Chapter 7. Imaging Studies in Orthopaedics

At the completion of this chapter, the reader will be able to:

1. List the various imaging studies available.

2. Discuss the advantages and disadvantages of each of the imaging studies.

3. Describe how the various musculoskeletal tissues are depicted in imaging studies.

4. Understand the strengths and weaknesses of each of the imaging studies.

5. Outline the rationale for the choice of one imaging technique versus another.

6. Describe how the results from imaging studies may help in the clinical decision-making process.

For health-care professionals involved in the primary management of neuromusculoskeletal disorders, diagnostic imaging is an essential tool. The availability of diagnostic images to physical therapists greatly depends on the practice setting. For example, physical therapists in the United States army, with primary-care physical therapy provided with credentials, have had privileges for ordering diagnostic imaging procedures since the early 1970s.1 Although, outside of the United States military health system, the ordering of imaging studies is not within the scope of physical therapy practice, clinicians frequently request or receive imaging study reports. Although the interpretation of diagnostic images is always the responsibility of the radiologist, it is important for the clinician to know what importance to attach to these reports, and the strengths and weaknesses of the various techniques that image bone and soft tissues, such as muscle, fat, tendon, cartilage, and ligament. In general, imaging tests have a high sensitivity (few false negatives) but low specificity (high false-positive rate), so are thus used in the clinical decision-making process to test a hypothesis but should not be used in isolation. In addition, imaging studies are expensive and somewhat more invasive compared to a physical examination, so the clinician must weigh the relative value of recommending an imaging study in relation to the working hypothesis. For example, when there is little likelihood that imaging will reveal anything that will change the course of treatment, the tests should be considered unnecessary.1 In addition, the clinician needs to understand that the results of an imaging study may not correlate with the results of the physical examination. Although imaging may provide evidence of pathology, the mere presence of the abnormality may or may not be relevant to the presenting signs and symptoms. In such situations, the clinician should place no more or less weight on the imaging than on other aspects of the decision-making process.

In 1895, Wilhelm Conrad Röentgen was experimenting with a type of electrical tube that produced an electrical discharge when a high voltage current was passed through it.2 When Röentgen shielded the tube with heavy black cardboard, he noticed that a fluorescent screen a few feet away lit up and glowed indicating that some form of energy was passing through the tube. Further experiments led Röentgen to discover that these energy waves could reliably reproduce images of the human skeleton on a glass photographic plate.2 Röentgen named these energy waves x-rays because “x” was the unknown quantity in a mathematical equation, and he was unsure of what the rays were composed of.2 In 1896, Henri Becquerel discovered the basic nature of radiation and almost immediately an article appeared in the Journal of the American Medical Association theorizing on the possible diagnostic and therapeutic uses of this new discovery.2 X-rays were soon determined to be part of the electromagnetic spectrum with the ability to penetrate through body tissues of varying densities. It was also discovered that the amount of beam absorbed as it passed through the body depended on the density of the tissue. This allowed physicians to use the images to view a number of anatomical structures. Initially, only small segments of the body could be radiographed in a single exposure—studies of large, thick body parts such as the abdomen, and hip could not be adequately covered. Then, in 1912, Dr Gustav Bucky published his findings describing a stationary, cross-hatched or “honey-combed” lead grid, which helped absorb scatter radiation and thus enhanced image quality. The grid consisted of wide strips of lead arranged in two parallel series that intersected at right angles. One disadvantage of the stationary grid is that the lead strips left “blank” or white lines on the film (“grid lines”). A few years later, Dr Hollis Potter introduced a multileafed focused grid, which moved the grid sideways across the film during the exposure, thereby blurring out the shadows of the grid strips, and further enhancing the image quality. Over the years, various mechanisms have been utilized to achieve this movement. Two physical factors responsible for grid efficiency are the grid ratio and grid frequency.

• Grid ratio: The height of the lead strip in relationship to the distance between them. Example: A 10:1 grid has lead strips 10 mm tall and these strips are 1 mm apart. The strips are ten times as tall as the distance between them.
• Grid frequency: Defined as the number of lead strips per centimeter (or per inch). The greater the frequency, the thinner the strips, and the greater the likelihood of scattered photons passing through.

Grid selection involves a compromise between film quality and patient exposure. High-ratio grids produce films with better contrast at the cost of increased patient exposure; however, proper alignment is more critical.

Conventional (plain film) radiography is generally considered to be the first order diagnostic imaging modality.3 The basic process is fairly simple. The patient's body part of interest is oriented in a prescribed position and the film plate, receptor or, detector is positioned to capture the particles of the X-ray beam that are not absorbed by the tissues of the body. Both sides of the film are thinly coated with a fluorescent gel, and then the film is placed within a two layered hard plastic shell, which protects the film and allows easy portability. An X-ray machine then directs electromagnetic radiation upon the specified region of the body.

Tissues of greater density allow less penetration of the X-rays and, therefore, appear lighter on the film. A difference in radio density is necessary for two structures to appear different on resultant radiographs. The following structures are listed in order of descending density: metal, bone, soft tissue, water or body fluid, fat, and air. Because air is the least dense material in the body, it absorbs the least amount of X-ray particles, resulting in the darkest portion of the film. Bones can have varying densities within the body. For example, cancellous bone is less dense than cortical bone and thus appears lighter than the cortical bone on the radiograph. Soft tissues often cannot be separated because they have similar radio densities.

Numerous technical factors are manipulated and equilibrated in order to produce a high-quality diagnostic image, while keeping the radiation dose as low as possible. Long focal film distances, short object film distances, small focal spots, short exposure time, tight collimation, and optimal film/screen combinations can all be used to enhance the image.4 Reducing radiation exposure to the lowest levels may be addressed by attention to details of patient centering, shielding, and collimation, reducing repeat films, and the timely calibration of X-ray equipment.4

Digital radiography exists in the form of computed radiography or direct radiography. Image processing and distribution is achieved through a picture archiving and communication system. However, the spatial resolution of digital radiography systems is not yet as great as that with film screen radiography.5

Plain-film, or conventional, radiographs are relatively inexpensive and give an excellent view of cortical bone (Figs. 7-1, 7-2, 7-3, 7-4, 7-5, 7-6, and 7-7). Radiographs may be more specific than MRI in differentiating potential causes of bony lesions because of the proven ability to characterize specific calcification patterns and periosteal reactions.1 Plain radiographs are not considered sensitive to the early changes associated with tumors, infections, and some fractures.6 However, they can be very helpful in detecting fractures and subluxations in patients with a history of trauma.7 Radiographs may also be used to highlight the presence of degenerative joint disease, which is characterized by an approximation of the joint surfaces on the radiograph. However, radiographs do not provide the most accurate image of soft tissue structures, such as muscles, tendons, ligaments, and intervertebral disks.

