Research Review By Dr. Joshua Plener©


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Date Posted:

July 2022

Study Title:

Extending the straight leg raise test for improved clinical evaluation of sciatica: validity and diagnostic performance with reference to the magnetic resonance imaging


Pesonen J, Schacklock M, Suomalainen J, et al.

Author's Affiliations:

Department of Rehabilitation Kuopio University Hospital; Department of Surgery, University of Eastern Finland; Neurodynamic Solutions, Adelaide, Australia

Publication Information:

BMC Musculoskeletal Disorders 2021; 22: 808.

Background Information:

Low back pain is a common cause of disability, and similar to other conditions, reliable and accurate tests should be used in a clinical setting when possible (1, 2). MRI is commonly used for individuals who have low back pain with radiating leg pain to determine if a lumbar disc herniation causing nerve root compression is present. However, even though considered a gold standard by some, MRIs have a high false positive rate, which could lead to unnecessary treatment.

In clinical practice, the straight leg raise (SLR) is a physical examination test that is commonly utilized and has been shown to have high sensitivity, but low specificity, for the detection of a lumbar disc herniation (3, 4). This generally means we can use the SLR to “rule out” a lumbar disc herniation (via negative SLR) but not to “rule in” this condition. Previous research has attempted to modify the traditional SLR to increase its diagnostic properties by adding a structural differentiation movement of hip internal rotation or ankle dorsi flexion, termed the extended SLR (5).

Extended SLR procedure and interpretation:
For the extended SLR maneuver, the patient lies supine on the examination table with the examiner passively lifting the subjects’ leg with their knee fully extended, hip in neutral rotation and ankle hanging freely. The leg is raised until the first symptoms appear or the subject’s ongoing symptoms in their lower extremity are aggravated by 30%. If the leg reaches hip flexion of 90 degrees with no response in their leg, the test is considered negative.

If the subject has a lower limb response, in order to determine if the response was due to neural or MSK origin, a location specific structural differentiation movement is added, which is selected based on the location of the symptoms. If symptoms are located distally below the knee, hip internal rotation is performed at the same degree of hip flexion of the evoked response, and for symptoms provoked proximally in the buttock and/or hamstring area, ankle dorsiflexion is performed, which was similar to the Braggards test (9). The extended SLR is considered positive if the differentiating movement increases the subject’s evoked symptoms.

The extended SLR is different from the traditional SLR in three ways:
  1. The evoked response does not need to reach below the knee
  2. The lower limb response does not need to emerge before 70 degrees but can happen anywhere from 0 to 90 degrees of hip flexion
  3. There is a structural differentiation maneuver added to the traditional SLR test
Previously, the extended SLR has demonstrated perfect interrater reliability between examiners in detecting sciatica patients (5). This current study aims to investigate whether the extended SLR is associated with pathological findings on MRI, in order to determine its usefulness for clinical decision making.

Pertinent Results:

40 subjects made up the study population, with 25 women and 15 men with an average age of 41. There were 28 lumbar disc herniations identified in the study and 25 neural compressions were visible on MRI scans.

In the sciatica patient group, 10/20 were judged negative on the traditional SLR due to hip flexion reaching over 70 degrees or the symptoms not reaching below the knee. However, among the positive extended SLR subjects, 17/20 had a lumbar disc herniation and 15/20 had nerve root compression noticeable on MRI scans. In the extended SLR negative group, 11/20 had a lumbar disc herniation on MRI and 10/20 showed nerve root compression.

A positive extended SLR finding was strongly associated with a lumbar disc herniation and neural compression, as the odds ratio for lumbar disc herniation was 8.0 (95% CI 1.3-51.2) and 5.6 (95% CI 1.1-29.0) for neural compression, which were statistically significant. For the comparison of the extended SLR and MRI findings of a lumbar disc herniation, the sensitivity was 0.61 and specificity 0.75, with the traditional SLR having a sensitivity of 0.32 and specificity of 0.92. For the comparison of the extended SLR and MRI findings of neural compression, the sensitivity was 0.60 and specificity 0.67, with the traditional SLR having a sensitivity of 0.28 and specificity 0.80.

Clinical Application & Conclusions:

Overall, this study demonstrated that the extended SLR is strongly associated with a lumbar disc herniation and nerve root compression on MRI. However, there is (still) poor overall agreement between MRI findings and the extended or traditional SLR, due to the high incidence of false positive findings on MRI.

The results of this study help to suggest that the extended SLR detects a subgroup of low back pain and sciatica patients that have a functional disturbance in the nerve root, such as mechanical sensitivity, chemical inflammation and/or impairment of movement. However, it does not identify any specific pathology. Therefore, the extended SLR appears to show greater ability to determine if a patient is suffering from sciatic nerve involvement, but doesn’t demonstrate superior outcomes for the use of this test in clinical practice to “rule in” a lumbar disc herniation and/or nerve root compression on MRI.

Reviewer Comment: For low back pain patients, structural differentiation movements appear to help determine if symptoms are arising from the neural structures. In this study, the MRI was used as the reference standard, but the utility of the MRI being used in this manner has been criticized for its high incidence of asymptomatic findings (6-8). This study demonstrates relatively low sensitivity and specificity values, which means you cannot confidently rule lumbar disc herniations and neural compression in or out. Utilizing a reference standard of clinical symptoms in addition to MRI findings may change the results and demonstrate a higher sensitivity and specificity. At this time, evaluation of the extended SLR with a better reference standard would be worthwhile in order to further assess the utility of this test.

