FRACTURE FREQUENCY	Section 5 of 10
Author Information Introduction Anatomy Radiographic Evaluation Fracture Frequency Fractures Of The Distal Humerus Other Elbow Injuries Summary Pictures Bibliography

The frequency with which various elbow fractures occur differs between children and adults. In adults, 50% of elbow fractures involve the radial head and neck, followed by 20% involving the olecranon. These fractures are relatively uncommon in children. Conversely, supracondylar fractures account for only 10% of adult elbow fractures, but they are the most common elbow fractures in children. In children, the most common elbow fractures are supracondylar (60%), lateral condylar (15%), and medial epicondylar (10%) (Rogers, 1978).

	FRACTURES OF THE DISTAL HUMERUS	Section 6 of 10
Author Information Introduction Anatomy Radiographic Evaluation Fracture Frequency Fractures Of The Distal Humerus Other Elbow Injuries Summary Pictures Bibliography

Supracondylar fracture

Supracondylar fractures are diagnosed with the help of radiographic findings by using both direct and indirect signs. The presence of a joint effusion does not specifically indicate that a fracture is present, but a joint effusion does signal that a fracture is likely, and a careful search is required. The anterior humeral line can be extremely useful in the diagnosis of supracondylar fracture; the line passes anterior to the middle third of the capitellum in 94% of cases. Images 5-6 demonstrate typical supracondylar fractures with abnormality of the anterior humeral line. Abnormality of the anterior humeral line indicates distal humeral deformity and, therefore, either an acute or previous fracture.

Supracondylar fractures may be complete or incomplete and have a wide range of severity. The usual classification defines supracondylar fractures as follows:

• Type 1 - Fractures with no displacement

• Type 2 - Fractures with mild displacement or angulation and an intact posterior cortex

• Type 3 - Fractures with displacement and complete cortical disruption (see Image 7)

With complete fractures, the fracture line and displacement are obvious. Even incomplete fractures often have enough disruption in 1 of the cortices (usually the anterior cortex) to make diagnosis easy (see Image 8). However, in approximately 25% of cases, the fracture may be subtle. These cases include greenstick and plastic bowing fractures. With greenstick fractures, cortical disruption is seen on the tensile side (usually the anterior cortex), and they may be accompanied by cortical buckling of the compression side (usually the posterior cortex). With plastic bowing, no discrete fracture line is present. Only deformity is observed, as demonstrated by the anterior humeral line. Subtle cortical deformity also may be present medially or laterally, and it may be associated with varus or valgus deformity.

In searching for subtle fractures, knowing their expected location is essential. On the frontal view, supracondylar fractures typically extend transversely through the metaphysis across the region of the olecranon fossa. With subtle fractures, the fracture line may be initially seen through only a portion of the metaphysis. With healing, sclerosis is demonstrated across the entire metaphysis, indicating the full extent of the fracture (see Image 9).

In the lateral projection, the fracture may be either transverse or oblique, typically extending from anterior and distal to posterior and proximal. Orientation of the fracture line in the sagittal plane has both diagnostic and clinical implications. Diagnostically, oblique fractures may be demonstrated more easily by using an AP view with cephalad angulation, which shows the fracture en face. Although not routinely acquired, this view may be useful when a fracture is highly suspected but not found on standard views. Clinically, an oblique fracture is important because it causes rotation at the fracture site to result in a varus or valgus deformity.

Complications

The 2 major complications of supracondylar fractures in children include cubitus varus (see Image 10), which is relatively common, and vascular injury, which is uncommon but has a considerable morbidity rate when present.

Cubitus varus is due primarily to alignment of the fracture at the time that it is set rather than to physeal injury leading to deformity from asymmetric growth. Because individual variation exists in the carrying angle, cubitus varus is best assessed by comparing the injured elbow with the contralateral side. This analysis is aided by the use of the Baumann angle, which is the angle between the humeral shaft and the distal humerus as defined by the growth plate between the capitellum and the metaphysis.

Although the physis in this region does not define the mechanical axis of the distal humerus, it serves as a well-defined marker that allows comparison of the orientation of the distal fragment to that of the contralateral elbow (see Image 11). Care must be taken to ensure a true AP view, because rotation leads to a change in the value of the Baumann angle. Although cubitus varus after supracondylar fractures is relatively common, in most instances, cubitus varus does not cause significant morbidity. In patients with more pronounced cubitus varus, corrective valgus osteotomy may be needed.

Vascular injury can be a severe complication of supracondylar fractures. With enough posterior displacement of the distal fragment, the brachial artery is subject to injury because it stretches across the fractured surface of the proximal fragment. Vascular insufficiency or swelling may lead to Volkmann ischemic contracture of the forearm, markedly limiting function of the extremity. Clinical assessment of vascular integrity at the time of presentation and after orthopedic manipulation as long as 48 hours later is the key to preventing Volkmann ischemic contracture. Although plain radiographs are not useful in the evaluation of vascular injury. In some patients, arteriography, Doppler US, or CT angiography may be ordered to evaluate arterial flow and anatomy and to guide treatment, although the appropriateness of these studies is controversial.

