Shoulder (modified transthoracic supine lateral)

The modified transthoracic supine lateral scapula is a modification of the supine lateral shoulder, used to safely image patients on spinal precautions, or patients who are unable to move; often employed in major trauma hospitals, it produces a diagnostic lateral projection of the shoulder with no elongation of anatomical structures. Orthogonal to the AP shoulder (note so is an axillary view); It is a pertinent projection to assess suspected dislocations, scapula fractures and degenerative changes.

Indication

The modified supine lateral view is performed to identify dislocations and scapula fractures when patients are unable to move and are supine.

Patient position

• patient is supine

Technical factors

• transthoracic lateral projection
• centering point
  • the tube is angled at 45 degrees across the patient
  • the detector is placed on a 45-degree stand under the table these are aligned and the patient table then moved into the line of x ray rather than moving the tube towards the patient, this is done to ensure the detector is cover and aligned to the angle of the tube
  • centering at the level of the glenohumeral joint at the center of the proximal humerus
• collimation
  • laterally to include the skin margin
  • medially to cover the entirety of the medial scapula
  • superior to the skin margin
  • inferior to the inferior angle of the scapula
• orientation  
  • portrait                       
• detector size
  • 24 x 30 cm
• exposure
  • will vary due to the air gap
  • 60-70 kVp
  • 10-20 mAs
• SID
  • 100 cm
• grid
  • yes (unless air gap method is accepted in your department)

Image technical evaluation

• this radiograph will have a similar appearance to the PA lateral scapular projection however to correct the image is the opposite to the PA
• the scapula is clearly demonstrated in a lateral profile, giving the clear appearance of a ‘Y’
• acromion and the coracoid process form the upper arms of the ‘Y’
• if intact, the humeral head is superimposed at the base of the ‘Y’

Practical points

This projection will yield a diagnostic image similar to the AP supine lateral shoulder, see figure 1 and 2.

The alternative projection, the transthoracic lateral projection, utilizes a similar technique with the exception of an angled detector on a stand. This technique results in elongation of anatomical structures figure 3 and should be avoided and angle detector is possible.

The lateral scapula projection can be technically demanding, especially when patients are in pain. An anecdotal method amongst radiographers is to feel for the medial border of the scapula and line it up with the anterior portion of the acromion and x-ray straight down the line.

The idea being, if they are lined up there will be a superimposition of the medial and lateral borders of the scapula and hence a perfect lateral position, although this isn't always the case.

The best defense against positional errors is having a thorough understanding of radiographic anatomy and how it changes positionally when assessing for under/over rotation of the lateral shoulder, assess the borders of the scapula.

Over rotation

Over rotation in this projection refers to the tube angle relative to the patient.

Over-rotation is clearly established as the lateral border of the scapular (significantly thicker than the medial) is projected over the thorax along with the humeral head; to adjust this, bring the tube to be more vertical for example 40 to 35 degrees.

Under rotation

Under rotation in this projection refers to the patient's  tube angle relative to the patient.

The lateral border, as well as the humeral head, will be sitting overly lateral in the image; to adjust this, bring the tube to be more horizontal for example 40 to 45 degrees.

History

This modified projection is also known as the ‘music stand’ method, radiographers used to bring sheet music stands to hold the cassette under the table, the advantage of the music stand being its slant and sheet holder; perfect for the cassette.