L4–L5 herniated disc: why that level, and what helps

If the pain starts in your lower back and runs down the outside of one leg, and an MRI report names the L4–L5 level, it helps to know what that actually means. An L4–L5 herniated disc is the same problem as a slipped disc anywhere in the spine, but this level has a particular pattern — and a particular sign worth knowing about.

Why the L4–L5 spine segment, and not another

L4 and L5 are the two lowest vertebrae of the lower back, and the disc between them sits where the mobile spine meets the fixed pelvis. That junction takes the most load and allows the most movement, so it wears faster than the levels above it. Together with L5–S1, just below, it accounts for most lumbar disc herniations.

A disc is a tough outer ring around a soft centre. A herniation is the centre pushing out through a tear in that ring. It matters less how big the bulge looks than whether it touches a nerve — an L4–L5 disc bulge seen on a scan is often causing nothing at all — and at L4–L5, the nerve alongside is the L5 root.

What an L5 nerve does, and what you feel when it is pressed

• Pain down the outside of the leg, often past the knee to the ankle or foot — what most people call sciatica
• Numbness or pins and needles on the top of the foot, particularly the web between the big toe and the second toe
• Difficulty lifting the front of the foot, or the big toe — foot drop, the sign most specific to this level
• Trouble heel-walking, which uses the same muscles

Back pain may be mild or absent. It is common for the leg to hurt far more than the back, and that pattern is a clue that a nerve, rather than a muscle, is involved.

Why discs herniate here

• Wear. Discs lose water and resilience from early adulthood, and most herniations happen between about 30 and 50.
• Lifting, especially while bending and twisting. That combination loads one side of the ring more than the other.
• Long hours of sitting or driving. Sitting loads a disc more than standing does, and prolonged driving adds vibration.
• Family history, smoking, which reduces the disc's nutrition, and excess body weight.
• A fall or accident — though often there is no single event at all.

A narrow spinal canal, present from birth, does not cause a herniation, but it leaves less room to spare, so a smaller one can cause more symptoms. See spinal stenosis.

What helps

Most L4–L5 herniated discs improve without an operation, usually within six to twelve weeks, and the herniated material often shrinks on its own. Treatment is stepped, and most people never go past the first steps.

• Staying active, while avoiding heavy lifting and long periods of sitting. Bed rest makes it worse, not better.
• Exercise and physiotherapy, to keep you moving and to take load off the irritated nerve.
• Medication for pain, and a different kind for nerve pain, which does not respond to ordinary painkillers.
• An injection near the nerve root, under imaging guidance, when the pain is not settling. It eases the pain while the disc recovers, rather than repairing anything.

When surgery is considered

Surgery comes into the conversation after several weeks of proper treatment — usually at least six — or sooner if weakness is getting worse, or if the red-flag symptoms above appear.

• Discectomy, removing the part of the disc pressing on the nerve, through a small incision with a microscope or tube
• Endoscopic discectomy, the same aim through an even smaller opening, using an endoscope

Surgery brings leg pain down faster than waiting does. It treats the nerve compression, not the wear in the disc itself, which is why it is kept for the people who need it. See decompression surgery.

Protecting the level afterwards

• Keep moving. Regular walking or swimming beats any single exercise.
• Lift with your legs, and turn your feet rather than twisting your back.
• Break up long sitting with a few minutes of standing or walking each half hour.
• Strength work for the trunk, built up gradually.

Who you will see

Spine problems at this clinic are seen by Dr Mathew Tung, a neurosurgeon treating brain, spine and nerve conditions, and Dr Lim Heng Hing, a Senior Consultant Orthopaedic and Spine Surgeon. Both use endoscopic and minimally invasive techniques where surgery is needed, and you do not have to choose between them before booking.

Related

Slipped disc · Sciatica · Foot drop · Lower back pain · Decompression surgery · All spine and neck conditions