Introduction

Knowing the reliability of the commonly used straight leg raise (SLR) test to detect radicular pain is important to use it consistently in clinical practice. Earlier systematic reviews have found that the SLR performs poorly in diagnosing lumbar radicular pain. An often overlooked problem with the SLR is that it may give a ‘positive’ outcome due to irritation of non-neural tissues. This may be part of the problem of why the SLR often has a poor diagnostic value, as stated by systematic reviews. Therefore, structural differentiation maneuvers are proposed to distinguish real neural tissue irritation from non-neural tissue sensitivity. The authors wanted to update the previous systematic review and thereby included the reliability of the SLR with structural differentiation.

Methods

A systematic review with meta-analysis was conducted including people older than 16 years who had low-back-related leg pain. Participants from any clinical setting could be included. The findings of the review were subdivided into patients presenting with low back-related leg pain and “mixed” samples of patients. The review followed the recommended PRISMA guidelines and the protocol was prospectively registered.

The interpretation of reliability coefficients to interpret the reliability of the SLR was as follows:

• 0.81 to 1.00 = substantial; 
• 0.61 to 0.80 = moderate; 
• 0.41 to 0.60 = fair; 
• 0.11 to 0.40 = slight; and 
• 0.00 to 0.10 = virtually none

Results

Meta-analysis revealed moderate inter-rater reliability in patients with low back-related leg pain and substantial reliability in a mixed sample of patients when the SLR was conducted with structural differentiation. (fig. 3a & 3b)

In a mixed sample, the inter-rater reliability was fair when the SLR provoked symptoms arose when the test was performed without structural differentiation. (fig. 4b).

Provoked pain below the knee showed fair inter-rater reliability when the SLR was performed without structural differentiation in a mixed sample. (Fig. 5)

When the SLR without structural differentiation provoked pain in the lower back and/or lower extremities, inter-rater reliability was fair in a mixed sample (fig. 6b).

The GRADE gives an idea about the confidence in the evidence and revealed that a positive SLR with structural differentiation had a moderate certainty in both the low back-related leg pain and mixed samples. Other conclusions drawn from the meta-analyses were from very low-certainty evidence.

Little less talking about the conclusions: what do they mean in practical terms? Structural differentiation to distinguish if the symptoms are truly attributable to irritation of nerve roots increases the reliability between different examiners compared to when it is performed without the differentiation. The SLR with differentiation reached moderate to substantial reliability as seen from the Kappa values and can therefore be used interchangeably between different examiners. When no such differentiation maneuver is performed, the reliability of the SLR drops. For the crossed SLR, no meta-analysis was possible, thus here the evidence remains inconclusive. The same was true when examining the reliability for the onset of pain below a certain ROM (for example below 75° of hip flexion).

Questions and thoughts

The study included participants “who presented with low back-related leg pain”. It is however unclear how they defined the relatedness of the leg pain with the lower back.

Participants from any clinical setting could be included. When looking at the settings where the included studies took place, it became clear that an important proportion of patients studied were in hospital/specialized clinics or referred by their general practitioner (and were thus not only seen in primary care). This may limit generalizability to patients seen in primary care or where direct access to physiotherapy is possible. The authors further state that “in participants with low back-related leg pain, the applicability of reliability data for identifying a positive SLR or crossed SLR was limited by most participants having severe symptoms that required hospitalization or bed rest. Thus, it seems this systematic review included patients with a more severe profile, which may overestimate the clinical utility of the findings. Let’s say, a blazing fire is easier to spot than a smoldering one. Patients with high symptomatology will be easier to diagnose than those with less evident symptoms.

Talk nerdy to me

The review was prospectively registered on PROSPERO and the GRADE framework was used to rate the confidence in the evidence. Other good methodological aspects were the use of different researchers to independently screen for full texts, extract data, and rate the risk of bias. Reference lists were searched, but not grey literature, unfortunately. Fifteen studies were included, but the meta-analyses included typically 2 but no more than 4 studies per meta-analysis with an overall limited number of participants, and this may be a limitation.

Using GRADE, the evidence could be downgraded due to the risk of bias, inconsistency, indirectness, or imprecision. Due to the risk of bias and due to indirectness, the evidence for the SLR with structural differentiation was downgraded from high to moderate confidence in samples with low back-related leg pain and mixed samples respectively.

In this review, we only discussed the findings that came forward from meta-analyses. This is due to the fact that the included studies had some methodological concerns (for example, they did not report about blinding of the raters). This also implies that the findings highlighted here display the most robust conclusions of the systematic review.

Take home messages

Structural differentiation maneuvers, like flexion of the neck, ankle dorsiflexion, or hip adduction, when added to the SLR show moderate to substantial inter-rater reliability in patients with low back-related leg pain and in mixed samples of participants. If the SLR is performed without structural differentiation, the meta-analyses reveal that the reliability is only fair. Therefore, to increase the reliability, you’d better add a structural differentiation to your classical SLR. No meta-analysis was possible for the crossed SLR, nor for SLR-provoked pain below a certain ROM threshold, and the evidence, therefore, remains inconclusive. If you want to read more about these structural differentiation maneuvers, we recently published another research review discussing the reliability when adding hip internal rotation or ankle dorsiflexion as differentiations to the SLR. You can read it at the following link: https://www.physiotutors.com/research/two-structural-differentiation-manoevres/

Reference

Nee, R. J., Coppieters, M. W., & Boyd, B. S. (2022). Reliability of the straight leg raise test for suspected lumbar radicular pain: A systematic review with meta-analysis. Musculoskeletal Science and Practice, 59, 102529.