X-elbow

Indication/Technique

Indication

The elbow X-ray examination is requested frequently. At the Emergency Assistance department, it is used primarily to demonstrate/exclude a fracture.
Other referrals to this examination come from e.g. GPs or orthopedists.  A frequently asked question is whether there is osteoarthritis in the elbow joint.

Technique

A standard series includes an anteroposterior (AP) image and a lateral image. Additionally, a radial head - capitellum image can be made.

AP image

The arm is in exorotation (palm of the hand pointing upward) and in full extension. The back of the arm should be in contact with the plate (fig. 1).
The joint is then imaged from above.  
A good image shows the elbow joint, plus 1/3 of the distal humerus and 1/3 of the radius/ulna.

Figure 1. Technique for AP image of the elbow.

Lateral image

For a purely lateral image, the shoulder should be at the same level as the elbow. Importantly, the medial side of the entire arm should be in contact with the table.   Sometimes a sand bag may prove helpful.  
The hand is turned vertically, the hand palm pointing toward the patient (fig. 2).   
The X-rays will pass through the joint parallel to the humeral epicondyles. 
A good image will show the elbow joint with about 1/3 of the distal humerus and 1/3 of the proximal radius/ulna.

Figure 2. Technique for lateral image of the elbow.

Radial head - capitellum image

For improved visualization of the radial head, a separate radial head image can be made, e.g. in dubious/subtle fractures. 
The elbow is positioned as in the lateral image. It is then imaged under a 45-degree angle, rather than cranial as in a purely lateral image (fig. 3).

Figure 3. Technique of a radial head image.

Normal anatomy

The elbow joint consists of 3 joints (fig. 4):

  1. Humeroulnar joint: the proximal ulna consists of the olecranon (posterior side) and the coronoid process (anterior side) and articulates with the humerus through the trochlea.  Its primary function is flexion and extension of the elbow.  
  2. Radiohumeral joint: the radial head articulates with the humerus though the capitellum.  Its primary function is pronation and supination of the lower arm.
  3. Proximal radioulnar joint: articulation between the radial head and the radial notch of the ulna. Its primary movement is rotation of the radial head. 

Figure 4. Normal anatomy of the elbow from anterior perspective.

Lateral image

The capitellum and trochlea project over each other. In order to distinguish them, it is advisable to look for the contours of the radial head; between the capitellum and the radial head is a small space (= joint space of the radiohumeral joint).
The distal humerus has a concave plane at both the anterior and posterior side; the coronoid fossa at the anterior side provides space for the coronoid process in flexion and the olecranon fossa at the posterior side (= deeper!) provides space for the olecranon during extension,  increasing the range of motion during elbow flexion and extension. 
The elbow joint has both anterior and posterior fat tissue, the so-called fat pads.  These pads are extrasynovial but are within the articular capsule. In many cases, the anterior fat pad is seen as a thin straight lucent (= black) line at the front of the distal humerus, this is a normal finding (fig. 5). Note that the surrounding musculature is denser (= whiter) than the fat pad; see the X-ray/CT technique course for additional information.  The posterior fat pad is invisible on normal images (the implications are explained in the Pathology section).

Figure 5. Normal anatomy on a lateral elbow image.

AP image

The humerus projects over the olecranon. 
The capitellum and radius are at the lateral side. At the medial side is the trochlea, articulating with the ulna (fig. 6).

Figure 6. Normal anatomy on an AP image of the elbow.

Radius - capitellum image

This image effectively visualizes the radial head and capitellum (fig. 7).

Figure 7. Normal anatomy on a radial head image.

Ossification centers in children

Cartilage is invisible on X-rays. 
In young children the elbow joint is not yet fully grown. As they mature, 6 ossification centers develop. The ossification centers grow and eventually fuse with the humerus/radius/ulna.

