L1–L2 nucleus !
The nucleus pulposus is the soft, gel-like centre of the L1-L2 disc in the lower back; it works like a water cushion that spreads the load.
Official name: L1-L2
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What it is
The soft, gel-like centre (nucleus pulposus) of the L1–L2 disc.
What it does
Works like a water cushion: it turns pressure from above into outward push on the fibre ring, spreading the load. It is under the most pressure when you bend forward and lift.
Key facts
- Where
- Centre of the L1–L2 disc, slightly toward the back, inside the annulus fibrosus
- Function
- Notochord-derived gel (about 70–90% water, proteoglycans); turns axial load into annulus tension; herniates posterolaterally toward the L2 root
Relations
- Behind
- Back of the annulus and the posterior longitudinal ligament, then the dural sac with the tip of the conus (usually near L1–L2) and the cauda equina
- Lateral
- Annulus with the psoas major arising from the sides of the disc and bodies; the L1 root leaves through the foramen at this level
Examination
- L2 root: weak hip flexion (iliopsoas) and numbness over the upper front of the thigh; the cremasteric reflex (L1–L2) may be reduced
On imaging
A Schmorl node is a rounded dent in the endplate continuous with the disc on MRI or CT; a recent one may show bright marrow oedema around it on T2 or STIR.
Common problems
- Squeezes out through a tear in the ring (herniation), usually backward and to one side, toward a nerve root.
- Loses water with age, so the disc gets thinner and stiffer.
How it is diagnosed
On MRI a healthy nucleus is bright on T2 images; a worn one turns dark ('black disc').
Treatment
- In a microdiscectomy only the loose piece that has pushed out is removed; most of the disc stays.
Clinical notes
- Several Schmorl nodes with wedged vertebrae and irregular endplates in a teenager suggest Scheuermann disease, which at the thoracolumbar junction can cause back pain
- Upper lumbar herniations are uncommon next to those at the two lowest levels; they tend to occur in older people and their thigh pain can be taken for hip disease
- Tuberculous spondylitis (Pott disease) favours the lower thoracic and upper lumbar spine; compared with pyogenic infection it tends to spare the disc longer and to form large paraspinal abscesses
Test yourself
Think of the answer, then tap the question to see it.
Where are Schmorl nodes from nuclei such as L1–L2 most frequent, and are they usually significant?
In the lower thoracic and upper lumbar spine, L1–L2 included; most are incidental.
Why can a central L1–L2 nucleus fragment give mixed cord and root signs?
It can reach the conus medullaris, which ends near this level, as well as the roots around it.
Which findings around the L1–L2 nucleus suggest Scheuermann disease in a teenager?
Several Schmorl nodes with wedged vertebrae and irregular endplates; at the thoracolumbar junction it can cause back pain.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- nucleus pulposus L1-L2 TA2 1686
- Official Spanish (DeCS)
- Núcleo pulposo L1-L2 DeCS D000070614
- English (TA2)
- L1-L2
Related
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Back, Nucleus Pulposus; Anatomy, Back, Intervertebral Discs; 7.3 The Vertebral Column (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.
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Representative model, for educational purposes only.
