📝 STANDARD DESCRIPTION:
Type: Cartilaginous (between bodies) + Synovial (between articular processes).
Between vertebral bodies:
- Intervertebral disc = fibrocartilage cushion (annulus fibrosus + nucleus pulposus).
- Allows slight movement; absorbs shock.
Between articular processes:
- Small synovial joints (zygapophyseal joints) — flat in thoracic region, restrict twisting.
Special Ligaments:
- Supraspinous ligament (over tips of spines) — continuation of nuchal ligament.
- Interspinous ligaments (between spines).
- Ligamentum flavum (yellow elastic, between vertebral arches — closes vertebral canal).
- Dorsal & Ventral longitudinal ligaments (along bodies, inside canal).
📚 DETAILED DESCRIPTION:
HOW THORACIC VERTEBRAE ARE LINKED
Each thoracic vertebra is connected to the next by joints at three sites: between bodies, between articular processes (left and right), and reinforced by ligaments along the spines.
1. INTERVERTEBRAL DISC: A pad of fibrocartilage between the bodies of two vertebrae.
• Outer ring = annulus fibrosus (tough fibres in layers).
• Inner core = nucleus pulposus (soft jelly-like).
The disc absorbs shock and allows a small amount of bending.
2. ZYGAPOPHYSEAL JOINTS: Small synovial joints between the cranial articular process of one vertebra and the caudal articular process of the next. In the thoracic region these surfaces are nearly flat and lie almost vertical, which strongly limits twisting — important because the rib cage needs a stable spine.
3. LIGAMENTS:
• Supraspinous ligament: Long fibrous band along the tips of all the spinous processes (continuation of the nuchal ligament from the neck). Resists over-flexion of the back.
• Interspinous ligaments: Short fibres filling spaces between adjacent spines.
• Ligamentum flavum (yellow ligament): Elastic, joins adjacent vertebral arches; closes the gap in the dorsal wall of the vertebral canal between vertebrae. Used as a landmark when doing epidural injections (needle 'pops' through it).
• Dorsal longitudinal ligament: Runs inside the vertebral canal along backs of vertebral bodies.
• Ventral longitudinal ligament: Runs along ventral surfaces of bodies.
MOVEMENTS PERMITTED: Very limited in the thoracic region — small flexion-extension; almost no rotation. This rigidity protects heart and lungs.
// COMPARATIVE ANALYSIS
| HORSE |
Withers region (T2-T9) very rigid; that's why horses cannot turn their back like a cat. |
| DOG |
More flexibility, especially at the anticlinal vertebra (T11) — allows the back to arch when running. |
| FOWL |
Most thoracic vertebrae fused (notarium) — no movement at all. |
CLINICAL RELEVANCE
Intervertebral Disc Disease (IVDD, especially in dogs): The soft nucleus pulposus bulges or ruptures and presses on the spinal cord — causes pain, weakness, paralysis. More common in dachshunds.
