science

Straight leg raise

Straight leg raise is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Straight leg raise rather than just read about it. In short: The straight leg raise is a test that can be performed during a physical examination, with the leg being lifted actively by the patient or passively by the clinician. If the straight leg raise is done actively by the patient, it is a test of functional leg strength, particularly the rectus femoris element of the quadriceps (checking both hip flexion and knee extension strength simultaneously).

Key takeaways

Straight leg raise belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Straight leg raise to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Straight leg raise from memory before moving on to harder problems.

Reference excerpt

The straight leg raise is a test that can be performed during a physical examination, with the leg being lifted actively by the patient or passively by the clinician. If the straight leg raise is done actively by the patient, it is a test of functional leg strength, particularly the rectus femoris element of the quadriceps (checking both hip flexion and knee extension strength simultaneously). If carried out passively (also called Lasègue's sign, Lasègue test or Lazarević's sign), it is used to determine whether a patient with low back pain has an underlying nerve root sensitivity, often located at L5 (fifth lumbar spinal nerve). The rest of this article relates to the passive version of the test.

Technique With the patient lying down on their back on an examination table or exam floor, the examiner lifts the patient's leg while the knee is straight. A variation is to lift the leg while the patient is sitting. However, this reduces the sensitivity of the test. In order to make this test more specific, the ankle can be dorsiflexed and the cervical spine flexed. This increases the stretching of the nerve root and dura.

Interpretation If the patient experiences sciatic pain, and more specifically pain radiating down the leg (radiculopathy), when the straight leg is at an angle of between 30 and 70 degrees, then the test is positive and a herniated disk is a possible cause of the pain. A negative test suggests a likely different cause for back pain. A positive straight leg test reproduces radiating leg pain. If it only causes back pain, then the test is negative. A meta-analysis reported the straight-leg test as having:

sensitivity 91% specificity 26% If raising the opposite leg causes pain (cross or contralateral straight leg raising):

sensitivity 29% specificity 88%

Lasègue's sign Lasègue's sign was named after Charles Lasègue (1816–1883). In 1864 Lasègue's medical student J.J. Forst described the signs of developing low back pain while straightening the knee when the leg has already been lifted. In 1880 Serbian doctor Laza Lazarević described the straight leg raise test as it is used today, so the sign is often named Lazarević's sign in Serbia and some other countries.

Illustrations

Worked examples

Example 1 — a first encounter with Straight leg raise

Start with the simplest possible case. Write down what Straight leg raise claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Straight leg raise before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Straight leg raise ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Straight leg raise

In research: Straight leg raise appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Straight leg raise in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Straight leg raise is common in secondary-school and first-year university syllabi. It links to neighbouring topics Medical signs, Musculoskeletal examination, Symptoms and signs: Nervous system, so understanding it makes those chapters shorter.
In everyday life: Look for Straight leg raise outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Straight leg raise in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Straight leg raise means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Straight leg raise out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Straight leg raise in simple terms?

Why does Straight leg raise matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Straight leg raise?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Straight leg raise.