Paediatric thumb (AP/PA view)

The anteroposterior (AP) or posteroanterior (PA) view of the thumb in paediatrics is part of a two view series and is orthogonal to the lateral view. Often the decision to choose between the AP or PA thumb depends on what the child can manage and how agitated they are. An AP thumb is ideal as there will be some magnification if the thumb is taken PA.

Indications

The AP/PA view is particularly useful in diagnosing fractures and foreign bodies in paediatrics. It also represents an orthogonal view of the lateral thumb view. 

Patient position

AP thumb

• patient is seated alongside the table or lying down with the affected arm extended
• arm is medially rotated until dorsal aspect of thumb is in contact with the image receptor

PA thumb

• patient is seated alongside the table or lying down with the affected arm extended
• thumb rests on a sponge, ensuring that the sponge is tall enough to demonstrate the thumb in a true PA position

Technical factors

• anteroposterior or posteroanterior projection
• centring point
  • first metacarpophalangeal joint space
• collimation
  • laterally to the skin margins
  • proximal to the carpometacarpal joint
• orientation
  • portrait
• detector size
  • 18 cm x 24 cm
• exposure ¹
  • 40-46 kVp
  • 0.8-2 mAs
• SID
  • 100cm
• grid
  • no

Image technical evaluation

Thumb must be visualised with equal concavities on both sides of the phalanx with interphalangeal joints open ². The correct thumb must be correctly labelled and identified. 

Practical points

Preparing the room beforehand (setting up the detector, exposure and preparing lead gowns) is important as paediatric patients may not remain still when their affected thumb is moved onto the detector. 

Immobilisation techniques

For this AP/PA view, it is particularly important to avoid superimposition of the other fingers; hence the child's parent or radiographer may need to assist in keeping other fingers still. 

It is also important for the radiograph to be free from motion artifact and rotation to avoid repeated x-rays.

• it may be necessary for the parent or radiographer to hold the patient in position
• ideally the parent should be in the child's direct line of sight
• techniques will vary based on the department
• distraction techniques can be utilised to avoid scattered radiation to parents and staff ³