Pathological conditionsPhysical injury
Physical abuse to bone and soft tissue represents the most common indication for radiologic examination of the musculoskeletal system. However, radiography does not constitute the most important part in the evaluation of trauma. The initial stage in the care of the injured patient should be to obtain a detailed history and to perform a careful physical examination, including determination of the mechanism of the injury,
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Figure 13.
Normal anatomy of the hand. a) PA radiograph, b) lateral radiograph. The joint surface of the distal end of the radius is angulated volarly 10 to 15 degrees. v = volar, d = dorsal. c) anatomic drawing of the bones of the carpus. d) Coronal CT section of the carpus and wrist. e) T1-weighted coronal MR image of the wrist.
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Figure 14.
Normal anatomy of the hip. a) Ap radiograph of the left hip. b) Transaxial CT section of the left hip c and d) T1-(c) and T2-weighted (d) coronal MR images of the adult hip. e) T1-weighted coronal MR-image of the right hip of a child
A = acetabulum, Af = femoral artery
C = femoral head, E = epiphysis, G = gluteal muscle,
M = metaphysis, T = greater trochanter, V = femoral vein, open arrows = hip joint capsule, white arrows = cartilage.
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Figure 15.
Normal anatomy of the knee joint. a) AP radiograph, b) lateral view, c) transaxial view of the patellar joint, d) transaxial CT section, e) T1-weighted transaxial MR image, f) T1-weighted sagittal MR image. AV = popliteal artery and vein, Bx = posterior cruciate ligament, Lp = patellar ligament, P = patella, Q = quadriceps tendon, white arrows = cartrilage, open arrows = joint capsule.
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whenever possible. A radiographic examination should never be considered a substitute for the history and the physical examination; serious injuries commonly exist in the absence of radiographic findings. It is mandatory that significant data provided by the history and the physical examination be included on the request for radiographic examination if a relevant and sufficient examination is to be obtained. In any case, the radiologist also should assess the injury by performing his or her own physical examination.
The initial radiographic examination should include well-known standard views, which are used because they have been found to demonstrate most abnormalities. To do less than this will compromise the evaluation. Under no circumstances should radiographs in a single plane only be considered adequate. Radiographs in two planes at right angles to each other are the minimum, although additional oblique views often are necessary. The imaging assessment of the injury may require information obtained from methods other than conventional radiographs, such as sonography, CT, MRI, or bone scintigraphy, which commonly demonstrate the extent of the injury within the soft tissue or bone marrow.
Successful treatment starts with accurate diagnosis. The physician should be familiar with the common pathogeneses of injury. Certain activities result in specific forms of injury, following a typical pattern commonly related to the age of the patient, the type of trauma, and its location. Insufficient knowledge of the mechanism and circumstances of injury is the most common reason for misinterpretation of radiographs after trauma. For this reason, emphasis in this chapter is placed on the general principles governing the analysis of the most common fractures and dislocations and on those injuries that, when overlooked, may result in serious complications.
Terminology
A fracture, in its most simple definition, is a break in the continuity of bone, cartilage, or both, with associated soft tissue injury. It should be stressed that in many injuries the therapeutic implications of the soft tissue lesion may be more important than the associated break of bone.
A closed fracture indicates that the skin is intact. An open fracture is characterized by disruption of the skin, which allows communication between the fracture and the outside environment.
A complete fracture occurs when the entire circumference (tubular bone) or both cortical surfaces (flat bone) have been disrupted (Fig. 16). A complete fracture may consist of two fragments (Fig. 16 d); however, if more than two fragments are present, the fracture is termed a comminuted fracture (Fig. 16 e). Incomplete fractures occur in the elastic bones of children and young adults and are classified into various types, including traumatic bowing (Fig. 16 a), torus fractures (Fig. 16 b), and infractions (greenstick fractures) (Fig. 16 c) (see also Chapter 14).
A transchondral fracture represents an injury to the joint. The fragments may consist of cartilage alone or both of cartilage and bone and are termed chondral and osteochondral fractures, respectively. Osteochondritis dissecans may be the result of such a lesion (Fig. 17). Bone scintigraphy is an important examination for detection these lesions, and CT and MRI are needed to visualize their full extent. Osteochondral fractures are seen most commonly in connection with ligamentous lesions of joints (e.g., injury of the femoral condyles in anterior cruciate ligament tears of the knee).
Bone bruise of the bone marrow is a term that has been introduced as a result of MRI findings in patients who have had an injury. It is considered to represent edema or bleeding secondary to traumatic trabecular lesions. A bone bruise is seen most commonly in cases of bone contusion and in early stages of stress fractures (Fig. 70).
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Figure 17.
Osteochondral injury of the dome of the talus.
a) AP radiograph of the left ankle 2 years after a fracture of the medial malleolus. A
defect with a fragment in the medial aspect of the talus (arrow) is seen.
b) Coronal CT section of the ankle joint. The defect of the talus is visualized clearly,
as is the migrating osteochondral fragment. C = calcaneus, L = lateral malleolus,
Ta = talus, Ti = tibia, open arrow = metal artefact caused by the head of the screw
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An impaction fracture results when one fragment of bone is driven into an apposing fragment. Two specific types of impaction fractures are recognized. A compression fracture most commonly involves the vertebral bodies. A depression fracture results when impacted forces occur between one hard bone surface and an apposing softer surface, typically represented by a fracture of the lateral tibial condyle after a valgus force is applied to the knee (Fig. 44).