The sequence of development of the ossification centers is fixed (fig. 8/9):

  • capitellum                        (+-1 year)
  • radial head                       (+-3 years)
  • medial (= internal) epicondyle    (+-5 years)
  • trochlea                         (+-7 years)
  • olecranon                         (+-9 years)
  • lateral (= external) epicondyle       (+-11 years)

Memory aid: CRIPTOE
The age at which the ossification centers exactly develop is not very important. More important is the order (particularly when assessing fractures).  The ages mentioned here are the ages at which they will almost certainly be present, however they usually develop even somewhat earlier.
Comment: a space is frequently visible between the lateral epicondyle and the humerus.  This is a normal finding as long as the epicondyle is parallel to the adjacent distal humerus

Figure 8. The ossification centers of the elbow.

Figure 9. Scroll through the images to see the development of the ossification centers in time.

Checklist

The following points may be used as a guide to assess an elbow X-ray.

  1.  Quality. Is this a purely AP/lateral image? Can everything be adequately assessed?
  2. Soft tissues: soft tissue swelling? Anterior/posterior fat pad displacement? 
  3. Normal radiocapitellar line? Normal anterior humeral line? (See pathology section.) 
  4. Pediatric: is the position of the ossification centers normal?
  5. Changes versus previous examinations?

Pathology

Fracture general

Lines (fig. 10):

  • A radiocapitellar line can be drawn on each image: it runs through the central radius and passes the central capitellum on a normal image. Important: this rule applies to EACH image, so not only a purely lateral image.  
  • The anterior humeral line is drawn along the front of the humerus and passes the anterior 1/3 of the capitellum.

When one of the above lines is abnormal, a fracture should be suspected.

Figure 10. Orientation lines in the elbow joint; normal radiocapitellar line & anterior humeral line.

Fat pads:

When there is joint effusion (fluid/blood/pus) or synovitis, the capsule will become distended.  Fat pads are located at the anterior and posterior side of the distal humerus. When the effusion becomes large enough, the fat tissue can be displaced away from the humerus.  This is termed a so-called ‘positive fat pad’ (fig. 11).

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Figure 11. Normal elbow versus joint effusion with positive fat pads. 

Important: In a trauma setting, a displaced posterior fat pad almost always indicates a fracture, particularly in adults. An abnormal posterior fat pad in children is relatively less specific than in adults, as soft tissue damage may also be associated with joint effusion.

Radial head fracture

Trauma mechanism

  • In many cases indirect trauma caused by valgus/pronation stress in an abducted arm.  A common cause is falling on an outstretched arm.

Findings (fig. 12b)

  • Often very subtle, fractures can therefore be overlooked easily.  
  • Look for joint effusion and therefore fat pad displacement. 
  • Watch carefully for cortex interruptions and densities that should not be there. 
  • Other abnormalities you may encounter include coronoid process fracture.  

Classification according to Mason (fig. 12a)

  • Type I: fracture without dislocation. 
  • Type II: partial intra-articular fracture with dislocation of > 2mm.
  • Type III: comminuted fracture of the entire radial head.
  • Type IV: fracture with dislocation of the elbow joint.

Figure 12a. Mason classification.

Figure 12b. Radial head fracture with positive anterior & posterior fat pad.

Radial head luxation

Radial head luxation means the radial head has become dislocated; the articulation with the ulna and humerus is abnormal. Always check the radiocapitellar line when a radial head luxation is suspected. In luxation, the line no longer runs through the central capitellum (fig. 13).

Figure 13. Radial head luxation in a 6-year-old child. Note the radiocapitellar line no longer runs through the central capitellum.

Pulled elbow/Nursemaid's elbow

A classical story where the child (particularly 2 or 3 years old) is suddenly pulled by the arm when it is in extension. The radial head becomes subluxated.  The child holds the elbow in flexion and pronation and refuses to extend the elbow. 
Theory: the radial head is fixed by the annular ligament.  The above-described force may cause subluxation of the radial head under the ligament. 
Treatment: multiple pronation/supination movements of the lower arm will cause the radial head to return to its anatomical position (sometimes with a ‘click’).
The X-ray will then be normal. A pulled elbow/Nursemaid's elbow is a clinical diagnosis.