Study Methods:

Forty subjects participated in this study, with 20 in the sciatic/symptomatic group and 20 in the control group, which consisted of low back pain patients and hip pain patients. The subjects were recruited consecutively from an institutional spine center, with participants allocated to their study group based on a combination of patient history, symptoms and clinical findings.

Sciatic symptomatic group – inclusion criteria:
  • Combination of sciatic symptoms and clinical findings indicative of sciatica
  • Positive extended SLR during the clinical examination
  • Radiating pain to the lower limb, either below or above the knee
Control group – inclusion criteria:
  • Local low back pain, greater trochanteric/hip/groin pain, with or without hamstring tightness
  • No signs of sciatica during the clinical examination with a negative extended SLR and no neurological findings indicating radiculopathy
Following group allocation, two independent blinded examiners completed the interrater reliability of the extended SLR, after which the subject’s MRI of their lumbar spine was evaluated and traditional SLR results were retrieved from the patient’s medical records.

Sample Size:
A sample size of 40 was utilized as reliability studies recommend a sample size of 40 for the Kappa statistic to be significantly greater than 0.4, which was the value of the null hypothesis.

MRI results were classified according to a 5-point scale, whereby grade 4 and 5 were deemed positive for nerve root compression as they indicate possible nerve root compression and definite nerve root compression respectively (10). For the definition of a lumbar disc herniation, the Combined Task Force classification was used, which required a lumbar disc extrusion, herniation or sequestration to be visible at the L4/5 or L5/S1 discs on a subject’s MRI scan (11). MRI images were analyzed independently and blinded from the patient’s clinical findings by 2 senior radiologists and a spine specialist clinician. If there was a difference in the initial interpretation of the images, a consensus for if a lumbar disc herniation or nerve root compression was present was determined through consultation of the two examiners.

Outcomes of interest:
The prevalence of lumbar disc herniation and nerve root compression was calculated within the study groups. The outcomes of the extended SLR and traditional SLR were compared with MRI results and cross tabulated to determine sensitivity and specificity values. Cohen’s Kappa Statistic was used to assess the agreement between the MRI and the extended SLR and traditional SLR results, with 95% confidence intervals calculated. To assess the association between the extended and traditional SLR results and findings on the MRI, odds ratios were calculated for lumbar disc herniation or nerve root compression using a binary logistic regression analysis adjusted with subjects age, gender, height and weight. The extended SLR test’s validity was determined based on its result of interrater agreement, determined by Cohen’s Kappa, and the prevalence of both lumbar disc herniation and nerve root compression.

Study Strengths / Weaknesses:

  • This study helps to provide a complete picture on the utility of the extended SLR in clinical practice as the reliability of this test has previously been reported (we reviewed that paper in 2021 on RRS).
  • This study is starting to uncover an alternate process to help identify leg pain arising from sciatic nerve irritation/compression, which is much needed.
  • Even though the desired sample size was reached, the study did have a relatively small sample size.
  • The traditional SLR was performed by a treating physician and not by blinded examiners.
  • There may have been a better reference standard that could have been used to determine the psychometric properties of the extended SLR, such as clinical symptoms in addition to imaging findings.

Additional References:

  1. James SLG, Abate D, Abate KH, et al. Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet 2018.
  2. Maher C, Underwood M, Buchbinder R. Non-specific low back pain. Lancet 2017.
  3. Ekedahl H, Jönsson B, Annertz M, et al. Accuracy of clinical tests in detecting disk herniation and nerve root compression in subjects with lumbar radicular symptoms. Arch Phys Med Rehabil 2018.
  4. van der Windt, D A, Simons E, Riphagen II, et al. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane Database Syst Rev 2010;(2): CD007431.
  5. Pesonen J, Shacklock M, Rantanen P, et al. Extending the straight leg raise test for improved clinical evaluation of sciatica: reliability of hip internal rotation or ankle dorsiflexion. BMC Musculoskelet Disord 2021.
  6. Brinjikji W, Luetmer PH, Comstock B, et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR Am J Neuroradiol 2015; 36: 811–6.
  7. Chou R, Fu R, Carrino JA, et al. Imaging strategies for low-back pain: systematic review and meta-analysis. Lancet 2009.
  8. Pesonen J, Rade M, Könönen M, et al. Normalization of spinal cord displacement with the straight leg raise and resolution of sciatica in patients with lumbar intervertebral disc herniation: a 1.5-year follow-up study. Spine 2019.
  9. Buckup K. Bragard Test. In: Buckup K, editors. Clinical Tests for the Musculoskeletal System. Stuttgart: Thieme; 2008. p. 59–60.
  10. van Rijn JC, Klemetsö N, Reitsma JB, et al. Observer variation in MRI evaluation of patients suspected of lumbar disk herniation. AJR Am J Roentgenol 2005.
  11. Fardon DF, Williams AL, Dohring EJ, et al. Lumbar disc nomenclature: version 2.0: Recommendations of the combined task forces of the North American Spine Society, the American Society of Spine Radiology and the American Society of Neuroradiology. Spine J 2014.

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