Nerve injuries may also complicate supracondylar fractures, occurring in approximately 5% of patients. These injuries most frequently involve the anterior interosseous branch of the median nerve.

Lateral condyle fracture

Fractures of the lateral condyle are the second most frequent elbow fracture in children, accounting for approximately 15%. Lateral condyle fractures are seen most often in children aged 4-10 years. Many pediatricians and emergency physicians are not as familiar with these fractures as they are with supracondylar fractures, and some lateral condyle fractures may be subtle. As a result, the radiologist is useful in diagnosing lateral condyle fractures and in alerting the clinical staff to the features of the fractures and the need for orthopedic treatment.

Lateral condyle fractures have 2 primary mechanisms of injury. With a fall on an outstretched arm with the elbow extended and the forearm abducted, the radius transmits an axial load on the capitellum, causing the lateral condyle to fracture. More frequently, the fractures are the result of traction force. The lateral condyle is the origin of the forearm extensor muscles, and traction from these muscles can cause the lateral condyle to fracture when acute varus stress is applied to an extended elbow with the forearm supinated. In this position, the olecranon is locked in the olecranon fossa, with the trochlear ridge of the olecranon serving as the fulcrum of the varus stress. This mechanism accounts for the finding that the fracture line usually extends toward the trochlear groove of the distal humerus. It also accounts for the association of olecranon fractures with lateral condyle fractures.

Although controversy existed previously, lateral condyle fractures are currently considered to be Salter-Harris type IV fractures. The fracture line usually begins in the lateral aspect of the metaphysis and extends medially through the metaphysis and crosses the physis into the epiphysis (see Image 12). In most patients, the fracture involves only the cartilaginous portion of the distal humeral epiphysis; therefore, the epiphyseal component of the fracture is not seen on radiographs. In 4 of 48 patients in whom the fracture line passed across the physis into the ossified portion of the capitellum, the radiographic appearances were those of a Salter-Harris type IV fracture (Jakob, 1975) (see Image 13).

More importantly, the presence of adjacent fractured bone margins of the metaphysis and epiphysis establishes the risk of bone bridging from the metaphysis to the epiphysis during healing. This bridging can cause focal growth plate closure, a recognized complication of Salter-Harris type IV fractures. For most patients in whom the ossified capitellum is not involved, the risk of focal growth plate closure is relatively low, similar to the risk in Salter-Harris type II or III fractures. The stability of the distal fragment is partly determined by whether the fracture extends all the way to the articular surface or whether a cartilaginous hinge remains intact to help prevent motion of the fracture fragment. In most patients in whom fracture extends to the articular surface, the fracture passes through the lateral portion of the trochlea so that the lateral crista of the trochlea is included in the fracture fragment, leading to instability of the trochleoulnar joint.

The Milch classification scheme for lateral condylar fractures defines type I fractures as those that pass through the ossified capitellum. These fractures enter the articular surface in the capitellotrochlear groove lateral to the lateral crista of the trochlea so that elbow stability is maintained (Milch, 1964). Milch type II fractures, the more common type, extend into the trochlea, leading to instability.

A staging system for classifying the severity of lateral condyle fractures is as follows:

• Stage I fractures are incomplete, with an intact cartilaginous hinge that may have some angulation but no true displacement.

• Stage II fractures are complete and have only a small amount of displacement of the distal fragment.

• With Stage III fractures, the distal fragment is significantly displaced, usually laterally and proximally, with instability of the elbow joint. In addition, traction from the common extensor muscles leads to rotation so that the cartilage-covered articular surface of the fractured lateral condyle is in contact with the metaphysis; this situation may result in malunion if not corrected.

Radiographic findings

The radiographic depiction of lateral condyle fractures depends on the degree of separation at the fracture site. If separation is significant, recognition of the fracture is easy (see Image 14), although distinguishing these fractures from supracondylar fractures depends on knowing the characteristic course. When no displacement is present, lateral condyle fractures may demonstrate subtle findings. A joint effusion helps in suggesting a subtle fracture, and lateral soft tissue swelling localizes the region to be examined most carefully.

Although posteriorly displaced lateral condyle fractures may show an abnormal relationship between the anterior humeral line and the capitellum, this finding is not as useful in lateral condyle fractures as in supracondylar fractures. These fractures often demonstrate only a subtle subcortical fracture line along the lateral aspect of the metaphysis (see Image 15). Therefore, only a very thin sliver of bone may be viewed; this finding represents the distal fragment that is otherwise primarily cartilage.

Oblique views may be required to depict these fractures, because they may not be seen on AP views. On lateral views, cortical disruption is usually seen posteriorly rather than anteriorly, as in supracondylar fractures (see Image 16).

