Back and vertebral column
Introducido| English | Significado |
|---|---|
| conus medullaris | conus medullaris |
| cauda equina | cauda equina |
| lumbar puncture | lumbar puncture |
| cauda equina syndrome | cauda equina syndrome |
A column that moves
- The spine is a stack of 33 vertebrae that shields the spinal cord and lets nerves out at 31 pairs of levels.
- It trades stability for movement, which makes it the site of most back pain and every spinal cord emergency.
Counting the vertebrae
- 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused) and about 4 coccygeal (fused): 33 bones, 24 of which move.
- The neck and lower back curve forwards (lordosis); the thoracic and sacral parts curve backwards (kyphosis).
Match each region to its number of vertebrae.
Dificultad 2/5 · 140 monedas + un pequeño bono en el primer intento de hoy
7 + 12 + 5 = 24 movable vertebrae above the fused sacrum and coccyx.
How many vertebrae are movable?
Dificultad 2/5 · 140 monedas + un pequeño bono en el primer intento de hoy
7 cervical + 12 thoracic + 5 lumbar = 24; the sacral and coccygeal ones are fused.
Where the cord ends
- In adults the cord ends at L1–2, as the conus medullaris 脊髓圆锥. Below that, the canal holds only nerve roots: the cauda equina 马尾.
- That is why a lumbar puncture 腰椎穿刺 at L3/4 or L4/5 is safe: the needle meets floating roots, not cord.
Why is lumbar puncture done at L3/4 or L4/5?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Below the conus the needle meets floating cauda equina roots, which move aside, rather than the cord.
Bone level is not cord level
- In the embryo cord and canal are the same length; then the spine grows faster. So roots run downwards before they exit, more steeply lower down.
- The gap grows down the spine: about one segment in the neck, two in the upper thorax, three or more lower down. A T10 vertebral injury damages the L1–2 cord segments.
A fracture of the T10 vertebra damages the T10 cord segment.
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
The cord is shorter than the spine; behind the T10 vertebra lie about the L1–2 cord segments.
Worked example: the dermatome ladder
- Thumb C6, nipple T4, umbilicus T10, big toe L5, the skin around the anus S3–5. Five rungs turn a sensory examination into a level.
- Together with the bone-to-cord gap, the ladder tells you both the cord segment injured and which vertebra to image.
Put these dermatome landmarks in order from the highest cord segment to the lowest.
Dificultad 3/5 · 200 monedas + un pequeño bono en el primer intento de hoy
Five rungs that are easy to test and spread from neck to sacrum.
Worked example: an emergency at the end of the cord
- (Fictional patient) Back pain, numbness of the "saddle" area and an inability to pass urine. A large disc at L4–5 is squeezing the roots of the cauda equina, including the sacral ones.
- These are roots, not cord, so the signs are bladder, bowel and saddle numbness: cauda equina syndrome 马尾综合征. Decompression is needed within hours.
Which combination should make you think of cauda equina syndrome?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
Compressed sacral roots give bladder, bowel and saddle signs; decompression is needed within hours.
Three common slips
- Bone level as cord level. The gap grows down the spine.
- The wrong root. The posterior ligament is strongest in the midline, so discs bulge to the side and press on the next root down: an L4/5 disc compresses L5.
- Moving sacral bones. The 5 sacral and the coccygeal vertebrae are fused.
An L4/5 disc bulges to the side. Which root is usually compressed?
Dificultad 1/5 · 100 monedas + un pequeño bono en el primer intento de hoy
The L4 root has already left above the disc, so a side bulge catches the next root down, L5.
Recap
- 33 vertebrae, 24 movable, with alternating curves.
- The cord ends at L1–2; below is the cauda equina, so lumbar puncture is safe at L3/4.
- Bone level ≠ cord level; five dermatome rungs read the level; saddle numbness with retention is an emergency.