An avulsion fracture occurs when an osseous fragment is pulled from the parent bone by a tendon or a ligament (Fig. 18). On the radiographs this type of fracture appears as a small thin cortical fragment dose to the joint. In the assessment of an avulsion fracture, the effect of ligamentous disruption on joint stability must be considered. In the intervertebral joints of the spine, the carpometacarpal joints of the hand, the ankle, and the articulations in the foot, a single fragment in one
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Figure 18.
Avulsion fracture of the medial malleolus (white arrow).
A fracture of the distal end of the fibula is observed (open arrow). The avulsion fracture and the widening of the joint space medially indicate a serious ankle in jury (supination-external rotation injury stage IV).
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Figure 19.
Lipohemarthrosis of the hip joint. Transaxial CT section of the right hip after trauma. The radiographic examination was normal. The joint capsule (arrowheads) is displaced from the femoral head. A fat-blood level is present (arrows). The fat (of lower density) is located above the blood.
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radiographic view may represent complete joint disruption (e.g., fracturedislocation) (see later).
A joint effusion containing blood and fat occurring after trauma is termed a lipohemarthrosis and is reliable evidence of an intraarticular fracture, the fat being released from the marrow. Radiographic examination using horizontal beam technique may demonstrate a fat-blood fluid level after injury to the joint and may represent the only sign of bone injury. Most commonly, this finding is seen in radiographs of a knee or shoulder, but it also may be noted in those of other articulations, including the elbow and hip (Fig. 19).
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Figure 20. Reporting of fractures (see text).
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An accurate and concise radiographic report is an important responsibility of the radiologist, yet one that commonly is ignored. A radiographic report that includes such terms as "satisfactory" or "unsatisfactory" in describing the position is of no value, as this decision is better left to the orthopedic surgeon. The report should accurately describe the characteristics of the injury and its type and stage, using precise and accepted terminology.
Location and appearance
The distance of the fracture from a defined landmark (e.g., a joint space), the course of the fracture (transverse, oblique, or spiral), and the number and displacement of fracture fragments are note d in the report.
Displacement (Fig. 20 a)
The radiographic report also describes the position of the fracture (i.e., the extent of the dislocation, expressed as a percentage of bone width as seen on two perpendicular views; Fig. 20 a); shortening or compression, measured precisely in centimetres or millimetres (Fig. 20 b); and angular displacement, reported in degrees, on frontal views (Fig. 20 c), on lateral views, and with internal or external rotation along the long axis of the bone (Fig. 20 d).
By convention, the displacement of the distal fragment is described in relation to the proximal one.
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Figure 21.
Fracture of the distal end of the radius (Colle's fractures).
a) PA view,
b) lateral view. The angulation occurs in a dorsal direction. v = volarly, d = dorsally.
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Injuries of the upper extremity
Fractures of the distal portion of the forearm and the wrist are the most common injuries of the entire skeletal system and among the injuries that are overlooked most frequently. These injuries are well suite d to illustrate the general principles that govern the analysis of fractures and dislocations as a whole.
Forearm
The distal end of the radius is expanded and has a slightly concave surface that articulates with the carpal bones (Fig. 13). In the lateral view, the distal surface of the radius is angulated 10 to 15 degrees in a palmar or volar direction (Fig. 13 b). A fracture of the distal portion of the radius most often reveals posterior angulation with impaction of its dorsal surface, a pattern commonly termed a Colle's fracture (Fig. 21). Although cortical disruption may not be seen in the frontal and lateral radiographs, the absence of palmar angulation of the joint surface is indicative of a radial fracture with dorsal impaction. The fracture often is comminuted, with articular involvement. In 60% of the cases there is an associated fracture of the styloid process of the ulna.
Injury to the distal portion of the radius in children may involve the physis, most commonly is a Salter-Harris type II injury (Chapter 14), and
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Figure 22.
Epiphysiolysis of the distal end of the radius with displacement in a dorsal direction, Salter-Harris type II in jury (see Chapter 14). Two years after the injury there is premature closure of the physis and severe deformity.
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may lead to displacement of the epiphysis (Fig. 22). In the child, bone displacement and angulation commonly occur in a dorsal direction.
A fracture of the distal end of the radius also may appear with volar angulation of the distal fragment. This fracture is the opposite of a Colle's fracture and therefore, often is referred to as a reverse Colle's fracture or Smith type fracture (Fig. 23). A striking similarity is seen in the appearance of a Colle's and a Smith type fracture on the posteroanterior (PA) view of the wrist. The precise diagnosis is made on the lateral view, which clearly demonstrates that in cases of a Smith type fracture, the distal fragment is displaced anteriorly with palmar angulation of the radial articular surface. The Colle's fracture and the Smith type fracture both are treated with closed reduction of the displacement even when comminuted and when intraarticular extension is present.
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Figure 23.
Fracture of the distal end of the radius of Smith type with displacement volarly (v).
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Figure 24.
lntraarticular fracture of the distal end of the radius, fracture-dislocation, Barton type. The volar lip of the distal portion of the radius is displaced in the proximal direction, together with the carpus.