Because several secondary ossification centers exist in the elbow, a small flake of bone adjacent to the metaphysis may be misinterpreted as a developmental center, such as the lateral epicondyle. However, because the lateral epicondyle is the last center in the elbow to ossify, most pediatric patients with lateral condyle fractures have elbows that are too immature to have a lateral epicondyle ossification center; therefore, the flake of bone must represent a fracture.

It may be tempting to regard such a subtle finding as too little to represent a significant fracture, and familiarity with these fractures is important in helping recognize them. However, note the following caution regarding subtle lateral condyle fractures: Partial overlap of the capitellum with the metaphysis may simulate a fracture when the lucency of the physis overlaps part of the metaphysis or when the double density of the capitellar and metaphyseal cortices simulates a fracture fragment.

Although a radiologic diagnosis in patients with lateral condyle fracture depends on plain radiographic findings, MRI, arthrography, or ultrasonography (US) may be useful in further evaluating the fractures, particularly with regard to the course of the fracture through the cartilaginous epiphysis (see Image 17). Other injuries that may be confused with lateral condyle fractures include supracondylar fracture and, in young infants, separation of the distal humeral epiphysis (transcondylar fracture, Salter-Harris type I).

Complications

The major complications of lateral condyle fractures in children include instability (see Image 18), malunion, and nonunion (leading to varus deformity or, less often, to valgus deformity over time). In the series by Jakob et al involving 48 patients with lateral condyle fractures, 20 patients had fractures that were minimally displaced, while 28 had significant displacement and required surgical reduction and fixation. Nonunion has been considered to be more of a problem in patients with minimally displaced fractures than in patients with significant displacement, presumably because the lack of surgical fixation allowed a small amount of motion and because of the development of fibrocartilage interposed between the fragments (Flynn, 1975). Delayed complications of lateral condyle fractures include ulnar neuritis and posttraumatic arthritis.

Lateral condyle fractures may be associated with other elbow fractures, particularly those involving the olecranon (see Image 19). However, they tend not to be associated with fractures remote from the elbow. Although lateral condyle fractures are associated with elbow dislocation, this is a direct result of the fracture, with loss of the stabilizing lateral crista as discussed above, rather than a separate injury.

Medial epicondyle fracture

Fractures of the medial epicondyle account for 10% of elbow fractures in children. They most often occur in children aged 7-15 years, with peak incidence in those aged 11-12 years. Approximately one half of medial epicondyle fractures are associated with elbow dislocation or subluxation. Medial epicondyle fractures are avulsion injuries caused by traction from the ulnar collateral ligament or the forearm flexor muscles that arise from the medial epicondyle.

The major mechanisms of injury include acute valgus stress during a fall on an outstretched arm, posterior stress with acute elbow dislocation, and chronic muscular traction from the flexor and pronator muscles such as that caused by throwing (eg, Little League elbow). Acute valgus stress may cause a compression injury on the lateral side of the elbow or a traction injury on the medial side. In adults, this stress most frequently causes a compression fracture of the radial head or neck, whereas in children, avulsion of the medial epicondyle is more common.

Radiographic findings

Medial epicondyle avulsions may include separation of the entire medial epicondyle from the metaphysis, avulsion of only part of the medial epicondyle (see Image 20), or avulsion of the epicondyle plus a small portion of the adjacent metaphysis. These in injuries resemble Salter-Harris type I, III, and II fractures, respectively, though the Salter-Harris classification is usually applied to injuries of the epiphyses rather than those of the apophyses.

Owing to traction from the forearm flexors, the medial epicondyle is displaced distally. Also, it is usually medially displaced from its anatomic position (see Image 21). Localized soft tissue swelling is usually present. In most patients, the medial epicondyle is extra-articular; therefore, a joint effusion is not present. In some patients, the medial epicondyle may be intra-articular, and in others, widening of the physis for the medial epicondyle may be subtle. Comparison views of the contralateral elbow may be useful.

Complications

The fractured medial epicondyle may become entrapped in the elbow joint, representing a major complication. With acute valgus stress, the medial side of the elbow joint is opened. When the medial epicondyle is pulled downward (distally) by the forearm flexor muscles, it may enter the medial joint space. When the valgus force is removed, the medial epicondyle may then become entrapped as the medial joint space closes (see Image 22).

Entrapment is particularly common after an elbow dislocation or subluxation. Recognition of such entrapment is important in making a diagnosis by using radiographic findings. This process is aided with the radiologist's familiarity with the normal developmental anatomy of the elbow. Because the entrapped medial epicondyle is positioned beneath the medial side of the distal humeral metaphysis, it may be misinterpreted as the ossification center for the trochlea. However, the trochlea does not become ossified prior to the medial epicondyle. Therefore, the trochlea should not be seen unless the medial epicondyle is identified as well. In addition, usually, the trochlea initially appears as multiple fragmented ossification centers compared to the smooth and regular appearance of the medial epicondyle.

