Low Back Pain — Full Text

This topic can apply to Upper Back Pain as well, but most back pain is felt in the lumbar area, by the curve of the lower back, between the hips. 

Sometimes there’s an obvious reason, like the pain begins while lifting a heavy object.  But it doesn’t really matter.  Back injury can occur from subtle movements, and pain may start 1-2 days later, when the patient doesn’t remember anything about what they might have done.  And I see many patients who attribute the pain is due to a trauma years before, which actually has nothing to do with it.

The vast majority of cases of Low Back Pain are due to 3-4 conditions, diagnosed primarily by a physical exam. Most of the conditions discussed below might or might not come and go, but the ones with asterisks (*) will persist until they resolve on their own, or worse.

Causes of Low Back Pain

Main Causes to ConsiderUncommon Conditions Not to Forget
Muscle Strain or Spasm / Ligament Sprain
Herniated Disk (includes Sciatica)
Spinal Stenosis
(simply due to age)
Bone Disease

Spinal Cord Disease *
Bone Cancer
(esp. if elderly) *
Ankylosing Spondylitis
Abdominal Diseases *
Herpes Zoster (Shingles) *

The vast majority of cases are due to non-serious Sprains and Strains, that almost always get better on their own eventually.  We diagnosis these after ruling out other conditions. But first, a few words about UNUSUAL CAUSES, some of which can be catastrophic (these will cause recent onset pain, not long-standing):

**  Spinal Cord Disease (including Cauda Equina syndrome)  —  We worry about this catastrophic cause of new acute low back pain in injection drug users (epidural abscesses), and in patients with a history of prostate, breast, or lung cancer (epidural metastases). Various tumors, infections, and other conditions can also occur, all rare.  If the spinal cord gets compressed, permanent paralysis can suddenly occur. The pain is often worse when lying on the back. May have extreme tenderness when we tap or pound on a single vertebra.

Red Flags (Danger Signs):

  • muscle weakness or loss of sensation in both legs (not just “feeling weak or numb,” but detected on physical exam). We test weakness by having the patient lift each leg against resistance (we push on it as they try). If they’re able to walk on their heels, there’s likely no weakness.
  • bowel / urinary incontinence (losing a large amount, not just stains or drops), or urinary retention (urge to pee but can’t, for hours)
  • numb / tingling in saddle area from anus to genitals
  • fever
  • any new very localized pain in a patient at risk.

If suspicious, we test for loss of anal wink reflex [touch the anus, & note if there’s no typical reflex contraction, i.e. no “wink”].  An MRI is needed to diagnose, usually done through an ER, since if we think this may be a serious possibility, we don’t want to waste time.

**  Bone Cancer  —  We’d suspect this in older patients if the pain is felt only on a single bone (vertebra).  The patient may also have experienced weight loss, fevers, or night sweats. If a simple blood test called the erythrocyte sedimentation rate (ESR, or “sed rate”) is >50, we’d be especially concerned.  Our first step: an X-Ray.

We can usually suspect bone cancer on physical exam by tapping each vertebra firmly, & finding localized tenderness in just one of them.  But even if the exam is negative, I still order x-rays on older persons with new-onset low back pain that occurred without a good explanation.  X-rays are virtually useless for the vast majority of patients with low back pain, but may be worth doing in the elderly, and patients with known cancer.

**  Abdominal Diseases Radiating to the Back  —  We consider conditions such as kidney stones, ectopic pregnancy, ruptured aortic aneurysm, etc., when patients who are at-risk for them get acute back pain that’s unaffected by movement.  If pain feels worse with one or another bending or twisting motion, we donโ€™t worry about these unusual situations.

**  Ankylosing Spondylitis  —  Also called axial spondyloarthritis, this is an inflammatory arthritis (that’s uncommon).  We think about it in patients under 40 y.o., if pain has been going on at least several months.  The KEY QUESTION: are symptoms are worst in the morning upon awakening (for at least 30-60 min.), and then ease up as the day goes on?  If so, we:

  • Measure to see if the spine stays abnormally straight while the patient bends forward (Schober’s Test);
  • Order an Erythrocyte Sedimentation Rate (ESR), a blood test for inflammation in general;
  • Consider a 1-view x-ray for sacroiliac joints (NOT a โ€œlow back seriesโ€ x-ray);
  • Refer to Rheumatology if the ESR rate is fairly high, or if thereโ€™s “sacroiliitis” on X-Ray.

**  Herpes Zoster (Shingles)  —  Like the chest & abdomen, Zoster can cause pain anywhere.  We’d look for pain on just one side of the back, with a bunch of red splotches or blisters in a row from spine to abdomen.

