Welcome to the second installment of “Inconceivable: medical terms that don’t mean what you think they mean.” For an introduction to this series, check out last month’s post. (h/t Dr. Faust of FOAMcast for pointing out the correct spelling of Mr. Montoya’s name)
This month we’re going to tackle a physical exam finding that is commonly misused…
You have a patient with right-sided lower back pain after lifting a heavy box at work. You lay the patient supine and raise his right leg off the bed. He reports that this reproduces his pain and causes a tightness in his hamstring. After two doses of appropriate analgesia, he feels well and you call his primary care physician to ensure close outpatient follow up. In your discussion, you mention a “positive straight leg raise.” Unfortunately, you would be mistaken; let’s take a closer look.
The straight leg raise (SLR) is a physical exam maneuver that evaluates for radicular pain suggesting intervertebral disk herniation. As a result of the spine’s natural curvature, greater than 95% of disk herniations occur at the L4/L5 or L5/S1 level, and thus the L5 or S1 nerve roots are most likely to be irritated.1
To correctly perform the test:
- Lay the patient supine with the affected (in our patient’s case, his right) leg extended. The contralateral leg may be straight or flexed at the knee and hip with foot flat on the bed.
- Raise the affected leg to approximately 70 degrees
- Determine the most distal point of radicular pain – i.e does the patient have pain in the thigh, knee, calf, and/or ankle of the raised leg?
A positive straight leg raise occurs when the patient feels pain radiating below the knee. This finding indicates intervertebral disk herniation with high sensitivity (90-95%) but poor specificity (20-30%). 1,2 Remember, simply having pain in the hamstring or reproducing the back pain does not count. A negative straight leg raise, as our patient had, is more suggestive of other injury such as lumbosacral strain.
After you’ve performed the SLR as described, you can further evaluate your patient’s pain with the crossed straight leg raise. Now, raise the contralateral leg and evaluate for the same radicular pain in the affected leg (in our example, you would raise the patient’s left leg and elicit pain below the right knee.) A positive crossed straight leg raise also indicates disk herniation but with reverse stats as the standard SLR – high specificity (about 90%) but with poor sensitivity (25-40%). 1,2
One final pro tip: If your patient is in too much pain to lay flat the SLR can be performed sitting up with leg extension creating similar angles and similarly stretching that S1 nerve root as in the traditional SLR.
- Bickley, Lynn S., Peter G. Szilagyi, and Barbara Bates. 2007. Bates’ guide to physical examination and history taking. Philadelphia: Lippincott Williams & Wilkins.
- van der Windt, et al. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane Database Syst Rev. 2010 Feb 17;(2):CD007431. doi: 10.1002/14651858.CD007431.pub2.