AN50.1-4 | Vertebral column — Gate Quiz

Correct. Secondary (compensatory) curvatures develop postnatally as adaptations to erect posture: the cervical lordosis develops at ~4 months when the infant lifts the head; the lumbar lordosis develops at ~12–18 months when the infant begins to sit, stand, and walk. Primary curvatures (thoracic kyphosis + sacral kyphosis) are present at birth, reflecting the foetal C-shaped flexure.

Primary curvatures (thoracic + sacral kyphosis) = present at birth (reflect the foetal posture). Secondary curvatures (cervical + lumbar lordosis) = develop after birth with erect posture. Remember: 2 primaries (thoracic, sacral) + 2 secondaries (cervical, lumbar).

Correct. The nucleus pulposus is the remnant of the notochord — the primitive axial structure present in all chordates. In early development, the notochord induces the overlying ectoderm to form the neural tube. As the vertebral column develops, most of the notochord is replaced by the vertebral bodies; the notochord persists in the centre of each disc as the nucleus pulposus.

The nucleus pulposus is the notochordal remnant — gelatinous, high water content, acts as a hydraulic shock absorber. It loses water content progressively with ageing (disc degeneration), predisposing to annular tears and disc prolapse.

Correct. L5 nerve root supplies: tibialis anterior + EHL (foot dorsiflexion = 'foot drop'), and sensation over the dorsum of the foot and first web space (L5 dermatome). The ankle jerk is S1 (gastrocnemius-soleus) — preserved when the L5 root is affected. L4–L5 disc herniation compresses the descending L5 root (which exits at L5–S1 foramen, one level below the disc).

L5 root = foot dorsiflexion (tibialis anterior, extensor hallucis longus) + first web space sensation + often preserved ankle jerk. L4–L5 disc herniation compresses the L5 root. S1 root (L5–S1 disc herniation) = absent ankle jerk + plantar flexion weakness + lateral foot sensory loss. The one-level lag rule: disc at L4–L5 compresses L5 root (exits at L5–S1).

Correct. The PLL is broad in the cervical region but narrows (tapers) toward a central band at the lumbar level — providing central reinforcement but little lateral support. The posterolateral corner of the lumbar annulus is therefore the weakest point, unprotected by the PLL. This, combined with torsional loading, explains why 95% of lumbar disc herniations are posterolateral.

PLL anatomy is the key to understanding PIVD: it is broad and protective in the cervical region; it tapers centrally in the lumbar region → leaves the posterolateral disc exposed → posterolateral herniation is the rule. Only massive central herniations (at L4–L5 or L5–S1) cause cauda equina syndrome.

Correct. Cauda equina syndrome (bilateral leg weakness/numbness + saddle anaesthesia + urinary retention or incontinence + reduced anal tone) from a massive central disc herniation is a surgical emergency. Decompressive surgery (discectomy/laminectomy) must be performed within hours — delays beyond 24–48 hours significantly worsen bladder, bowel, and lower limb outcomes. This is one of the few true surgical emergencies in orthopaedics/neurosurgery.

Cauda equina syndrome = EMERGENCY. The cauda equina (L2–S5 nerve roots) in the lumbar cistern is compressed by the prolapsed disc → bilateral leg deficit + saddle anaesthesia + urinary retention/incontinence + reduced anal sphincter tone. Prognosis for bladder/bowel recovery depends on the duration of compression before decompression. 'Operate within 24 hours' is the standard recommendation.

Correct. Isthmic spondylolisthesis is caused by a stress fracture (spondylolysis) of the pars interarticularis — the narrow bridge of bone between the superior and inferior articular processes of the vertebral arch. When the pars fractures bilaterally, the posterior elements are separated from the vertebral body, allowing the body (and the vertebral column above) to slide forward over the sacrum.

Isthmic spondylolisthesis = stress fracture of the pars interarticularis (= spondylolysis). Risk factors: repetitive hyperextension (gymnastics, fast bowling in cricket, weightlifting). L5–S1 is the most common level. On oblique X-ray, the 'Scottie dog' sign — a crack through the dog's neck = spondylolysis; slippage = spondylolisthesis.

Correct. Ankylosing spondylitis causes enthesitis (inflammation at ligament/tendon insertions on bone) → ossification of the outer annulus fibrosus (syndesmophytes — bridging the disc space corner to corner) and the anterior and posterior longitudinal ligaments → "bamboo spine" on X-ray. The entire disc space is bridged by bone on both sides — fusion of adjacent vertebral bodies.

Bamboo spine in AS: ossification of the outer annulus fibrosus (syndesmophytes bridging vertebral body corners) + anterior and posterior longitudinal ligaments + posterior ligaments → complete fusion of the spinal column. This explains the dramatically reduced spinal mobility and the increased risk of fracture from minor trauma.

Correct. A sacral dimple with a hair tuft (hypertrichosis), combined with a low-lying conus (below L2 at L4) and thickened filum terminale on ultrasound, indicates tethered cord syndrome (a form of occult spinal dysraphism). The conus is anchored by the thickened filum, preventing normal ascent. As the child grows, traction on the tethered cord causes progressive neurological deficits (lower limb weakness, bladder dysfunction, scoliosis). Surgical release of the filum terminale is required to prevent progression.

Tethered cord syndrome: conus below L2 + thickened filum terminale + overlying cutaneous stigmata (hair tuft, dimple, haemangioma, lipoma). Distinguished from benign sacral dimple (small, below L5, no associated features) by the conus level on ultrasound/MRI. Must be released surgically — the 'tethered' cord is stretched as the spine grows → progressive neurological injury.

Correct. The sacroiliac joint is a combined joint: the anterior/inferior part is a synovial joint (with articular cartilage, synovial membrane) and the posterior/superior part is a syndesmosis (fibrous joint, held by the posterior sacroiliac ligaments — the strongest in the body). In older individuals (especially males), the synovial part may become fibrous/partly fused.

The sacroiliac joint has a complex structure: synovial anteroinferiorly (allowing minimal gliding) + syndesmosis (fibrous, extremely strong posterior ligaments) posterosuperiorly. Movement is minimal — slight nutation during pregnancy. The posterior sacroiliac ligaments are the strongest in the body.

Correct. In adolescent idiopathic scoliosis, the lateral curvature is always accompanied by vertebral body rotation toward the convex side. The ribs attach to the vertebral bodies — rotation of the vertebral bodies toward the convex side rotates the attached ribs posteriorly on that side → posterior rib prominence = "rib hump." On the concave side, the ribs are rotated anteriorly → anterior rib fullness. This rotational component is best appreciated on Adam's forward bending test and is measured with a scoliometer.

The rib hump in scoliosis is a 3D deformity: lateral curvature + vertebral rotation. The vertebral bodies rotate toward the CONVEX side → ribs on the convex side are pushed posteriorly (rib hump). Adam's forward bending test removes the postural component and reveals the true structural rib hump. The Cobb angle measures the lateral curvature; the rib hump measures the rotational component.