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Figure 25.
CT of Bartan type fracture-dislocation. Sagittal CT section through the base of the third metacarpal bone (m), the capitate (c), the lunate (l), and the distal end of the radius (r). The fracture is intraarticular with displacement of the volar lip.
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The Barton fracture represents a classic example of a fracture-dislocation. In 1838 Barton described a fracture of the rim of the distal radial joint surface in the coronal plane with the volar lip of the distal end of the radius being displaced proximally together with the carpal bones (Figs. 24, 25). Fractures involving the volar rim are more common than those involving the dorsal rim (original Barton fracture). Open reduction with fixation of the larger fragments is required in this type of fracture dislocation. The Barton fracture may be associated with a Smith type fracture, which may lead to some diagnostic confusion, and conventional tomography or sagittal CT images may be helpful to confirm the presence of disruption of the radiocarpal joint (Fig. 25).
Hand
The Bennett fracture is an oblique fracture of the base of the first metacarpal bone. The metacarpal bone is pulled dorsally and radially by the abductor pollicis longus tendon. The fracture extends into the first
Carpometacarpal joint, isolating a fragment consisting of the volar lip of the base of the first metacarpal bone. This volar fragment remains in place (Fig. 26). The Bennett fracture requires surgical reduction with pin fixation. Conversely, a transverse fracture at the base of the first metacarpal bone is relatively benign and without joint instability, but it may be comminuted with intraarticular extension (Rolando fracture). Fracture-dislocations may be seen in any carpometacarpal joint. In the fifth carpometacarpal joint the injury commonly is termed the reverse Bennett injury (Fig. 27). Fracture-dislocations of other carpometacarpal joints are relatively rare but important to diagnose (Fig. 28). These injuries are overlooked easily because many bones are superimposed in the lateral view. Physical examination is extremely important and even the smallest bone fragment seen in any of the views may indicate a fracture-dislocation. Conventional tomography and CT are valuable for visualizing the injury and associated bone displacement (Fig. 28). Displacement of the metacarpal bones occurs in the dorsal and proximal direction and requires pin fixation after reduction.
Carpus
Disruption of ligaments between the carpal bones may result in displacement and instability between the carpal bones, most commonly between the scaphoid and the lunate. To assess these lesions, knowledge of normal anatomy in the frontal as well as the lateral view is necessary. Carpal instability commonly is visualized only at dynamic examination during which documentation is afforded by video recording or fluoroscopy during active or passive movement of the wrist.
Scaphoid
The most commonly fractured carpal bone is the scaphoid. Generally such fractures occur between the ages of 15 and 40 years; they are rare in childhood and after the age of 60 years. Approximately 70% of the fractures of the scaphoid occur in the waist (Fig. 29). The clinical sign of a scaphoid fracture is tenderness in the anatomic snuffbox. At radiography the fracture line may be so fine that it is obscured, and several views with varying degrees of angulation may be required before the fracture is identified.
In some cases the fracture simply is not apparent on the initial examination despite strong clinical suspicion. In this situation the wrist is
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Figure 29.
Fracture of the scaphoid.
a) Old fracture through the scaphoid with delayed union. The density of the proximal fragment is increased relative to the distal fragment and remaining carpal bones. The increased density may indicate osteonecrosis of the proximal fragment.
b) T1-weighted coronal MR image of the wrist demonstrates normal bone marrow signal intensity of the proximal fragment but decreased signal intensity of the fracture and the distal fragment.
c) T1-weighted image after intravenous injection of gadolinium contrast agent. There is enhancement of the fracture area and the distal fragment, indicating vital bone. This was confirmed at surgery, during which the fracture was found to have healed with fibrous union.
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placed in a cast or plaster splint and re-examined in 7 to 10 days. If strong clinical suspicion still exists, a bone scan or MRI will exclude or confirm the presence of an occult fracture or a bone contusion. Should the patient be lost to follow-up, delayed union or non-union of a scaphoid fracture may occur with or without osteonecrosis of the proximal fragment (Fig. 28).
Fractures of the remaining carpal bones are relatively rare.
Phalanges and metacarpal bones
Fractures of the phalanges are more common than those of the metacarpal bones, and fractures of the distal phalanges account for more than half of all fractures of the hand. Phalangeal fractures commonly are
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Figure 30.
A boxer's fracture of the fifth metacarpal bone with delayed union.
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comminuted and work-related. A characteristic injury of the fifth and sometimes the fourth metacarpal bone is the boxer's fracture resulting from a blow struck with the fist. The distal fragment characteristically is angulated volarly. Reduction of the fracture fragment may be difficult, and healing may be delayed (Fig. 30).
Metacarpophalangeal joints and interphalangeal joints
In the assessment of ligamentous injuries of the joints of the fingers, diagnosis of a ligament tear usually is accomplished clinically. The initial radiographic examination is normal except in those cases in which a small avulsed triangular fragment appears at the site of the insertion of the collateral ligament. A typical lesion, termed the "gamekeeper's thumb", is an injury to the ulnar collateral ligament of the metacarpophalangeal joint of the thumb. The lesion is particularly common in skiers.
