The intervertebral discs lie between the vertebral bodies: a firm fibrous ring with a soft, gel-like core. They absorb shocks and keep the spine flexible. Over the years they lose water and elasticity. If the fibrous ring tears, material from the core can escape and press on a nerve root – this is a slipped disc. It most often affects the lumbar spine, less often the neck.
Typical is pain that runs from the back into the leg, often below the knee, and that can be stronger than the back pain itself. There may also be tingling, numbness or weakness, for example when lifting the foot. If the herniation is in the cervical spine, the symptoms radiate into the shoulder and arm.
In most people, the symptoms subside within a few weeks: the body often partly breaks down the escaped tissue, and the irritation of the nerve eases. That is why treatment starts conservatively, with movement, pain relief and physiotherapy. Without paralysis or sensory disturbances, an MRI is usually not needed in the first two weeks.
Surgery is considered if the leg pain does not ease sufficiently over six to twelve weeks despite consistent treatment, or if paralysis is present or getting worse. How large the herniation looks on the image is not the only deciding factor. What matters is whether the findings and the symptoms match.