**  Scoliosis  —  We can identify this easily by watching the patient from behind while they bend forward.  Scoliosis that wasn’t detected & treated in childhood can cause worsening problems with age.

Now That Weโ€™re Done With The Rare Cases, onward to:


We diagnose these based primarily on our physical exam, which we perform systematically:

**  Bone Disease (fracture, metastasis, infection)  —  Not as common as the others below, but important. We just discussed this above, suspecting it if there’s tenderness to tapping on a single vertebra, or a single part of the pelvic bone, and no other area is tender when we palpate.  We confirm with x-ray.  These conditions actually arenโ€™t common, but they’re the first thing we look for during physical exam.  If we don’t find such tenderness, x-rays are not going to be useful, because all they show is bone.

**  Herniated Disk (a.k.a. “pinched nerve,” “slipped disk,” “Sciatica”)  —  Disks are pieces of cartilage between the vertebral bones, that allow the spine to bend.  A “herniation” means the disk has bulged or ruptured in a way that puts pressure on a nerve.

Pain radiates down a single area in one leg (usually going down to the foot if the common Sciatic Nerve is involved).  There may be muscle weakness, tingling or decreased sensation, and/or loss of a reflex (usually at the heel) in just one leg.  A test called the “straight-leg raise” is positive on physical exam.

**  Spinal Stenosis  —  Narrowing of the spinal canal, which occurs mainly in the elderly.  We suspect it not by physical exam, but by symptoms.  Pain occurs with walking, but is not immediately relieved with stopping to rest (like that due to poor circulation).  The person must sit, & still maybe wait a few minutes.  Or the person can continue walking, to see if pain is relieved with bending over, like hunched while holding on to a shopping cart (not so with poor circulation, which won’t ease up while still walking).

Still, physical exam is important to be sure the narrowing isn’t causing actual nerve damage in addition to the pain.  We look for muscle weakness, loss of sensation, and abnormal reflexes in the legs.

**  Muscle Strain / Ligament Sprain  —  This is the most common cause of low back pain.  Our main findings on exam are pain with movements, maybe muscle tenderness (not just on one specific bone), and NO FINDINGS suggesting bone or disk disease, nor of spinal stenosis.

The Clinician’s Systematic Approach

Letโ€™s discuss all this a little more.  A patient with low back pain looks comfortable at rest, winces with movements.  Maybe there was an injury or event that triggered the pain, but maybe not.  Strains or sprains can occur from minor abrupt movements, with pain beginning 1-2 days later as swelling develops within muscle fibers.  But disk herniation can also occur very subtly.  So we examine the lower back:

Step 1 — Ranges of Motion: flexing forward, bending backwards, sideways bending, twisting.  We expect at least one movement to hurt, and can see how disabled a person is.

Step 2 — Seek Localized Bony Tenderness to Tapping:  We begin by lightly pressing on each lumbar vertebra.  If there’s no tenderness, we tap.  Still non-tender, we tap harder.  Pound.  Do the same on the pelvic bone.  No localized tenderness means no bone disease or epidural catastrophe.

Step 3 — Palpate the muscles.  Lack of tenderness doesnโ€™t exclude a simple strain or sprain, but if we find tenderness or muscle spasm, it confirms these eventual diagnoses.

Step 4 —  Test Muscle Strength (ideally with patient lying face-up on the exam table).  We have them flex their hips against resistance (they try to lift the leg, while we press down against it).  Straighten the knees against resistance.  We can also test hips by spreading legs apart, squeezing them together, rolling their foot in & out, all against resistance.  Same with pointing the foot back (for the ankle).  Some muscles like hip extension, knee flexion, and pointing foot down are most accurately tested lying face-down (against gravity).  Confession — I virtually never have a patient roll over for this, unless I’m real suspicious of muscle weakness.

  • THE BIG TOE !!!  —  The most important group of all for testing muscle strength, pointing it back & then down while we press against it (resistance).  We must never forget to test the big toe!  Thatโ€™s because one-sided motor weakness suggests a herniated (slipped) disk, & a somewhat serious one if it’s affecting strength.  The most common disks to herniate are between vertebrae L4-L5 and L5-S1, affecting the sciatic nerve, which controls the big toe.

Step 5 — Test the Deep Tendon Reflexes (Knee and Heel), looking for one-sided weaker reflex as a sign of a herniated disk, especially in the heel (for L4-L5, and L5-S1 disks).

Step 6 — Straight-leg Raise (SLR).  We cradle the heel & lift a relaxed straight leg.  At point of back pain, we pause; then abruptly yank the foot back at the ankle.  Positive finding is when this final maneuver provokes sudden pain, in the low back (not behind the knee, which just indicates tight hamstring muscles).  Pain on the other side of the back is strongly significant.

