Lower Back Pain From a Car Crash: 5 Lumbar Injuries

If your lower back hurts after a car crash, you don’t have “back pain.” You have one of five specific lumbar injuries, each with its own mechanism, its own anatomical home in your spine, and its own treatment path.

A muscle strain typically heals in two weeks. A herniated disc compressing your S1 nerve root can take three months and a surgical referral. A compression fracture at T12 is a different situation entirely. The doctor you call, the imaging you actually need, the timeline you’re looking at, and the financial stakes of getting your medical records right all change depending on which injury you have.

For the broader picture of why pain shows up days later and why adrenaline masks injuries at the scene, see our guide on pain after a car accident.

Key Takeaways

• Five distinct injuries cause most lower back pain after a car crash: sprain or strain, herniated disc, facet joint injury, compression fracture, and sciatica as a symptom.
• Roughly 95 percent of lumbar disc herniations happen at L4-L5 or L5-S1, the two lowest motion segments in the spine.
• Compression fractures from crashes concentrate at the thoracolumbar junction (T11 to L2), where the rib-stabilized thoracic spine meets the mobile lumbar spine.
• Pain that travels below the knee with numbness or weakness is more likely disc-related. Pain that stops at the knee with no neurological signs is more likely a facet joint problem.
• Medical bills come out of your pocket unless your records connect them to the crash. California’s two-year filing deadline under CCP § 335.1 matters less than what’s in your medical record when you file.

Why the Lumbar Spine Takes the Hit

Your lumbar spine is built to handle axial load. Five vertebrae (L1 to L5) carry most of your upper body’s weight through their discs and facet joints. In a crash, those forces overwhelm the system in milliseconds.

In a rear-end collision, the pelvis rotates rearward into the seatback first, driving the lumbar spine into flexion and compression, then the torso lurches forward on rebound. Frontal crashes concentrate axial compression at the lower thoracic and upper lumbar segments. Side impacts add rotational shear, which the facet joints aren’t built to absorb.

Two areas get injured disproportionately: the thoracolumbar junction (T11 to L2, where compression fractures cluster) and the L4-L5 and L5-S1 segments (where disc herniations cluster).

Why Documentation Beats Diagnosis

Medical bills don’t pause while you wait to feel better. PT sessions, imaging, copays, and lost wages add up fast, and unless you’ve connected those costs to the crash on paper, they’re your problem. Your health insurance pays the medical providers first, but it can come back later and claim that money from any settlement through subrogation. The at-fault driver’s insurance won’t pay anything without a documented medical record tying your symptoms to the collision.

California gives you two years to file a personal injury claim. Most people focus on the deadline, but the real issue is what your medical record looks like by the time you do.

A herniated disc diagnosed three months after the crash invites the obvious question from the defense: Was it really caused by the collision, or was it pre-existing? The answer your records can support depends on what you did in the first weeks. Document the symptoms, see a doctor within 72 hours, and follow the evidence-based escalation. The contemporaneous medical record is what makes a serious lumbar claim work.

The Five Lumbar Injuries From a Crash

Lumbar sprain and strain

A strain is a muscle or tendon injury. A sprain is a ligament injury. Both come from the same crash mechanics, and together they make up the most common back injury from car accidents.

You’ll feel localized pain and stiffness in the muscles alongside your spine, with muscle spasm and restricted movement. Pain doesn’t radiate down your legs. No numbness or weakness. Cleveland Clinic notes that most people with lumbar strain or sprain symptoms improve in about two weeks with relative rest, ice and heat, NSAIDs as directed, and a gradual return to activity. Imaging usually isn’t indicated unless pain persists beyond four to six weeks.

These are also the cases insurers most often dismiss as “minor.” Consistent follow-up and documented PT matter even when symptoms feel manageable, because gaps in treatment become arguments for the defense.

Herniated and bulging disc

The disc between two vertebrae has a gel-like center (the nucleus pulposus) surrounded by a tough fibrous ring (the annulus fibrosus). A crash that combines axial compression with flexion drives the nucleus posteriorly against the weakest part of the annulus. When fibers tear, nuclear material can escape into the spinal canal and come into contact with a nerve root.

About 95 percent of lumbar disc herniations happen at L4-L5 or L5-S1. L4-L5 herniations typically compress the L5 nerve root, causing pain radiating along the lateral leg into the top of the foot and weakness in lifting the big toe. L5-S1 herniations typically compress the S1 root, causing pain down the back of the leg into the heel, with diminished Achilles reflex and weakness pushing off when you walk. Most symptomatic disc herniations resolve within 6 to 12 weeks without surgery. When they don’t, your doctor will discuss injections or surgical options.

An imaging-confirmed disc herniation tied to the crash records carries far more weight in a claim than back pain without objective findings.

Facet joint injury

The facet joints are paired synovial joints connecting one vertebra to the next at the back of the spine. In the lumbar region, they’re oriented near-vertically, which permits bending and side flexion but resists rotation. Hyperextension and rotation in a crash can tear the joint capsule and produce persistent localized facet pain. Lumbar facet joints are estimated to cause 15 to 45 percent of chronic low back pain.

