Traumatic Elbow Injuries: What the Orthopedic Surgeon Wants to Know

©RSNA, 2013 • radiographics.rsna.org

The elbow consists of three primary articulations that provide two degrees of freedom of motion. Flexion and extension movements are centered at the ulnotrochlear articulation, and pronation and supination are centered at the radiocapitellar and radioulnar articulations.

The elbow articulations are stabilized by the medial (ulnar) and lateral (radial) collateral ligament complexes .

The medial collateral ligament (MCL) complex is made up of anterior, posterior, and transverse bundles. The lateral collateral ligament complex is made up of the radial collateral ligament (RCL), the lateral ulnar collateral ligament (LUCL), and the annular ligament, as well as the functionally irrelevant accessory collateral ligament.

The ulnohumeral articulation, the anterior bundle of the MCL, and the LUCL are the primary stabilizing structures of the elbow.

Secondary stabilization is provided by the radiocapitellar articulation, the common flexor-pronator tendon, the common extensor tendon, and the joint capsule

Functional Anatomy of the Elbow

Computer-generated lateral three-dimensional (3D) view of the elbow demonstrates the normal anatomic configuration of the lateral collateral ligament complex, which includes the LUCL (red), RCL (blue), and annular ligament (yellow). (b) Computer-generated medial oblique 3D view shows the normal configuration of the anterior (red), posterior (blue), and transverse (yellow) MCL bundles

Common Injury Patterns

Radial Head and Neck Fractures

Radial head and neck fractures are the most common elbow fractures in adults, comprising approximately 33%–50% of elbow fractures, and are seen in roughly 20% of elbow trauma cases.

Radial head and neck fractures are most often associated with a FOOSH-type injury mechanism that results from axial loading during forearm pronation with extension or relative flexion of 0°–80°, which causes the radial head to forcefully impact the capitellum of the humerus .

In reporting radial head fractures by using the Mason-Johnston system, it is most helpful to describe the degree of displacement, the amount of articular surface involved, and the presence of comminution or associated dislocation.

The diagnosis is usually made at initial radiography, with subtle radial head fractures indicated by the presence of elevation of the anterior and posterior fat pads , which are intracapsular but extrasynovial .

Cross-sectional imaging is not usually required for evaluating isolated radial head fractures, but MR imaging has proved effective for identifying fractures in adults with a radiographic finding of joint effusion .

Mason-Johnston classification system

type I: characterized by no or only minimal (<2 mm) displacement type II:defined by displacement of 2 mm or more and articular surface involvement of less than 30%

type III, defined by comminution of the radial head; and type IV, defined by associated proximal radial dislocation. Conservative treatment is usually recommended for type I fractures (green box) and for type II fractures with a preserved range of motion (yellow box), whereas surgery is indicated for type II fractures with a poor range of motion and for type III and IV fractures (red boxes

Oblique (a) and lateral (b) radiographs of the elbow demonstrate a nondisplaced radial neck fracture with anterior and posterior fat pad elevation (black arrows in b), findings indicative of a Mason-Johnston type I injury. In radial neck fractures, the normal mild concave curvature of the anterior cortex of the base of the radial head is lost and an abrupt offset between the radial head and neck (white arrow) is created

Lateral radiograph of the elbow during extension demonstrates a displaced radial head fracture (arrow) that involves less than 30% of the articular surface, a finding indicative of a Mason-Johnston type II fracture

Essex-Lopresti Fracture-Dislocation

An uncommonly seen but clinically important fracture pattern, which involves a comminuted fracture of the radial head with dislocation of the distal radioulnar joint and disruption of the interosseous membrane, producing the oft-cited “floating radius”.

The mechanism is most likely a variation of that present in a FOOSH-type injury.

Because Essex-Lopresti fractures nearly always require surgical intervention, their detection is of paramount importance.

The diagnosis is often suspected because of reported wrist pain or tenderness, which prompts initial radiography .