Making The Diagnosis

If thereโ€™s localized tenderness to tapping on a single vertebra, no other tenderness, & no reason to suspect rare epidural catastrophes [see below], we get an x-ray of the Lumbo-Sacral Spine for Bone Disease.  This is uncommon.

Otherwise (or if the x-ray shows no bone disease), weโ€™re left with deciding between Herniated Disk vs. uncomplicated Muscle Strain / Ligament Sprain.  We look for a disk; if there are no findings, itโ€™s Muscle Strain / Ligament Sprain.  So we diagnose Herniated Disk if any one-sided findings:

  • Weakness when testing strength against resistance, especially of the big toe
  • Decreased reflex
  • Positive Straight-Leg Raise
  • Tingling (by patient report) in a pattern corresponding to a single nerve

The latter two, without weakness or reflex changes, are enough to convince me that a disk is possible.  The first two abnormalities indicate the problem is more serious. 

We may also diagnose Herniated Disk if a patient describes classic “Sciatica”  —  pain that’s felt all the way down the outside of one leg (not the entire leg).  They may also have tenderness if we press in a certain part of the buttock (the “sciatic notch”).

We diagnose probable Spinal Stenosis in the older patient who has low back pain while walking, that eases up with sitting, or just by bending forward while continuing to walk. Symptoms may vary from side to side, but include both sides in one way or another.

X-Rays and MRI’s for Low Back Pain????  Almost never indicated!!!!  Studies invariably reveal very low rates of serious diseases like cancer (in the range of 1/1000), and no specific clinical clues have been shown to be helpful.  One study found โ€œclinician judgmentโ€ was a useful criterion.

So, modestly speaking, whatโ€™s my โ€œclinical judgmentโ€?

I send patients to the ER for urgent MRI if I suspect epidural disease [extremely rare], based on some combination of:

  • Numbness / Tingling in saddle area between genitals & anus, plus Loss of Anal Wink
  • Weakness of both legs (on strength testing against resistance)
  • Localized tenderness to tapping on a single vertebra
  • Fever (by thermometer)
  • High-Risk Patient: IV Drug User / Cancer (esp. prostate, breast, lung) / Immunocompromised

I order regular X-Rays if I suspect a fracture or cancer of bone:

  • Localized tenderness to tapping on a vertebra
  • Weight loss, night sweats
  • New, unusual pain in an elderly person, or patient on chronic steroids

I might order an x-ray for an elderly person with long-standing chronic back pain, to diagnose osteoarthritis.  There’s nothing that can be done beside pain control, but at least they offer a diagnosis.  I do the same if I suspect scoliosis from physical exam (an abnormal curve in the spine from childhood, that can deteriorate with age & cause significant pain).

Lots of people get MRIs for low back pain, supposedly to diagnose herniated disks or spinal stenosis.  But the problem is that there are lots of false positives!  In studies, many people with no back pain at all have a wide variety of abnormalities that can be interpreted as “herniated disks.”  Almost 50% of adults over age 60 without any symptoms may have an MRI positive for spinal stenosis!  Orthopedists & Neurosurgeons ignore MRI findings unless they match well with a physical examination that pinpoints problems with specific nerves. For example, I had a patient with classic symptoms of a herniated disk, and a classic MRI abnormality, but the latter was on the other side! No surgery for him.

Patients who require MRIs are those who may need surgery [why do a test unless we intend to act on it?].  There are two treatments for herniated disks: 1) Time (over 70% resolve on their own within 3 months); and 2) Surgery.  If pain isn’t bad enough for a patient to desire surgery, they don’t need an MRI.  If the symptoms and physical exam don’t fit a specific nerve and disk, surgery is less likely to help, regardless of the MRI.

In terms of spinal stenosis, treatment options are ongoing pain medication or surgery [time wonโ€™t work; physical therapy & epidural injections have never been shown to help].  If the pain is such that a patient would truly desire the procedure, by all means they should get an MRI, although most surgeons won’t operate unless there’s also a neurologic abnormality like leg weakness.  A major or progressing neurological abnormality requires surgery much sooner.

Summary Conclusions

  • Serious causes of Low Back Pain are rare, and are predictable from symptoms & physical exam. Watch out for Red Flags (Danger Signs) described above
  • Most Low Back Pain is due to muscle strains or ligament sprains, which aren’t identifiable by any x-ray or MRI
  • Herniated Disks usually get better on their own.  The only other option is surgery; but MRIs give lots of false-positives if there are no specific abnormalities on physical exam
  • MRI should be obtained for suspected Spinal Stenosis if a patient desires surgery

This may sound nihilistic or fatalistic, but maybe that’s how life is, too.

See also Low Back Pain for the clinicianโ€™s condensed thought-process when face-to-face with a patient.

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