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Lumbar obliques and the Scottie dog
45° obliques; posterior obliques show the downside facet joints; the pars is the Scottie dog's neck.
Positioning
Lumbar obliques show the zygapophyseal (facet) joints and the pars interarticularis. Most are AP posterior obliques, RPO and LPO, with the patient semi-supine and the body turned 45 degrees, supported with sponges and the knee of the upside flexed for balance. Posterior obliques show the joints on the side down, closest to the IR: an RPO shows the right joints. If anterior obliques are taken instead, RAO and LAO, they show the side up, farthest from the IR. The joints are not all at the same angle: about 50 degrees is best for the upper lumbar spine and about 30 degrees for L5–S1, so 45 degrees is the usual compromise for L3.