Spine

 Sacro Iliac Joints AP Oblique 
Indications for imaging
Trauma, pain.

 

Anatomy  Demonstrated
 Sacro iliac joint. (Raised side in posterior oblique position)


Sacro Iliac Joints AP Lt Posterior Oblique Anatomy
Meschan, I. 1955 An Atlas of Normal Radiographic Anatomy Saunders, London

 

Basic Patient Position
The examination may be performed either prone or supine, supine will be described here prone is shown by way of comparative example) In the supine position the joint space on the raised side is visualised.
The patient lies supine on the table midline in line with the midline of the table, from this position the patient is rotated so the affected side is raised and the midsaggital plane is at an angle of 30 degrees from horizontal, and the patient supported on radio lucent pads.
Sacro Iliac Joints PA (RPO) & AP (RAO) Oblique Patient Position
Meschan, I. 1955 An Atlas of Normal Radiographic Anatomy Saunders, London

 
Radiation protection
There are many local rules for gonad protection however the following should be taken into account. The 28 day rule should be applied for female patients.
In males direct lead rubber gonad protection can be applied at all times

 
Central Ray
The vertical central ray is directed to a point one third of the distance from the raised ASIS to the patient's midline. Cranial inclination of up to 15 degree may help demonstrate the inferior joint space more clearly. Exposure is made on suspended expiration.

 
Exposure Factors
Kv mAS FFD (cm) Grid Focus AEC Cassette
85 60 100 Yes Broad Yes 18 x 24 cm

 
Evaluation of the Image
 ID and markers must be present and correct in the appropriate area of the film
Evidence of collimation on four sides equally around the centering point.
Optimal exposure should penetrate all the bone structures and contrast should be low enough to visualise fully the bone and soft tissue structures.
Limits of the examination, the SIJ.



 Sacro Iliac Joints AP Oblique (LPO) Radiograph
(inferior limits missed off!)


Related Projections
SIJ PA

 
Additional modalities
CT
MRI