A Review on Reading Elbow Radiographs
case presentation
A healthy, 16-year-old man presents after a fall during gym class playing dodgeball. He states that he was trying to dip away from a ball and landed on an outstretched arm. He is having a difficult time fully extending his elbow on examination and there is tenderness that localizes to the radial head. Which of the following can be indicative of a fracture around the elbow?
A. Abnormal supinator line
B. Abnormal pronator line
C. Popeye sign
D. Reverse Popeye sign
introduction
Though there have been advances in elbow imaging in the past couple decades, conventional radiography remains the most appropriate initial imaging technique of the elbow and its disorders. It is important for sports medicine providers to be comfortable ordering and interpreting radiographs of the elbow. This post will focus mostly on radiographs with closed physes.
The elbow articulation is made up of three congruous joint surfaces and is considered a trochoginglymoid joint [2]. The trochoid (pivoting) components consist of the radiohumeral and proximal radioulnar joints, which allow for axial rotation of the forearm. The ginglymus (hinge) component is created by the ulnohumeral joint, allowing for flexion and extension. Full hinge motion is assisted by the deep invaginations of the distal humeral olecranon and coronoid fossa.
A routine radiographic evaluation of the elbow includes an anteroposterior (AP) and true lateral view. For the AP view the elbow should be fully extended with the forearm supinated, allowing optimal visualization of the medial and lateral epicondyles, radiocapitellar joint, and estimation of the carrying angle [Figure 1]. The carrying angle is the angle formed between the longitudinal axes of the humerus and the forearm on AP projection, normally between 11 and 13° of valgus [1,2].
Image 1: Labeled AP radiograph of the elbow. Adopted from [3].
The lateral view should be obtained with the elbow in 90° of flexion and the forearm in neutral (thumb up) position (Figure 2). A true lateral radiograph allows a “teardrop” appearance to be formed by the boundaries of the coronoid and olecranon fossae. The ulnotrochlear joint, coronoid process, and olecranon process are well seen in this projection.
Image 2. Lateral radiograph of the elbow showing the “teardrop” appearance of the coronoid and olecranon fossa. Adopted from [2].
In the setting of trauma or arthrosis, additional oblique radiographs may be of benefit. An internal oblique view with the extended elbow fully pronated or an external oblique view with the extended elbow supinated. The internal oblique position crosses the proximal radius over the ulna, superimposing most of these structures. The coronoid process, however, is visible without superimposition and is best demonstrated on this view. The external oblique position best demonstrates the radial head, neck, and tuberosity as well as the proximal radioulnar joint viewed free of any superimposition.
Figure 3. Internal oblique radiograph of the elbow labeled. Adopted from [3].
Figure 4. External oblique radiograph of the elbow. Adopted from [3].
The lateral oblique view is similar to the AP except that the hand and forearm are fully externally rotated. As with any complex joint, numerous special projections exist to demonstrate different perspectives sought on specific structures.
Figure 5. Outline for evaluation of the elbow radiograph. Adopted from [2].
Trauma to the elbow is common in all age groups. The mechanism of injury is often a fall on an outstretched hand. Athletic activities also provide occasions for direct trauma as well as repetitive microtrauma and overuse conditions seen in adolescents and young adults [3].
A paradox is observed in the functional potential of the posttraumatic elbow and the radiologic findings of the posttraumatic elbow. Weissman and Sledge note that after fracture healing, the final clinical result may not coincide with the final radiographic appearance [4]. That is, “excellent function may coexist with distorted anatomy, and poor function may be present in spite of optimal radiographic appearances.”
Some subtle fractures may not be easily seen on radiographs. However, the joint effusion that any fracture produces is less challenging. At the elbow, this joint effusion creates two abnormal soft tissue signs that are highly associated with fracture. The positive fat pad sign and the abnormal supinator line are radiographic soft tissue clues to underlying fracture.
Fat pads are located anteriorly and posteriorly at the fossae of the distal humerus. Normally, the anterior fat pads of the coronoid and radial fossae are visualized on the lateral radiograph superimposed together as a thin, triangular lucency just anterior to the distal humerus. The posterior fat pad lies deep in the olecranon fossa and is not normally visible on the lateral radiograph. A positive fat pad sign is produced when an effusion distends the capsule enough to displace the fat pads from their normal position—rendering them visible as radiolucent structures within the gray soft tissues. Note that although the positive fat pad sign is most often associated with fracture, any condition that produces enough joint effusion will also displace the fat pads. Examples include hemophilia, inflammatory arthritis, infection, intra-articular masses, and osteochondritis dissecans.
