate the tumor borders and help identify the type of tumor.

Specificity depends on the morphology, behavior after application of contrast medium, and, to a lesser extent, the Tl and T2 relaxation times.

Differentiating tumor from surrounding tissue in MR images is possible with a high degree of accuracy using fat-suppressing sequences (to distinguish it from healthy marrow) and Tl sequences before and after application of gadolinium-DTPA.

Figs. 9.53a-c MR images of the sacral region.
(a) GRE (500/10, out of phase) in the sagittal plane showing a well-demarcated tumor mass that includes the sacrum and extends into the pelvis and the spine. It is relatively homogeneous with slightly increased signal intensity.
(b) CRE (500/10, out of phase) in the sagittal plane after administration of gadolinium-based contrast medium. Contrast-medium enhancement is seen in the tumor masses, which continue to be well demarcated.
(c) GRE (500/10, out of phase) in the coronal plane. The tumor is still well demarcated and includes the entire sacrum except for the lateral mass adjacent to the joint. This was diagnosed as a recurrent chondrosarcoma.

Figs. 9.54a, b MR images of the pelvis.
(a) STIR 1900/125 in the coronal plane showing a mass of high signal intensity that includes the iliac spine but also extends into the pelvis and into gluteal musculature.
(b) STIR 3000/100 in the transverse plane showing destruction of the iliac spine by tumor tissue of median signal density. The far posterior portions of the tumor again appear with high intensity and surround the iliac wing.
This was diagnosed as a largely necrotic metastasis to the iliac wing.

MRI can demonstrate whether a tumor respects bone borders or has passed through them, particularly in the sacroiliac joints and the facet joints (Figs.9.55a–e).

Lipomas are easily identified and distinguished from non-fatty tissue because of’their high fat content. However, intracutaneous lipomas without a discernible mass can avoid detection. Differentiating intracutaneous lipomas and liposarcomas can also be difficult. Septation in sarcomas is one criterion for differentiation.

Inflammatory Changes

In osteomyelitis the physician will only be able to document pathologic findings about 10 days to 2 weeks after the onset of clinical symptoms using conventional radiography or CT. MRI can detect changes in bone as early as 3 days after infection. Nuclear medicine studies are similarly sensitive but less specific. Inflammation produces hyperemia and edema in the marrow. The increased fluid content extends the Tl relaxation time, which reduces the signal in a Tl-weighted sequence. At the same time, hyperemia and edema will extend the T2 relaxation time and increase the signal in T2-weighted sequences. Since marrow has a high content of fatty tissue, these findings are often difficult to discern in T2-weighted sequences because fat also has a long T2 relaxation time. For this reason, fat-suppressing pulse sequences are preferred. These sequences visualize the free water content of tissue with high signal intensity according to its relaxation time (Figs.9.56a-c), The criterion for differentiating chronic from acute osteomyelitis is the perio steal zone of irritation, which can be readily demonstrated in the Tl-weighted images after administration of gadolinium-DTPA. Chronic osteomyelitis can be recognized by the reactive thickening of the cortex. The reactive periosteal halo is also missing in chronic osteomyelitis except when it is reactivated. However, the early acute process is not sharply demarcated. The change extends over a wide area of the marrow. A sequestrum resulting from osteomyelitic changes will be discernible in all sequences as a zone of low signal intensity within the inflamed area.

Soft-tissue infections appear in T2-weighted images as areas of high signal intensity, showing significant diffuse boundary disruption visible as contrast enhancement. If an abscess develops, the abscess itself will appear as a homogeneous structure of high signal intensity in T2-weighted and fat-suppressing pulse sequences. The abscess membrane is usually hyperemic and will show circumscribed halo-like enhancement after administration of gadolimum-DTPA(Figs.9.57a-c,9.58a,b).

Figs. 9.55a–e MR images of the pelvis,
(a) STIR 1900/125 in the coronal plane showing a mass of high signal intensity in the left inferior pubic ramus that disrupts the boundary of the bone and extends into soft tissue. (b, c) GRE (500/10, out of phase) in the transverse plane. No lesion is discernible.
(d, e) GRE (500/10, out of phase) in the transverse plane after administration of gadolinium-based contrast medium. A circumscribed area of increase signal intensity in the superior and inferior pubic rami with significant boundary destruction. The mass is seen to extend into the adductors that insert here.
This was diagnosed as a metastasis of an adenocarcinoma to the left superior and inferior pubic rami.

Figs. 9.56a-c MR images of the pelvis.
(a) STIR 1900/125 in the coronal plane showing an area of increased signal intensity in the body of the right ilium that also involves the lateral mass of the sacrum. There is an increase in signal intensity around the bone in the gluteal musculature of the right side.
b) GRE (500/10, out of phase) in the coronal plane. Signal intensity is increased in the body of the right ilium compared with the contralateral side.
(c) GRE (500/10, out of phase) in the coronal plane after administration of gadolinium-based contrast medium. Significant signal enhancement is seen in the body of the ilium and in the tissue surrounding the bone.
This was diagnosed as osteomyelitis of the right ilium extending to the right lateral mass of the sacrum.

Figs. 9.57a–c MR images of the pelvis.
(a) STIR 1900/125 in the coronal plane showing strips of increased signal intensity in the right gluteal musculature extending into the sheath of the biceps femoris. At the level of the trochanter there is a relatively circumscribed subcutaneous area with a halo of increased signal intensity. Increased signal intensity is also seen in the skin.
(b) GRE (500/10, out of phase) in the coronal plane after administration of gadolinium-based contrast medium. The infiltrated area appears enhanced, and the decrease in signal intensity in the fatty tissue is apparent.
(c) GRE (500/10, out of phase) in the sagittal plane. A circumscribed area of increased signal intensity is visible at the level of the greater trochanter.
This was diagnosed as an abscess of the gluteal musculature at the level of the greater trochanter with infiltration into the biceps femoris.

Figs. 9.58a, b MR images of the pelvis.
(a) STIR 1900/125 in the coronal plane showing a large infiltrative process of high signal intensity extending from the psoas and iliopsoas through the inguinal region into the adductors and vastus medialis. There is a zone of increased signal intensity in the femoral head and the right acetabulum. A moderate effusion into the hip is present.
(b) PS 500/10 in the coronal plane after administration of gadolinium-based contrast medium showing significantly increased signal intensity in the iliopsoas. The process shows reduced signal intensity with increased marginal signal intensity in the adductors and vastus medialis.
This was diagnosed as an abscess proceeding from the psoas with a large abscess cavity in the adductors and vastus medialis. The image shows accompanying inflammation of the hip and the onset of osteomyelitis of the right femoral head and acetabulum.

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