L4 and L5 sit in the lower back, with L5 resting just above the sacrum and the top of the pelvis.
L4 and L5 are the two lowest movable vertebrae in the lumbar spine. If you place your hand on your lower back, they sit below the waistline area and above the tailbone region. L5 is the last lumbar vertebra. Right under it sits the sacrum, which links the spine to the pelvis.
People usually hear “L4-L5” after an X-ray, MRI, or back pain visit. That label can sound abstract. It gets easier once you picture the lumbar spine as a stack of five weight-bearing bones. L1 starts the lumbar section. L5 ends it. So L4 and L5 are near the bottom of that stack, where the lower back carries a lot of body weight and movement.
Where L4 And L5 Sit In Your Spine
Your spine has sections: cervical in the neck, thoracic in the mid-back, lumbar in the lower back, then the sacrum and coccyx below. According to AAOS Spine Basics, the lumbar spine has five larger vertebrae because this part of the back carries more of the body’s weight.
That means L4 and L5 are not in the middle of your back and not in the tailbone itself. They are in the lower lumbar area, close to the beltline and just above the bony top of the pelvis. In many people, the L4-L5 level lines up near the area where the iliac crests, or the upper rim of the hip bones, can be felt from the back.
What Sits Around Them
L4 and L5 are surrounded by structures that matter just as much as the bones themselves:
- The L4-L5 disc, which sits between the two vertebrae
- Facet joints, which help guide motion
- Ligaments and muscles that steady the lower back
- Nerve roots that pass nearby on their way into the legs
This is one reason the area gets so much attention in scans and back pain notes. A sore muscle can hurt there. A worn disc can hurt there. A pinched nerve can also start there and send pain, tingling, or numbness down the leg.
Where Is L4 And L5 In Relation To The Pelvis?
A simple way to place them is to start from the bottom. The sacrum is the shield-shaped bone between the hip bones. L5 sits right on top of the sacrum. L4 sits right on top of L5. So, if someone says “lower lumbar” or “just above the sacrum,” they are usually talking about the zone where L4 and L5 live.
That lower position also explains why this area takes a beating. It bends, twists, and absorbs force when you sit, stand, lift, walk, or stumble. The farther down you go in the lumbar spine, the more load those levels tend to handle.
Why The L4-L5 Level Gets Mentioned So Often
The L4-L5 level is a common trouble spot because it combines motion and load. The disc has to cushion force. The joints have to let you move. The nearby nerves need enough room to pass through. If one part swells, bulges, slips, or narrows, symptoms can show up fast.
An NCBI Bookshelf review on lumbar disc herniation notes that most lumbar disc herniations happen at L4-L5 or L5-S1. That fits what many patients hear after imaging: the lower lumbar levels are frequent sources of disc-related pain and leg symptoms.
What L4 And L5 Do
L4 and L5 help with the daily work of the lower back. They let you bend forward, lean back a bit, and shift weight as you move. They also help transfer force from the upper body into the pelvis and legs.
These vertebrae do not work alone. The disc between them acts like a cushion. The facet joints in the back of the spine help direct motion. Muscles around the trunk keep the area steadier while you change position.
Why Their Location Matters For Symptoms
Because L4 and L5 sit close to nerve roots, pain from this level does not always stay in the back. Some people feel it in the buttock, outer thigh, shin, or foot. Others feel weakness, pins-and-needles, or numb patches instead of plain pain.
The exact pattern depends on what is irritated and where. A strained muscle, worn joint, bulging disc, or narrowing around a nerve root can all feel different even when the trouble starts in the same lower back zone.
| Structure | Where It Sits | What It Does |
|---|---|---|
| L4 vertebra | Second-lowest lumbar vertebra | Helps bear weight and allows lower back motion |
| L5 vertebra | Lowest lumbar vertebra, right above the sacrum | Transfers force from the spine into the pelvis |
| L4-L5 disc | Between L4 and L5 | Cushions load and helps absorb shock |
| Facet joints | Back of the L4-L5 level | Guide bending and twisting |
| L4 nerve root | Near the L4-L5 region | Helps carry signals to parts of the thigh and leg |
| L5 nerve root | Near the lower lumbar exit zone | Helps carry signals into parts of the leg and foot |
| Sacrum | Directly below L5 | Links the spine to the pelvis |
| Paraspinal muscles | Around the lower lumbar spine | Help steady posture and movement |
Common Problems Around L4 And L5
When a report mentions L4 and L5, it often points to one of a few patterns. Each one can produce lower back pain, leg pain, or both.