Radius and ulna
Fractures of the shafts of the bones of the forearm are quite common, often caused by a fall on the outstretched hand resulting in a compression force along the longitudinal axes of the bone. The fractures also may be caused by a direct blow to the forearm. These forces usually result in a fracture of both bones, and the diagnosis usually is obvious both clinically and radiographically. Two views of the forearm are required to
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Figure 31.
Galeazzi injury with isolated fracture of the radius and displacement of the distal radioulnar joint (arrow).
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Figure 32.
Monteggia injury with isolated fracture of the ulna and dorsal angulation associated with ventral dislocation of the radial head.
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confirm the diagnosis; however, care should be taken to include both the elbow and the carpal bones in the examination so any associated dislocation or fracture will not be overlooked. Fractures of the shaft of both bones of the forearm rarely are merely angulated, either ventrally or dorsally. Almost always, some degree of rotation of the distal fragment is seen. To maintain a normal range of supination and pronation it is important that the degree and nature of the rotational displacement be determined radiographically after fracture reduction and fixation.
A fracture of a single bone of the forearm is less common. As a general rule, an isolated fracture of either the ulna or the radius indicates a high probability of displacement of the other bone at the elbow or the wrist.
The definition of the Monteggia lesion includes radial head displacement in any direction associated with a fracture of the ulnar shaft. The fracture of the ulna is located in the proximal third in 89% of the cases, in the middle third in 10% of cases, and in the distal third in 1% of cases. The direction of the displacement of the radial head and the angulation of the ulnar fracture are characteristic. Most common (65 %) is an anterior dislocation of the radial head associated with fracture of the ulnar diaphysis at any level, with anterior angulation at the fracture site (Fig. 32). Less common (18%) is a posterior dislocation of the radial head associated with fracture of the ulnar diaphysis with posterior angulation at the fracture site. In children the ulnar component of the Monteggia lesion often is a greenstick fracture or, on occasion, a bowing type of injury. Most commonly, treatment requires open reduction of the fractures.
A direct blow may result in isolated fracture of one bone particularly the ulna, without either fracture or dislocation of the other. Isolated fractures of the radius usually occur at the junction of the middle and distal thirds of the bone and almost invariably are associated with dislocation of the distal radioulnar joint with disruption of the triangular fibrocartilage (Fig. 31). Treatment almost invariably requires open reduction. It is important to look for evidence of redislocation on follow-up radiographic examinations of the Monteggia lesion and, in particular, the Galeazzi fracture.
Elbow
The elbow articulation is composed of three distinct joints, the humeroulnar, the humeroradial, and the radioulnar, all contained within one single synovium-lined cavity, the capsule of the elbow joint. The capsule comprises two distinct layers, the inner (synovial) layer and the outer (fibrous) layer. Fat interposed between these two layers, both anteriorly and posteriorly, is termed the anterior and posterior fat pads. The initial examination of the traumatized elbow includes anteroposterior (AP) and lateral views. In many cases the injury is obvious (Fig. 34), but fractures with minor degrees of displacement or subtle injuries may be difficult to see. Therefore, analysis of radiographs of the injured elbow should include a search for the fat pad sign (Fig. 33). An intraarticular fracture may allow blood and marrow contents to collect within and to expand the joint (lipohemarthrosis). If a positive fat pad sign is not present in a child or adult, significant intraarticular injury is unlikely. However, the fat pad sign is not specific for trauma; any cause of a joint effusion or synovitis may give rise to this sign.
The most common injuries of the elbow in adults are fractures of the radial head and neck (50%), fractures of the olecranon (20%), dislocations and fracture-dislocations of the elbow (15%), and supracondylar fractures of the humerus (10%). Approximately one half of all fractures of the radial head and neck are undisplaced, and oblique views frequently
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Figure 33.
Traumatic hemarthrosis of the elbow joint, the fat pad sign A fracture of the radial head, Salter Harris type II (white arrow), is seen. A joint effusion displaces the ventral as well as the dorsal fat pad (white arrowhead). A normal ossification centre of the olecranon is present.
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Figure 34.
Displaced supracondylar fracture of the humerus in a child.
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Figure 35.
Fracture of the surgical neck of the humerus (black arrow) with moderate displacement. Soft tissue calcification is present about the greater tuberosity (white arrow).
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are necessary to disclose them. Fractures of the olecranon usually are obvious and readily demonstrated at radiography in the lateral projection. Most fractures of the olecranon are displaced and require open reduction and fixation. The elbow is the third most common site of joint dislocation in adults, the shoulder and interphalangeal joints of the fingers being the two most frequent. The elbow is the most common site of dislocation in children. Soft tissue lesions commonly are the most important sequelae of these injuries.
In children the supracondylar fractures are by far the most frequent (60 %), and fractures of the radial head and neck are rare, most commonly seen as a Salter-Harris type II injury (Fig. 33). Many supracondylar fractures are barely visible and recognized only by joint effusion and characteristic posterior angulation of the distal fragment. After open or closed reduction, it is important to determine external or internal rotation of the distal fragment (Fig. 9).
