Study of the Diagnostic Accuracy of the Neurodynamic Tests in Patients With Lumbar Radiculopathy

Background and justification Background Lumbar radiculopathy is a relevant cause of disability and morbidity and may constitute between 23 and 57% of the cases of patients with low back pain and represents an important expense due to the sick leave and health care that may be required. It is a pathological process that can affect different lumbar roots and can cause radiating symptoms that manifest in the territory of the lower limb that includes this root. Some studies estimate the prevalence in the general population to be between 1.6 and 13.4%, with the predominant age range being between 45 and 64 years of age and affecting men more frequently than women.

Protrusion or migration of the lumbar intervertebral disc is the most common cause of nerve root irritation and subsequent radiculopathy. Disc herniation is define as a localised displacement of disc material beyond the normal margins of the intervertebral disc space resulting in pain, weakness or numbness in a myotomal or dermatomal distribution.

In clinical practice, the diagnosis of lumbar radiculopathy involves the use of several tools and procedures including neuropathic pain screening, clinical neurological examination, electro-diagnostic, nerve root block and radiological imaging. The gold standard for the diagnosis of lumbar disc herniation is surgery; however, when assessing the validity of subjective tests or physical examination findings, the use of cross-sectional imaging as a gold standard may be considered an acceptable substitute, always bearing in mind that the results of any imaging test should be closely correlated with the clinical examination.

Many clinical guidelines advise muscle strength testing, sensory testing and different neurodynamic tests for the diagnosis of lumbar disc herniation with radiculopathy.

Neurodynamic tests represent a structured sequence of movements aimed at increasing the mechanical stress on the neural tissue, and are now an important aspect of the physical examination of the patient when there is suspicion of neural involvement, allowing assessment of the physiological and mechanical capabilities of the nerve. These neurodynamic tests include the mechanism of structural differentiation that allows a specific assessment of neural tissue and makes it possible to rule out a musculoskeletal origin of the patient's symptoms.

When used in isolation, the diagnostic performance of most physical tests (muscle weakness or paresis, muscle atrophy, impaired reflexes, sensory deficits) is poor. Some tests (forward flexion, hyperextension test and Slump test) perform slightly better, but the number of studies is small.

Rapid and accurate clinical diagnosis is essential in the management of these patients in order to decide on the correct treatment.

Justification The clinical manifestations caused by a herniated disc are derived from the possible involvement of the nerve root, and neurodynamic tests could presumably help us to detect the pathology by testing neural mechano-sensitivity. Neurodynamic tests are interpreted using structural differentiation, range of motion and sensory responses as the location or quality of symptoms in relation to the contralateral limb and compared with normalisation results in healthy populations. However, existing studies of the Straight Leg Raise test are not very sensitive and those of the Slump test with better sensitivity results are very scarce.

Once symptoms compatible with nerve root involvement due to disc herniation are found, the test of choice to diagnose the pathology is magnetic resonance imaging. Nerve conduction tests are also effective to see the real neural involvement that radiculopathy may be causing, but these complementary tests may take a long time or even be inaccessible, and early treatment may be essential.

The two neurodynamic tests that have been shown to modify tension and/or generate forces on lumbar nerve roots are the Straight Leg Raise test and the Slump test. However, many studies to date have concluded that these tests have low sensitivity and specificity. The causes of this low validity could be the ambiguity of the diagnostic criteria including the modification of symptoms with structural differentiation, which is essential for a correct interpretation of the test and subsequent diagnostic suspicion. Most existing studies on the diagnostic accuracy of these neurodynamic tests do not include structural differentiation in their diagnostic criteria.

However, neurodynamic tests are an affordable, simple and quick tool available to all clinicians trained in neurodynamics. By defining the diagnostic criteria more precisely and using magnetic resonance imaging as the gold standard, the validity of these neurodynamic tests could be improved, making them useful diagnostic tools in clinical contexts.

A rapid diagnosis could ensure the good evolution of the patient by reducing the time to decide on the treatment to be carried out.

Hypothesis The Neurodynamic Straight Leg Raise and Slump tests with precise diagnostic criteria are valid tools for the diagnosis of lumbar radiculopathy.

Objectives Main objective To study the diagnostic accuracy of the Slump and Straight Leg Raise neurodynamic tests in patients with lumbar radiculopathy.