An entrapped medial epicondyle may be difficult to detect on the frontal view and is often better depicted on the lateral view. A clue to an entrapped medial epicondyle on the frontal view is widening of the medial joint space. However, widening of the joint space may be difficult to evaluate in patients in whom the elbow is immature when the largely cartilaginous trochlea makes the normal gap between the distal humerus and ulna appear quite wide.

In the radiographic evaluation of pediatric elbow trauma, assessing the status of the medial epicondyle is important, particularly after an elbow dislocation. If the elbow is mature enough for ossification of the medial epicondyle to be expected, the position of the medial epicondyle should be verified. If the medial epicondyle is not seen in its normal anatomic position, it should be searched for elsewhere, including within the elbow joint.

Avulsion fractures of the medial epicondyle may occur prior to ossification, and they cannot be detected on plain radiographs. However, such an injury may be suggested by localized tenderness and soft tissue swelling and by the presence of a posterolateral elbow dislocation. Stress radiographs demonstrating widening of the medial joint space with valgus stress indicate either avulsion of the medial epicondyle or disruption of the ulnar collateral ligament. In children, the ligaments are generally stronger than the bone; therefore, avulsion fractures occur more frequently than ligamentous injury, as with medial epicondyle injuries. MRI is useful in identifying these fractures. Conventional, magnetic resonance, or CT arthrography may be helpful in searching for a cartilaginous entrapped medial epicondyle in patients in whom the medial epicondyle is intra-articular.

Medial condyle fracture

Fracture of the medial condyle is an uncommon injury in children. Similar to lateral condyle fractures, these are typically Salter-Harris type IV injuries. The fracture extends through the metaphysis and into the epiphysis, typically arising just above the medial epicondyle and extending to the trochlear groove (see Image 23).

In young patients with a nonossified or only partially ossified trochlea, the epiphyseal component of the fracture is not visible, and only the metaphyseal flake is identified. The medial epicondyle is included in the distal fragment. Similar to lateral condyle fractures, medial condyle fractures have a high risk of instability and may be complicated by nonunion. Although differentiating medial condyle from medial epicondyle fractures is important, the distinction is not always easy with radiographs.

The presence of a metaphyseal flake fracture is not specific because some medial epicondyle avulsions may extend into the metaphysis as a Salter-Harris type II fracture. In general, medial condyle fractures (Salter-Harris type IV injuries) have larger metaphyseal components than medial epicondyle fractures that involve the metaphysis. Medial condyle fractures are more likely to have a joint effusion, although joint effusions may be seen with medial epicondyle avulsion fractures. Clinical features that suggest a medial condyle fracture include instability and a limitation of elbow motion.

Transcondylar fracture

The term transcondylar fracture is used for fractures that separate the entire distal humeral epiphysis from the metaphysis. In most patients, these fractures occur entirely through the growth plate, resulting in a Salter-Harris type I fracture, although the fracture may extend into the metaphysis with a Salter-Harris type II injury. Transcondylar fractures most often occur in young children (<2 y), and they are reportedly associated with birth injury and child abuse. The mechanism of injury is believed to be rotational shear (Bright, 1974).

In a transcondylar fracture, the epiphysis is usually medially displaced relative to the metaphysis (see Image 24). The proximal radius and ulna maintain a normal relationship to the epiphysis; hence, the forearm bones are also displaced relative to the humeral metaphysis. In young children in whom the distal humeral epiphysis is not yet ossified, this malalignment of the forearm bones and the distal humeral metaphysis causes confusion with an elbow dislocation. Often, the capitellum has ossified, allowing it to serve as an important marker in the otherwise cartilaginous distal humeral epiphysis.

Demonstration of normal alignment between the proximal radius and the capitellum (radiocapitellar line) and normal alignment of the proximal radius and ulna with each other are the keys to differentiating transcondylar fracture from elbow dislocation. If the capitellum is not ossified and if it cannot be used to evaluate elbow alignment, medial displacement of the forearm bones relative to the distal humeral metaphysis should suggest a transcondylar fracture because the distal fragment is usually displaced medially. Conversely, in true elbow dislocations, the radius and ulna are dislocated either laterally and posteriorly (in children >2 y) or primarily posteriorly (in children <2 y). MRI, US, or arthrography may be used to directly depict the relationship of the cartilaginous distal humeral epiphysis to the metaphysis (see Image 25).

Some transcondylar fractures include a small portion of the metaphysis, which is helpful in recognizing that a fracture is present (see Image 26). However, this finding may cause the injury to be confused with a lateral condyle fracture. The distinction of the 2 fractures is important because lateral condyle fractures are often unstable and require operative fixation, which is frequently not necessary for transcondylar fractures because of its greater stability after reduction.

Features that help in distinguishing the 2 fractures include alignment of the radiocapitellar joint and the direction of displacement. In transcondylar fractures, radiocapitellar alignment remains normal, whereas in lateral condyle fractures, the distal fragment is often displaced or rotated as described above, with alteration of the radiocapitellar alignment. Because the lateral crista of the trochlea is often included in the fracture fragment, the elbow joint loses lateral support in lateral condyle fractures. Lateral displacement of the proximal forearm bones results, rather than the medial displacement that typically seen in transcondylar fractures.