Figure 6: Fat pad sign on lateral elbow radiograph. Adopted from [2].
The fat plane overlying the supinator muscle is sometimes referred to as the supinator line. It is normally seen on the lateral radiograph as a thin, lucent line parallel to the anterior aspect of the proximal third of the radius approximately 1 cm from the anterior margin of the radius. In virtually all cases of acute radial head fracture, this line may become elevated, widened, or blurred. Conditions other than trauma causing this abnormal soft tissue sign include infection and inflammatory diseases.
Figure 7. Abnormal supinator line. Adopted from [20].
Most fractures and dislocations at the elbow result from falls on an outstretched hand with or without an abduction or adduction component, or a force applied through a flexed elbow. Fractures of the radial and ulnar shafts are more often caused by direct trauma, often associated with violent blows, motor vehicle accidents, or falls from heights [2]. Providers should keep these things in mind when evaluating radiographs and when taking history.
Elbow dislocations are most often caused by a fall on an outstretched hand that levers the olecranon away from the trochlea. Dislocations of the elbow joint are described by the direction that the radius and ulna have displaced in relation to the distal humerus. Three types of elbow dislocations are those involving the following: 1. Only the radius 2. Only the ulna 3. Both the radius and ulna together [2]. The most common type, accounting for 80% to 90% of all elbow dislocations, involves both the radius and the ulna, displaced in a posterior or posterolateral direction.
The most common tendon ruptures of the elbow involve the biceps and triceps tendons. Biceps tendon tear may occur at the origin of the long head of the biceps tendon, superior glenoid tubercle, or at its attachment to the radial tuberosity. The former injury commonly occurs in the elderly and is associated with rotator cuff tear. The latter injury tends to occur in the dominant arm of active men as a result of sudden loading, such as in lifting or catching a heavy object. On lateral radiograph of the elbow, a complete distal biceps rupture is manifested by proximal retraction of the muscle belly, giving a “Popeye” appearance. On lateral radiograph, triceps tendon rupture is diagnosed when there is an avulsion of the olecranon tip [3].
Figure 8. Lateral elbow radiograph showing a distal biceps tendon deformity or “Popeye” appearance. Adopted from [2].
First described in 1814 by Giovanni Monteggia, the Monteggia dislocation/fracture involves fracture of the ulnar shaft with associated dislocation of the radiocapitellar joint. The ulnar fracture will show apex-medial angulation and the radial head often dislocates anteriorly [2].
The Galeazzi dislocation/fracture was first described in 1943 by Galeazzi. This injury involves an obvious oblique and displaced, with angulation, fracture of the radial shaft. However, the dislocation of the distal radioulnar joint may be subtle [2].
A highly comminuted or impacted fracture of the radial head may be associated with dislocation of the distal radioulnar joint. The force of the injury is directed along the interosseous membrane of the forearm, which disrupts the distal radioulnar joint, as described by Essex-Lopresti.
Summary
In summary, the routine radiologic evaluation of the elbow includes three projections demonstrating the distal humerus, proximal ulna, proximal radius, and their associated articulations. These include the anteroposterior, lateral and oblique views. Most fractures and/or dislocations are associated with falls and providers should also image the forearm if a fracture or dislocation is suspected.
CASE CONCLUSION
A. The fat plane overlying the supinator muscle is sometimes referred to as the supinator line. It is normally seen on the lateral radiograph as a thin, lucent line parallel to the anterior aspect of the proximal third of the radius approximately 1 cm from the anterior margin of the radius. In virtually all cases of acute radial head fracture, this line may become elevated, widened, or blurred. Conditions other than trauma causing this abnormal soft tissue sign include infection and inflammatory diseases.
– More Elbow Pain: https://www.sportsmedreview.com/by-joint/elbow/
– More Elbow Pain from Wiki Sports Medicine: https://wikism.org/Elbow_Pain_Main
References
- Cain EL Jr, Dugas JR, Wolf RS, et al: Elbow injuries in throwing athletes: a current concepts review. Am J Sports Med 31:621-635, 2003
- Grayson, David E. “The elbow: radiographic imaging pearls and pitfalls.” Seminars in roentgenology. Vol. 40. No. 3. WB Saunders, 2005.
- McKinnis, Lynn N. Fundamentals of musculoskeletal imaging. FA Davis, 2013.
- Weissman, B, and Sledge, C: Orthopedic Radiology. WB Saunders, Philadelphia, 1986.
