What does a positive cross straight leg raise (CSLR) test indicate in a patient with sciatica?

How the Positive Cross Straight Leg Raise Test Works in Sciatica

A positive cross straight leg raise (CSLR) test occurs when raising the unaffected leg reproduces the patient's sciatic pain in the affected leg, strongly indicating disc herniation with nerve root compression. This test has high specificity (88%) but lower sensitivity (29%) for diagnosing lumbar disc herniation. 1

Mechanism of Action

• The CSLR test works by creating tension on the sciatic nerve and nerve roots on the contralateral side through mechanical displacement of the dural sac 1, 2
• When the unaffected leg is raised, it causes the dural sac to shift toward the symptomatic side, compressing an already irritated or compressed nerve root against a herniated disc or other space-occupying lesion 2
• This mechanical displacement creates tension across the nerve root, reproducing the patient's radicular symptoms in the affected leg 1
• The test is considered positive when the patient's sciatic pain is reproduced in the affected leg when the unaffected leg is raised between 30-70 degrees 3, 1

Diagnostic Value

• The CSLR test is more specific (88%) but less sensitive (29%) than the standard straight leg raise (SLR) test, which has high sensitivity (91%) but lower specificity (26%) 1, 4
• A positive CSLR test is associated with a herniated lumbar disc in 97% of patients, making it a highly reliable diagnostic sign 5
• The test is particularly valuable because it helps rule out non-organic causes of pain, as it's difficult for patients to anticipate that raising the unaffected leg would reproduce pain in the affected leg 1, 6
• The diagnostic accuracy of SLR tests generally decreases with age, with the area under the ROC curve decreasing from 0.730 in younger patients (16-25 years) to 0.515 in older patients (76-85 years) 7

Clinical Significance

• A positive CSLR test strongly suggests the presence of a significant disc herniation that is compressing a nerve root 1, 5
• Patients with a positive CSLR test often have poorer response to conservative management but generally good outcomes with surgical intervention 5
• The test should be performed as part of a comprehensive neurological examination that includes assessment of motor strength, reflexes, and sensory distribution 1
• The CSLR test should be used in conjunction with other clinical findings and imaging when making treatment decisions, not as a standalone diagnostic tool 1, 6

Common Pitfalls and Considerations

• The test may be negative despite the presence of disc herniation if the herniation is small or not significantly compressing the nerve root 4
• