Vertebral column
Vertebral column: joints, ligaments, intervertebral discs and blood supply
Spine films, CT and MRI are read by checking alignment, vertebral parts, discs and ligaments. CPSP asks about atypical cervical vertebrae and their fractures, which ligament tears or ossifies, how discs herniate and degenerate, and how infection and tumour reach the spine.
Curves, levels and counting
- Primary curves (thoracic and sacral kyphosis) are present at birth and formed by the bodies. Secondary curves (lordoses) are formed mainly by wedge-shaped discs: cervical lordosis at about 3 months (head control), lumbar lordosis when the child stands and walks.
- Surface levels: iliac crests at L4 (lumbar puncture landmark), umbilicus at the L3–L4 disc, xiphisternal joint at T9.
- Transitional vertebrae (sacralised L5, lumbarised S1): count from C2 down as well as up.
- Cervical roots exit above the vertebra of the same number, so a C7–T1 lesion compresses C8; lumbar roots exit below their pedicle.
Cervical vertebrae and their injuries
| Structure | Point | Injury or imaging |
|---|---|---|
| Atlas (C1) | No body or spinous process; ring of two arches and lateral masses | Jefferson fracture (axial load): burst ring; lateral mass overhang over about 7 mm means transverse ligament rupture |
| Axis (C2) | Dens held against C1 by the transverse ligament | Hangman fracture: both C2 pars in hyperextension. Dens base fracture often fails to unite (watershed blood supply) |
| Atlanto-axial joint | Pivot joint | Main site of head rotation; atlantodental interval normally up to 3 mm in adults; widened in rheumatoid arthritis and Down syndrome |
| Uncovertebral joints | Raised lateral lips of C3–C7 bodies | Osteophytes narrow the foramen and compress the root |
- The vertebral artery usually enters the C6 transverse foramen.
Lumbar vertebra on radiographs
- Oblique view "Scottie dog": nose = transverse process, eye = pedicle, ear = superior articular process, neck = pars interarticularis, front leg = inferior articular process. A "collar" is a pars defect (spondylolysis); forward slip of L5 on S1 is isthmic spondylolisthesis (young gymnasts; a palpable step; the slipped L5 can mimic the sacral promontory).
- Frontal view: loss of one pedicle outline (winking owl) suggests metastasis; myeloma tends to spare the pedicle early.
- The basivertebral vein makes a normal Y-shaped channel in the back of the body on CT.
- Three columns: anterior (front two-thirds of the body, anterior longitudinal ligament), middle (back third of the body, posterior longitudinal ligament), posterior (arch and ligaments). Middle column failure with a retropulsed fragment is a burst fracture; a wedge fracture involves the anterior column only.
Joints and ligaments
- Between bodies: secondary cartilaginous joints (symphyses), hyaline end plates joined by a fibrocartilage disc. Facet joints are synovial (osteoarthritis, effusions).
| Ligament | Feature | Imaging and clinical link |
|---|---|---|
| Anterior longitudinal | Broad and strong | Torn in hyperextension (first phase of whiplash); TB spreads beneath it |
| Posterior longitudinal | Narrow in the lumbar region | Discs herniate posterolaterally; ossification (OPLL) narrows the cervical canal |
| Ligamentum flavum | Elastic, joins laminae | Loss of resistance in epidural; hypertrophy gives a trefoil canal and neurogenic claudication |
| Supraspinous and interspinous | Midline | Bypassed by the paramedian approach when calcified |
- DISH: flowing ossification along the front of four or more vertebrae, mainly right-sided, disc heights and sacroiliac joints normal. Ankylosing spondylitis starts in the lower iliac side of the sacroiliac joints (thinner iliac cartilage).
Intervertebral disc
- Annulus fibrosus: fibrocartilage lamellae. Nucleus pulposus: notochord remnant rich in proteoglycan and water, so bright on T2.
- The adult disc is avascular, fed by diffusion through the end plates; only the outer annulus enhances. In children the disc still has vessels, so discitis can start in the disc.
| Finding | Meaning |
|---|---|
| Dark disc on T2 | Loss of proteoglycan and water (degeneration; common with age) |
| Gas in the disc (about −900 HU) | Vacuum phenomenon: nitrogen in a degenerate disc |
| Bright spot in the dark posterior annulus | Annular fissure |
| Disc tissue in a corticated end plate defect | Schmorl node |
- Posterolateral L4–L5 herniation compresses the traversing L5 root (weak big toe extension, numb dorsum of foot); a far-lateral herniation at the same level catches the exiting L4 root (weak knee jerk). A large central herniation causes cauda equina syndrome.
Blood supply and its consequences
- Segmental arteries (posterior intercostal and lumbar, from the aorta) curve round each body and send branches through the foramina.
- In adults, haematogenous pyogenic spondylodiscitis begins in the subchondral bone at the end plate (end-arterial supply), then destroys the disc: disc space loss, T2 bright disc, oedema in both adjacent bodies.
- Tuberculosis spreads under the anterior longitudinal ligament over several levels with large paraspinal abscesses and early disc sparing (no disc-digesting enzymes); late collapse gives a gibbus. Metastases spare the disc.
- The valveless vertebral venous plexus (Batson) links pelvic and intercostal veins to the epidural veins, so prostate and breast cancer reach the spine without lung or liver deposits. It enlarges in IVC obstruction.
| Body lesion | Clue |
|---|---|
| Haemangioma | Bright on T1 and T2 (fat); thick dots of bone on axial CT |
| Osteoporotic collapse | Band of oedema under the end plate, rest of marrow normal, posterior wall not bulging |
| Metastatic collapse | Whole body replaced, convex posterior wall, pedicle involved |
- Development: vertebrae come from somite sclerotomes. Failed segmentation gives Klippel–Feil fused cervical vertebrae; failed fusion of two halves gives a corticated butterfly vertebra. The sacral hiatus (unfused S5 laminae) lies below the dural sac.
Remember The disc herniates where the posterior longitudinal ligament is weakest: posterolaterally, catching the root that crosses the disc, not the one leaving above it.
Exam trap Tuberculosis spares the disc early; pyogenic infection destroys it early.
Exam trap A cervical disc compresses the root numbered by the lower vertebra; C7–T1 means C8.
Test yourself on this topic
5 of the 68 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 58-year-old woman with long-standing rheumatoid arthritis needs a general anaesthetic. A flexion lateral radiograph of the neck is taken to measure the gap between the back of the anterior arch of the atlas and the front of the dens. Above which value is this gap abnormal in an adult?
Answer: 3 mm
The atlantodental interval is normally up to about 3 mm in adults and up to 5 mm in children, because the transverse ligament of the atlas holds the dens against the anterior arch. Rheumatoid synovitis erodes the transverse ligament and the dens, so the atlas slides forward on flexion and the interval widens. The cord can then be compressed between the dens and the posterior arch, which is a danger during intubation.
Atlantodental interval
- Normal adult: up to 3 mm
- Child: up to 5 mm
- Held by the transverse ligament
- Widened in rheumatoid arthritis
Remember RA neck: flexion films before anaesthesia.
Exam trap Down syndrome also causes atlanto-axial instability from ligament laxity.
Why the other options are wrong
- 1 mm Too small; normal adults may reach 3 mm.
- 6 mm Clearly abnormal, but the upper normal limit is lower.
- 9 mm Marked instability, not the threshold.
- 12 mm Far above the normal limit.
A 70-year-old diabetic man has a stiff back. He has thick, flowing ossification of the anterior longitudinal ligament along seven adjacent thoracic vertebrae, mainly on the right, with normal disc heights and normal sacroiliac joints. What is the most likely diagnosis?
Answer: DISH (skeletal hyperostosis)
Diffuse idiopathic skeletal hyperostosis (DISH) is ossification of the anterior longitudinal ligament and paravertebral soft tissue along at least four contiguous vertebrae, with preserved disc height and normal sacroiliac joints. It is common in older men, especially with diabetes and obesity. In the thoracic spine it is usually right-sided because the pulsating descending aorta on the left seems to inhibit bone formation.