Disc Bulge Or Herniation
The disc between L4 and L5 can bulge or tear. If disc material presses on a nearby nerve root, pain may travel down the leg. Some people also notice tingling, numbness, or weakness.
Facet Joint Wear
The small joints behind the vertebrae can get irritated or arthritic. That pain often stays more in the back, though it can spread into the buttock area.
Spinal Stenosis
This means narrowing around the nerves. It may lead to leg pain, heaviness, or numbness that gets worse with walking or standing upright.
Spondylolisthesis
This is a slip of one vertebra over another. It can happen at the lower lumbar levels and may irritate nerves or create mechanical back pain.
MedlinePlus lists warning signs with back pain that deserve prompt medical care, such as loss of bowel or bladder control, weakness, numbness in the buttocks or pelvis, trouble walking, fever, or pain after a bad fall. Their page on acute low back pain lays out those red-flag symptoms clearly.
How Doctors Find The L4-L5 Level
Clinicians use a mix of touch, symptoms, strength testing, reflexes, and imaging. During an exam, they may press on the lower back, check where pain travels, and test leg strength or sensation.
Imaging can add detail:
- X-rays show bone alignment and can spot slippage or wear
- MRI shows discs, nerves, and soft tissue
- CT can help when bone detail is needed
On a report, you may see “L4-L5 disc bulge,” “L4-L5 stenosis,” or “degenerative change at L4-L5.” That wording does not always mean a person needs surgery. Scan results need to match the person’s symptoms and exam.
| Finding At L4-L5 | What A Person May Feel | Usual Next Step |
|---|---|---|
| Muscle strain nearby | Local lower back pain and stiffness | Rest, gradual movement, home care |
| Disc bulge | Back pain, leg pain, tingling | Exam, then MRI if needed |
| Nerve root irritation | Pain or numbness down one leg | Neurologic exam and symptom tracking |
| Facet joint wear | Aching lower back, worse with extension | Clinical exam, sometimes imaging |
| Stenosis | Leg heaviness or pain with walking | Imaging and function-based care plan |
| Spondylolisthesis | Back pain, tightness, nerve symptoms | X-ray or MRI, then tailored treatment |
How To Picture L4 And L5 On Your Own Back
You cannot label each vertebra with perfect accuracy at home, but you can get close. Put your hands on the top of your hip bones at the sides, then trace toward the spine. That area lines up near the lower lumbar region. L4 is often around that zone. L5 sits just below it, then the sacrum starts under L5.
That rough map is useful for body awareness. It is not a substitute for imaging or a clinical exam, though. Pain felt “at L4-L5” can still come from muscles, joints, discs, or nerves nearby.
When L4-L5 Pain Needs Prompt Care
Get prompt medical care if lower back pain comes with bowel or bladder trouble, new leg weakness, numbness in the saddle area, fever, major trauma, or pain that is severe and not settling. Those signs call for faster assessment than routine back soreness.
For day-to-day aches without red flags, the first steps are often simpler: keep moving within reason, avoid bed rest for long stretches, and get checked if symptoms travel down the leg, keep getting worse, or fail to ease over time.
What To Keep Straight About L4 And L5
L4 and L5 are the bottom two movable bones of the lumbar spine. They sit in the lower back, with L5 right above the sacrum. That low position, plus the load they carry, is why this level shows up so often in back pain visits, scan reports, and leg symptom patterns.
If a report mentions L4-L5, the plain-language meaning is simple: the issue is near the bottom of the lower back, just before the spine meets the pelvis.
References & Sources
- American Academy of Orthopaedic Surgeons (AAOS).“Spine Basics.”Shows the spine sections, notes that the lumbar spine has five vertebrae, and places the lower back above the sacrum.
- NCBI Bookshelf.“Lumbar Disc Herniation.”States that most lumbar disc herniations occur at L4-L5 or L5-S1 and explains the anatomy of the lumbar disc.
- MedlinePlus.“Low Back Pain – Acute.”Lists red-flag symptoms that call for prompt medical care, including bowel or bladder changes, weakness, numbness, and trouble walking.