Secondary objectives

• To analyse the diagnostic accuracy of the Slump test with structural differentiation in the detection of lumbar radiculopathy.
• To analyse the diagnostic accuracy of the straight leg raise test in the detection of lumbar radiculopathy.
• To compare the diagnostic accuracy of the Slump test versus the Straight Leg Raise test in this pathology.
• To study the diagnostic validity of the Slump test including nerve conduction tests together with the standard MRI pattern.

Procedure The patient who is prescribed the nerve conduction test and who has undergone or is awaiting an MRI scan will be informed of the possibility of participating in the study and those who agree to participate voluntarily will sign the informed consent form.

Once the consent has been signed, data will be collected from the patient's clinical history. The assessor will take the data from the patient's history and exclude those who do not meet the inclusion/exclusion criteria. Age, sex, weight and height shall be recorded in the medical record.

The assessor will perform the neurodynamic straight leg raise test with the Bragard manoeuvre, the Slump test and the modified Slump test. In addition, each patient will complete the pain scales for neuropathic pain assessment (DN4), the Oswestry Low Back Pain Disability Scale and the Visual Analogue Scale (VAS), recording the data from these tests.

The physiotherapist in charge of performing the tests will not know the results of the imaging tests.

The Straight Leg Raise test or also known as the Lasègue test is performed with the patient in the supine position and, without moving the spine, the leg is passively raised while maintaining knee extension until symptoms appear. The test is considered positive if the patient does not reach an amplitude of 70° of hip flexion and this amplitude is different with respect to the other limb, no structural differentiation is specified to rule out muscular structures. The classic Lasegue test repeated the manoeuvre with knee flexion and hip flexion, and was considered positive if the second manoeuvre did not reproduce the symptoms and the first did. In the study the investigators will perform the Straight Leg Raise test with the addition of the Bragard manoeuvre which involves dorsiflexion of the ankle and involves more pretension of the neural system and with structural differentiation.

The Slump test adds tension on all lumbar nerve roots and includes the mechanism of structural differentiation as opposed to the classic Straight Leg Raise test. The test is performed in a seated position, with flexion of the cervical, dorsal and lumbar spine. The physiotherapist extends the patient's knee to the presence of symptoms and, depending on the region of symptoms, a remote joint movement is performed to establish a differential diagnosis between pain of musculoskeletal origin and pain of neural origin. The modified Slump test to further pretension the sciatic nerve involves maximum lumbar flexion, contralateral lumbar tilt of the roots to be assessed and internal hip rotation of the homolateral limb.

Diagnostic criteria for neurodynamic tests. The test is considered positive if the structural differentiation is positive and any of these criteria are met:

• It reproduces the patient's symptoms.
• It produces symptoms with decreased range of motion with respect to the other limb.
• It produces symptoms with asymmetry in the location or type of symptom perceived with respect to the other limb.

Statistical analysis All data analysis will be performed with IBM SPSS Statistics (Version 21.0.0.0). For the descriptive analysis of quantitative variables, indices of central tendency and indices of dispersion will be used. For qualitative variables, a study of frequencies will be carried out to find out what percentage of them are present.

Prior to the study, quantitative variables will be analysed to determine normality using the Kolmogorov-Smirnov test.

For the validity study, the sensitivity, specificity, predictive values and probability ratios of the Slump test and the Straight Leg Raise test will be calculated. Contingency tables 2x2 will be drawn up for the results of each of the tests, with their diagnostic criteria, with the MRI and electrophysiological tests. A 95% confidence interval will be established for these values.

Ethical aspects The study to be carried out does not involve any invasive procedure and does not pose any risk to the subjects participating in it. In the performance of the neurodynamic tests, the symptoms that the patient already has due to the neural response of the test can be reproduced.

Subject data will be coded in such a way that no personal patient data will be included in the study database and no one other than the investigators will have access to the database.

Participants will not receive financial or other compensation for their participation in the study.

All participants will be informed in writing, by means of an information sheet, and will be required to sign the informed consent form.

Timeline The project will start once it receives the approval of the Clinical Research Ethics Committee of Aragon (Spain). Subjects will be scheduled according to their availability and that of the investigators. Fieldwork is expected to last 1-2 years. Subsequently, data will be analysed and published in an estimated period of 1 year.

Budget The project has no funding. The materials used belong to the principal investigator and the clinical neurophysiology service of the Hospital Clínico Universitario Lozano Blesa located in the city of Zaragoza (Aragón, Spain).