Radiographs are a 2-D representation of a 3-D structure. During the initial exposure to reading radiographs, it is important that the clinician examines as many “normal” radiographs as possible. There is a great deal of variation in the human body and a great deal of variation in what is considered to be normal. When evaluating radiographs, a systematic approach such as the mnemonic ABCS is recommended8:

• A: Architecture or alignment. The entire radiograph is scanned from top to bottom, side to side, and in each corner to check for the normal shape and alignment of each bone. The outline of each bone should be smooth and continuous. Breaks in continuity usually represent fractures. Malalignments may indicate subluxations or dislocations, or in the case of the spine, scoliosis. Malalignment in a setting of trauma must be considered traumatic rather than degenerative until proven otherwise.4
• B: Bone density. The clinician should assess both general bone density and local bone density. The cortex of the bone should appear denser than the remainder of the bone. Subchondral bone becomes sclerosed in the presence of stress in accordance with Wolff's law9 and increases its density. This is a radiographic hallmark of osteoarthritis.
• C: Cartilage spaces. Each joint should have a well-preserved joint space between the articulating surfaces. A decreased joint space typically indicates that the articular cartilage is thinned from a degenerative process such as osteoarthritis.
• S: Soft tissue evaluation. Trauma to soft tissues produces abnormal images resulting from effusion, bleeding, and distension.

For all joints and regions, there are standard, or routine, radiographic series that are typically obtained.10 A radiographic series is a group of X-rays films, taken of one area of the body, from different angles. These groups of films have been standardized by long years of experience and standards of care to provide all the needed information about an area of interest. For example, a standard chest X-ray uses certain established angles and amounts of radiation to enhance the view of the soft tissues of the heart and lungs, whereas a rib series uses an entirely different set of angles and radiation to bring out the bony detail with more clarity. In addition to the standard series, there are also additional or special views that can be ordered to visualize a particular structure more effectively10 (Table 7-1). For example, a patient presenting with pain in the “anatomic snuffbox” area of the wrist may have a fracture of the scaphoid bone, requiring a special view of the area rather than a standard wrist series. It is important that the clinician has an appreciation of various views and what each represents.

Radiographs, like all medical procedures, have risks and benefits. Ionizing radiation can increase the risk of cancer, and in sufficient doses can cause death.11 In addition to the health risks, the overutilization of radiologic studies has become a significant economic problem in the United States.12 For these reasons there has been an increased need for clinical prediction or decision rules indicating a need for radiography for specific types of injury at certain areas of the body. A clinical decision rule (CDR) is a tool that can quantify individual contributions from the components of the examination to determine the diagnosis, prognosis, or treatment for a given patient.1

Clinical Applications

Cervical Spine

CDRs for reevaluation of cervical spine injuries remain controversial, although consensus exists that cervical radiographic studies are over utilized in the emergency department.13 In addition to the routine projections for the cervical spine, the anteroposterior (A-P) and lateral views, a number of other views can be used to aid in the evaluation of trauma and arthritis (Table 7-1). The A-P view provides information about the shape of the vertebra, the presence of any lateral wedging or osteophytes, and the disk space. In the lower cervical spine the A-P view can also provide information about the presence of a cervical rib. The lateral view provides information about the lordosis and general shape of the cervical curve and cervical vertebrae. This view also provides information about any anterior or posterior displacement of the vertebrae, the size of the disk space, the integrity of the vertebral edges (lipping), facet subluxation, soft tissue abnormalities, and the presence of any osteophytes. By measuring the prevertebral soft tissue width at the anteroinferior border of the C-3 vertebra, a determination can be made as to the presence of edema or hemorrhage if the width is wider than the normal 7 mm.14

Radiographic images are limited in their ability to detect instability of the craniovertebral region because of very incomplete image definition of soft tissues, but the disruption of normal skeletal relationships may indicate a loss of integrity of the interposed tissues. To measure the degree of atlantoaxial subluxation, the anterior atlantodens interval (AADI), which measures the spatial relationship between the odontoid process and the anterior arch of the atlas has been used. Before skeletal maturity, this value may be up to 4–5 mm. In adults and older children, a value of 3 mm is generally considered to be the upper limit of normal.16 Roche and colleagues17 have proposed that 3–6 mm suggests transverse ligament damage and greater than 6 mm implies alar ligament injury. However, AADI interpretations must be used with caution. The posterior atlantodens interval (PADI), which is the distance between the posterior surface of the odontoid and the anterior margin of the posterior ring of the atlas, may be a more valuable measurement, as it results in a more accurate reflection of canal size and potential for neurologic compromise. A PADI of 40 mm is considered the lower limit to avoid encroachment onto the spinal cord.17

Thoracic Spine

Standard views of the thoracic spine include the A-P view and lateral view (Table 7-1).

A-P view. This view is used to help the clinician determine if there is any wedging of the vertebrae (suggestive of structural kyphosis resulting from conditions such as Scheuermann's disease or a wedge fracture), whether the disk spaces appear normal, whether there is normal symmetry of the ribs, whether there is any malposition of the heart and lungs, whether any scoliosis is present, and whether the ring epiphysis, if present, is normal. From a disease perspective, in patients with suspected ankylosing spondylitis, the clinician is observing for a bamboo spine. The Cobb method is a technique used to measure spinal curvature in cases of suspected scoliosis. A line is drawn parallel to the superior cortical plate of the proximal end vertebra and to the inferior cortical plate of the distal end vertebra. A perpendicular line is then used to join each of these lines, and the angle of intersection of the perpendicular lines is the angle of spinal curvature resulting from scoliosis.

Lateral view. This view is to help the clinician determine if there is a normal kyphosis, whether the disk spaces appear normal, the angle of the ribs, the presence of any osteophytes, whether there is any wedging of the vertebrae, and whether there are any Schmorl's nodules, indicating herniation of the intervertebral disk into the vertebral body.

