The most commonly taken X-rays are anterior-posterior (AP) or lateral. AP is a front-to-back view of the spine. Lateral is taken from the side. A third type of X-ray called oblique is a view from the side but taken at an angle.
Each view gives the doctor different information about the condition of the spine. Location, type, and degree of deformity or pathology can be assessed from X-rays. For example, the oblique view allows for a better view of the pars interarticularis. This is part of the vertebra where the facet (spinal) joint attaches to the bone.
The oblique view is taken if the doctor suspects a condition called spondylolisthesis. A fracture at the pars results in the vertebral body slipping forward over the vertebra below. This is a condition that may require surgery.
The dynamic flexion-extension (F/E) X-rays you mentioned are taken in the standing position. First, the patient bends forward as far as possible. An X-ray is taken of the lumbar spine in this position. Then the patient straightens up and extends or bends backward as far as possible. Another X-ray is taken.
Dynamic F/E X-rays offer information about the spinal instability with movement. This type of data can help the surgeon when considering or planning surgery. They can help rule out the need for surgery as well.