In most cases, patients with transcondylar fractures have a good prognosis, although diagnosis and treatment are precarious. In some patients, impaction of the epiphysis on the medial aspect of the metaphysis may cause growth plate injury, leading to subsequent varus deformity (see Image 27). Keep in mind the association of transcondylar fracture with child abuse.

	OTHER ELBOW INJURIES	Section 7 of 10
Author Information Introduction Anatomy Radiographic Evaluation Fracture Frequency Fractures Of The Distal Humerus Other Elbow Injuries Summary Pictures Bibliography

Fractures of the proximal radius

Most proximal radial fractures in children are either Salter-Harris type II injuries that extend through the growth plate and the lateral aspect of the metaphysis or metaphyseal fractures that extend across the neck near the growth plate, but they do not involve the growth plate directly. Rarely, a Salter-Harris type IV fracture extends vertically through the metaphysis and epiphysis, crossing the physis. With some proximal radial fractures, no displacement of the epiphysis occurs, and detection of the fracture depends on the metaphyseal component, which may show only subtle abnormal angular deformity. This finding must be distinguished from the normal angulation that is usually present at the junction of the radial neck and shaft (see Image 28).

The radial head epiphysis may also show displacement with varying amounts of shift and angulation that may lead to limitation of motion of the proximal radioulnar joint (Wedge, 1982). Proximal radial fractures may result in abnormal articulation of the radial head and capitellum and therefore are fracture/dislocations. Displacement of the radial head may be marked, usually with the head displaced distally, and its articular surface may be rotated into the coronal plane posteriorly. However, the displacement may also be lateral (see Image 29). These cases may be due to transient posterior elbow dislocation.

When the proximal radius and ulna then are forced anteriorly and the dislocation is reduced, the capitellum may shear off the radial head, leaving it posteriorly displaced. During the reduction of these completely displaced fractures, the radial head may become inverted so that the physeal fracture surface of the radial head articulates with the capitellum. Less often, as the proximal radius and ulna are dislocating posteriorly, the capitellum may cause the radial neck to become fractured, and it may force the radial head anteriorly and distally.

Complications

A major complication of a radial neck fracture is limitation of motion at the proximal radioulnar joint, which mostly limits supination. This complication is usually caused by malalignment of the radial head and neck, and more severe limitation of motion may be caused by radioulnar synostosis. Radial head displacement or injury to the proximal radial growth plate may also cause growth arrest, leading to radial shortening that may affect the wrist joint. Proximal radial fractures in children have a high association with other injuries, which most frequently involve the olecranon. The identification of a proximal radial fracture should alert the examiner to carefully search for other injuries.

Fractures of the proximal ulna

Fractures of the proximal ulna are uncommon in children, accounting for 6% of elbow fractures. In evaluating the proximal ulna in children, the normal olecranon apophysis must not be mistaken for a fracture fragment. The olecranon apophysis usually appears in children aged approximately 10 years, and it fuses by age 18 years. The normal apophysis may have separate ossifications centers near its tip.

The olecranon apophysis fuses in an anterior-to-posterior direction, and radiographs may reveal a residual posterior cleftlike lucency with well-defined sclerotic margins. The characteristic location of the olecranon ossification centers, their smooth uninterrupted cortical margins, and the typical appearance of the partially fused physis help in distinguishing olecranon ossification from fractures at that site.

Most proximal ulnar fractures involve the olecranon process. The 3 major mechanisms of injury include direct impaction; distraction stress from the triceps muscles; and valgus or varus stress with the elbow in extension, which locks the olecranon into the distal humerus.

Radiographic findings

Distraction stress on the olecranon may occur from falling on an arm with the elbow partially flexed so that acute hyperflexion stress is applied against the triceps or from excessive muscular activity, which is often associated with throwing. Distraction fractures have a particularly high incidence in patients with osteogenesis imperfecta, including patients with relatively normal-appearing bones and few fractures elsewhere (see Image 30). Distraction fractures of the olecranon may be subtle, or they may have significant proximal displacement of the fracture fragment. These fractures are usually Salter-Harris type II injuries that include a metaphyseal fragment of variable size. Salter-Harris type I fractures that pass entirely through the physis of the olecranon apophysis may occur, but they are relatively uncommon. The detection of these fractures requires a high index of suspicion and comparison with the noninjured elbow.

When the elbow is fully extended, the olecranon becomes locked into the olecranon fossa, making it susceptible to fracture by varus or valgus stress. These fractures may be subtle and have only a linear lucent line through the trabecular region (see Image 31). In other patients, the fracture is best seen at the proximal tip of the olecranon metaphysis (see Image 32).

Complications

Valgus stress fractures may be associated with compression fractures of the radial neck or avulsion of the medial epicondyle. Varus stress fractures may be associated with a lateral condyle fracture (see Image 33) or a lateral dislocation of the radial head (type 3 Monteggia fracture/dislocation).

Olecranon fractures have a high incidence of associated injuries, which are believed to have the highest association with proximal radial fractures, although several are associated with lateral condyle fractures.

Fractures of the coronoid process are infrequent in children, but they may be seen with posterior elbow dislocation.

Elbow dislocation

The elbow is the most frequently dislocated joint in children, whereas in adults, dislocations of the shoulder and interphalangeal joints of the fingers are more common. Elbow dislocation accounts for approximately 5% of elbow injuries in children. The mechanisms of dislocation include a fall on an outstretched arm with the elbow partially flexed and forced hyperextension, although both mechanisms more frequently result in fractures than in dislocations. The most common direction of displacement is posterior or posterolateral (see Images 34-35), although lateral and anterior dislocations also occur.

Dislocations often are associated with fractures, most often involving the medial epicondyle and coronoid process of the ulna. Other fractures that may be associated with elbow dislocations include fractures of the proximal radius, particularly fractures in which the radial head is markedly displaced and rotated into the coronal plane; fractures of the lateral condyle; and remote fractures in the same extremity, most often the distal radius and ulna. Detection of an elbow dislocation should alert the radiologist to carefully search for the other injuries.

Radiographic findings

Elbow dislocations are usually readily apparent on radiographs. In young patients, alignment of the radiocapitellar joint is evaluated by using the radiocapitellar line, whereas in the more mature skeleton, articulating surfaces of the radial head and capitellum are revealed directly. The articular relations of the medial condyle and proximal ulna are not as easy to evaluate in the immature skeleton.

After spontaneous reduction, prior elbow dislocation can be suggested by the identification of the fractures described above. In patients younger than 2 years, elbow dislocations are exceedingly rare, and transcondylar fracture (distal humeral epiphyseal separation) is often mistaken for elbow dislocation. Radiographic findings that indicate transcondylar fracture rather than dislocation include maintenance of normal radiocapitellar relations and medial displacement of the forearm bones.

Complications

Complications of elbow dislocation in children include associated fractures, neurologic injury (usually involving the ulnar nerve or the anterior interosseous branch of the median nerve), joint contracture, and heterotopic ossification in the regions of the disrupted medial or lateral collateral ligaments. Vascular complications are less common than neurologic injury and are usually accompanied by severe injuries, often including open fractures (Wheeler, 1967).

Monteggia fracture/dislocation

Monteggia fracture/dislocation involves dislocation of the radial head accompanied by fracture of the proximal or mid ulna, with the apex of the ulnar fracture pointing in the same direction as the radial head dislocation. Normal articulation of the medial condyle and proximal ulna is maintained. In 55-85% of patients, the radial head is anteriorly dislocated, with an associated apex anterior ulnar fracture (Monteggia type 1 injury). In the remainder of patients, fractures/dislocations are divided equally between posterior (Monteggia type 2 injury) and lateral (Monteggia type 3 injury) dislocation of the radial head. Lateral (Monteggia type 3) injuries most often occur in children aged 5-9 years (see Image 36).

Simplistically, a Monteggia fracture/dislocation can be thought of as the result of a force that dislocates the radial head and simultaneously fractures the ulna in the same direction. However, in most patients, the injury is due to a fall onto a pronated forearm, which forces the arm into hyperpronation. This motion causes the ulna to fracture and contact the proximal radius, forcing the radial head to become dislocated from the capitellum.

In children, an ulnar fracture often may be manifested by plastic bowing without a discrete fracture line (see Image 38). In some patients, the finding may be subtle, and recognition of this injury requires a high index of suspicion and the use of comparison views of the contralateral forearm when needed. Most cases of isolated radial head dislocation in children are likely to actually be Monteggia fracture/dislocation with a subtle ulnar bowing fracture. Conversely, ulnar fractures in a child are often accompanied by a radial fracture or dislocation, even if the ulnar fracture is a relatively subtle greenstick injury. If an associated radial fracture is not identified, a careful search should be made for a radiocapitellar dislocation or subluxation. The elbow should be well visualized in all patients who have an ulnar injury with or without associated radial fracture.

A Monteggia variant has fractures of the radius and ulna. The radial fracture is so close to the joint that the injury that it may superficially resemble a radial head dislocation. In these cases, only the radial head is still in alignment with the capitellum. The rest of the radius appears dislocated with respect to the capitellum; however, this is a displaced fracture rather than a dislocation (see Image 37). In cases in which the radial head is not yet ossified, this injury cannot be distinguished from a true Monteggia fracture/dislocation by using plain radiographs.

A similar situation occurs in the wrist in children, that is, a fracture through the distal ulnar physis may occur in association with a distal radial diaphyseal fracture and result in a pseudo-Galeazzi injury (see Image 39). In fact, Monteggia variant and pseudo-Galeazzi injuries are forearm fractures involving both bones, with 1 of the fractures occurring so close to the joint that a dislocation is erroneously suggested.

