Anatomy of muscles of the back are covered in Section 2.4, Muscles and Nerves. (Muscles that are readily visible are trapezius, latissimus dorsi, and teres major.)

Vertebrae and Corresponding Structures

Level	Corresponding Structure
C2–C3	Mandible
C3	Hyoid bone
C4–C5	Thyroid cartilage
C6	Cricoid cartilage
C7	Vertebra prominens
T3	Spine of scapula
T4/5	Sternal angle (of Louis)
T7	Inferior angle of scapula
T8	Inferior vena cava pierces diaphragm
T10	Xiphisternal junction
T10	Esophagus enters stomach
T12	Aorta passes behind diaphragm
L1/2	Spinal cord ends (cauda equina starts)
L3	Subcostal plane
L3–L4	Umbilicus
L4	Bifurcation of aorta
L4	Iliac crests—supracristal line
S2	End of dural sac
S2	Level of posterior superior iliac spines

Clinical Points

Lumbar Puncture

Lumbar puncture is performed for retrieval of cerebrospinal fluid (CSF) from the lumbar spinal cistern. The patient is placed in the left decubitus position, flexed in the fetal posture with the supracristal line vertical. Puncture should be made at the L3/4 (immediately superior) or L4/5 (immediately inferior) interspace in the midline of the back, to avoid the spinal cord.

Memory Aids

Lumbar puncture: To keep the cord alive, keep the needle between L3 and L5!

2.2 Bones and Ligaments

Study Aims

At the end of your study, you should be able to:

• Identify the significant parts of a typical vertebra and understand regional variations

• Identify the specialized vertebrae

• Know the attachments and function of the vertebral ligaments

• Describe the spine, its curvatures, and gross vertebral column movements

• Describe the type, location, and movements of the joints of the vertebral column

Guide

Vertebral Column

• Approximately 72 to 75 cm long (25% of length because of intervertebral discs)

• 33 vertebrae (can vary, 32–34)

• 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 (3–5) coccygeal

• Typically have body; vertebral arch (2 laminae, 2 pedicles) and foramen; spinous (1) and transverse (2) processes; articular processes (4)

• Fibrocartilaginous intervertebral discs

• Allow movement between vertebral bodies (in cervical, thoracic, and lumbar regions)

• Curvature (may be primary or secondary—see below)

• Cervical anterior convexity (2°)

• Thoracic anterior concavity (1°)

• Lumbar anterior convexity (2°)

• Sacral anterior concavity (1°)

Vertebrae

Vertebrae	Distinctive Features
Cervical	Small bodies, large vertebral foramina, foramina in transverse processes, anterior and posterior tubercles, bifid spinous processes
Thoracic	Heart-shaped bodies, long spinous processes angled posteroinferiorly; costal facets for rib articulation on bodies and transverse processes
Lumbar	Large kidney-bean-shaped bodies, sturdy laminae, thick and short spinous processes, mammillary processes on posterior surface of superior articular facets (processes)
Sacral	Fused as sacrum, four pairs of dorsal and ventral foramina for nerve exit and triangular sacral canal
Coccygeal	Fused as small triangular bone—the coccyx

Joints

• Intervertebral (IV) discs

• Connect articulating surfaces of adjacent vertebral bodies

• Integral part of secondary cartilaginous joints between vertebral bodies (except C1/2)

• Composed of tough annulus fibrosus surrounding an avascular, gelatinous nucleus pulposus

• Act as “shock absorbers” and semifluid ball bearings to provide small movements between individual vertebrae

• Zygapophysial (or facet) joints

• Synovial joints between superior and inferior articular processes

• Surrounded by thin, loose articular capsule

• Permit gliding movements between vertebrae

• Atlanto-occipital joints

• Synovial joints between lateral masses of atlas and occipital condyles

• Permit flexion/extension and some lateral bending and rotation

• Atlanto-axial joints

• Three synovial joints between inferior lateral masses of C1 and superior facets of C2 and between anterior arch of C1 and dens of C2

• Permit rotation of C1 (and head), which is limited by alar ligaments

• Costovertebral joints: synovial, between vertebrae and ribs (see Section 3, Thorax)

• Sacro-iliac (SI) joints: synovial joints (see Section 5, Pelvis and Perineum)

Ligament	Features
Anterior longitudinal	Limits extension Maintains stability of IV discs
Posterior longitudinal	Limits flexion Prevents IV disc herniation
Intertransverse	Limits lateral bending
Interspinous	Limits flexion
Supraspinous	Limits flexion
Ligamenta flava	Limits flexion Preserves curvature of column Prevents injury to IV discs
Ligamentum nuchae	Prevents cervical hyperflexion Attachment site for trapezius and rhomboid minor