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April 2022

Reliability of the straight leg raise test for suspected lumbar radicular pain: A systematic review with meta-analysis

Nee R, Coppieters M & Boyd B

Department of Physical Therapy, Samuel Merritt University, Oakland CA, USA; Menzies Health Institute Queensland, Griffith University, Australia; Amsterdam Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, the Netherlands

Musculoskeletal Science and Practice 2022; 59:102529.

Clinical practice guidelines recommend clinicians use the passive straight leg raise (SLR) test to assist in detecting radicular pain in low back pain patients, while a positive crossed SLR may indicate pain secondary to a lumbar disc herniation (1-3). When performed, the SLR mechanically provokes irritated lumbosacral nerve roots, resulting in radicular pain (4). However, when performing the SLR, symptoms related to the irritation of non-neural tissues may also occur, and structural differentiation techniques are required to help distinguish symptoms arising from neural tissue vs. non-neural tissue irritation. To review (we reviewed a paper on this on RRS in 2021), structural differentiation can be accomplished via the extended SLR (ESLR) test, which is performed using the same fundamental technique as the traditional SLR. The leg is lifted passively towards 90 degrees with the hip neutral and the knee in full extension, as per the standard SLR test. When a response is evoked, the tester internally rotates the hip or dorsiflexes the ankle, based on the location of the evoked response – that is, whether proximal (buttock/hamstring) or distal (below the knee). The additional movement is designed to focus on nerve movement without moving adjacent musculoskeletal structures. To clarify, in patients reporting symptoms in the gluteal or hamstring region, the additional movement is passive ankle dorsiflexion, to a maximum of 90 degrees of dorsiflexion (referred to as distal structural differentiation for proximal symptoms – putting more strain in the sciatic nerve without further stretching the hamstrings). Hip internal rotation is utilized when the patient reports symptoms below the knee (proximal differentiation for distal symptoms – stressing hip musculature without further tensioning the sciatic nerve).

Despite clinical practice guidelines recommending the use of SLR testing, systematic reviews suggest that the SLR performs poorly when diagnosing lumbar radicular pain (2, 5-7). One possibility for this is insufficient reliability, which may contribute to inconsistent patient categorization and lead to inaccurate expectations about the management of these patients’ symptoms.

This systematic review aimed to provide an updated summary of the SLR and crossed SLR reliability in patients with suspected lumbar radicular pain.

Four studies reported reliability on the SLR or crossed SLR in three distinct samples of participants with low back related leg pain. Regarding the QAREL assessment, only 2 out of the 4 studies clearly prevented an order effect by varying the order of raters, and only two of the four studies clearly ensured each participant’s condition remained stable by using a suitable time interval between examinations.

Eleven studies reported reliability in 14 distinct “mixed” samples of participants with low back related leg pain or low back pain only. Regarding the QAREL assessment, two main issues that were identified in these studies included the fact that only 5/11 studies varied the order of raters and used structural differentiation techniques to categorize the SLR as positive or negative. As well, only 3/11 studies blinded raters to other clinical information and no studies were clear about blinding raters to additional cues about participants.

Overall, the confidence in the inter-rater reliability when a positive SLR induced provocation of lower extremity pain or symptoms was moderate to very low. Furthermore, confidence in the inter-rater reliability for identifying a positive crossed SLR was moderate to very low.

SLR Provoking Symptoms WITH Structural Differentiation:
The meta-analysis showed moderate inter-rater reliability for identifying a positive SLR based on provocation of symptoms that changed with structural differentiation in patients with low back related leg pain. In addition, a meta-analysis showed substantial inter-rater reliability for this definition of a positive SLR in “mixed” samples of participants.

SLR Provoking Symptoms WITHOUT Structural Differentiation:
The intra-rater reliability for identifying a positive SLR based on provocation of symptoms without structural differentiation in patients with low back related leg pain was moderate to substantial, and the inter-rater reliability was slight to moderate. In addition, a meta-analysis showed fair inter-rater reliability for this definition of a positive SLR in mixed samples of participants.

Only studies evaluating a “mixed” population were identified and a meta-analysis showed fair inter-rater reliability.

SLR Provoking Low Back and/or Lower Extremity Pain WITHOUT Structural Differentiation:
One study reported slight inter-rater reliability for identifying a positive SLR based on provocation of lower extremity pain without structural differentiation in patients with low back related leg pain.

Two studies assessed “mixed” samples of participants assessing intra-rater and inter-rater reliability for identifying a positive SLR based on provocation of pain in the buttock or more distally, and inter-rater reliability when a positive SLR was defined as provocation of back and lower extremity pain. The intra-rater reliability was rated as moderate and inter-rater reliability was rated as fair.