The clinical signature: axial low back pain, often unilateral, worse with extension and rotation (leaning back or twisting), better with flexion. Pain can refer to the buttock or posterior thigh but typically does not extend beyond the knee, and there’s no dermatomal sensory loss or motor weakness. That distinction matters for what comes next.

Facet injuries are routinely disputed by insurers because they don’t show on standard imaging. The clinical record of pain patterns, provocation testing, and response to facet blocks becomes the documentation that supports the claim.

Compression fracture

A compression fracture is a failure of the anterior vertebral body under axial load. In high-energy car crashes, these concentrate at the thoracolumbar junction. T11 through L2 accounts for roughly 60 to 80 percent of all spinal fractures, and around 27 percent of thoracolumbar injuries present with neurological deficit. Pain is severe, midline, worse with standing, better lying down.

X-ray is the first imaging step. CT shows bony detail. Stable fractures get pain control and bracing. Unstable fractures or those with neurological compromise are surgical. For neurologically intact fractures that don’t improve after four to six weeks, AAOS supports kyphoplasty as an option.

These are among the easier lumbar injuries to document for a claim because they show clearly on imaging. The settlement question usually becomes long-term care costs and mobility limitations, not whether the injury happened.

Sciatica

Sciatica isn’t a diagnosis. It’s a symptom of something else, almost always nerve root irritation at L5 or S1. The most common underlying cause is a herniated disc, though facet hypertrophy and pre-existing stenosis aggravated by the crash can produce the same picture.

Mayo Clinic lists violent injury, including traffic accidents, among the recognized causes.

Pain radiates from the lower back through the buttocks and into the leg, usually below the knee and sometimes into the foot. It follows a dermatome, so it tracks a predictable line. Numbness, tingling, or weakness in the same area is common. Sitting, coughing, and sneezing typically make it worse.

An imaging study identifying the underlying cause is what links the sciatica to the crash in a claim. Sciatica documented only by patient-reported symptoms is weaker evidence than sciatica tied to a specific disc or stenosis finding on MRI.

Facet or Disc? Where the Pain Travels Tells You

The single most useful clinical distinction for post-crash lower back pain is whether the pain stops at the knee or goes below it.

Symptom	More likely facet	More likely disc/ radiculopathy
Where does pain travel?	Buttock or back of thigh, stops at the knee	Below the knee, often into the foot
Dermatome pattern?	No specific pattern	Follows L5 or S1 distribution
Numbness or weakness?	No	Often yes
What makes it worse?	Extension, rotation, twisting	Sitting, coughing, sneezing
Imaging needed?	Often not initially	MRI if persistent or with a deficit

That distinction guides which specialist you see and which imaging you need. “Pain stops at my knee and gets worse when I lean back,” sends a doctor in one direction. “Pain goes into my foot, and my big toe feels numb,” sends them another.

When Imaging Is Actually Indicated

Most law firm articles tell crash victims to demand an MRI on day one. The actual standard of care says the opposite. The American College of Physicians recommends against routine immediate imaging for acute low back pain, absent severe or progressive neurologic deficits or red flag signs of serious underlying pathology.

The defensible escalation:

• History and physical exam first. A neurological screen plus the straight leg raise test catches most disc-related radiculopathy.
• X-ray when a fracture is suspected after significant trauma.
• MRI is the gold standard for disc and nerve pathology, typically reserved for symptoms persisting beyond about six weeks, focal neurologic deficits, or red flags that develop earlier.
• CT for fine bony detail when MRI is contraindicated.

This matters legally, too. Pursuing the evidence-based pathway gives you a medical record defense experts can’t credibly attack. A clean MRI ordered for a clean indication carries more weight than an MRI ordered prematurely on demand.

When to Go to the Emergency Room

It’s advisable to get to an emergency room immediately if you have any of these:

• Loss of bladder or bowel control
• Numbness in the groin, buttocks, or inner thighs (saddle anesthesia)
• Sudden bilateral leg weakness or progressive weakness in either leg
• Severe abdominal pain or distention along with back pain
• Foot drop (inability to lift your foot)

The first three together suggest cauda equina syndrome, which is a surgical emergency. The standard window for decompression is 24 to 48 hours. Don’t wait it out.

For the full red flag list across all post-crash pain types, see our pillar article.

What to Do Next

If you have any red flag symptoms above, go to an emergency room now. If you haven’t seen a doctor and it’s been less than 72 hours, get evaluated this week. Skip the demand for advanced imaging unless red flags develop. Let the physical exam guide the escalation. And start a dated pain journal today, because that record is part of your documentation trail.

For the timing reality, see our back pain days after a car accident article. For how medical bills and liens interact with settlements once a claim moves forward, see our California medical liens guide.

If symptoms persist past two weeks, if numbness or weakness shows up, or if you want help building the documentation trail correctly from here, contact DK Law for a free consultation.