Humerus
Fractures of the humeral shaft are common. The shaft of the humerus, with its wide range of motion and relatively unprotected position, is exposed to a variety of stresses that may result in injury. With displaced fractures, associated injuries of nerves, particularly the radial nerve, are common. Fractures of the proximal portion of the humerus (Fig. 35) most often result from the moderate trauma sustained in a fall from the standing position, landing on the outstretched hand. The prevalence of fracture is two to three times greater in women than in men, and this fracture is associated with an increased prevalence of other fractures, particularly of the distal end of the radius and proximal portion of the femur, in patients with osteoporosis. The fractures through the surgical neck may consist of two fragments but commonly are comminuted, with significant displacement and multiple fragments involving the joint surface. In the presence of severe comminution, CT is helpful in determining displacement and rotation of fracture fragments and their relation to the glenoid fossa. During the post-injury period, the humeral head may be displaced inferiorly to such an extent that the joint surface becomes incongruent giving a false appearance of traumatically induced inferior subluxation or dislocation. The displacement may be related to the joint effusion and, in some cases, the weight of the cast.
Glenohumeral joint
The glenohumeral joint is the most commonly dislocated joint in the body, accounting for over 50% of all dislocations. Such dislocations are uncommon in children. Glenohumeral dislocations are classified as anterior, posterior, inferior, or superior. Approximately 40% of anterior dislocations are recurrent. Although posterior dislocations account for only 3 % of all dislocations, they are troublesome because of the ease and frequency with which the diagnosis is missed on the initial evaluation. Posterior dislocations may be bilateral and commonly are associated with seizures and drug abuse.
In 95% of dislocations of the glenohumeral joint, the humeral head is displaced anteriorly. The diagnosis of anterior dislocation usually is obvious on physical examination. Radiographic examination is confirmatory, and the dislocation is best demonstrated using the axial or semiaxial view. The dislocated humeral head most often rests in the subcoracoid position. Three different complications may be seen: avulsion fracture of the greater tuberosity (15%); compression fracture of the humeral head (Hill-Sach's defect) (60%); avulsion fracture of the anterior rim of the glenoid (10%) or, alternatively, a lesion of the anterior portion of the glenoid labrum, (Bankart lesion), either of which may result in joint instability and recurrent dislocation.
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Figure 36.
Partial tear of the supraspinatus tendon.
T1-weighted coronal MR image shows increased signal intensity of the supraspinatus tendon (arrow) and reduced signal intensity in the subdeltoid fat (arrowheads). T2 weighted MR images confirmed the presence of the tear.
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The bone lesions are best demonstrated by CT and the soft tissue lesion of the anterior labrum by CT arthrography, MRI, or sonography (Fig. 12).
The rotator cuff in the subacromial space contains four tendons, the subscapular, supraspinatus, infraspinatus and teres minor tendons. Anterior dislocations occurring in persons over the age of 45 years frequently are complicated by tears of the rotator cuff, but such tears more commonly are the result of degenerative and inflammatory conditions (Fig. 36). Diagnosis of a total tear of one of these tendons is based on the clinical examination and commonly is confirmed at arthrography, sonography or MRI. Partial tears of the rotator cuff most commonly involve the anterior portion of the supraspinatus ten don and their visualization by imaging techniques remains a challenge.
Acromioclavicular joint
Displacements of the acromioclavicular joint are visualized on the frontal projection of the shoulder with proximal displacement of the lateral portion of the clavicle relative to the acromion. Demonstration of acromioclavicular joint instability by passive traction of the upper extremity has little clinical significance today.
Clavicle
The clavicle is a very frequent site of fracture. Most fractures of the clavicle are complete and displaced, but they may appear as either a greenstick
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Figure 37.
The Garden classification of fractures of the femoral neck.
Figure 38.
Types of intertrochanteric fractures of the proximal end of the femur, classified according to the number and localization of fragments.
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or a bowing injury as well.
Scapula
Fractures of the scapula commonly are associated with other fractures. Usually they result from a direct blow to the shoulder, as in a motor vehicle accident. CT plays a role in the assessment of complex injuries to the scapula by establishing the relationship of major fragments.
Injuries of the lower extremity
Pelvis, hip, and femur
Fractures of the femoral neck (Fig. 37) and the intertrochanteric region (Fig. 38) begin to appear after the age of 45 years, and the frequency then increases progressively with increasing age, especially in women, reflecting the effects of osteoporosis. Fractures of the proximal end of the femur constitute a major public health issue because of their frequency, morbidity, mortality, and cost. Most fractures are displaced; however, even undisplaced fractures of the femoral neck should not create
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Figure 39.
Osteosynthesis of femoral neck fracture.
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Figure 40.
Displaced fractures of the pubic rami associated with fracture of the left portion of the sacrum (arrows).
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diagnostic problems. The demonstration by sonography or CT of a lipohemarthrosis (Fig. 19) is indicative of an intracapsular fracture. In the absence of joint effusion a fracture of the femoral neck is unlikely. If an effusion is present, extension and internal rotation of the hip will lead to elevation of intracapsular pressure and result in severe pain. The pain and increased intraarticular pressure are diminished by flexion and external rotation of the hip or by joint aspiration. Displaced as well as undisplaced fractures require surgical procedures (Fig. 39).
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Figure 41.
Hip joint dislocation.
a) AP radiograph of the left hip after a motor vehicle accident. A large fragment appears at the medial aspect of the neck. The position of the femoral head, relative to the acetabulum, simulates loss of joint space.
b) CT examination confirms the presence of dislocation
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After an injury to the hip joint, a fracture of the acetabulum or the pubic rami must be excluded. Therefore, the radiographic examination should include views of the entire pelvis including both hips and sacroiliac joints.
