L2–L3 nucleus !
The nucleus pulposus is the soft, gel-like centre of the L2-L3 disc in the lower back; it works like a water cushion that spreads the load.
Official name: L2-L3
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What it is
The soft, gel-like centre (nucleus pulposus) of the L2–L3 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 L2–L3 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 L3 root
Relations
- Behind
- Annulus and posterior longitudinal ligament, then a dural sac that holds only cauda equina roots
- Lateral
- Psoas major, inside which the lumbar plexus forms; the L2 root exits through the foramen at this level
Examination
- Femoral nerve stretch test: with the patient prone, bending the knee stretches the L2–L4 roots; pain in the front of the thigh suggests an upper lumbar root, such as L3 from an L2–L3 fragment
On imaging
Infection: a bright nucleus on T2 with eroded endplates on both sides and enhancement after contrast. Degeneration is the opposite: a dark nucleus with intact endplates.
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
- Disc-space infection is a recognised complication after discectomy or discography, since instruments enter the nucleus
- The L3 root supplies skin down the front of the thigh to the inner knee, so pain from an L2–L3 fragment can be mistaken for knee or hip disease
- Spondylodiscitis here can spread into the psoas major, which arises from the sides of these discs; a psoas abscess gives flank or groin pain and a hip held bent, with pain on stretching it into extension (psoas sign)
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Why can a blood-borne infection settle in the lumbar disc itself (discitis) in a child?
In children the disc still has a blood supply; a small child may refuse to walk or sit.
Why does disc-space infection in adults usually start in the endplates rather than the L2–L3 nucleus?
The adult nucleus is avascular, so infection begins in the endplates and spreads to the disc (spondylodiscitis).
How does infection differ from degeneration of the L2–L3 nucleus on MRI?
Infection: bright nucleus on T2, eroded endplates on both sides, enhancement after contrast. Degeneration: dark nucleus with intact endplates.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- nucleus pulposus L2-L3 TA2 1686
- Official Spanish (DeCS)
- Núcleo pulposo L2-L3 DeCS D000070614
- English (TA2)
- L2-L3
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.