Lumbar Spine

Routine projections for the lumbar spine are the posteroanterior (P-A) or A-P, and lateral views (Table 7-1). Lower back radiographs have been described as the single most overprescribed diagnostic imaging procedure.18,19 Specific guidelines have been developed by the Agency for Health Care Policy and Research to help reduce the ordering of lumbar plain films that are of minimal diagnostic value.18 Imaging in the event of spinal trauma must be fully evaluated regarding the forces involved as well as the metabolic bone health of the patient.1 Symptoms that are not relieved by rest or changes in position, symptoms that sharply increase with movement, unremitting paraspinal musculature spasm, and an unwillingness to move the spine all suggest a spinal fracture.1

Pelvis

Routine projections for the pelvis are outlined in Table 7-1. Additional views include the following:

Prone view of the symphysis pubis. This view improves detail of the symphysis in patients with groin strain, as well as demonstrating the pubic rami. The view is taken with the patient lying prone to bring the symphysis close to the film and with 20–30 degrees of cranial tube angulation.

Obturator view. This view, which can be obtained supine or prone, provides the clinician with more detail of the pubic rami and ischial tuberosities. In the supine position, the cranial angulation of the tube is 25–30 degrees and, if the prone position is used, the angulation is caudal. The primary beam is centered just below the inferior margin of the symphysis.

Flamingo views. These views of the symphysis are used in the diagnosis of pelvic instability by demonstrating movement of the symphysis under weight-bearing stress. Two P-A views of the symphysis are obtained with weight bearing on each leg in turn. Any movement at the symphysis in excess of 2 mm is considered abnormal.

Cone P-A/A-P view. These views of the sacroiliac joints (SIJs) are used when an abnormality of the SIJ is suspected on a routine view of the pelvis. A tube angulation of about 30 degrees is used although this will vary depending upon the lumbar curve.

Shoulder

Radiographic examination of the shoulder girdle may be tailored to be given clinical situation. A trauma series consists of an A-P, axillary, and scapular lateral views (Table 7-1).

• A-P view. A true A-P of the shoulder girdle is one in which the X-ray beam is perpendicular to the scapula. This requires obliquing the patient 45 degrees such that the scapula itself is parallel to the X-ray cassette. In this way, the glenohumeral (GH) joint is seen without overlap of the humeral head and glenoid fossa. One view that is helpful in the evaluation of impingement syndrome is the outlet view, which centers the beam at the coracoacromial arch. A standing bilateral A-P image is used to assess the clavicle and acromioclavicular (AC) joint.
• Axillary. This view shows the relation of the humeral head to the glenoid and is used to diagnose anterior and posterior dislocations at the GH joint, AC joint dysfunctions, and to look for avulsion fractures of the glenoid or a Hill-Sachs lesion (see Chapter 16). The technique requires that the patient be able to abduct the arm 70–90 degrees.
• Scapular-Y. The “scapular-Y” view, obtained by tilting the X-ray beam approximately 60 degrees relative to the A-P view, provides good visualization of the humerus relative to the glenoid and the acromion and coracoid process.20
• Stryker notch view. The patient is positioned in supine with the arm forward flexed and the hand on top of the head. The beam is centered on the coracoid process. This view is used to assess a Hill Sachs lesion or a Bankart lesion (see Chapter 16).
• West Point view. The patient is positioned in prone. This projection gives a good view of the glenoid to delineate glenoid fractures.
• Arch view. The arch view is used to determine the width and height of the subacromial arch and helps to determine the type of acromial arch (see Chapter 16).

Elbow

The standard X-ray series of the elbow includes A-P and lateral views (Table 7-1).21

• A-P view. The A-P view is taken with the elbow extended and the forearm supinated, with the X-ray beam directed perpendicular to the anterior aspect of the elbow. The A-P view demonstrates the humeroradial, humeroulnar, as well as the medial and lateral epicondyles. The carrying angle of the elbow can also be measured from the A-P view.
• Lateral view. The lateral view is taken with the elbow flexed at 90 degrees and forearm in a neutral position, with the X-ray beam directed perpendicular to the lateral aspect of the elbow. The lateral view best demonstrates the coronoid process of the ulna and the tip of the olecranon. Fat pads are also best identified on the lateral view.

Special views can be ordered to help define specific symptomatic areas and include oblique, axial, radial head, and stress views.

Medial Oblique Views

This view is taken with the arm internally rotated, the elbow extended, and the forearm pronated. This view allows better visualization of the trochlea, olecranon, and coronoid process of the ulna.

Lateral Oblique Views

This view is taken with the arm externally rotated, the elbow extended, and the forearm supinated. The lateral oblique view provides good visualization of the radiocapitellar joint, proximal radioulnar joint, and medial epicondyle. Often nondisplaced or minimally displaced fractures and loose bodies not seen on the A-P or lateral views will be demonstrated on the oblique views.

Axial View

The axial view is obtained with the arm on the cassette, the elbow flexed to 110 degrees, and the X-ray beam directed perpendicular to the arm. The reverse axial view is obtained with the forearm on the cassette, the elbow completely flexed, and the beam projected perpendicular to the forearm. The axial and reverse axial views best demonstrate the olecranon fossa and the olecranon, respectively.

Radial Head View:

The radial head view will help identify occult radial head fractures. This view is obtained with the elbow flexed to 90 degrees and the beam angled at 45 degrees to the lateral elbow. A-P stress views demonstrate subtle changes in joint space and congruency with varus or valgus stress on the elbow. These changes are then compared to the nonstressed A-P view or to a stress view of the opposite side. Widening of the radiocapitellar joint with varus stress reflects injury to the lateral ligaments. Widening of the humeroulnar joint with valgus stress reflects injury to the medial ligaments.

The radiocapitellar view is especially helpful in demonstrating radial head and capitellum fractures. A line drawn through the mid portion of the radius normally passes through the center of the capitellum on the lateral view of the elbow. The lateral projection, angles the central beam cranially, projecting the radiocapitellar joint free of the ulnar trochlear articulation. Views of the cubital tunnel can be obtained with the elbow flexed approximately 45 degrees, and the forearm supinated with its posterior (dorsal) surface against the X-ray cassette. The central ray is angled approximately 20 degrees with respect to the olecranon process. This is particularly useful for looking at the bony aspect of the cubital tunnel where the ulnar nerve lies and can show osteophytes and loose bodies.

Wrist

In addition to the standard and special radiographic views depicted in Table 7-1, an anterior oblique position or semi-supinated oblique view may be obtained for the evaluation of arthritis. From the lateral position, the forearm is supinated until the wrist forms an angle of approximately 45 degrees with the plane of the film. The pisiform-triquetral joint compartment is only seen with such a view. Early erosions that are associated with inflammatory arthritis, especially rheumatoid arthritis, may occur at this joint. Stress views of the first carpometacarpal joints can be obtained by asking the patient to press the tips of the thumb together with the hands in a nearly lateral position. Radial subluxation of the first carpometacarpal joint is most commonly seen in basal joint osteoarthritis.