Fractures of the acetabulum commonly are subtle and may require oblique views for diagnosis. Lipohemarthrosis with increased intracapsular pressure commonly is seen after fractures of the acetabulum. Fracture of the pubic rami may result in disruption of the entire pelvic ring. Indeed, fractures of the pubic rami are associated almost invariably with other fractures of the pelvic ring, especially a vertical fracture of the sacrum adjacent to the sacroiliac joint (Fig. 40). These secondary sacral fractures often are inapparent on the radiographs but are confirmed at scintigraphy, CT, or MRI.
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Figure 42.
Osteonecrosis of the femoral head after fracture of the neck. Almost nothing remains of the head, and the nail is penetrating the acetabulum.
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Dislocations and fracture-dislocations of the hip are relatively rare injuries, resulting from severe trauma, most commonly motor vehicle accidents (Fig. 41). CT is essential in the management of these injuries.
Osteonecrosis of the femoral head after displaced fractures of the femoral neck and hip dislocations occurs with a frequency of more than 20%. Ischemia of the femoral head can be demonstrated shortly after injury by means of bone scan, but radiographic changes rarely are seen within the first year after the injury (Fig. 42).
Subtrochanteric fractures commonly are considered a subgroup of the intertrochanteric fractures, occurring in the elderly as a result of falls or metastatic disease and in the young as a result of severe trauma. Fracture of the femoral shaft in the young adult is the result of severe violence and in the elderly person generally is related to metastatic disease. Such fractures also occur in children, in whom growth disturbance may follow the injury. Spontaneous correction of angular and rotational deformity may take place in young children but not in adolescents and adults. Rotational displacement after fem oral shaft fractures is determined by measurement of the femoral neck anteversion by CT (Fig. 10).
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Figure 43.
Classification of supracondylar fractures of the femur.
a) transverse,
b) unicondylar, and
c) intercondylar.
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Knee
Supracondylar fractures (Fig. 43) are most common in elderly women and are associated with other diseases, such as osteoporosis, osteoarthrosis, rheumatoid arthritis, or neurologic disorders.
Tibial plateau fractures more commonly involve the lateral plateau (75 %) and are caused by a valgus force to the knee. The fem oral condyles generally are stronger than the tibial plateaus. It is important to determine the presence and depth of depression of the fracture fragments, a factor that has surgical implications. The extent of the displacement may not be immediately obvious on standard radiographs (Fig. 44). If the fractures are comminuted, surgical reconstruction may be difficult and the development of secondary osteoarthrosis is not uncommon.
Fractures of the patella occur by direct blows or indirectly from tension forces generated by the quadriceps muscle. The most common fracture is transverse and, if displaced, requires open reduction and fixation.
Dislocation of the patella is a common injury. Lateral dislocations predominate. The dislocation results from an abrupt femorotibial rotation occurring during running or dancing with the knee in flexion and with external rotation of the tibia. Recurrent dislocation may occur because of weakening or tears in the medial retinaculum (Fig. 7) or as a result of anatomic factors, including dysplasia of the femoral condyles or of the patella, high position of the patella (patella alta) in its relation to the femoral condyles, or joint laxity, allowing abnormal femorotibial rotation.
During analysis of routine radiographs, which includes assessment of the transaxial view, it is important for the radiologist to realize that dislocation frequently is associated with chondral or osteochondral
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Figure 44.
Fracture of the lateral tibial condyle after a fall from a height.
a) The radiograph shows displacement of fragments of a lateral condyle, but the
severity of displacement cannot be assessed.
b) T1-weighted sagittal MRI scan of the lateral femoral and tibial condyle. Advanced
displacement of osteochondral fragment (white arrows) is present. The tibiofibular
joint is indicated (black arrow).
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Figure 45.
Tear of the anterior cruciate ligament.
T1-weighted sagittal MR image. The posterior cruciate ligament (white arrow) is well demonstrated, but only a small portion of the anterior cruciate ligament is visible.
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fractures. These arise either from the medial facet of the patella, or from the lateral edge of the fem oral condyle, or from both locations. Numerous operations are proposed to prevent recurrent patellar dislocation, but many of these result in a high frequency of secondary osteoarthrosis. Recurrent dislocation is rare after the age of 30 years.
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Figure 46.
Sagittal instability after complete tear of the anterior cruciate ligament.
a) Standing lateral view of the knee joint without load to the joint.
b) With weightbearing, displacement of 12 mm occurs.
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b
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Disruption of the anterior cruciate ligament is a common injury, which is associated with sport activities. The diagnosis of a complete tear is made on clinical examination. Arthroscopy or MRI is confirmatory (Fig. 45). Complete tears, as well as partial tears, may require surgical reconstruction. Functional instability of the knee joint is a predisposing factor for osteoarthrosis and commonly is demonstrated in the routine lateral view of the knee joint if performed with the knee weightbearing (Fig. 46).
Tears of the menisci represent the most common internal lesion of the knee joint. The diagnosis of meniscal tear depends on clinical examination and arthroscopy (at which time fine repair can be performed). Arthrography is a reliable technique to demonstrate and localize meniscal lesions, but, in large part, it has been replaced by arthroscopy or MRI, or both (Fig. 47).
