[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Spine](https://durgical.com/en/anatomy/region/spine/) › L3–L4 disc [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Spine](https://durgical.com/en/anatomy/region/spine/) # 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](https://durgical.com/en/anatomy/region/spine/) bend and twist. Official name: L3-L4 [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=spine&select=disc_l3_l4&side=r) Opens in the Durgical app, no sign-up needed. ## 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 points - L4 root picture: weak ankle dorsiflexion ([tibialis anterior](https://durgical.com/en/anatomy/tibialis-anterior-muscle/)) and knee extension, a reduced or absent knee jerk, numbness of the inner leg down to the medial malleolus - Usually the first interspace above the Tuffier line, and a standard site for lumbar puncture - Adjacent-segment degeneration above an L4–L5 fusion often shows up at L3–L4 ## Key facts **Where** Between L3 and L4 bodies; thick lumbar disc, taller in front (lumbar lordosis) **Attaches** Annulus fibrosus anchored to the [endplates](https://durgical.com/en/anatomy/vertebral-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](https://durgical.com/en/anatomy/abdominal-aorta/) just before it divides into the [common iliac arteries](https://durgical.com/en/anatomy/common-iliac-artery/) (about the L4 body), with the [inferior vena cava](https://durgical.com/en/anatomy/inferior-vena-cava/) to its right **Behind** [Posterior longitudinal ligament](https://durgical.com/en/anatomy/posterior-longitudinal-ligament/) and the dural sac with the [cauda equina](https://durgical.com/en/anatomy/cauda-equina/); behind the canal, the [ligamentum flavum](https://durgical.com/en/anatomy/ligamenta-flava/) **Lateral** [Psoas major](https://durgical.com/en/anatomy/psoas-major/) and the [lumbar plexus](https://durgical.com/en/anatomy/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](https://durgical.com/en/anatomy/skin/), the supraspinous and [interspinous ligaments](https://durgical.com/en/anatomy/interspinous-ligaments/) and the ligamentum flavum before the dura; the [conus medullaris](https://durgical.com/en/anatomy/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 - [Vertebral osteomyelitis](https://durgical.com/en/conditions/vertebral-osteomyelitis/) ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/l3-l4/) 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 - [L3–L4 nucleus](https://durgical.com/en/anatomy/l3-l4-spine-and-pelvis/) - [L3 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra-spine-and-pelvis-l3/) - [L4 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra-spine-and-pelvis-l4/) - [L4 nerve root](https://durgical.com/en/anatomy/l4/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=7567); [Anatomy, Back, Intervertebral Discs](https://www.ncbi.nlm.nih.gov/books/NBK470583/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/l3-l4/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/l3-l4/