The carpal tunnel view is taken with the wrist hyperextended. The X-ray beam is angled along (parallel to) the volar aspect of the wrist showing the bony anatomy of the carpal tunnel. This view is helpful in detecting erosions in the carpal tunnel and may detect occult fractures of the hook of the hamate, which may be difficult to see on routine radiographs.

Motion series of the wrist may aid in the detection of ligamentous injuries that result in instability. This includes P-A radial and ulnar deviation views and lateral volar and dorsiflexion views. Such static views may be normal in the setting of ligamentous injury and dynamic video fluoroscopy of the wrist may be required. The clenched fist anterior–posterior view may demonstrate a scapholunate dissociation by driving the capitate proximally between the lunate and scaphoid. Specialized views of the scaphoid itself have been designed for the detection of occult fractures.

Hand

All significant hand injuries, including those with any degree of swelling, should be evaluated radiographically even if the likelihood of a fracture seems remote.22 Chip or avulsion fractures may not be suspected on the basis of the clinical examination and yet if undetected and untreated may result in a significant disability.22 Rotational deformity involving the metacarpal or proximal phalanx can result in a poorly functioning partially disabled hand. With a rotational alignment of the distal interphalangeal joint, the planes of the fingernails are not parallel when one compares the planes of the injured nail to the normal fingernail of the opposite hand.

In addition to the standard and special radiographic views depicted in Table 7-1, stress views of the first metacarpophalangeal joint may be required for evaluation of the ligamentous injuries. Specifically, abduction stress views of the injured and normal form may demonstrate widening of the ulnar aspect of the joint with radial subluxation of the proximal phalanx when the ulnar collateral ligament is disrupted, as with the “game-keeper thumb” (see Chapter 18). Fractures of the fourth and fifth metacarpal are frequently undetected until a lateral view with 10 degrees of supination is obtained.22 Second and third metacarpal injuries are often detected on a lateral view with 10 degrees of pronation.22 Finger injuries require a true lateral view without superimposition of the other digits.22

Hip

There are two projections in the routine hip series (Table 7-1):

• A-P view. This view allows the clinician to:
  • compare the two hips for symmetry.
  • note the neck shaft angle (coxa vara or coxa valga), and the shape of the femoral head.
  • view the joint spaces (presence of osteophytes or arthritis), pelvic lines, and other landmarks.
  • note the presence of any bone disease (e.g., Legg–Calve–Perthes disease).
  • note any evidence of fracture, dislocation, or pelvic distortion.
• Lateral-oblique view. This view allows the clinician to look for any pelvic distortion or any slipping of the femoral head.

In addition to the standard and special radiographic views, cross-table lateral filming is the best approximation of a true lateral film of the hip and is particularly useful in assessing subtle subcapital fractures and as a postoperative evaluation of hip arthroplasty. The patient is positioned in supine with the film cassette centered at the greater trochanter. The knee and hip of the unaffected side are flexed. The central ray is perpendicular to the long axis of the femoral neck and the film cassette. The Judet view is used if there is a suspicion of a fracture in the region of the acetabulum. This view is taken by rolling the patient 40 degrees one way and then the other, acquiring images in both positions by using a straight tube centered on the femoral head.

Tibiofemoral Joint

In addition to the standard and special radiographic views depicted in Table 7-1, weight-bearing views of the knees with and without flexion are particularly helpful in the evaluation of arthritis and the detection of joint space narrowing which may not be as obvious with nonweight-bearing or nonstanding views. Weight-bearing with flexion is particularly helpful in the detection of osteoarthritis when focal cartilage loss can be seen posteriorly. The Ottawa knee CDRs and the Pittsburgh CDRs are guidelines for the selective use of radiographs in knee trauma. Application of these rules may lead to a more efficient evaluation of knee injuries and a reduction in health costs without an increase in adverse outcomes.12 The Ottawa knee CDRs, which have been demonstrated to have near 100% sensitivity for knee fractures and reduce the need for knee radiographs by 20% when used by emergency physicians,3 is summarized in Table 7-2. The Pittsburgh CDR of the knee indicating the need for radiographic studies is summarized in Table 7-3.

Patellofemoral Joint

• Lateral radiographs.23 Radiographs should include a lateral view with posterior condyles approximated as closely as possible. The distance between the lateral femoral condyles and the trochlea is a measure of trochlear depth. The absence of the groove at any point along the trochlear arc is pathologic. The convergence of the bony trochlea and the lateral femoral condyles on a lateral radiograph is termed the crossing sign.
• Axial radiographs.23 The axial view should be obtained in the manner described by Merchant and colleagues but with the knee flexed 50 degrees rather than 45 degrees to better detect abnormal tilt and lateral displacement. Lateral displacement, in particular, is most pronounced in the early degrees of flexion, before the patella engages the trochlear groove.

Ankle

The Ottawa ankle CDR was developed to help predict fractures in patients with ankle injuries and has been shown to be 100% sensitive and 40% specific and to reduce the need for emergency department ankle radiographs by 36%.3,24 Using this CDR, radiography is indicated if any of the following are present:

• Bone tenderness at the posterior edge or tip of the lateral malleolus.
• Bone tenderness at the posterior edge or tip of the medial malleolus.
• Inability to bear weight both immediately and in the emergency department.

Standard views of the ankle include the A-P, mortise, and lateral views (Table 7-1):

• A-P view. This view provides the clinician with information about the shape, position, and texture of the bones, and helps determine whether there is any fractured or new subperiosteal bone.
• Mortise view. This view provides information about the ankle mortise and the distal tibiofibular joint.
• Lateral view. This view provides the clinician with information about the shape, position, and texture of bones, including the tibial tubercle, talus, and calcaneus.

Other nonroutine views include the following:

• Dorsoplantar view of the foot. This view provides information with regard to the forefoot.
• Medial oblique view of the foot. This view provides information about the tarsal bones and joints and the metatarsal shafts and bases. In addition this view can highlight any pathology in the calcaneocuboid joint.

Stress views of the ankles are routinely utilized for assessment of instability and injury to the lateral collateral ligament of structures (Table 7-1). Both the affected and normal side are examined for comparison. Complete tears of the deltoid ligament may be demonstrated with eversion stress. However, the value of stress roentgenograms of the ankle is a controversial topic.25,26 The stress views include inversion to assess talar tilt and the anterior drawer stress. The accuracy of these tests increases with the use of local anesthesia and a comparison with the uninvolved ankle.