Tibia and fibula
It is important that radiographic evaluation of all fractures of the diaphyses, tibia, and fibula allows visualization of the entire length of the bones, the knee, and the ankle joint. Fractures of the tibia frequently are associated with fractures of the fibula, often located at a point remote
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Figure 47.
Tear of the medial meniscus. T2-weighted sagittal MR image of the medial portion of the femur and tibia using gradient echo technique. There is a normal low signal intensity in the anterior horn of the medial meniscus (black arrow). In the posterior horn of the meniscus a tear is seen (white arrow). V = joint effusion, B = Baker cyst.
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a
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Figure 48.
Fracture of the lower leg and ankle of a child.
a) The radiograph demonstrates a spiral fracture extending distally through the physis and the epiphysis with slight displacement.
b) T1-weighted coronal MR image of the ankle demonstrates the extension of the lesion within the physis and epiphysis of the distal tibia as well as the distal fibula.
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b
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from the site of the tibial fracture, and the fractures commonly occur in association with injury of the ankle joint. Indirect forces result in spiral or oblique fractures of the tibial shaft, and often the fibula remains intact (Fig. 48). High energy forces may result in comminuted fractures of the tibia, usually including the fibula. The distal half of the tibia is the most
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Figure 49.
Staging of supination-external rotation injury of the ankle according to Lauge Hansen.
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common site of delayed union or non-union in the entire skeleton, and these complications are increased in frequency if an open fracture is complicated by infection. Isolated fractures of the fibula most commonly are associated with an injury to the ankle or a direct blow.
Ankle
The ankle is the most commonly injured joint in the body. Most ankle injuries occur in a fall with the foot planted or fixed to the ground as the leg either angulates or rotates about it. On the basis of mechanism of injury, four categories can be distinguished by characteristic fibular fractures, the Lauge Hansen classification:
(1) Supination-external rotation (70%)
(2) Supination-adduction (rare)
(3) Pronation-external rotation (20%), and
(4) Pronation-dorsiflexion (rare)
Each type of injury occurs in a predictable sequence, and therefore the presence of a characteristic fracture indicates the presence of specific ligamentous injuries, even if such injuries are not obvious on the radiograph.
Supination-External Rotation (SER) (Figs. 49, 50)
| Stage 1 (SER -1) : |
Rupture of the inferior anterior tibio-fibular ligament |
| Stage 2 (SER-2) : |
Stage 1 plus oblique spiral fracture of the lateral malleolus
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| Stage 3 (SER-3) : |
Stages 1 and 2 plus fracture of the posterior lip of the distal end of the tibia or a tear of the posterior tibiofibular ligament |
| Stage 4 (SER-4) : |
Stages 1 to 3 plus transverse or oblique fracture of the medial malleolus or a tear of the deltoid ligament |
Pronation-External Rotation (PER) (Figs. 51, 52):
| Stage 1 (PER-1) : |
Transverse fracture of the medial malleolus or tear of the deltoid ligament |
| Stage 2 (PER-2) : |
Stage 1 plus tear of the inferior anterior tibiofibular and interosseous ligaments |
| Stage 3 (PER-3) : |
Stages 1 and 2 plus tear of the interosseous membrane to the leve1 of a spiral fracture of the fibula 7 to 8 cm or more proximal to the tip of the lateral malleolus |
| Stage 4 (PER-4) : |
Stages 1 to 3 plus avulsion fracture of the posterior lip of the tibia or a tear of the posterior tibiofibular ligament |
This system indicates that stages 3 and 4 injuries cannot be excluded radiographically in the absence of a fracture of the posterior lip of the tibia and medial malleolus, respectively.
The supination-adduction or pronation-dorsiflexion injuries are seldom seen and, therefore, a detailed stage classification is not given.
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Figure 53.
Osteochondral fracture of the dame of the talus, osteochondritis dissecans. T2-weighted caranal, gradient echo MR image of an ankle in a young woman one month after injury to the ankle. The cartilage has high signal intensity. The osteochondral lesion appears at the medial aspect of the dame of the talus (arrow). The lesion is covered by cartilage.
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If an isolated fracture of the medial malleolus is present or the patient has clinical evidence of a deltoid ligament lesion but no fracture is seen in the distal end of the fibula, radiographs of the entire lower leg are required to rule out fracture of the proximal portion of the fibula as part of a pronation-external rotation injury.
Ankle injuries may be associated with different degrees of displacement with or without widening between the talus and the malleolus. Severe displacement should be reduced in the emergency room prior to examination in the radiology department, and assessment of any vascular lesion is mandatory to prevent delay in treatment.
Most orthopedic surgeons agree that stages 3 and 4 ankle injuries are unstable and require internal fixation of the fracture site and that the ligamentous injury should be identified and sutured at the same time (Fig. 50). Ankle lesions in children are relatively rare. Involvement of the physis, especially Salter-Harris types III or V (Fig. 48), is associated with a high rate of premature closure of the growth plate.
Foot
Injury to the tarsus requires a number of specific radiographic views to assess complete fractures or avulsion fractures. CT is useful and easily performed in different planes, especially for evaluation of the talus and the calcaneus (Fig. 17). Ankle injuries may be associated with osteochondral fractures of the dome of the talus, resulting in osteochondritis
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Figure 54.
