Lumbar, Sacrum & Coccyx – Anatomy and Radiographic Techniques

Lumbar Vertebrae

The five largest and strongest vertebrae in the vertebral column, designed to bear increasing body weight toward the inferior end.

Intervertebral Disks

Cartilaginous structures located between vertebral bodies, common sites of injury and pathology in the lumbar region, acting as cushions and facilitating movement.

Intervertebral Foramina

Openings formed by the superior and inferior vertebral notches of adjacent pedicles, through which spinal nerves and vessels pass. Best demonstrated on a lateral lumbar radiographic image.

Zygapophyseal Joints

Synovial, diarthrodial joints with plane (gliding) movement, formed by the superior and inferior articular processes of adjacent vertebrae. They form an angle open from 30^{\u00b0} to 50^{\u00b0} to the MSP.

Pars Interarticularis

The portion of the lamina between the superior and inferior articular processes, radiographically demonstrated on oblique lumbar images and forming the 'neck' of the Scottie dog.

Scottie Dog

A radiographic appearance seen on oblique lumbar images, where the anatomy of the lumbar vertebrae resembles a dog. The parts include: head/neck (pars interarticularis), ear (superior articular process), eye (pedicle), nose (transverse process), and front leg (inferior articular process).

Sacrum

A shovel-shaped bone situated inferior to L5, formed by the fusion of five segments, with an apex pointing inferiorly and anteriorly. Features include sacral foramina, alae, and the promontory.

Sacroiliac Joint

A joint formed by the articulation of the auricular surface of the sacrum with the ilium. These joints open obliquely posteriorly at about 30^{\u00b0}.

Coccyx

Typically comprises four fused segments, with an apex (distal tip) and base (broader superior part). Its curvature is normally anteriorly, often more pronounced in men.

L3 Vertebra Landmark

The central ray for an AP lumbar projection is typically centered at the midline at the level of the lower costal margin, which corresponds to approximately L3.

Lumbar Lordosis Reduction

Achieved in supine AP lumbar positioning by flexing the hips and knees, with plantar aspects of the feet on the table, to improve disk space visibility.

Oblique Lumbar Rotation

A standard rotation of 45^{\u00b0} is used to demonstrate the zygapophyseal joints and pars interarticularis (Scottie dog anatomy).

AP Axial Sacrum Angulation

Requires 15^{\u00b0}–20^{\u00b0}} cranial angulation, with specific adjustments for sacroiliac joint visualization (males ~$30^{\u00b0}$; females ~$35^{\u00b0}$).

AP Axial Coccyx Angulation

Typically requires 5^{\u00b0}} caudal angulation, which can be increased to $$10^{\u