The Slump test and Prone Knee Bend: neurodynamic examination for sciatic and femoral nerve tension
In short
Neural tissue must slide and elongate during daily movements. When disc bulges or foraminal stenosis compress dural sleeves, neurodynamic tension tests reproduce sharp radicular symptoms. Learn the step-by-step Slump test and Prone Knee Bend procedures.
In this guide (6 sections)
Neurodynamics: mechanical interface and dural excursion
The nervous system is a continuous biomechanical and physiological tract spanning from the cranial dura down to distal digital nerve terminals. In healthy adults, peripheral nerves slide up to 15 mm relative to surrounding myofascial interfaces during joint excursion.
When an intervertebral disc herniation, osteophyte, or swollen facet joint encroaches on a nerve root canal, the neural connective tissue (epineurium and perineurium) develops ischemia, mechanosensitivity, and adhesions. Neurodynamic tests apply progressive longitudinal traction to confirm neural involvement.
The Slump Test: Step-by-step clinical execution
Described by Geoffrey Maitland, the Slump test is more sensitive than the traditional Straight Leg Raise (SLR) test because it incorporates trunk and cervical flexion to maximally traction the entire neuraxis.
| Sequence Step | Manoeuvre Details | Biomechanical Effect | |
|---|---|---|---|
| 1. Seated Slump | Patient sits on the edge of the plinth, thighs supported, hands clasped behind the lower back. Ask the patient to collapse the thoracic and lumbar spine into flexion while keeping the cervical spine upright. | Stretches the thoracolumbar dural tube. | |
| 2. Overpressure & Neck Flexion | Examiner places one hand across the upper back to maintain trunk slump. Patient flexes the chin down to the chest. Examiner adds gentle cervical overpressure. | Tractions cranial dura and spinal cord downward. | |
| 3. Knee Extension | While maintaining trunk and neck flexion, patient slowly extends the symptomatic knee as far as possible. | Tenses the sciatic nerve across the posterior hip and knee. | |
| 4. Ankle Dorsiflexion | Examiner dorsiflexes the foot and ankle. | Maximally tensions the tibial and common peroneal nerve branches. | |
| 5. Structural Differentiation | Ask the patient to lift their head into cervical extension while keeping the knee extended and ankle dorsiflexed. | If radicular leg pain diminishes upon cervical release, the pain is neural. If pain remains unchanged, it is hamstring or musculoskeletal. |
Posterior thigh tightness during knee extension is normal in healthy individuals. A test is positive only if it reproduces the patient specific radicular symptoms (shooting pain, burning, paresthesia) and improves immediately when the cervical spine is lifted into extension.
Prone Knee Bend (Femoral Nerve Stretch Test)
While the SLR and Slump test examine the lower lumbosacral roots (L4, L5, S1), the Prone Knee Bend (also known as the femoral nerve stretch or Wassermann test) evaluates the upper lumbar roots (L2, L3, and L4).
| Examination Stage | Execution Steps | Clinical Findings | |
|---|---|---|---|
| Starting Position | Patient lies prone on the examination table. Pelvis remains flat against the plinth. | Ensures symmetrical lumbar spine position. | |
| Passive Knee Flexion | Examiner slowly and steadily flexes the patient knee toward their buttock until full flexion or symptom onset. | Stretches the femoral nerve and quadriceps muscle. | |
| Hip Extension Sensitizer | If knee flexion alone is asymptomatic, examiner gently extends the hip off the plinth while maintaining knee flexion. | Maximally tensions the L2-L4 nerve roots exiting the upper lumbar spine. | |
| Positive Sign | Reproduction of burning, sharp pain, or numbness across the anterior thigh or groin. | Confirms upper lumbar disc herniation or femoral nerve radiculopathy. |
Neural flossing and mobilization protocols
Once neural mechanosensitivity is identified, physiotherapists avoid aggressive stretching that increases nerve ischemia. Instead, oscillatory sliding techniques (nerve flossing) restore longitudinal mobility.
- Sciatic Nerve Sliders (Gentle Phase): Seated on a chair: as you extend your knee and point your toes upward, tilt your head backward into cervical extension. As you bend your knee back, bring your chin to your chest. The nerve slides without experiencing tension.
- Repetition and Frequency: Perform 10 to 15 slow, rhythmical repetitions 2 to 3 times daily. Movements must remain pain-free or produce only mild transient sensation that resolves instantly.
- Contraindications to Neurodynamic Mobilization: Do not perform neural flossing during progressive neurological deficits (foot drop, loss of deep tendon reflexes, or bladder dysfunction requiring emergency surgical review).
Frequently asked clinical questions
Is the Slump test more sensitive than the Straight Leg Raise (SLR)?
Yes. Clinical systematic reviews report the Slump test has a sensitivity of approximately 83% compared to 64% for the standard Straight Leg Raise test. It is particularly useful for detecting mild or subtle nerve root adhesions that escape detection during supine testing.
Can neural flossing make sciatica worse?
Aggressive neural tensioning during the acute inflammatory phase of a disc herniation can aggravate nerve root edema. Patients should begin with low-amplitude neural sliders under professional physiotherapy supervision.
Evidence sources and clinical references
- Maitland Physiotherapy: Peripheral and Spinal Neurodynamics: https://elsevier.com
- Spine Journal: Diagnostic accuracy of neurodynamic testing for lumbosacral radiculopathy: https://thespinejournalonline.com
- Indian Association of Physiotherapists: Clinical Standards for Spine Care: https://physiotherapyindia.org
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