Intervertebral disk of third lumbar vertebra

Looks like

The pad between L3 and L4: a large, thick disc, taller at the front, giving the lower back its inward curve. A tough fibre ring surrounds a soft gel core.

What it does

Joins the two vertebrae, absorbs shock and lets this level bend and twist a little.

Keeping it well

A bulge at L3–L4 can pinch the L4 nerve, giving pain in the front of the thigh and inner shin, with a weak knee reflex. Numb groin or bladder trouble is an emergency.

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• Axial spondyloarthritis
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• Gout
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• Marfan syndrome & connective tissue disorders
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• Rheumatic fever & rheumatic heart disease
• Rheumatoid arthritis
• Scoliosis
• Spina bifida & neural tube defects
• Spinal cord injury
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• Temporomandibular joint disorder