Shoulder x-ray interpretation

Don’t be bamboozled by a paediatric shoulder x-ray. Use an ABCD approach and pick up some tips and tricks in our step-by-step guide.

A – An adequate x-ray 

Is it the right patient, and do you have the 2 views you want to see? The typical views are AP (external rotation) and the scapular Y view. (If you’re not sure why, then this meme may help.) Occasionally, an axillary view is added to assess for dislocations and glenohumeral instability. 

B – Bones

Go through the bones one at a time. Follow the cortex of every bone in each view. Look for disruption or a buckle in the cortex or any fracture fragments. They should all be smooth.  

• The clavicle is a good bone to start with – it is by far the most common paediatric shoulder injury. Midshaft fractures account for 80% of clavicle fractures. Make sure there are no distal or medial fractures, as they can often be subtle. 

• Move onto the proximal humerus – check the epiphysis and metaphysis. A normal humeral head looks like a walking stick on the AP view. The most common fracture of the humerus is a metaphyseal fracture. Metaphyseal fractures occur in ages 5-12, and Salter-Harris fractures outside of this range. 

• Don’t forget the scapula, seen best on the Y view. Management is conservative but a fracture here indicates a significant trauma. 

Like the paediatric elbow, the paediatric shoulder has ossification centres, so X-ray appearances differ depending on the child’s age.

At birth, the humeral diaphysis, mid-position of the clavicle, and the body of the scapula are ossified—the rest are essentially cartilage.

The proximal humerus has three ossification centres:

• Head – 1 year of age
• Greater tubercle – 3 years
• Lesser tubercle – 5 years

• The scapula has seven secondary ossification centres. 

Look carefully for the following two – if they appear early, they may be the only sign of an avulsion fracture:

• The sub-coracoid ossification centre appears between 8 and 10 years and completely fuses between 16 and 17, forming the upper third of the glenoid articular surface. If it appears before the age of 8, this may indicate an avulsion (pulled by the long head of the biceps at its attachment to the superior glenoid). 
• The inferior glenoid ossification centre appears at the lower two-thirds of the glenoid articular surface. It grows and fuses to form a horseshoe-shaped epiphysis that combines with the glenoid rim and sub-coracoid ossification centre. This appears between 14 and 15 years (although sometimes as young as 11), with complete fusion by 17 to 18. It can be challenging to view on standard radiographs, but sometimes it can be seen on the Grashey (AP oblique) view 

A top tip: If you are unsure whether what you are seeing is an avulsion fracture or a simple ossification centre, then press directly on the patient where the fragment is. If this isn’t painful, it is highly likely to be an ossification centre, not an avulsion.

Range of movement is another great giveaway – having an avulsion fracture, and intact range of movement is quite hard! If in doubt, speak to a friendly radiologist (in hours) or be conservative and place in an arm sling and bring back to clinic (out of hours) for re-assessment (when the x-ray will have been reported).

Don’t forget the other bones that don’t make up the shoulder. Have a look for rib fractures, and if you see old healing rib fractures, then consider non-accidental injury.

C – Connections and Connective Tissue

Are all the bits connected to where they should be? Ask yourself a few questions when you’re looking at the different joints.

Glenohumeral joint:

• Do the articular surfaces of the humerus and glenoid have 2 parallel lines with an even joint space?
• Does the humeral head sit evenly on the glenoid in all views?
• Does the humeral head sit adjacent to the glenoid on the AP view? Does it sit over the glenoid on the Y view? If the answer to these questions is no, and instead, the humeral head is lying under the coracoid process, this indicates an anterior shoulder dislocation.

Anterior Shoulder Dislocation (AP and Y views). The humeral head is located beneath the coracoid on the AP view and is no longer located centrally on the Y view. In addition, there is flattening of the humeral head, suggesting a Hill Sachs lesion (more on this in the upcoming shoulder dislocation post)

• Has the humeral head lost its characteristic walking stick appearance on the AP view? Does it instead look rounder, like a light bulb? If the answer to these questions is yes, this suggests a posterior shoulder dislocation.

• Is there a joint effusion or lipo-haemarthrosis present? This could indicate an intra-articular fracture of the glenoid or the humeral head. 

Acromioclavicular (AC) joint:

• Does the bottom of the acromion line up with the bottom of the distal clavicle? If there’s a step, think clavicle fracture or physeal injury

• Is there a widening of the acromioclavicular joint (normal is 5-8mm) or coracoclavicular distance (normal is 10-13mm)? A widened AC joint > 8mm suggests an AC ligament rupture. If the coracoclavicular (CC)  distance is >13 mm consider CC ligament rupture. If you’re unsure, get weighted views of both AC or CC joints to compare each side (literally with the child holding weights in each hand to stress the joints).

D – Don’t forget the other tissues

Always look around the area for foreign bodies or subcutaneous emphysema indicating a pneumothorax or pneumomediastinum. If there are, a dedicated chest X-ray should be performed.

And finally, although the above may seem complicated, realistically common things are common.

• Clavicle Fractures. By far the most common. 80% are mid-shaft and occur following a fall onto the outstretched hand or shoulder or direct trauma from a seatbelt or during sport.
• Proximal humeral fractures. These occur in older children. 
• Anterior shoulder dislocation. Usually in older children playing sports. Falls result in forced ABDuction, external rotation, and extension. Account for 95% of shoulder dislocations. 

Don’t miss

Acromioclavicular Joint injuries – widening or step at acromioclavicular joint and/or increased coraco-clavicular distance.

Rib fractures – healing rib fracture? Consider NAI. 

References

1. JS. Zember, ZS Rosenberg, S. Kwong, SP. Kothary, MA. Bedoya. Normal Skeletal Maturation and Imaging Pitfalls in the Pediatric Shoulder.  Radiographics. 2015 Jul-Aug;35(4):1108-22
2. https://radiopaedia.org/articles/paediatric-shoulder-radiograph-an-approach