Shoulder (outlet view)

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The outlet or Neers projection of the shoulder is a specialized projection demonstrating the coracoacromial arch often utilized in the investigation of shoulder impingement .

This projection is most commonly seen in orthopedic clinics and closely resembles a lateral scapular projection but incorporates a 10-15 degree caudal angulation of the tube.

The outlet projection is not advisable in acute imaging of the shoulder as tube angulation may result in elongation of decisive structures. For lateral views of the shoulder in trauma see lateral shoulder view.

Indication

The outlet view is performed to assess subacromial impingement. This view is often performed instead of a lateral shoulder view for the impingement series only.

Patient position

  • erect or sitting, facing the upright detector
  • rotated in an anterior oblique position, so the anterior portion of the shoulder is touching the upright detector
  • the hand is placed on the patient's abdomen with the arm flexed
  • the degree of anterior rotation can vary from patient to patient
  • scapula should be end-on to the upright detector, and this can be done via palpation of the scapula border

Technical factors

  • posteroanterior lateral projection
  • centering point
    • the level of the glenohumeral joint on the posterior aspect of the patient (5 cm below the top of the shoulder)
    • 10-15 degree caudal angulation of the x-ray tube 
    • central to the medial scapula border
  • 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
    • 60-70 kVp
    • 10-20 mAs
  • SID
    • 100 cm
  • grid
    • yes

Image technical evaluation

  • the scapula is demonstrated in a lateral profile, giving the clear appearance of a ‘Y'
  • clear visualization of the supraspinatus outlet 
  • 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

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 is not 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, evaluate the borders of the scapula.

Over rotation

Over rotation in this projection refers to the patient's unaffected side sitting too far away from the image receptor, otherwise known as lying ‘too square’ to the detector.

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, rotated the unaffected side towards the image receptor slightly.

Under rotation

Under rotation in this projection refers to the patient's unaffected side sitting too close to the image receptor, otherwise known as lying ‘flat’ to the detector.

The lateral border, as well as the humeral head, will be sitting overly lateral in the image; to fix this, rotated the unaffected side away from the detector to increase obliquity.