SLR Provoking Pain Below a ROM Threshold WITHOUT Structural Differentiation:
One study reported fair inter-rater reliability for identifying a positive SLR based on pain provocation below 45 degrees of hip flexion in low back related leg pain patients. One study reported fair inter-rater reliability for identifying positive SLR based on pain provocation below 75 degrees in a mixed sample of participants.

Crossed SLR:
Intra-rater reliability for identifying positive crossed SLR based on provocation of low back and/or lower extremity symptoms in patients with low back related leg pain was moderate to substantial, and inter-rater reliability was fair to moderate. The inter-rater reliability for this definition of a positive crossed SLR in two mixed samples of participants was virtually none to moderate.

Measuring SLR ROM:
One study reported moderate to substantial inter-rater reliability for measuring SLR ROM in asymptomatic and symptomatic limbs respectively for low back related leg pain.

Three studies reported intra-rater or inter-rater reliability for measuring SLR ROM in a mixed sample study. Intra-rater reliability was substantial, with an intra-session smallest detectable difference at a 95% confidence level value of 6.1 degrees, and inter-rater reliability was substantial with an intra-session smallest detectable difference at a 95% confidence level value of 17.7 degrees.

This systematic review summarized the reliability of SLR and crossed SLR in patients with suspected lumbar radicular pain. In low back related leg pain samples, reliability data was limited by small samples and the fact that most participants having severe symptoms that warranted hospitalizations or bed rest (in other words, not the typical patients we would see in a chiropractic office!).

The overall confidence in the evidence for definitions of a positive SLR or crossed SLR commonly used to detect lumbar radicular pain was moderate to very low. Inter-rater reliability for identifying a positive SLR was moderate for low back related leg pain samples to substantial for mixed samples when a positive test provoked the patient’s symptoms and those symptoms changed with structural differentiation techniques. Large errors occurred when different clinicians measured SLR range of motion on the same patients.

Previous reviews stated that the SLR performs poorly in diagnosing lumbar radicular pain (2, 5-7). The most common definition used in previous literature for a positive test was provocation of pain/symptoms below the knee and these reviews did not address whether structural differentiation impacted diagnostic performance. In this current review, the poor diagnostic performance doesn’t appear to be a result of limitations in SLR reliability, as this review demonstrates provoking pain below the knee without structural differentiation had fair reliability, while provoking a patient’s specific symptoms and changing those symptoms with structural differentiation had at least moderate reliability.

Overall, the reliability data of the SLR suggests that clinicians should use structural differentiation manoeuvres during SLR testing. There is a lack of clarity about crossed SLR reliability and therefore this test should be interpreted cautiously. In addition, measurement error likely prohibits using SLR ROM for clinical decision making.

Eligibility Criteria:
Study participants were 16 years of age or older presenting with low back related leg pain in any clinical setting. The SLR with or without structural differentiation and the crossed SLR could be performed in isolation, or as part of a clinical examination of low back related leg pain. Included studies could assess the reliability of identifying a positive SLR or crossed SLR, or measure SLR range of motion. Studies needed to be English, peer reviewed publications, and report reliability data. During the SLR maneuver, provocation of lower extremity symptoms or pain had to be part of the definition of a positive test.

Studies that focussed on conditions associated with neuropathy other than lumbar radicular pain, such as diabetic neuropathy, were excluded.

Study Identification and Selection:
MEDLINE and CINAHL were searched for studies published before April 2021. Two reviewers screened the articles with reference lists of included studies and previously published systematic reviews as well.

Risk of Bias Assessment:
Two reviewers independently assessed risk of bias using the Quality Appraisal Tool for Studies of Diagnostic Reliability (QAREL). In particular, for QAREL item 9, repeated measures needed to occur within 24 hours and for intervals greater than 24 hours, data had to demonstrate participants symptoms status was similar at each measurement session. Furthermore, for QAREL item 10, studies investigating reliability of identifying a positive SLR, needed to incorporate structural differentiation into testing.

Reliability Outcomes:
Reliability coefficients were interpreted as substantial (0.81 to 1), moderate (0.61 to 0.80), fair (0.41 to 0.60), slight (0.11 to 0.4) and virtually none (0 to 0.10) (8).

Data Analysis:
Meta-analyses were performed when similar criteria were used to interpret SLR or crossed SLR responses in two or more similar samples.

GRADE was used to assess the confidence in the estimates of inter-rater reliability for identifying a positive SLR or crossed SLR. GRADE was used to assess the evidence based on risk of bias, inconsistency, indirectness or imprecision.