The anterior drawer test is performed with a lateral view of the ankle in neutral position, while attempting to manually translate the foot anteriorly with respect to the leg.25,26 The sagittal plane translation of the talus with respect to the tibia is measured. When compared with the same foot unstressed, anterior subluxation of more than 3 mm is considered to indicate an anterior talofibular ligament (ATFL) injury.27

The talar tilt test is used more often and is felt to be more reliable. In this examination, a mortise or A-P view of the ankle held in neutral position to slight plantar flexion with an inversion stress applied to the foot is obtained.25,26 The angle to be measured is that formed by a line parallel to subchondral bone of the distal tibia and proximal talus. It is the consensus that a talar tilt test is positive, when the injured ankle has a stressed tibiotalar angle of 528–15 degrees29 greater than the uninjured side. However, the absolute number of degrees is not as important as the functional instability of the patient, as laxity does not always mean instability.25,26

Stress Radiograph

A stress radiograph is a procedure using radiographs taken while a stress is applied to a joint. An unstable joint demonstrates widening of the joint space when the stress is applied. For example, spine flexion and extension views can be helpful in assessing spinal mobility and stability and are typically ordered in the acutely injured athlete when there is a high degree of suspicion of spine injury. Greater than 2 mm of motion beyond normal at any segmental level in the spine would suggest instability and warrant further examination.

Video Fluoroscopy

Fluoroscopic procedures involve the use of X-rays to evaluate the quality and quantity of joint motion. Because of the relatively high exposure of radiation with this technique, it is used mainly in the detection of joint instability.

Contrast-Enhanced Radiography

Contrast-enhanced radiography procedures involve the use of a contrasting agent to highlight different structures. These agents may be administered orally, rectally, or by injection. Different contrast media may be used and include radiopaque organic iodides and radiotranslucent gases. Contrast-enhanced radiography procedures include the following:

• Arthrography. Arthrography is the study of structures within an encapsulated joint using a contrast medium with or without air that is injected into the joint space. The contrast medium distends the joint capsule. This type of radiograph is called an arthrogram. An arthrogram outlines the soft tissue structures of a joint that would otherwise not be visible with a plain-film radiograph. This procedure is commonly performed on patients with injuries involving the shoulder or the knee. The primary general indications for performing a conventional arthrogram are30
  • to confirm intracapsular positioning of a needle or catheter following a joint aspiration or prior to an anesthetic joint injection
  • in place of an MR scan (see later) if it is not available, contraindicated, or if the patient is too obese for the gantry or is claustrophobic
  • for the diagnosis and treatment of adhesive capsulitis

Arthrography can also be performed in conjunction with magnetic resonance imaging (MRI) or computed tomography (CT) (see later).

• Myelography. Myelography is the radiographic study of the spinal cord, nerve roots, dura mater, and spinal canal. The contrast medium is injected into the subarachnoid space, and a radiograph is taken. This type of radiograph is called a myelogram. Myelography is used frequently to diagnose intervertebral disk herniations, spinal cord compression, stenosis, nerve root injury, or tumors. The nerve root and its sleeve can be observed clearly on direct myelograms. When myelography is enhanced with CT scanning, the image is called a CT myelogram (see later).
• Diskography. Diskography is the radiographic study of the intervertebral disk. A radiopaque dye is injected into the disk space between two vertebrae. A radiograph is then taken. This type of radiograph is called a diskogram. An abnormal dye pattern between the intervertebral disks indicates a rupture of the disk. The indications for lumbar or cervical diskogram are30
  • severe or unremitting low back or neck pain with or without radicular symptoms in a patient with negative standard imaging studies or degenerative disk disease
  • for use in preoperative planning prior to spinal fusion to include only those painful disk levels
  • in the evaluation of neural foramina masses, which may represent an extruded disk herniation or nerve sheath tumor
  • to determine accurate needle placement prior to chymopapain injection
  • persistent pain in the postoperative period
• Angiography. Angiography is the radiographic study of the vascular system. A water-soluble radiopaque dye is injected either intra-arterially (arteriogram) or intravenously (venogram). A rapid series of radiographs is then taken to follow the course of the contrast medium as it travels through the blood vessels. Angiography is used to help detect injury to or partial blockage of blood vessels. The indications for angiography are30
  • as a diagnostic study, following possible vascular injury from trauma
  • embolization of active bleeding sites not amenable to surgical control, such as within the pelvis
  • evaluation of bone and soft tissue tumors (the findings will assess neovascularity of the lesion, the extent of the tumor, and invasion or impingement of major vessels)
  • preoperative or palliative intra-arterial embolization or chemotherapy
  • diagnosis and treatment of arteriovenous malformations
  • evaluation of the arterial anatomy prior to bone or soft tissue grafts
  • diagnosis of arteritis that is further complicating collagen vascular disease

Computed Tomography

The word “tomography” is derived from the Greek tomos (slice) and graphia (to write). CT images are useful to evaluate injured areas where the 3-D configuration of the structure make the plain radiographs difficult to interpret.31 The CT image is not recorded in a conventional radiographic manner. A CT scanner system, also known as computerized axial tomography (CAT) and computerized transaxial tomography (CTI), consists of a scanning gantry, which holds the X-ray tube and detectors (moving parts), a moving table or couch for the patient, an X-ray generator, computer processing unit, and a display console or workstation.32 Images are obtained in the transverse (axial) plane of the patient's body by rotating the X-ray tube 360 degrees.

The images are produced by rotating a thin collimated X-ray beam through a 180-degree arc around the patient such that structures of a certain depth will be stationary in the beam and appear with enhanced clarity, whereas tissues superficial and deep to this level will be relatively obscured by motion. The basic principle of any tomographic system is that all parts of the object that are perpendicular to the direction of the tube motion are maximally blurred, whereas those parts that are parallel to the direction of motion are not blurred but merely elongated.

