How to Perform the Femoral Nerve Traction Test

The femoral nerve traction test, also called the femoral nerve stretch test or prone knee bend test, is a clinical examination used to detect irritation or compression of the upper and mid-lumbar nerve roots, primarily L2 through L4. While the straight leg raise dominates the conversation around lumbar radiculopathy, it mainly targets the lower nerve roots (L5, S1). The femoral nerve traction test fills the gap by stressing the nerve roots that sit higher in the lumbar spine, where disc herniations are less common but no less painful when they occur.

How the Test Is Performed

In its classic form, you lie face down on an examination table. The examiner bends your knee, bringing the heel toward your buttock, which puts the femoral nerve on stretch. Pain that radiates into the front of the thigh or down toward the knee during this maneuver is considered a positive result, suggesting that one of the upper lumbar nerve roots is being compressed or irritated. Some clinicians add hip extension by lifting the thigh slightly off the table with the knee still flexed, which increases the tension along the nerve.

A positive test typically reproduces or worsens the symptoms you came in with, not just general tightness or a pulling sensation. The distinction matters: plenty of people with stiff quadriceps muscles will feel a stretch in the front of the thigh during knee flexion. The finding that carries diagnostic weight is the reproduction of your familiar nerve-type pain, especially if it travels along the femoral nerve distribution.

Which Nerve Roots Get Stretched

The femoral nerve forms from the L2, L3, and L4 nerve roots, and the test is designed to pull on those roots where they exit the spinal column. A cadaveric study analyzing nerve root movement during different degrees of knee flexion found that the L2 and L3 roots stretched reliably during the test, while the L4 root behaved inconsistently across specimens. In some cadavers, L4 showed little lengthening during the classic prone knee bend; in others, it even shortened slightly depending on the position used.¹

This finding is clinically relevant because L4 radiculopathy is probably the most common upper lumbar problem clinicians are trying to detect. If the L4 root does not stretch uniformly during the classic test, some true L4 problems could be missed. The same cadaveric study found that a modified version of the test, performed with additional hip extension, did a better job of loading the L2 and L3 roots, though L4 remained variable. The practical takeaway is that a negative prone knee bend does not confidently rule out L4 involvement, and clinicians sometimes combine the test with other maneuvers to improve detection.

Diagnostic Accuracy

The numbers on how well the test performs vary depending on the study and the population examined. A systematic review of clinical neurological examination in lumbar radiculopathy reported a sensitivity of 100% and a specificity of 83% for the femoral nerve stretch test, though these figures came from a small sample and carried wide confidence intervals.² Other estimates place the sensitivity lower, in the range of 43 to 60%, suggesting the test catches roughly half of confirmed mid-lumbar radiculopathy cases.³

That spread in reported sensitivity probably reflects differences in how strictly a “positive” result was defined and which patient populations were tested. Regardless, the test’s real strength shows up in its positive likelihood ratios. A study evaluating physical examination tests for mid-lumbar nerve root impingement found that the femoral stretch test and crossed femoral stretch test both had positive likelihood ratios at the top of the scale, meaning a positive result greatly increases the probability that a mid-lumbar nerve root is truly being compressed on imaging.⁴ In plain terms, when this test is positive, it tends to mean something. When it is negative, you cannot be as confident the problem is absent.

The straight leg raise, by contrast, targets L5 and S1 and has limited usefulness for detecting problems at higher lumbar levels. A study looking at disc herniations found that roughly 77% of patients with L1 through L3 herniations had a positive femoral stretch test, compared with about 43% of those with L3-L4 herniations.⁵ The test performs best when the problem sits at the highest lumbar levels and becomes less reliable as you move down toward L4.

The Crossed Femoral Stretch Test

Just as there is a crossed straight leg raise for the lower lumbar spine, there is a crossed femoral stretch test for the upper lumbar spine. In this variation, stretching the opposite leg reproduces pain on the affected side. The logic is the same: if pulling on the contralateral nerve root provokes symptoms, the compression is probably substantial enough to tug on the nerve root from the other side, which makes the finding more specific for a true structural problem like a disc herniation.

One of the known weaknesses of the standard femoral stretch test is that it can be falsely positive. Tight or injured muscles in the front of the thigh and problems in or around the hip joint can both mimic a positive result.⁶ The crossed version helps filter out those false positives because it is harder for a local muscle or joint issue to produce pain on the other side of the body. When both the standard and crossed tests are positive, the clinician can be more confident that a nerve root is the culprit.

The Slump Knee Bend Variation

Another way to increase the sensitivity of femoral nerve testing is to add spinal flexion. The slump knee bend test (sometimes called the femoral slump test) is performed in side lying rather than prone. The examiner flexes your knee and extends your hip, as in the standard test, but also has you curl your head and thoracic spine forward. This combination loads the nervous system from both ends, stretching the nerve roots at the spinal level while simultaneously pulling the femoral nerve distally through the thigh.⁷

An important feature of the slump knee bend is how a positive result is confirmed. Reproduction of your symptoms during the maneuver is step one. But the clinician then asks you to extend your neck, looking up toward the ceiling. If that neck movement alleviates the symptoms, it strongly suggests the pain is coming from neural tension rather than a local muscle or joint problem. The neck is nowhere near the thigh, so its ability to change the symptoms points to the continuous nerve pathway as the source.⁸ This structural differentiation step gives the slump version a diagnostic edge over the simpler prone knee bend in some clinical situations.

How Results Line Up with MRI

Clinicians often want to know whether a positive bedside test actually predicts what they will see on imaging. In one study of patients with lumbosacral disc herniations, the femoral nerve stretch test was positive in about 40% of the sample.⁹ That number underscores the test’s limited sensitivity when applied broadly across all lumbar levels, since many of those patients had lower lumbar herniations where the femoral nerve is not the primary structure under tension.