Pulled elbow

A pulled elbow is a distraction injury. It is also called nursemaid's elbow and other names, and it usually results from a sudden pull on the hand. In children younger than 5 years, the annular ligament is relatively loose, allowing the radial head to be pulled through it when acute traction is suddenly placed on a pronated forearm (which is the usual position of the forearm when a child is being pulled along by an adult). Although the annular ligament becomes transiently interposed between the radial head and capitellum, this movement does not cause recognizable widening of the radiocapitellar joint. Therefore, elbow radiographic findings are normal in a pulled elbow. MRIs should demonstrate the abnormal relationship of the radial head and annular ligament, but such studies are seldom needed.

	SUMMARY	Section 8 of 10
Author Information Introduction Anatomy Radiographic Evaluation Fracture Frequency Fractures Of The Distal Humerus Other Elbow Injuries Summary Pictures Bibliography

Radiographic evaluation of acute elbow trauma in children can be difficult because of the multiple ossification centers that appear in this region. However, acute elbow trauma provides an excellent example of how an understanding the developmental anatomy of the region plus knowledge of the mechanism of injury and the most frequent fracture patterns and associations can greatly aid in the radiographic analysis.

See eMedicine article Salter-Harris Fractures for more information. For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles Broken Elbow and Elbow Dislocation. For additional reading, see the articles by Barton et al and Skaggs et al, as well as those in the Bibliography.

	PICTURES	Section 9 of 10
Author Information Introduction Anatomy Radiographic Evaluation Fracture Frequency Fractures Of The Distal Humerus Other Elbow Injuries Summary Pictures Bibliography

