Back pain. It happens to everyone, and it sucks.

It's also one of the most non-specific complaints, ranging from lumbar strain to aortic aneurysm.

I. Red Flags for Imaging
  A. > 50 y/o
  B. trauma
  C. immunocompromised with fever

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  D. IVDA
  E. saddle anesthesia
  F. persistent/unrelenting pain at night OR rest
  G. anti-coagulant use
  H. urinary retention/incontinence
  I. stool incontinence
  J. bilateral radiculopathy

In the ED, what are we looking for?
 I.   Cauda Equina
 II.  Epidural Abscess
III.  Epidural Hematoma
IV.  Spinal Cord Compression
V.   Osteomyelitis
VI. Vertebral Fracture
VII.Thoracic Aneurysm

Now the question is, which imaging?
X-Ray:fracture, tumor, infection
MRI: neurological deficits

Some significant exam findings:
Lhermitte's sign: shock like pain down spine during spine flexion. You can ask patient from standing to touch their toes. In school, this was pathopneumonic for multiple sclerosis.
Straight leg (supine): pain along nerve root when patient flexes hip with leg straight
Extensor Babinski sign: (I was taught there was no such thing as a positive Babinski sign, rather you have to describe the response from the great toe) run a blunt instrument from the heel to the metatarsal pads in a curve. (Remember this is a normal response in infants)
Hoffman's reflex: flicking the nailbed of the middle finger illicits flexion of thumb.

Remember Waddell's sign? 3 or more findings are suggestive of a "non-organic" cause of back pain (aka crazy)
I. Tenderness
   A. Superficial
   B. Non-anatomic
II. Simulation
   A. Axial loading- neck pain
   B. Rotation- during rotation c/o leg pain
III. Distraction
   A. Straight Leg Raise- done in the traditional supine and then sitting.
IV. Regional
   A. Sensory- not conforming to neuroanatomy
   B. Weakness
V. Over-reaction

Labs: If you are worried about infection, get a CBC, ESR, CRP. Otherwise, get a UA.

Treatment:
I think this is the hardest part, people are not going to be satisfied because of the back pain and loss of function. You tell the patient about NSAIDs but they will tell you it doesn't do a thing. Then you go towards muscle relaxants (Robaxin, Baclofen, etc.) maybe even with narcotics. That is an acceptable treatment and given the limited duration of therapy in the ED setting. I would limit to no more than 3-4 days.

Muscle Relaxants:
 I.  Baclofen (Gablofen) 5mg TID
 II. Cyclobenzaprine (Flexeril) 5-10mg TID
III. Methocarbamol (Robaxin) 1500mg QID
IV. Metaxalone (Skelaxin) 800mg TID

Surgical consultation if cord compression, infection, tumor.
Epidural Abscess: Vancomycin 60mg/kg IV plus Flagyl 500mg
Osteomyelitis: Vancomycin works too!

References:
Cline, D.M., Ma, O.J., Cydulka, R.K., Meckler, G.D., Handel, D.A., & Thomas, S.H. (2012). Tintinalli's Emergency Medicine Manual (7th ed.) McGraw Hill Professional: Columbus, OH.