Supracondylar fracture of the distal humerus is the most common and problematic elbow fracture that occurs in children. This fracture represents between 55% and 80% of all children’s elbow fractures. It occurs from a fall, usually from a height greater than 2 feet (14). In 95% to 98% of such cases, the injury occurs in the outstretched arm with the elbow extended. In only 2% to 5% of patients does this injury occur in the flexed elbow.

The extension-type supracondylar fracture of the distal humerus has been classified into three types. Type IA nondisplaced fractures can be challenging to diagnose radiographically because the fracture line may be difficult to detect (Fig. 12.9). The diagnosis is based on clinical examination, which reveals tenderness, both laterally and medially over the distal humeral condyles. Although radiographs may show no cortical disruption, a posterior fat pad is often present. This injury is treated conservatively with long-arm cast placement with the elbow positioned in 90 degrees of flexion. Type IB minimally displaced/medial compression injury must be carefully evaluated by radiography to avoid underestimating the degree of deformity (Fig. 12.10). Underestimation of deformity can lead to subsequent cubitus varus alignment of the elbow. Type IIA hyperextension/posterior cortex intact injury is best diagnosed on the lateral radiograph. Fractures with extension of the humeral/capitellar relationship of more than 20 degrees will require reduction. Type IIB, displaced and angulated with osseous contact
at the fracture line, demonstrates both rotational and hyperextension deformity radiographically, but with some cortical contact remaining, usually on the posterior aspect of the humerus (Fig. 12.11). Both Types IIA and IIB will require closed reduction in the operating room. Type III completely displaced fracture generally results from an extension-type injury as previously noted. With this mechanism of injury, the distal fragment is displaced posteriorly. In the paucity of cases in which the mechanism of injury is of the flexion type, there is anterior displacement of the distal fragment (14–17).

The complications of the supracondylar injury may be more likely to require assessment by MRI than the osseous injury itself. The incidence of nerve damage from the fracture is reported to be approximately 10% (14, 16, 18). The most commonly injured nerve in a displaced supracondylar fracture is the anterior interosseous branch of the median nerve (Fig. 12.12). After the median nerve, the nerves most likely injured include, in decreasing frequency, the radial and ulnar nerves. Ulnar neuropathies have also been reported as an iatrogenic complication from medial pin placement. In such cases, the neuropathy has been reported to resolve in 1 to 6 months after pin removal (16, 18, 19).

In approximately 10% of cases of displaced supracondylar fracture, the radial pulse will be absent at presentation. In greater than 90% of these cases, the pulse will return with closed reduction and pinning of the fracture under general anesthesia (20). In one study reviewing 13 patients with a pulseless, pink hand after closed reduction and percutaneous pinning of the supracondylar fracture, all patients were found to have vascular injuries involving the brachial artery. In this setting, segmental pressure monitoring, color flow Doppler scanning, and MR angiography were recommended for evaluation of brachial artery patency and collateral circulation around the elbow (21).

Compartment syndrome represents an all but obsolete complication of the supracondylar fracture. This is believed to be the result of the institution of immediate closed reduction and percutaneous pinning (19). In the setting of compartment syndrome, however, the MRI findings can be somewhat nonspecific. These include swelling of the affected extremity with abnormalities of signal intensity within the involved compartment, generally high signal intensity on fluid-sensitive sequences. Diagnosis is established by a combination of physical examination and intracompartmental pressure measurements. The
former reveals tense induration of the compartment in question. Intracompartmental pressure measurements should not exceed 30 mmHg. If it does, fasciotomy is indicated.

The transcondylar fracture is considered a rare injury and has been grouped with the supracondylar fracture. Indeed, the transcondylar fracture can resemble a supracondylar fracture. The fracture line in a transcondylar fracture, however, usually extends transversely across the condyles and often has an intra-articular component. These fractures are frequently unstable and unite slowly when treated conservatively. The transcondylar fracture can be treated with percutaneous pinning. This injury, especially with intra-articular extension, can be complicated by avascular necrosis.

Intercondylar fractures in adults present the most difficult challenge of all fractures encountered in the distal humerus (Figs. 12.13 and 12.14). These fractures are relatively rare and are typically observed in patients older than age 50 years (22, 23). They are produced by direct trauma to the elbow in which the ulnar articular surface is driven against the articular surface of the distal humerus (24). The classification system for this type of fracture is based on radiographic assessment and includes four types: (i) Type 1 fractures are undisplaced fractures extending between the capitellum and
trochlea; (ii) Type 2 fractures are displaced T or Y fractures with the fracture extending from the groove on the articular surface of the trochlea, proximally between the condyles, then dividing transversely or obliquely across the shaft, separating the condyles from each other without rotation; (iii) Type 3 fractures are fractures with rotational displacement of the condyles; and (iv) Type 4 fractures are those with severe comminution of the articular surface and wide separation of the condyles (25). The goal of imaging is to show the extent of bone damage and planes of the fracture lines. This is probably best achieved through the use of multidetector computed tomography.