Caption: Picture 1. Normal notch. Two examples of the normal notchlike step off of proximal radial metaphysis in patients of different ages. A, demonstrates the normal angulation between the radial neck and shaft. B, More mature elbow.
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Caption: Picture 2. Normal radial tuberosity. A, On the lateral view, the radial tuberosity is seen en face and appears as a lytic defect. B, On the frontal view, radial tuberosity is clearly recognizable. This view demonstrates the normal angulation between the radial neck and shaft.
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Caption: Picture 3. Fat pad signs indicate an elbow joint effusion. Lateral view shows the posterior fat pad, which is always abnormal when seen with the elbow positioned in right-angle flexion. The anterior fat pad is demonstrated and abnormally elevated. Although the anterior fat pad can be seen without an effusion, it should not be elevated to this degree.
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Caption: Picture 4. Normal lines. Lateral view shows the 2 lines used for radiographic analysis in patients with elbow trauma. The solid anterior humeral line is drawn along the anterior cortex of the distal humeral metaphysis and should pass through the middle third of the capitellum. Passage of the anterior humeral line either anterior to the capitellum or through the anterior third of the capitellum demonstrates that the capitellum is portioned too far posteriorly; this finding indicates a distal humeral fracture. The dashed radiocapitellar line is drawn through the radial neck and should pass through the capitellum. This relation should be examined on a frontal view as well. Failure of the radiocapitellar line to pass through the capitellum indicates radiocapitellar dislocation.
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Caption: Picture 5. Typical supracondylar fracture. Fracture is obvious on both the anteroposterior (A) and lateral (B) views. Lateral view demonstrates an abnormal relation of the capitellum to the anterior humeral line, which passes along the anterior margin of the capitellum. Compare these images with the lateral view of the contralateral elbow (C), which shows the anterior humeral line passing normally through the middle third of the capitellum.
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Caption: Picture 6. Typical supracondylar fracture. Anteroposterior (A) and lateral (B) views. Note the abnormal relation of anterior humeral line and the lateral view.
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Caption: Picture 7. Supracondylar fracture. Anteroposterior (A) and lateral (B) views show significant medial and posterior displacement of a distal fragment.
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Caption: Picture 8. Supracondylar fracture. Anteroposterior view shows disruption of the medial cortex.
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Caption: Picture 9. Supracondylar fracture. Initial lateral (A) view shows an abnormal anterior humeral line indicative of a fracture. On the initial anteroposterior view (B), the fracture is subtle and is seen only medially. Follow-up anteroposterior (C) and lateral (D) views demonstrate the fracture better. On the anteroposterior view in C, the fracture can be seen clearly to extend all of the way across the metaphysis.
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Caption: Picture 10. Supracondylar fracture. Cubitus varus. A, Anteroposterior view shows a varus deformity of the distal humerus from a previous well-healed supracondylar fracture. B, On the lateral view, the capitellum remains posteriorly positioned, a finding typical of a previous supracondylar fracture.
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Caption: Picture 11. Baumann angle. A 5-year-old boy with previous left distal humeral supracondylar fracture. A, Anteroposterior view of the left elbow. B, Comparison anteroposterior view of right elbow. The Baumann angle usually is defined as the angle between the growth plate for the capitellum and a line drawn perpendicular to the humeral shaft. Rather than drawing the extra perpendicular line, the Baumann angle was measured as 90° minus the angle between the capitellar growth plate and the humeral shaft. In this patient, the uninjured right elbow has a Baumann angle of 12°, and the previously injured left elbow has a Baumann angle of only 2°. This finding indicates a varus deformity of the left distal humerus.
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Caption: Picture 12. Lateral condyle fracture. Initial anteroposterior (A) and lateral (B) views show a nondisplaced lateral condyle fracture. A subsequent anteroposterior view (C) shows lateral displacement of a distal fragment. An anteroposterior tomogram (D) obtained at that time shows both the displacement and the course of the fracture line through the epiphysis to the articular surface of the trochlea. Most patients with lateral condyle fractures are young, and the epiphyseal extension of the fracture is within the growth cartilage and thus not identifiable on plain radiographs.
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Caption: Picture 13. Lateral condyle fracture passing through the ossified portion of the capitellum. Anteroposterior view shows the lateral condyle with a fracture line passing through the metaphysis and capitellum, crossing the growth plate.
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Caption: Picture 14. Displaced lateral condyle fracture. Anteroposterior view shows an obvious lateral condyle fracture with lateral displacement of the fragment, rotation, and downward displacement due to muscular traction.
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Caption: Picture 15. Subtle lateral condyle fracture. Anteroposterior (A) and lateral (B) views. In this patient, the only sign of the fracture is the thin metaphyseal flake on the anteroposterior view.
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Caption: Picture 16. Lateral condyle fracture. Anteroposterior (A) and lateral (B) views. On the lateral view, cortical disruption is usually seen posteriorly rather than anteriorly as in supracondylar fractures.
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Caption: Picture 17. Fat-suppressed T2-weighted coronal MRI shows that the fracture extends through the metaphysis into the epiphysis, although the articular surface remains intact.
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Caption: Picture 18. Lateral condyle fracture with instability. Initial anteroposterior (A) and lateral (B) views show a nondisplaced lateral condyle fracture. Subsequent views (C and D) show posterior displacement of a distal fragment.
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Caption: Picture 19. Lateral condyle and olecranon fractures. Anteroposterior (A) and lateral (B) views show combined fractures of the distal humeral lateral condyle and olecranon process of the ulna.
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Caption: Picture 20. Medial epicondyle avulsion fracture in an 11-year-old girl with an avulsion of part of the left medial epicondyle (A). Compare the simultaneous view of the uninjured right elbow (B) and a previous view of the left elbow obtained when the patient was aged 10 years (C).
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Caption: Picture 21. Medial epicondyle fracture with distal displacement of a fracture fragment. Anteroposterior views of the injured left elbow (A) compared with the uninjured right elbow (B).
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Caption: Picture 22. Medial epicondyle fracture with entrapment in an 8-year-old boy. Anteroposterior (A) and lateral (B) views of the injured right elbow compared with anteroposterior (C) and lateral (D) views of the uninjured left elbow. Note the normal position of the medial epicondyle in left elbow, which is not seen in the right elbow.
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Caption: Picture 23. Medial condyle fracture. Anteroposterior (A) and lateral (B) views. Vertically oriented fracture begins along the medial aspect of the distal humeral metaphysis and extends to the growth plate. Similar to lateral condyle fractures, the fracture continues through the epiphysis, but it cannot be seen in this patient because the entire trochlea is still cartilage and has not yet become ossified.
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Caption: Picture 24. Transcondylar fracture. Anteroposterior (A) and lateral (B) views of the injured left elbow with anteroposterior (C) and lateral (D) views of the right elbow for comparison. The capitellum (along with the remainder of the cartilaginous epiphysis) is medially and posteriorly displaced relative to the metaphysis. Radiocapitellar alignment remains normal.
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Caption: Picture 25. Transcondylar fracture. Anteroposterior (A) and lateral (B) views. The position of the tiny ossification center for the capitellum suggests that it is displaced posteriorly; this is confirmed on the arthrogram (C).
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Caption: Picture 26. Transcondylar fracture. Anteroposterior (A) and lateral (B) views. Transcondylar fracture with typical posterior and medial displacement of the distal fragment. On the lateral view, a thin metaphyseal flake is present posteriorly and indicates a Salter-Harris type II injury rather than the usual Salter-Harris type I injury.
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Caption: Picture 27. Transcondylar fracture. A, Initial anteroposterior view shows typical medial displacement of the capitellum and forearm bones. B, Subsequent radiograph shows abnormality of the medial condyle and varus deformity from a growth plate injury.
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Caption: Picture 28. Radial neck fracture. Anteroposterior view shows a mildly abnormal angular configuration of the lateral aspect of the proximal radial metaphysis. This finding is indicative of a nondisplaced fracture.
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Caption: Picture 29. Displaced proximal radial fracture. Anteroposterior view shows a Salter-Harris type II fracture of the proximal radius with lateral and distal displacement of the radial head, which is positioned along the lateral aspect of the proximal radial metaphysis.
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