The radiographic features of distal radioulnar joint dislocation can be subtle, but a radioulnar distance discrepancy of more than 5 mm on lateral radiographs of the injured wrist relative to the contralateral uninjured wrist is considered diagnostic.

Radiographically occult injuries of the distal radioulnar joint are not uncommon, and in ambiguous cases, CT or MR imaging can be helpful in depicting dynamic instability or soft-tissue injury.

Although CT and MR images showing Essex-Lopresti injuries often demonstrate comminution of the radial head, which is a surgical indication, patients with borderline injuries to the radial head may erroneously receive only conservative therapy if the distal radioulnar joint injury is not detected.

Essex-Lopresti Fracture-Dislocation

Computer-generated 3D view of a left forearm shows a common Essex-Lopresti injury mechanism:

a FOOSH produces axial loading along the forearm (long yellow arrow), with resultant distraction forces at the distal radioulnar joint (short yellow arrows).

Forces are transmitted primarily through the radial head (red “starburst”) and interosseous membrane (red polygon).

Frontal radiograph of the elbow depicts a comminuted radial head fracture (arrow). Lateral radiograph of the wrist shows dorsal subluxation of the distal ulna with widening of the radioulnar distance (arrow), findings suggestive of distal radioulnar joint dislocation in the setting of wrist pain

Distal Humerus Fracture

Computer-generated 3D view of the humerus shows the two bone columns that provide primary load-bearing support to the arm:

the lateral column, which extends distally to the capitellum articulation,

And

the medial column, which extends to the medial epicondyle. Column disruption compromises structural stability.

With distal humerus fractures, it is most critical to report the salient radiographic findings that guide treatment: column involvement, the direction and degree of displacement of epicondylar avulsion fractures and single-column fractures, and the presence of comminution or two-column injury.

Radiography generally is sufficient for the initial identification and classification of distal humerus fractures . However, after a fracture of the distal humerus is identified at radiography, CT is usually performed to ensure accurate fracture classification because of the high incidence of severe injuries that ultimately require surgery.

MR imaging is not usually indicated, because the incidence of postoperative instability has been shown to be low in most cases of uncomplicated fracture fixation with adequate bone union, as the collateral ligament complexes often remain intact at their proximal attachments on the fractured humerus .

Jupiter and Mehne classification system

Treatment options for the various types of humeral fracture:

Epicondylar avulsion fractures (type A1 fractures; green box) with minimal (<1 cm) displacement can be treated conservatively

single-column fractures without comminution (fracture types B1–B3; yellow boxes) can be treated conservatively at first but will likely require surgery

comminuted or two-column fractures (types A2, A3, and C1–C3; red boxes) require surgery

(a) Frontal radiograph shows a mildly displaced medial epicondylar fracture (arrowhead) with soft-tissue swelling, findings of an AO-ASIF type A1 fracture. An associated anteromedial coronoid facet fracture (black arrow) and a depressed intraarticular radial head fracture (white arrow), as well as the degree of medial epicondylar fragment displacement, are indications for surgical repair. (b) Frontal radiograph shows a transverse metaphyseal fracture (arrowhead) and a minimally displaced intraarticular fracture of the distal humerus (arrow), findings of AO-ASIF type C1 injury. (c) Frontal radiograph depicts a comminuted intraarticular fracture of the distal humerus (arrow), an AO-ASIF type C3 fracture

The coronoid process makes up the anterior margin of the ulnohumeral articulation and serves to resist varus stress and prevent posterior elbow subluxation .

The coronoid process also serves as the site of anterior attachment of the joint capsule, insertion of the MCL, and insertion of the brachialis muscle at its anterior aspect .

The coronoid process, which provides static axial stability to the extended elbow, has been shown to fracture in isolation with axial loading over the range of 0°–35° of elbow flexion; it also may fracture in conjunction with the radial head over 0°–80° of flexion .

Coronoid Process Fracture

Tiny coronoid process tip fractures most commonly occur as a complication of subluxation or dislocation, predominantly during axial and posteromedial rotatory loading, and they may herald additional occult damage to bone or soft tissue (eg, lateral collateral ligament complex injuries) .

