Purpose of the Straight Leg Raise Test

The straight leg raise test is done to gauge several aspects of your legs' strength and stability. It's most often performed to check muscle function but can be altered to look at nerve function, as well.

The test is performed while you lie flat on a bed. Either you or the examiner then raises your leg, possibly with light resistance, to get an idea of the legs' strength and functionality.

Testing the Extensor Mechanism

Most often, the straight leg raise test is used to assess the function of the quadriceps muscle and its attachment to the shin bone. An inability to perform a straight leg raise can be caused by disruption of the:

• Quadriceps tendon
• Patella (knee cap)
• Patellar tendon

If you have a condition such as a torn quadriceps tendon or a patella fracture, you'll likely be unable to perform this maneuver. 

Because of the disruption of the extensor mechanism, despite your effort to lift the leg, there is nothing to pull against, and therefore you can't perform this function. A straight leg raise test is the key diagnostic test to assess for these conditions.

Testing Nerve Irritation

The straight leg test can be altered to test sciatic nerve function rather than muscle and tendon function. The sciatic nerve exits from the lumbar spine (lower back), then passes behind the hip and down the back of your leg.

Conditions that cause sciatic nerve irritation include:

• Spinal stenosis
• Disc herniations
• Sciatica

Rather than having you attempt the leg raise, the examiner lifts your heel with the knee in a straight position. When it's as high as possible, the examiner points your toes toward your head. 

This stretches the nerve and can recreate symptoms of nerve pain going down the leg. This type of test is called a tension sign and can be very helpful in determining the best treatment for a nerve condition.