Like conventional radiography, CT also uses radiation, but instead of a unidirectional beam, both the radiation source and detector systematically encircle the body. The X-rays are absorbed in part by the patient's body. The amount of X-rays transmitted through the body is detected on the opposite side of the gantry by an array of detectors. Each array detector responds to the amount of rays detected by downloading data to the system's computer, which assigns a numeric value based on the attenuation property of the various tissues of the body, and then forms an image based on the differential absorption of the X-rays. These attenuation values, or relative attenuation coefficient (μ), are expressed in Hounsfield units (HU) and are normalized to water.4 Hence, water measures 0 HU, bone (the highest absorption values) measures >400 HU, muscle measures 40 HU, fat measures −120 HU, and air (the lowest absorption values) measures −1000 HU.32 In essence, the CT image is a map of the linear attenuation value of the tissue. By adjusting the level and the width of the displayed ranges of HU (window), the operator can study different tissues optimally. Software has been introduced through the years to allow for fast image reconstruction in any desired plane (2 D) or surface reconstruction (3 D).32 The continuous movement offered by spiral CT, referred to as multislice or multidetector CT scanners, greatly reduces scan time. These newer multislice CT scanners represent a major improvement in helical CT scan technology, wherein simultaneous activation of multiple detector rows positioned along the longitudinal or z-axis (direction of table or gantry) allows acquisition of interweaving helical sections.33 With this design, section thickness is determined by detector size and not by the collimator (a device that filters a stream of rays so that only those travelling parallel to a specified direction are allowed through) itself.33

Image quality in CT imaging depends on a variety of factors, which are mostly selected by the operator. Two parameters are used to define the image quality of a given system: spatial resolution and contrast resolution:32

• Spatial resolution: Spatial resolution is defined as the ability of the system to distinguish between two closely spaced objects. For improvement of spatial resolution, the operator selects a small matrix size (256 × 256), small field of view, and thin slices. Special reconstruction algorithms can also be chosen to improve spatial resolutions.
• Contrast resolution: Contrast resolution is defined as the ability of the system to discriminate between two adjacent areas with different attenuation values. The operator has several choices to improve contrast resolution: appropriate selection of reconstruction algorithm, tube current (measured in milliamperes), scanning time (measured in seconds), pixel size (matrix), and slice thickness. It must be remembered that increasing tube current or scanning time increases the radiation dose. Another strategy to increase contrast resolution is to use contrast material, either intra-articular or intravenous. The contrast resolution of CT is dramatically better than conventional radiography (approximately 100 times), and the images provide greater soft tissue detail than do plain films.4

Provided the patient remains motionless during the study, the CT scan provides good visualization of the shape, symmetry, and position of structures by delineating specific areas (Fig. 7-8). This information can be helpful in the examination of acute trauma, aneurysms, infections, hematomas, cysts, and tumors.

Clinical Applications

Cervical Spine

CT is most often utilized in the cervical spine examination in the assessment of potential fractures, but may not be the modality of choice when used in isolation for soft tissue imaging. For example, the accuracy of CT imaging ranges from 72% to 91% in the diagnosis of disk herniation, but approaches 96% when combining CT with myelography.34,35 A CT myelogram (CTM) is a diagnostic tool that uses radiographic contrast media (dye) that is injected into the subarachnoid space (cerebrospinal fluid, CSF). After the dye is injected, the contrast medium serves to illuminate the spinal canal, cord, and nerve roots during imaging. The low viscosity of the water-soluble contrast permits filling of the nerve roots and better visualization.4

Shoulder

CT is typically used for suspected fractures, particularly of the glenoid rim.

Elbow, Forearm, Wrist, and Hand

CT is preferred over radiography in cases of suspected ligamentous instability. In addition, fracture lines and fragment locations can best be delineated with the help of CT. CT has also been used to provide accurate assessment of the reorientation of the distal radius articular surface following fracture, which is critical in determining whether closed or open reduction is the preferred course of action.37

Pelvis and Hip

CT of the hip and pelvis is helpful with identifying the spatial relationships of fractures of the femoral head and acetabulum and any associated fragments, particularly in cases of complicated fractures.38 CT is also recommended when considering congenital hip dysplasia, preoperative prosthesis planning, and the detection of neoplasms.39

Knee

CT scans often used to view soft tissues as well as bone of the knee joint complex.

Ankle and Foot

CT often enables delineation of cortical and trabecular orientations of bone, and the articular surfaces in the joints better than plain films. This is particularly true in cases such as a talar dome injury.

Magnetic Resonance Imaging

MRI has been a viable imaging technique since the early 1980s and has now become the standard modality for differentiating among soft tissues in the neuromusculoskeletal system.40 Unlike CT, which depends upon multiple thin slices of radiation that are “backplotted” through Fourier transformers, MRI is the result of the interaction between magnetic fields, radiofrequency (RF) waves, and complex image reconstruction techniques. Normally, the axes of protons in the body have a random orientation. However, if the body or body part is placed within a high magnetic field, the protons align themselves parallel with, or perpendicular to, the direction of the magnetic field. Protons also have a natural spinning motion at a specific frequency (Lamor frequency). When an RF pulse of the same frequency as that of the spinning protons within the magnetic field is applied, the protons are deflected from their newly unlined axis by a specific angle with the degree of deflection being dependent on the strength of the applied RF wave pulse. The protons, now spinning synchronously or coherently at an angle with the magnetic field, induce a current in a nearby transmitter–receiver coil or antenna. This small nuclear signal is then recorded, amplified, measured, and localized (linked to the exact location in the body where the MRI signal is coming from), producing a high contrast, clinically useful MR image. The signal starts to decay as soon as the RF pulse is discontinued and the protons begin to relax back to a state of equilibrium. The decaying of the signal is intimately related to two factors:

• The realignment of the protons within the magnetic field (longitudinal relaxation).
• The loss of coherence or synchrony (dephasing) of the protons as they continue spinning at an angle to the magnetic field (transverse relaxation).

These two phenomena, called relaxation times T1 and T2 respectively, are biological parameters with tissue specific relaxation constants for different types of tissue and their molecular composition. For example, tissues such as water have very mobile protons that return very quickly to alignment in the magnetic field, whereas bone protons are largely immobile. T1 and T2 can be measured independently to create images that are dependent on different T1 values of the tissues (T1-weighted images, T1WI) or on different T2 values (T2-weighted images, T2WI). Images containing T1 and T2 information are called balanced images or proton density-weighted images (PDWI). Contrast between tissues is dependent on the differences between T1, T2, and PD values on T1WI, T2WI, or PDWI. For example, fat (including marrow fat) is bright on T1WI, while CSF is dark, and structures with high fibrous tissue content such as tendons, ligaments, and cortical bone are also dark. With T2WI, fluid including CSF, synovial fluid, and edema is bright, while the fat signal varies, and fibrous structures such as tendons, ligaments, and cortical bone are again dark.

