11.2 Thoracic & Lumbar Spine, Sacrum & Coccyx

11.2 Thoracic & Lumbar Spine, Sacrum & Coccyx

Quick Answer: Image the thoracic spine with AP and lateral (add swimmer’s for the upper T-spine when needed). Image the lumbar spine with AP, lateral, L5–S1 spot, and 45° obliques when pars/facets are in question—know the Scottie dog. Sacrum = AP axial cephalad + lateral; coccyx = AP axial caudad + lateral. Watch for compression fractures on laterals and keep scoliosis series reproducible and dose-aware under Canadian RTR practice.

Thoracolumbar and sacrococcygeal radiography dominate outpatient back-pain work-ups and appear throughout trauma series. On the CAMRT exam, expect items that combine centering landmarks, CR angulation direction (cephalad vs caudad), oblique anatomy identification, and pathology patterns such as wedge compression fractures—high secondary-weight skeletal content under clinical procedures and image analysis.

Thoracic Spine — AP

Evaluation criteria: All twelve thoracic vertebrae (or the ordered segment) included; spinous processes midline (rotation); vertebral bodies and disk spaces demonstrated; sternoclavicular joints and pedicles reasonably symmetric; exposure penetrates both upper and lower thoracic regions (anode-heel and exposure technique matter).

Rotation clues: Spinous processes off midline; unequal pedicle-to-spinous distance; clavicles asymmetric relative to spine.

Thoracic Spine — Lateral

Evaluation criteria: Open intervertebral disk spaces (spine parallel to IR); posterior ribs largely superimposed (rotation control); T-spine vertebral bodies in profile; proximal humeri not obscuring upper T-spine more than unavoidable; full segment included.

Upper thoracic / swimmer’s for T-spine

When shoulders obscure T1–T3, use a swimmer’s lateral (arm nearest IR up, opposite shoulder depressed) centered near T1–T2, or department-specific arm positions. Same principle as cervical swimmer’s: separate the cervicothoracic/upper thoracic junction from shoulder girdle density.

Lumbar Spine — AP (or PA)

PA lumbar is used in some scoliosis and dose-reduction pathways (beam enters posteriorly, reducing gonad/breast dose concepts in serial imaging)—know that both exist; follow the order and protocol.

Evaluation criteria: Spinous processes midline; SI joints equidistant; pedicles symmetric; intervertebral spaces reasonably open; psoas margins often visible; markers correct; collimation not clipping transverse processes needed for the clinical question.

Lumbar Spine — Lateral

Evaluation criteria: Open lumbar disk spaces; posterior vertebral margins nearly superimposed (rotation); intervertebral foramina of lumbar spine visualized (lumbar foramina face laterally—unlike cervical); pedicles superimposed; soft-tissue and bony detail sufficient for height loss assessment.

Support the natural waist curve with a sponge when the spine sags into a “hammock”—sag closes disk spaces and mimics pathology.

L5–S1 Spot (Lumbosacral Junction)

The L5–S1 joint is often closed or poorly seen on the full lateral because of beam divergence and pelvic thickness.

Evaluation: Open L5–S1 intervertebral joint space; L5 and upper sacrum demonstrated without excessive pelvic superimposition; no rotation.

Lumbar Obliques — The Scottie Dog

45° posterior (RPO/LPO) or anterior (RAO/LAO) obliques demonstrate the pars interarticularis and zygapophyseal joints. The classic Scottie dog appearance on an oblique lumbar radiograph:

A radiolucent collar across the Scottie’s neck suggests spondylolysis (pars defect). Spondylolisthesis is forward slippage of one vertebra on another, often related to bilateral pars defects—best appreciated on the lateral.

Exam tip: If the stem asks which structure is the Scottie dog’s neck, answer pars interarticularis. If the clinical history is young athlete with extension back pain, think pars defect and ensure obliques/lateral quality.

Sacrum

Why cephalad for sacrum? The sacrum curves posteriorly; cephalad angulation reduces foreshortening and projects the sacrum with less pubic superimposition.

Coccyx

Do not confuse angles: Sacrum cephalad, coccyx caudad on AP axial projections. Mixing them is a classic MCQ trap.

Empty bladder when possible for AP sacrum/coccyx improves visualization and patient comfort; follow department prep policies. Use tight collimation and gonad-dose awareness consistent with current facility guidance—never sacrifice required anatomy for decorative shielding placement.

Scoliosis Series Concepts

Scoliosis imaging evaluates lateral curvature, often in adolescents, with serial follow-up. Core ideas for the RTR:

You are not expected to measure Cobb angles as a radiologist would, but you must produce images on which curvature and endpoints can be assessed without rotation artifact or clipped anatomy.

Compression Fracture Recognition (Link to RTR.6)

Lateral thoracic and lumbar images are primary plain-film tools for vertebral compression fractures (osteoporosis, trauma, pathologic).

Positioning quality affects diagnosis: A rotated lateral underestimates or mimics height loss; closed disk spaces from sagging spine confuse endplate assessment; underexposure hides cortical lines. Critique exposure, rotation, and support before attributing every contour change to disease.

Positioning Summary Table — T/L Spine, Sacrum, Coccyx

Bottom Line for Thoracolumbar & Sacrococcygeal RTR Work

Center with crest and T7 landmarks, keep the long axis of the spine parallel to the IR on laterals, and use the correct cephalad vs caudad axial angles for sacrum and coccyx. Deploy L5–S1 spots and Scottie-dog obliques when the clinical question targets the lumbosacral junction or pars. Treat compression fracture evaluation as a partnership between geometry quality and pathology pattern recognition. Produce scoliosis images that are complete, comparable, and dose-conscious. That combination of procedure skill and image analysis is high-yield for CAMRT skeletal gen-rad competencies.