Trick of the Trade: Crossed straight leg raise test
A 35 year old man presents with low back pain which radiates down his right leg to the level of the knee. Is this sciatica?
Low back pain is one of the most common chief complaints that we see in the Emergency Department. In addition to the examination of the back and distal neurovascular function, we also need to test for evidence of a radiculopathy (compression or inflammation of a nerve root typically from a herniated disk). Because most disk herniations occur at the L4-L5 and L5-S1 level, you should test for irritation of the L4-S1 nerve roots. This is the sciatic nerve.
The straight leg raise (SLR) maneuver tests for such irritation. By passively elevating the patient's extended right leg, this maneuver stretches the sciatic nerve. If compressed or inflamed, this maneuver will reproduce pain in the sciatic nerve distribution. Note that isolated back pain with this maneuver does NOT mean a positive SLR test.
In a 2010 Cochrane review, the SLR test yielded a high sensitivity (92%) and low specificity (28%). This means that a negative SLR almost rules out a sciatic radiculopathy and disk herniation at the L4-L5 and L5-S1 level.
What about all those patients who have back pain and a little hamstring muscle vs sciatic nerve irritation with the SLR maneuver? Is there a more specific test?
Trick of the Trade:
Crossed Straight Leg Raise maneuver
For a patient with back pain radiating down their right leg, also perform the crossed SLR maneuver. If elevating their LEFT leg passively reproduces pain down his/her affected RIGHT leg, this is highly predictive of a sciatic radiculopathy and disk herniation. The crossed SLR maneuver essentially stretches the left L4-L5-S1 nerve root and thus tugs on the right L4-L5-S1 nerve root.
The 2010 Cochrane review shows that the crossed SLR has a low sensitivity (28%) but really high specificity (90%) for disk herniation.
van der Windt DA, Simons E, Riphagen II, Ammendolia C, Verhagen AP, Laslett M, Devillé W, Deyo RA, Bouter LM, de Vet HC, & Aertgeerts B. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane database of systematic reviews (Online). 2010 Feb 17;(2):CD007431. PMID: 20166095