L3–L4 disc !
The L3-L4 disc is the cushion between the L3 and L4 vertebrae in the lower back; it absorbs shock and lets the spine bend and twist.
Official name: L3-L4
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What it is
The cushion between L3 and L4: a tough outer ring of fibres (annulus fibrosus) around a soft centre.
What it does
Absorbs shock, spreads load across the vertebrae and lets the spine bend and twist, while holding the bones together.
Key facts
- Where
- Between L3 and L4 bodies; thick lumbar disc, taller in front (lumbar lordosis)
- Attaches
- Annulus fibrosus anchored to the endplates and ring apophyses of L3 and L4; anterior and posterior longitudinal ligaments
- Function
- Absorbs and spreads load; posterolateral herniation usually compresses the L4 root (far-lateral: L3)
Relations
- In front
- Abdominal aorta just before it divides into the common iliac arteries (about the L4 body), with the inferior vena cava to its right
- Behind
- Posterior longitudinal ligament and the dural sac with the cauda equina; behind the canal, the ligamentum flavum
- Lateral
- Psoas major and the lumbar plexus; the L3 root exits through the foramen at this level, while the L4 root runs down behind the disc to its own foramen
How to find it
The Tuffier line, joining the tops of the iliac crest on both sides, crosses about the L4 spinous process or the L4–L5 interspace; the L3–L4 interspace is the gap felt just above it, best opened by curling the back forward.
Examination
- Patellar (knee-jerk) reflex: reduced or absent on the affected side with L4 (and L3) root compression
- Heel walking: difficulty on one side points to weak ankle dorsiflexion (L4, L5)
On imaging
MRI is the test of choice: a paracentral L3–L4 herniation presses on the traversing L4 root, a far-lateral one on the exiting L3 root. With a thickened ligamentum flavum and facet joints, axial T2 shows canal stenosis, often at this level and L4–L5. Flexion–extension radiographs look for instability; after a fusion below, imaging checks this level for adjacent-segment change.
Common problems
- Herniation (slipped disc): the gel pushes through a tear in the ring and presses on a nerve root, causing sciatica down the leg.
- Degeneration with age: the disc dries out, loses height and can bulge, sometimes with back pain.
- Tears in the ring (annular fissures) that can cause back pain.
How it is diagnosed
History and exam (the straight-leg raise test, strength, reflexes and feeling in the leg). MRI shows the disc and which nerve is pressed; it is usually done only if pain lasts more than about 6 weeks or there are warning signs.
Treatment
- Most herniations improve within weeks to months: staying active, physical therapy, pain medicine, sometimes an epidural steroid injection.
- Severe or lasting leg pain, or weakness: microdiscectomy to remove the herniated piece.
- Urgent surgery if there are signs of cauda equina syndrome (numbness in the saddle area, bladder or bowel changes).
- Selected cases of disc collapse with instability: fusion with a cage and bone graft.
Clinical notes
- At lumbar puncture the needle passes skin, the supraspinous and interspinous ligaments and the ligamentum flavum before the dura; the conus medullaris lies well above
- The L4 root also supplies the tibialis anterior, so a severe L4 lesion can add to foot drop, though L5 is the usual culprit
Development
In young children small vessels still reach the disc through the endplates; they regress during childhood. This is why blood-borne discitis can start in the disc itself in a toddler (often lumbar, with refusal to walk), while in adults infection starts in the endplate.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
What is the L4 root picture from an L3–L4 disc herniation?
Weak ankle dorsiflexion (tibialis anterior) and knee extension, a reduced or absent knee jerk, and numbness of the inner leg down to the medial malleolus.
How is the L3–L4 interspace found at the bedside?
The Tuffier line, joining the tops of the iliac crests, crosses about L4 or the L4–L5 space; L3–L4 is the gap felt just above, opened by curling the back forward.
Which ligaments does a midline lumbar puncture needle cross at L3–L4 before reaching the dura?
The supraspinous ligament, the interspinous ligament and the ligamentum flavum, after the skin; the conus medullaris lies well above.
Which level often shows adjacent-segment degeneration above an L4–L5 fusion?
The L3–L4 disc, the level just above the fusion.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- discus intervertebralis L3-L4 TA2 1684
- Official Spanish (DeCS)
- Disco L3-L4 DeCS D007403
- English (TA2)
- L3-L4
- Also called
- fibrous ring · fibrocartilago intervertebralis
Related
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Back, Intervertebral Discs.
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Representative model, for educational purposes only.