Essex-Lopresti fracture

A comminuted fracture of the radial head by a fall on an outstretched arm may be associated with tearing of the interosseous membrane of the lower arm.  The force released during the trauma will be transferred distally through the interosseous membrane to the distal radioulnar joint (DRU joint), causing luxation of the DRU joint.  This trauma type is also known as the Essex-Lopresti fracture. 
Unfortunately the Essex-Lopresti fracture is not always recognized, simply because the wrist joint is not imaged. This may eventually cause permanent lower arm/wrist symptoms.
Learning point: in a comminuted fracture of the radial head, the wrist joint should always be imaged to exclude an Essex-Lopresti fracture.

Figure 14. Essex-Lopresti fracture. The AP image of the elbow reveals a radial head fracture-luxation; the AP image of the wrist shows luxation of the distal radioulnar joint (DRU joint).

Monteggia fracture

A proximal ulnar fracture may be associated with tearing of the interosseous membrane (= fibrous connection between the ulna and radius), continuing up to the stabilizing ligaments surrounding the radial head. This will eventually result in a radial head luxation. The combination of a proximal ulnar fracture and radial head luxation is termed a Monteggia fracture. The trauma mechanism is frequently a fall on an outstretched arm. 
The ulnar fracture is usually recognized easily, but the radial head luxation can be very subtle. This may lead to an untreated radial head luxation (with associated complications). So always check the position of the radial head in the presence of a proximal/mid-shaft ulnar fracture. 

Figure 15. Monteggia fracture; fracture of the proximal ulna and radial head luxation. Note the abnormal radiocapitellar line.

Supracondylar humeral fracture

Children often fall on an outstretched hand.  In this setting, the supracondylar humeral fracture is the most common fracture in children.

Trauma mechanism (fig. 16)

  • Falling on an outstretched arm, resulting in hyperextension. The olecranon bends backward too far, compressing the weak point in the distal humerus, the coronoid fossa (mechanism similar to bottle opener). 

Findings

  • Joint effusion with displaced fat pads (= positive fat pads). 
  • The anterior humeral line no longer runs through the middle 1/3 segment of the capitellum, but the capitellum is often posterior of the anterior humeral line. 
  • A cortex interruption proximal of the humeral condyles.  Note: cortex interruption is sometimes difficult to see due to impression. 

Figure 16. Mechanism of the supracondylar humeral fracture.

Figure 17. Supracondylar humeral fracture in a 9-year-old child.

Supracondylar humeral fractures may be very subtle. Sometimes there is only a positive fat pad and an abnormal anterior humeral line.

Lateral humeral condylar fracture

After the supracondylar fracture, the lateral humeral condylar fracture is the next most common fracture in children.  A fracture of the lateral humeral condyle is caused by a varus force. This may be caused by direct trauma from lateral or when the child falls on the lateral side of its arm. 
The extension of the fracture line is variable.
The Milch classification distinguishes two types (fig. 18):

  • Type 1 (least common): the fracture runs through the ossification centers and reaches up to the surface of the radiocapitellar joint.  This is a Salter-Harris type IV fracture. 
  • Type 2 (most common): the fracture is medial of the capitellum and ends in the non-ossified cartilage.  As the non-ossified cartilage is not visible on X-ray, it is not always clear whether the fracture continues (= Salter-Harris type IV) up to the joint surface or not (= Salter-Harris type II).

Note: you may want to consult the Fracture General Principles course for the Salter-Harris classification.

Figure 18. Lateral humeral condylar fracture according to the Milch classification.

Figure 19. Lateral humeral condylar fracture continuing into the capitellar ossification center (Milch type 1).

Medial humeral epicondylar fracture

The medial epicondyle of the humerus is the insertion site of the lower arm flexor muscles.  In the event of a strong force (as in throwing a ball) an avulsion fracture may develop of the medial epicondyle (= little leaguer's elbow).  In a severe dislocation, it may become trapped in the joint (fig. 20/21).

