From the Guidelines
The straight leg raise (SLR) test has a modest specificity of 26% for diagnosing herniated disc, as reported in the study by the American College of Physicians and the American Pain Society 1. The test is performed by having the patient lie supine while the examiner passively lifts the patient's straightened leg. A positive test occurs when the patient experiences radiating pain down the leg (sciatica) at an angle less than 60 degrees. Some key points to consider when interpreting the results of the SLR test include:
- The SLR test is more sensitive than specific, with sensitivity around 91% 1, making it better at ruling out disc herniation when negative than confirming it when positive.
- For improved diagnostic accuracy, clinicians should combine the SLR with other neurological tests such as crossed straight leg raise (which has higher specificity of 88% 1), contralateral SLR, motor testing, sensory testing, and reflex assessment.
- The test works by stretching the sciatic nerve and nerve roots, creating tension that reproduces pain when nerve roots are compressed or inflamed, as occurs with disc herniation affecting the L4-S1 nerve roots. It is essential to consider the limitations of the SLR test and to use it in conjunction with other diagnostic tools to ensure accurate diagnosis and effective treatment of lumbar disc herniation.
From the Research
Specificity of the Straight Leg Raise Exam
- The specificity of the straight leg raise (SLR) exam has been found to be low in several studies, ranging from 0.10 to 1.00, with a pooled estimate of 0.28 2.
- A study published in 2011 found that the SLR test had a specificity of 0.74 for detecting lumbar disc herniation (LDH) 3.
- Another study published in 2021 found that the extended SLR (ESLR) test had a specificity of 0.45 for LDH and 0.50 for nerve root compression (NC) 4.
- A pilot study published in 2012 found that the SLR test had a specificity of 0.429 for detecting LDH, while the slump test had a specificity of 0.714 5.
Factors Affecting Specificity
- The specificity of the SLR exam has been found to decrease with age, with a study published in 2011 finding that the area under the curve (AUC) decreased from 0.730 in the 16- to 25-year subgroup to 0.515 in the 76- to 85-year subgroup 3.
- The use of location-specific structural differentiation movements, such as hip internal rotation or ankle dorsiflexion, has been found to improve the specificity of the SLR exam 4, 6.