Introduction

The straight leg raise (SLR) is a test frequently applied in clinical practice, but its diagnostic properties leave areas for improvement. The classical SLR test stresses the sciatic nerve but tissues surrounding the course of the sciatic nerve also get tensed. Therefore, a positive SLR means more than solely a lumbar disc herniation as was thought before, and nowadays this test is used as a test to assess neural mechanosensitivity. The authors described two structural differentiation maneuvers for the extended SLR (ESLR) to distinguish neural from musculoskeletal problems and tested its interrater reliability to ascertain if hip internal rotation and ankle dorsiflexion would produce consistent responses in patients with LBP, with and without sciatica.

Methods

Forty subjects presenting to the authors’ institutional spine center were included in the study, twenty of them in the sciatica group and the other half in the control group. All of them were examined by a study controller with a complete clinical examination and a thorough patient history. The criteria for sciatic symptoms were defined as having unilateral leg pain, worse than back pain, the appearance of clinical neurological deficits in muscle strength and/or skin sensation, and reflexes) and positive neural tension test signs including straight leg raise (SLR) and extended SLR (ESLR). The control group subjects had pain in the low back, greater trochanter, and/or hip with or without tightness in the posterior thigh.

The ESLR was performed as the classical SLR but two adaptations were implemented. When the patient’s symptoms were provoked, two structural differentiation maneuvers were performed. With the provocation of symptoms in the gluteal or hamstring region, the differentiation was passive ankle dorsiflexion, while hip internal rotation was used in case pain was provoked in the calf. It was explained that this stresses the nerve more without moving the adjacent musculoskeletal tissues. For example, with calf pain arising, hip internal rotation does not increase the tension on the calf muscles, which may trouble the interpretation of the result as it may increase discomfort. Rather, it increases tension on the sciatic nerve and moves the nerve without moving the calf muscles.

The ESLR was considered positive when the two structural differentiation maneuvers led to an increase in the subject’s symptoms, and negative when the differentiation led to no increase of symptoms or in case no symptoms arose before or at 90° of hip flexion. The outcomes of interest were interrater agreement, the overall agreement between the ESLR and the traditional SLR. Kappa values were used to express these outcomes.

Results

Forty subjects were included in the study with a mean age of 41 years (range: 22-64 years). The mean ESLR angle for the sciatic group was 60 ± 19° (range 30°- 85°) while the control group’s mean ESLR angle was 84° ± 8° (range 70°- 90°).

The overall agreement was 92.5%. Examiners 1 and 2 had an almost perfect agreement with a kappa of 0.85. The overall agreement between the different examiners and the study controllers was high: 92.5%, 95%, and 97.5%. The prevalence of sciatic symptoms was high, with nearly half of the included patients (48.75%) showing these signs and symptoms.

Questions and thoughts

When the ESLR was compared to the traditional SLR, the agreement was not perfect: 0.50 (range 0.27-0.73). All patients with a positive ESLR were not considered positive with the execution of the classical SLR. Six out of twenty subjects of the sciatic group had negative SLRs due to the hip flexion angle reaching over 70 degrees, and four out of twenty were negative as the evoked symptoms with the traditional SLR were limited to the hamstring and/or gluteal region. This could mean that the ESLR may be more valuable as it can differentiate better between symptoms of neural and musculoskeletal origin, especially since the agreement between the examiners was rather high.

The results should however be interpreted with some caution as the subjects were recruited from a spine clinic. As you can see from the high prevalence (nearly 50%!), we should assume that these outcomes are not widely generalizable to common physiotherapy practice where much lower prevalences may be expected.

“The moderate agreement found between ESLR and traditionally performed SLR does indicate the potential of ESLR in integrative interpretation as to clear ambiguousness found in traditional SLR testing, especially in situations in which traditional SLR is eliciting symptoms over 70 degrees and when reproduction of symptoms does not occur below the knee.”

Talk nerdy to me

No reference standard was used, and this may be considered a limitation. Instead, a thorough anamnesis, together with the evaluation of the clinical signs and symptoms was conducted. However, the aim of this study was not to compare the diagnostic accuracy, but rather reflect on the interpretation of different examiners, and therefore the lack of a reference standard does not pose a problem.

Importantly, the appearance of a positive test cannot tell you about the exact source of symptoms, as many mechanisms can lead to increased neural sensitivity. However, it appears that the ESLR may be of use to differentiate between musculoskeletal and neural causes of sciatica(-like) symptoms. These differentiations were based on scientific studies examining the effects of these segmentations on the movement of the sciatic nerve.

Another good aspect of the differentiation procedure is that it may identify neural symptoms in the upper leg, whereas the classical SLR requires a reproduction of symptoms below the knee in order to be considered positive.

A limitation of the present study lies in the fact that the traditional SLR was performed by an unblinded physician. The recruitment of subjects in a specialized spine center severely influences the prevalence of sciatica, and therefore these results are not directly generalizable to common physiotherapy practice.

Take home messages

The present study showed that the interobserver agreement of the ESLR is high. Although no information on the diagnostic accuracy is present, the ESLR with its two structural differentiation maneuvers as described in this study may be of value to differentiate between symptoms of neural or of musculoskeletal origin when evaluating a patient with suspected sciatica.

Reference

Pesonen, J., Shacklock, M., Suomalainen, J. S., Karttunen, L., Mäki, J., Airaksinen, O., & Rade, M. (2021). Extending the straight leg raise test for improved clinical evaluation of sciatica: validity and diagnostic performance with reference to the magnetic resonance imaging. BMC Musculoskeletal Disorders, 22(1), 1-9.