Figure 20. Avulsion fracture of the medial epicondyle with varying degrees of dislocation.  Illustration 4 shows significant dislocation where the medial epicondyle has become trapped in the joint.

A displaced fat pad may be absent and the avulsion fracture may be very subtle. Sometimes an image of the contralateral (unaffected) elbow can be helpful.
TIP:

  • the trochlear ossification center appears AFTER the appearance of the medial epicondyle on an elbow X-ray. When in the absence of a medial epicondyle an ossification center is nevertheless visible at the location of the trochlea, be aware this may be the dislocated medial epicondyle (and therefore not the trochlear ossification center). 
  • Always look for the presence of soft tissue swelling at the medial side. This may be an indication/substantiation of a medial epicondylar fracture diagnosis. 

Figure 21. A medial epicondylar fracture with some dislocation in a 9-year-old child.  Also note the associated marked soft tissue swelling.

Olecranon fracture

The triceps insert on the olecranon. In the event of a fracture, traction of the triceps may displace the loose fragment in the cranial direction.

Trauma mechanism

  • Direct fall on olecranon.
  • Fall on extended arm with some flexion in the elbow.
  • Avulsion fracture.
  • Stress fracture (e.g. in top athletes).  

Findings (fig. 22)

  • Often easily recognized on lateral images with obvious cortex interruption. 
  • There is usually proximal dislocation of the fragment.

Figure 22. Olecranon fracture.

Distal humeral fracture

Elderly osteoporotic patients may develop a distal humeral fracture after a fall, which is frequently a (simple) transversal fracture. 
In younger patients, intercondylar fractures are also seen with a T or Y configuration. The intra-articular fracture may continue up to the trochlea. 

Note: in an extra-articular fracture the distal humerus, displaced fat pads may be absent.

Elbow luxation

A fall on an outstretched hand with the elbow in hyperextension may cause elbow luxation. An elbow luxation is virtually always a posterior luxation; the olecranon is posterior of the humerus (fig. 23).
Luxation is regularly associated with fractures, particularly of the radial head and coronoid process.
The combination of a posterior elbow luxation, radial head fracture and coronoid process fracture is also termed the ‘terrible triad’.

Figure 23. Posterior elbow luxation, associated with a small chip fracture (possibly originating from the coronoid process).

Osteoarthritis

Osteoarthritis is wear and tear on the cartilage. It is associated with a diversity of symptoms. Patients may complain about progressive load-dependent pain and/or reduced elbow function. 
The osteoarthritis may be primary with no obvious identifiable cause. Secondary osteoarthritis may develop after e.g. a fracture or secondary to joint disease (e.g. rheumatoid arthritis or infection). 

Radiological characteristics of osteoarthritis (fig. 24):

  • Narrowing of the joint space (secondary to cartilage loss).
  • Subchondral sclerosis (increased bone production secondary to increased pressure with cartilage loss)
  • Osteophyte formation (bone exostoses attempting to increase the joint surface)
  • Subchondral cysts (secondary to microfractures of the subchondral bone and pressure of the synovial fluid)

Figure 24. Osteoarthritis at the elbow (the humeroulnar joint and the radiohumeral joint and the proximal radioulnar joint).

Sources

  • B.J. Manaster et al. The Requisites – Musculoskeletal Imaging (2007).
  • N. Raby et al. Accident & Emergency Radiology – A Survival Guide. (2005).
  • K.L. Bontrager, J.P. Lampignano. Textbook of Radiographic Positioning and Related Anatomy. 2014 (8th edition)

Author

Authors:

  • drs. M. Özdemir (resident radiology & nucleair medicine)
  • dhr. A. Bubberman (Advanced Practioner Radiology LUMC) 
  • dr. H.M. Kroon (musculoskeletal radiologist LUMC)

Image editing:

  • drs. A van der Plas (MSK radiologist Maastricht UMC+)

30/06/2016 (translated to English: 16/06/2017)

Copyright
All the work (text, illustrations, visual elements) seen on this website is copyright by Annelies van der Plas.
It may not be used without written permission of Annelies van der Plas.

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