Anatomy and Positioning of the Chest, Extremities, and Spine
Core concepts
Know landmark anatomy for each region. Chest: clavicles, scapulae, lung fields, heart borders; the PA chest uses a 72-inch SID to reduce magnification, with the patient upright and shoulders rolled forward. Extremities: know joints, epicondyles, and the rule of two views at 90 degrees. Spine: cervical, thoracic, lumbar regions, vertebral body landmarks, and the difference between AP, PA, lateral, and oblique projections. Understand central ray placement and part positioning to open joint spaces and reduce overlap.
Traps
Questions often test which projection best demonstrates a structure - for example, the lateral chest for retrosternal space, or the oblique for intervertebral foramina. Another trap is confusing AP vs. PA effects on magnification and organ dose. Watch for items on patient rotation (a rotated chest shows asymmetric clavicles) and collimation to the part. For extremities, remember that joints require two orthogonal views to rule out dislocation or fracture.
Worked example / rule of thumb
A patient cannot stand for a chest exam. Rather than a supine AP (which magnifies the heart and may show fluid levels poorly), use a semi-erect or seated position when possible. Rule of thumb: position for the anatomy, not the habit - the central ray must pass through the part with the receptor parallel to it.
Key points
- PA chest at 72 inches reduces heart magnification.
- Two orthogonal views for every extremity joint.
- Obliques demonstrate foramina and joint spaces.
- Rotation is a common cause of repeat chest images.
- Collimate to the part and center the central ray.