Type 1 fractures are usually immobilized with a plaster splint with gradual motion instituted after healing has occurred. Type 2 and 3 fractures are treated by open reduction and internal fixation. Type 4 fractures, also referred to as “the bag of bones,” is usually treated nonoperatively. Poor results posttreatment are the result of heterotopic ossification, infection, ulnar nerve palsy, fixation failure, and nonunion. Imaging should be directed at the detection of these potential and not infrequently encountered complications in the posttreatment intercondylar fracture (24, 26).

Condylar fractures are considered uncommon injuries that occur primarily in the setting of the skeletally immature patient. Lateral-sided injury occurs more frequently than its medial counterpart (Fig. 12.15). As a result of the involvement of both articular surface as well as the condyle, both restriction of motion and instability can result from this injury, especially if the fracture fragment is large. Fragment size and presence or absence of disruption of the lateral trochlear ridge, the structure that separates the trochlea and capitellum, comprise the elements on which the classification system for this type of fracture is based. In Type I fracture, the fragment is small and the lateral trochlear ridge is not involved. In Type II fracture, however, the fragment is larger and contains the separated condyle and extends through the lateral trochlear ridge. Type II injury allows translocation of the radius and ulna in a medial to lateral direction and can result in a fracture–dislocation (27, 28). When the condyle is displaced, open reduction and internal fixation are the best treatment.

Although trochlear fractures are extremely rare, fracture of the capitellum is one of the most common purely intra-articular fractures that occur about the elbow (Figs. 12.16 and 12.17). The mechanism of injury involves a direct force to the capitellum transmitted through the radial head resulting in a varying size shear fracture. It is important to differentiate fractures of the capitellum from fractures of the lateral condyle, because the latter often result in significant instability of the ulnohumeral joint. Fractures of the capitellar articular
surface alone, although producing an intra-articular fragment, do not result in instability.

Classification of fractures of the capitellum depends on the size of the articular fragment and the degree of comminution. A Type 1 fracture constitutes a large fragment of bone and articular cartilage, a Type 2 fracture is characterized by a small shell of bone and articular cartilage, and a Type 3 fracture is a comminuted fracture.

In general, the diagnosis is based on radiographic examination. Often the anteroposterior radiograph will
not define the fracture, especially if it is Type 2 and small. Small fragments residing in the superior joint may be confused with fragments of the radial head, but radial head fragments rarely migrate to the superior joint space.

Methods of treatment include closed reduction, open reduction with and without internal fixation, excision of fragments, or insertion of a prosthesis. Closed reduction is almost never successful. Advocates of fragment excision believe that the operation is simple and offers a simple definitive procedure. Advocates of open reduction and internal fixation, however, point to the fact that with excision, a raw osseous surface is created that is prone to late valgus deformity.

Isolated fractures of the epicondyles are rarely encountered in the adult and are more frequently seen in the child or adolescent. In the setting of the skeletally immature patient, these injuries fall under the category of the chondroepiphyseal injury (29–32). When this injury does occur in the adult, it happens more on the medial side than the lateral and is believed to be the result of a direct force applied to the epicondyle. Radiographs reveal a fracture fragment that is displaced in a distal or anterior direction as a result of the unopposed action of the forearm flexor muscles.

Pediatric elbow injuries that result from repetitive throwing-type activities are common. Several studies have documented that 20% of pitchers aged 10 to 14 years experienced elbow pain at one time or another during their careers. Many pediatric throwing injuries occur at or about secondary ossification centers. The appearance of these secondary ossification centers in boys generally occurs at the following ages: capitellum at 2 years of age, radial head at 5 years, medial epicondyle at 7 years, trochlea at 9 years, olecranon at 10 years, and finally, the lateral epicondyle at 11 years. In girls, these centers tend to appear half to 1 year earlier. Fusion occurs in the early to midteens in boys and the early teens in girls.

Similar to the adult, the cause of most throwing injuries in the adolescent is secondary to the mechanics of throwing, which results in medial tension overload, extension overload, and lateral compression. Medial-sided
injuries are the most common. The chronic forces of valgus overload produce age-dependent changes such as apophysitis in childhood and epicondylar avulsion in the more mature athlete. With repetitive valgus overload, lateral-sided injuries such as Panner’s disease and osteochondritis dissecans of the capitellum and radial head, respectively, can result. Finally, posterior patterns of injury consistent with olecranon apophysitis and posteromedial impingement can be seen (33).

Accurate diagnosis of injuries of the elbow in the pediatric population is difficult. This is the result of the large number of developing ossification centers, the variable imaging appearance of those centers as well as the cartilaginous component of the centers rendering them invisible on conventional radiography. MRI offers a diagnostic role in this setting, allowing delineation of injury types.