The specific techniques for obtaining the MRI are called pulsed sequences. These pulse sequences result from changing imaging parameters such as the repetition time (TR), echo time (TE), or angle of deflection (RF or flip angle) (FA). By changing these parameters, the operator can control the rate of repetition of the RF pulses (TR), the time elapsed between an RF pulse and the production of the signal or echo (TE), and the intensity of the applied RF pulse which determines the FA. Images obtained using short TR and short TE will produce T1-weighted contrast. Images obtained with long TR and long TE will produce T2-weighted contrast, and images obtained with long TR and short TE will produce PD-weighted contrast. The latter sequences are termed spin echo (SE) and have been a mainstay of lumbar spine imaging. Table 7-4 itemizes the differences in signal intensities on T1-weighted and T2-weighted MR images.

Because of the unique properties of magnetic imaging, MRI is subject to a number of artifacts. The most important of these are metallic artifacts, specifically those produced by ferromagnetic objects, which distort the alignment of protons in the scanner's main magnetic field.4 Such spatial distortion may produce grossly erroneous measurements. Somewhat less common artifacts include banding artifacts, “wraparound” (an adjacent area wrapping into the area of interest, seen on very small fields of view) and chemical shift artifact (seen when tissues and markedly different chemical structures lie directly adjacent to one another, for instance, at the discovertebral interface).4

Clinical Applications

The advantages of MRI include its excellent tissue contrast, ability to provide cross-sectional images, noninvasive nature, and complete lack of ionizing radiation. MRI provides an excellent view of anatomic and physiologic tissues (Figs. 7-9 and 7-10). It is commonly used to assess the CNS and soft tissue injuries. In addition, MRI has been shown to be sensitive in the detection of occult bone lesions, and it can also detect and help assess both occult and traumatic bone lesions, especially occult stress and posttraumatic fracture.31 General contraindications for MRI include4

• intracranial aneurysm clips
• cardiac pacemakers
• some prosthetic heart valves
• implanted cardiac defibrillators
• carotid artery vascular clamp
• spinal cord stimulators (neuro stimulators)
• insulin infusion pump (implanted drug infusion device)
• bone growth stimulator
• metallic hardware, devices, fragments
• hearing aids and dentures (must be removed)
• cochlear implants, ocular implants, penile implants
• some shrapnel and bullets
• intraocular foreign bodies
• tattooed eyeliner
• some types of makeup

Spine

The combination of multiplanar capabilities and high contrast resolution that MR images provide are ideal for spinal imaging. MRI has demonstrated excellent sensitivity in the diagnosis of lumbar disk herniation, and is considered the imaging study of choice for detection and staging of demyelinating disorders involving the spine (e.g., multiple sclerosis) and syringomyelia and for detecting nerve root impingement, although the latter use is tempered by the prevalence of abnormal findings in asymptomatic subjects.41 It can, however, detect ligament and disk disruption, which cannot be demonstrated by other imaging studies.42,43

Shoulder

The main indications for MRI of the shoulder include rotator cuff pathology, GH joint instability, and shoulder pain of unknown etiology.

Elbow

The main indications for MRI at the elbow joint are to differentiate bone and soft tissues, study mass lesions, tendon and ligamentous lesions, osteochondral lesions, pediatric elbow fractures, compressive neuropathies, and miscellaneous conditions.40

Hand and Wrist

The most frequent indications for MRI of the hand and wrist include: the evaluation of palpable mass lesions, ligamentous tears, triangular fibrocartilage complex tears, posttraumatic avascular necrosis of the scaphoid, Kienböck's disease (avascular necrosis of the lunate), tendon tears, and compressive neuropathies.40

Hip

MRI is most commonly used in the hip to evaluate for the presence of avascular necrosis or osteonecrosis of the femoral head.40 Other indications for MRI of the hip include transient osteoporosis of the hip, osteochondral lesions, tumors, synovial chondromatosis, and pigmented villonodular synovitis (PVNS).40

Knee

The knee is one of the areas of the musculoskeletal system most commonly imaged by MRI. Meniscal and ligamentous injuries (Figs. 7-9 and 7-10) can be diagnosed with an accuracy of almost 95%.40

Ankle and Foot

The most common indications for MRI of the ankle include: tendon lesions, osteochondritis dissecans, chronic ankle instability, and pain of unknown etiology.40

Diagnostic Ultrasound (Ultrasonography)

Ultrasonography evolved with the development of military sonar, the sending and recording of a certain frequency of sound wave as it is transmitted and then reflected off various objects. Although initially used primarily for abdominal imaging, ultrasound imaging is rapidly becoming appreciated for its musculoskeletal applications. Diagnostic and therapeutic ultrasounds are similar in that both produce frequencies greater than 20,000 Hz. Continuous or pulsed therapeutic ultrasound produces 1 MHz or 3 MHz thermal and nonthermal energy, whereas diagnostic ultrasound produces pulsed waves at 7.5–20 MHz that are processed to produce pulsed echo images. A diagnostic ultrasound system is composed of a set of transducers, a power system, and computer unit with a display screen. The transducer, which is the device that sends and receives the ultrasound waves, is composed of an array of quartz crystals that generate these waves. As ultrasound waves are transmitted through the body, they are reflected at tissue interfaces, and the time it takes for the waves to be reflected back to the transducing probe allows the computer to produce an image. The reflectivity of the sound wave is influenced by two factors as follows44:

• Acoustic impedance of the two tissues composing the interface. Acoustic impedance is the product of the density of the material and the speed of sound transmission within the substance. The reflectivity is greatest at the interfaces between tissues of dissimilar acoustic impedance.
• The angle of incidence of the sound beam. When the angle of incidence of the sound beam is at 90 degrees or perpendicular to the tissue interface, the reflectivity is highest and decreases with increasing angle.

At highly reflective interfaces, almost all of the energy of the sound beam is reflected, producing a sound void area beneath the interface. This occurs between soft tissues and air or calcium. The sound beam appears to be enhanced when it passes through tissue such as water or other fluids that do not absorb ultrasound, therefore, showing as sound void areas. Thus, different tissues transmit sound waves at different velocities and, therefore, create different images. More dense tissue such as bone and collagen reflects more waves than less dense tissue such as water or fat.