Displaced fracture-dislocation of the first through fourth tarsometatarsal joints, the Lisfranc joint (arrows), and avulsion fractures between the base of second and third metatarsal bones (short arrow).
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dissecans, which can be depicted by CT or MRI (Figs. 17,53).
Fracture-dislocation of the tarsometatarsal joint, commonly referred to as the Lisfrane dislocation, is an important injury, not to be ignored or missed. When the components are displaced, the injury is rarely overlooked (Fig. 54). If the bones are displaced slightly or are undisplaced, the lesion may be misinterpreted as a "simple" abnormal distortion of the foot. The result of conservative treatment may be poor. Subtle findings indicating the true nature of the injury include the following:
(1) one or more avulsion fractures of the bases of the metatarsal bones (Fig. 55), (2) widening between the bases of the first and second metatarsal bones (Fig. 55), (3) one or more fractures through the bases of the second, third, or fourth metatarsal bones or (4) fracture or avulsion fracture of the lateral aspect of the cuboid bone (Fig. 55 d).
When one or more of these lesions are present, the diagnosis of a fracture-dislocation of the Lisfrane joint is justified. CT in the longitudinal plane will demonstrate the true nature of the injury, revealing multiple avulsion fractures about the tarsometatarsal joints that are inapparent on plain radiographs (Fig. 55 d). Open reduction with pin fixation is the treatment of choice.
Transverse fractures of the proximal portion of the fifth metatarsal bone are relatively common. Two distinct types occur: one is an avulsion fracture of the tip of the tuberosity, where the peroneus brevis tendon is attached. The other transverse fracture of the proximal shaft of the
fifth metatarsal bone commonly is referred to as the Jones fracture. In children the longitudinally oriented apophysis found at the lateral margin of the base of the fifth metatarsal bone may be mistaken for an avulsion fracture.
The remaining fractures of the shaft and neck of the metatarsal bones and phalanges usually are the result of heavy objects falling on the foot and rarely give rise to diagnostic difficulties.
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Figure 56.
Stress fracture (march fracture) of the second metatarsal bone. The radiograph demonstrates periosteal thickening and a small fracture line at the medial aspect of the bone. The patient had had symptoms for six months, but relief of pain occurred after one month at rest.
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a
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Figure 57.
Stress fracture of the tibia of a child.
a) The radiograph demonstrates periosteal proliferation at the lateral aspect of the tibia. b) Note increased uptake at bone scintigraphy. Although the lesion could represent a benign tumor (osteoid osteoma) or osteomyelitis, the patient had pain only during physical activity, which confirmed the diagnosis of a fatigue fracture.
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b
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Stress fractures
Two types of stress fracture can be recognized: a fatigue fracture, resulting from the application of abnormal stress or torque to a bone with a normal elastic resistance, and an insufficiency fracture, occurring when normal stress is placed on a bone with deficient elastic resistance.
Pain with pain relief at rest or with reduced physical activity is typical of fatigue fractures. The most common fatigue fracture is that of the
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Figure 58.
Periosteal proliferation of the distal end of the tibia and fibula in chronic venous insufficiency.
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metatarsal shafts, often called the march fracture (Fig. 56). Stress fractures of the shafts of the long bones usually show periosteal proliferation (Fig. 57) and, sometimes, a horizontally oriented linear defect. Bone scan demonstrates increased radionuclide uptake and MRI, using fat suppression sequences, shows extensive abnormalities within the bone marrow.
The differential diagnosis of the imaging findings of stress fractures include tumors (Fig. 88) and osteomyelitis. In adition, hypertrophic osteoarthropathy and venous insufficiency may lead to periosteal proliferation (Fig. 58).
Stress fractures about the knee and hip are described in relation to osteoarthrosis.
Osteochondritis dissecans
Osteochondritis dissecans generally is believed to represent a sequela of osteochondral fractures caused by shearing, rotatory, or tangentially aligned impaction forces (Figs. 17, 53). The most typical location is in the medial or lateral femoral condyles (Fig. 59). Osteocartilaginous
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Figure 59.
Osteoehondritis dissecans of the lateral femoral condyle.
a) The AP radiograph of the knee reveals a typical osteochondral lesion with a defect containing a fragment, located centrally in the femoral condyle.
b) Sonography with sagittal sectioning of the posterior aspect of the lateral femoral condyle demonstrates the normal cartilage of the condyle (arrowheads) and a defect not covered by cartilage (arrow).
F = femoral condyle, T = tibial condyle
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b
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fragments may be partially or completely detached, but often they are covered with cartilage and may be visualized by sonography or MRI (Fig. 59). Other locations of osteochondritis dissecans are the patella, the talus (Figs. 17, 53), and the capitulum of the humerus.
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Figure 60.
Osteoarthrosis and arthritis.
Schematic drawing contras ting the typical anatomic changes in osteoarthrosis (a) and inflammatory joint disease (arthritis) (b).
a) Local joint space narrowing, marginal osteophytosis, subchondral sclerosis, and cysts in the weightbearing or pressure area. Secondary synovitis is evident.
b) Synovitis, eroding both the articular cartilage and the adjacent bone (bare areas and subchondral bone) is observed.
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Niels Egund, Kjell Jonsson, Holger Pettersson and Donald Resnick