The severity and extent of small coronoid tip fractures therefore cannot be adequately evaluated with radiography alone , and a radiographic finding of a seemingly tiny coronoid tip fracture should prompt additional imaging .

Adequate evaluation of coronoid process fractures requires characterization of the fracture fragment size and the degree of anteromedial facet and potential coronoid base involvement. CT evaluation of coronoid process fractures is recommended, and early evaluation with with 3D reconstructions often obtained for full evaluation of the morphologic characteristics of fractures.

MR imaging can be used to detect bone edema in cases with ambiguous radiographic or CT findings and to evaluate for soft-tissue injuries relating to isolated coronoid process fracture, prior elbow subluxation, or frank dislocation .

O’Driscoll system

Computer-generated en face 3D view of the coronoid process shows the O’Driscoll fracture classification system, which comprises three fracture types (I, II, and III) defined on the basis of their location in the 3D anatomy. Type I injuries involve the coronoid tip and affect approximately one-third of the coronoid process. Type II injuries are characterized by anteromedial facet involvement to a varying degree, with more medial involvement representing a more severe injury subtype. Type III injuries are the most severe, with the fracture involving at least half of the coronoid process

Lateral radiograph of the elbow demonstrates an apparently tiny fracture of the coronoid tip (arrow).

Sagittal (b) and 3D volume-rendered (c) images from subsequent CT depict extension of the coronoid tip fracture through the anteromedial facet (arrow), a finding that indicates an increased risk for elbow instability

Coronal (a) and axial (b) CT images demonstrate a comminuted fracture (arrow) extending through the anteromedial facet of the coronoid process, a finding of an O’Driscoll type II fracture requiring surgical repair to prevent joint instability.

Coronal (a) and axial (b) T2-weighted fat-saturated MR images show a fracture of the anteromedial facet of the ulnar coronoid process (arrow), with high signal intensity representing edema in the bone and in soft tissue surrounding the distal MCL.

Classification of olecranon fractures is based on the presence or absence of comminution, displacement, and involvement of other osseous structures (eg, the coronoid process).

Patients with nondisplaced fractures that are less than 2 mm wide, with no increase in displacement over 90° of flexion or during active extension, can usually undergo a trial of conservative therapy . Displacement of fracture fragments (with a gap of >2 mm), increased displacement during elbow flexion or extension, and the presence of comminution are surgical indications.

The presence of comminution should be specifically emphasized, because it is an indication for the use of a plate instead of a tension band–wire construct for fixation .

Radiography is generally sufficient for initial and postreduction evaluations , but CT is often performed in cases in which surgical repair is indicated. MR imaging is occasionally used in ambiguous cases or when the presence of stress fractures is suspected.

MR imaging allows excellent evaluation of the triceps tendon and is often indicated in cases of avulsion-type fracture .

Olecranon Fracture

Transverse fractures can be treated with tension banding and Kirschner wires

comminuted (b) and oblique (c) fractures are often best managed with plate fixation and bicortical screw fixation, respectively

Coronoid process involvement usually requires medial plate fixation to prevent chronic instability.

Lateral radiograph of the elbow demonstrates a comminuted fracture of the olecranon (arrow). Comminution and fragment displacement qualify this injury for surgical treatment.

Lateral radiograph (a) and sagittal intermediate-weighted MR image (b) depict an avulsion fracture of the olecranon at the site of triceps tendon insertion (arrow). The degree of displacement qualifies this injury for surgical treatment

Elbow Dislocation Elbow dislocation is the second most common type of joint dislocation in adults, after shoulder dislocation .

Adult elbow dislocations are most commonly posterior in direction. Anterior dislocations of the elbow are rare and are most often seen in children, in whom they are usually the result of rebound after posterior dislocation .

Divergent dislocations involve interposition of the distal humerus between the proximal radius and ulna, with the proximal radius and ulna dislocated in divergent directions .