More encouragingly, when the femoral nerve stretch test and straight leg raise were analyzed together as a combined neurodynamic testing battery, patients who tested positive had roughly eight times the odds of showing nerve root compromise on MRI compared with those who tested negative.¹⁰ The combination of tests covering both upper and lower lumbar nerve roots appears to be far more useful than either test alone when it comes to predicting what imaging will reveal.

False Positives and What Can Mimic a Positive Result

A test that stretches the front of the thigh is inevitably going to provoke discomfort in people who have hip problems, quadriceps injuries, or simply very tight muscles. This is the main pitfall. A stiff hip flexor from too much sitting, a healing quadriceps strain, or osteoarthritis of the hip can all produce anterior thigh pain during knee flexion and hip extension that looks on the surface like a positive femoral stretch test.

The key differentiator is the quality and location of the pain. Nerve root pain tends to be sharp, electrical, or burning and follows a dermatomal pattern down the front or inside of the thigh. Muscular tightness feels like a deep stretch that stays localized. Hip joint pain often centers in the groin. In practice, though, these patterns overlap enough that the test alone rarely settles the diagnosis. It works best as part of a broader examination that includes reflex testing at the knee, sensory testing along the inner shin and ankle, and assessment of quadriceps strength. The study that found very high positive likelihood ratios for the femoral stretch test also found that patellar reflex testing and medial ankle pinprick sensation testing were strong independent predictors of mid-lumbar nerve root impingement.¹¹ A cluster of positive findings across multiple tests builds a much stronger case than any single maneuver.

Agreement Between Examiners

A test is only useful in practice if different clinicians agree on whether it is positive or negative. Here, the femoral nerve stretch test has a documented weakness. A pilot study evaluating inter-examiner reliability of common spine screening tests found a kappa value of 0.47 for the femoral stretch test, which represents only moderate agreement.¹² For comparison, most of the other physical examination procedures in the same study exceeded a kappa of 0.9, meaning near-perfect agreement.

Why would this test be harder to agree on? The threshold between “that is normal stretching” and “that reproduced the patient’s complaint” depends heavily on how the examiner interprets the patient’s reaction. A grimace during knee flexion might be scored as positive by one clinician and as simple tightness by another. Standardizing the test, for instance by requiring the patient to confirm that the maneuver reproduced their specific symptoms and not just any discomfort, could improve consistency. But this reliability limitation is worth keeping in mind when a single examiner’s finding is being used to make a treatment decision.

When the Problem Is the Femoral Nerve Itself

Not every positive femoral stretch test points to a disc herniation or spinal nerve root compression. The femoral nerve can be damaged along its course through the pelvis and thigh by mechanisms that have nothing to do with the spine. A review of femoral neuropathy cases found that the most common causes were compression (about 40% of cases) and stretch injuries during surgery (about 35%).¹³ Inflammatory causes accounted for a smaller share. Presenting symptoms included weakness in the vast majority, sensory loss in about three-quarters, and pain in roughly half.

This matters because a patient with femoral neuropathy from, say, a retroperitoneal hematoma pressing on the nerve in the pelvis can have a positive femoral stretch test without any spinal pathology whatsoever. The same goes for someone who developed femoral nerve damage after hip surgery. In these cases, nerve conduction studies and electromyography can help localize the lesion to a point along the nerve rather than at the spine, guiding treatment in a very different direction.

Femoral Nerve Testing in Anterior Knee Pain

The prone knee bend has found a second life outside the world of spinal diagnostics. Researchers studying patellofemoral pain, the common condition where pain centers behind or around the kneecap, have used it to assess whether abnormal femoral nerve tension contributes to symptoms. A cross-sectional study of patients with patellofemoral pain found that a positive prone knee bend was significantly associated with quadriceps muscle shortness and with higher pain intensity.¹⁴ In that context, the test is being used less as a way to detect a disc herniation and more as a way to identify abnormal neural mechanosensitivity that might be perpetuating knee pain.

The idea is that when the femoral nerve does not glide smoothly through the tissues surrounding it, the resulting tension can sensitize the structures around the knee. This is a different clinical question from “is there a disc pressing on a nerve root,” but it uses the same physical maneuver. Therapists who find a positive result in someone with anterior knee pain may incorporate neural mobilization techniques, gently moving the limb through ranges that encourage the nerve to glide, as part of a rehabilitation program. Whether you are face down on a table for a spinal work-up or an anterior knee pain evaluation, the test itself looks the same; what changes is the clinical interpretation and the treatment plan that follows.

Practical Considerations for Getting Tested

If your primary complaint is pain in the front of your thigh, groin, or inside of your knee, and your clinician suspects an upper lumbar disc herniation, the femoral nerve stretch test is one of the first bedside checks that should happen. It takes less than a minute, requires no equipment, and when positive, it meaningfully raises the probability that imaging will confirm a structural problem at L2 through L4. Given the moderate inter-examiner reliability discussed earlier, it is reasonable to expect that the test will be combined with other findings, including reflex testing, sensory examination, and potentially the crossed or slump variations, before a diagnosis is made.

The test is generally safe for most people, but it should be performed cautiously or avoided in those with recent hip replacement, unstable spinal fractures, or conditions where forceful knee flexion could cause harm. Pain during the test that stops when the knee is straightened is expected and not a sign of damage. Pain that persists after the leg is returned to a resting position, or that worsens substantially, warrants further evaluation. For clinicians, the evidence suggests that the femoral nerve stretch test is best understood not as a standalone diagnostic tool but as one piece of a broader physical examination, and that its greatest value lies in what a positive result tells you rather than what a negative result rules out.