Ultrasonography is perhaps more operator dependent than any other imaging modality.44 The ultrasound transducer must be held at a 90-degree angle to the scanning target tissue to prevent artifacts so that the maximal number of waves will be processed into an accurate image. Technical considerations are also important because it is necessary to operate with high resolution transducers to obtain images with sufficient diagnostic information. Despite its disadvantages, ultrasonography is a readily available technique, is less expensive than most other imaging modalities (with the exception of plain films), does not involve ionizing radiation, and is noninvasive.44 In addition, it allows real-time imaging, a feature that is very useful to some conditions, such as snapping tendon syndrome or developmental dysplastic hip, where dynamic imaging provides additional information.44 Some of the disadvantages of ultrasonography, including those already mentioned, are a small field of view and the presence of artifacts. Comet fail artifact is caused by deep echogenicity bands that cross tissue boundaries and is usually associated with metal or glass foreign bodies. Other artifacts are refraction and reverberation. Refraction occurs when the ultrasonography probe is not maintained at a 90-degree angle (perpendicular) to the examined tissues which can cause an incorrect depiction of structure or lesion. Reverberation occurs at highly reflective interfaces causing the appearance of phantom structures.

Ultrasonography can be used to diagnose any pathological condition that is located superficially enough to be detected by the transducer, and is currently used in orthopaedics to help detect soft tissue injuries, tumors, bone infections, and arthropathy and to evaluate bone mineral density. Tendons are well-suited because of the parallel fascicles of collagen and the ground substance which provide different receptivity, attenuation, and backscatter. Ultrasonography is particularly useful in staging muscle injuries, allowing for a more accurate estimate of when an athlete can return to sport. Ultrasound imaging may also be used to assess the degree and quality of fracture healing and in the detection of synovitis and wood and plastic foreign bodies. Finally, ultrasonography can be used to confirm proper placement of an injection and provide diagnostic information as well as to provide treatment for inflammatory conditions such as bursitis, intraarticular loose bodies, cysts, and nerve thickening. Future uses for ultrasound imaging will likely include the placement of tissue grafts (stem cells, platelets, matrixes) to aid in the healing of injuries because of its real-time imaging capabilities.

Radionucleotide Bone Scanning

Radionucleotide scanning studies involve the introduction of bone seeking isotopes, which are administered to the patient orally or intravenously and allowed to localize to the skeleton. The photon energy emitted by the isotopes is then recorded using a gamma camera 2–4 hours later. The pathophysiologic basis of the technique is complex but depends on localized differences in blood flow, capillary permeability, and metabolic activity that accompany any injury, infection, repair process, or growth of bone tissue.31 The most common radionuclide scanning test is the bone scan (Fig. 7-11). This test is used to detect particular areas of abnormal metabolic activity within a bone. The abnormality shows up as a so-called hot spot, which is darker in appearance than normal tissue. The bone scan is an extremely sensitive but fairly nonspecific tool for detecting a broad range of skeletal and soft tissue abnormalities. An abnormal bone scan may indicate tumor, avascular necrosis, bone infection (osteomyelitis), Paget's disease, or recent fracture. Comparison of the affected and unaffected side is generally used to detect differences in uptake. Whole body or spot views, patient positioning, and the number of views employed depend on the indication for the examination.

Three Phase Bone Scan

The three phase bone scan consists of the following image phases45:

1. Flow study. The injection is the same as for a routine bone scan, but imaging is begun immediately after the injection. Sequential images are obtained every 2–3 seconds for 60 seconds.

2. Blood pool. Immediately following the flow study, a blood pool image is obtained over the area of interest. This image serves as a marker of extravascular tissue activity.

3. Delayed static images. After a minimum of 2 hours, images are obtained over the area of interest. These images demonstrate radioisotope uptake in the osseous structures.

SPECT Scan45

Single photon emission computed tomography (SPECT) scanning improves both the detection and localization of an abnormality by permitting spatial separation of bone structures that overlap on standard planar images. After acquisition of the study, a computer is used to reconstruct images in axial, sagittal, and coronal planes. To date, bone SPECT has been found to be of particular clinical value in studies of the vertebral column and has been shown to be more sensitive than plain film radiology, with the majority of SPECT lesions corresponding to identifiable disease on CT. SPECT scanning is a highly sensitive means of detecting spondylolysis, a fracture of the pars interarticularis.

Clinical Applications

Radionucleotide bone scans are used throughout the body. Applications of the radionuclide bone scan can be divided into traumatic and nontraumatic categories as follows31:

• Traumatic.
  • Fractures.
  • Anatomically difficult locations. These include the scapula, sternum, sacrum, and portions of the pelvis.
  • Occult fractures (nondisplaced or stress fractures). Bone scans can reveal metabolic disturbance at a fracture site within 24 hours of the injury, long before a conventional radiograph shows any abnormality and often before they are symptomatic.31 Such fractures include the tibia (Fig. 7-11), scaphoid, radial head, and the femoral neck. Stress fractures of the metatarsals and other bones are seen on bone scan up to 2 weeks before becoming visible on plain radiographs.
  • Traumatic osteonecrosis without fracture.
• Nontraumatic
  • Osteomyelitis. This condition causes localized increased uptake of the isotope which is visible on bone scan within 48 hours of the beginning of infection.
  • Tumor, primary or metastatic. These are usually detectable by bone scan by the time they cause symptoms. The ability of the scan to cover the whole skeleton is particularly useful for determining the presence and extent of metastatic disease.
  • Occult fractures.
  • Tendinitis and tenosynovitis.
  • Hip pain.
  • Adults: aseptic necrosis, arthritis, transient osteoporosis, occult femoral neck fracture. Aseptic necrosis appears either as a hotspot overlying the femoral head or as a cold central area surrounded by a ring of increased uptake. Transient osteoporosis, an entity mainly affecting young men, also demonstrates increased uptake of the femoral head when viewed under a bone scan. However, transient osteoporosis displays a decreased bone density when viewed on plain films. Arthritis causes increased uptake of isotope in periarticular bone on both sides of the joint. Occult femoral neck fractures resulting from normal stress placed on bones weakened by osteoporosis are seen on bone scan as bands of increased uptake localized to the neck of the femur.
  • Children: arthritis, Legg–Perthes disease. The bone scan in Legg–Perthes disease reveals decreased up-take at the femoral head early in the disease. Later, a ring of increased uptake may surround the cold spot.

• 1. Which imaging study is generally considered to be the first order diagnostic imaging modality?

• 2. List the following structures in order of descending density: air, water or body fluid, metal, bone, soft tissue, and fat.

• 3. Which imaging modality gives the best view of cortical bone?

• 4. What conditions are stress radiographs helpful in detecting?

• 5. Which of the imaging modalities relies on the use of a very powerful magnet to produce images?

• 6. Which of the imaging studies is used to study structures within an encapsulated joint using a contrast medium with or without air that is injected into the joint space?

• 7. What is the radiographic study of the vascular system called?

• 8. What are the two parameters used to define image quality of a CT scan?

Answers