Posterior dislocations are often associated with radial head fractures because of axial compression on the capitellum . Coronoid process fractures are also commonly seen and likely are due to a shearing mechanism where the trochlea impacts the coronoid process tip during dislocation . Flexor-pronator and brachialis muscle injuries are commonly seen and can contribute to instability.

Elbow Dislocation

Lateral radiographs show simple (a) and complex (b) posterior elbow dislocations. Simple dislocations may be treated conservatively, but the presence of an associated comminuted radial head (Mason-Johnston type IV) fracture in complex dislocations (arrow in b) necessitates surgical repair.

Computer-generated images of the elbow show the stages of posterior elbow subluxation and instability. (a) Stage 0 injuries are characterized by baseline anatomic alignment with no instability. (b) Stage I injuries involve damage to lateral ligamentous structures such as the LUCL and RCL, with resultant PLRI. (c) Stage II injuries involve capsular and lateral soft-tissue damage that leaves the trochlea perched on the coronoid process. (d) Stage III injuries are defined by varying degrees of damage to medial structures, especially the anterior bundle of the MCL, with frank posterior elbow dislocation

Coronal intermediate-weighted fat-saturated image from MR arthrography demonstrates disruption of the RCL and LUCL, with marked contrast material accumulation around the lateral humeral condyle (arrow). Disruption of the LUCL has been associated with PLRI

Coronal short inversion time inversion-recovery (a) and gradient-echo (b) MR images obtained after reduction for posterior dislocation depict a bone marrow contusion (arrow in a) in the lateral capitellum and lateral epicondyle, an injury produced by impact of the radial head. Full-thickness tears of the MCL (arrow in b) and LUCL complex (arrowhead in b) also are seen

Postreduction lateral radiograph of the elbow demonstrates the drop sign (arrow), an appearance created by an ulnohumeral distance of 4 mm or more. This finding may be predictive of the development of PLRI.

Postreduction lateral radiograph shows a comminuted radial head fracture (arrow) and coronoid process fracture fragment (arrowhead) in the setting of severe complex posterior elbow dislocation, injuries known as the Terrible Triad .

The combination has been described as the “terrible triad” because it is associated with extensive ligament damage that could result in chronic instability and severe arthritis if inadequately treated .

Monteggia fracture-dislocation was initially described as a fracture of the proximal ulna in association with anterior dislocation at the radial head but was later redefined as any ulnar fracture with radiocapitellar dislocation .

Monteggia injuries are classified within the Bado system on the basis of the direction of dislocation, angulation of the ulnar fracture fragment, and the presence or absence of an associated fracture of the radius .

Monteggia Fracture and Dislocation

Bado classification of Monteggia fractures

type I, fracture of the proximal or middle third of the ulna with anterior angulation of the apex and associated anterior dislocation of the radial head (a); type II, fracture of the proximal or middle third of the ulna with posterior angulation of the apex and associated posterior dislocation of the radial head

type III, fracture of the proximal ulna with lateral dislocation of the radial head (c); and type IV, fracture of the proximal or middle third of the ulna and radius with anterior dislocation of the radial head

Oblique frontal radiographic view of the forearm shows a transverse fracture of the ulnar diaphysis (arrowhead) with anterior angulation of the apex and predominantly anterior dislocation of the radial head (arrow), findings of a Bado type I Monteggia fracture

Conclusion

The evaluation of traumatic elbow injuries requires not only the radiographic detection of bone abnormalities but also the inference of potential associated secondary occult bone and soft-tissue injuries that could place the patient at risk for chronic joint instability.

An intuitive understanding of the most common injury mechanisms will help direct the early imaging evaluation as appropriate to facilitate detection of the most clinically relevant associated injuries.

The radiologist’s role as a consultant also necessitates that imaging findings be communicated in the most clinically relevant way to ensure effective early evaluation and intervention.

By adopting the clinically most relevant classification systems used by their colleagues in orthopedic surgery, radiologists can minimize the potential for inappropriate or delayed treatment