DISH
- Flowing ossification over 4 or more vertebrae
- Disc height kept, SI joints normal
- Thoracic: right side (aorta on left)
- Older men, diabetes
Remember Candle-wax ossification in an old diabetic: DISH.
Exam trap DISH can cause dysphagia when large cervical anterior spurs press on the oesophagus.
Why the other options are wrong
- Ankylosing spondylitis Gives thin marginal syndesmophytes and fused sacroiliac joints in younger men.
- Degenerative spondylosis Causes disc narrowing with osteophytes, not flowing ossification over many levels.
- Alkaptonuric ochronosis Causes dense calcified discs with narrowing.
- Tuberculous spondylitis Destroys vertebral bodies and discs with a paraspinal abscess.
On an oblique lumbar radiograph, each vertebra outlines a 'Scottie dog'. The transverse process forms the nose, the pedicle forms the eye and the pars interarticularis forms the neck. Which part of the vertebra forms the dog's ear?
Answer: Superior articular process
On the oblique view the posterior elements make the shape of a dog: transverse process as the nose, pedicle as the eye, superior articular process as the ear, pars interarticularis as the neck, inferior articular process as the front leg and lamina as the body. A lucent band across the neck is a pars defect (spondylolysis). Knowing the outline lets the reader find each part on a single view.
Scottie dog
- Nose: transverse process
- Eye: pedicle
- Ear: superior articular process
- Neck: pars; collar = spondylolysis
Remember Collar on the dog's neck: pars defect.
Exam trap A pars defect may be seen only on oblique views or CT; lateral films can miss it without slip.
Why the other options are wrong
- Inferior articular process Forms the front leg.
- Spinous process Projects backwards and is not part of the head.
- Lamina Forms the body of the dog.
- Vertebral body Lies in front and does not form the outline.
A labourer at a brick kiln feels a sudden snap at the base of his neck while flinging heavy loads of clay overhead with a shovel. A lateral radiograph shows an oblique avulsion fracture. Which part of which vertebra is most likely broken?
Answer: Spinous process of C7
The clay-shoveller fracture is an avulsion of the spinous process of C7, less often C6 or T1. C7 has a long, non-bifid spinous process (vertebra prominens) to which trapezius, rhomboids and the ligamentum nuchae attach. Forceful muscle pull with the neck flexed avulses the tip. It involves only the posterior element and is a stable injury.
Clay-shoveller fracture
- Avulsion of C7 spinous process
- Pull of trapezius and rhomboids
- C7 = vertebra prominens
- Stable injury
Remember Shovelling snap at neck base: C7 spine.
Exam trap C7 is the first spinous process easily felt, but in some people T1 is more prominent.
Why the other options are wrong
- Dens of C2 Broken by falls and axial loading, not by shovelling.
- Transverse process of C1 Rarely fractured alone.
- Lamina of C5 Lamina fractures follow direct or extension injuries.
- Body of T1 Vertebral body fractures need axial loading.
A 62-year-old woman treated for breast cancer has back pain from a lytic metastasis in L2. Which part of the vertebra is characteristically destroyed, so that one of its two oval outlines disappears on a frontal radiograph?
Answer: Pedicle
Metastases reach the vertebral body through the blood, especially through the valveless vertebral venous plexus, and spread into the pedicle. On a frontal radiograph each pedicle is seen end-on as a cortical oval over the upper lateral body, so destruction of one pedicle makes the vertebra look like a winking owl. About half of the bone must be lost before a lytic lesion shows, so the sign is often late.
Winking owl sign
- Pedicles seen end-on as ovals
- Missing oval = pedicle destruction
- Typical of metastasis
- Disc space usually spared
Remember Missing pedicle oval: think metastasis.
Exam trap Myeloma, unlike metastasis, tends to spare the pedicle early because it contains less red marrow.
Why the other options are wrong
- Spinous process Forms the owl's beak and is not lost here.
- Transverse process Projects laterally beyond the body.
- Intervertebral disc Lies between bodies and is not visible as an oval.
- Inferior articular process Overlaps lower down and is not seen end-on.
Where this sits in the CPSP syllabus
- Diagnostic Radiology, Paper 2: Spine, Vertebral column: joints, ligaments, intervertebral discs and blood supply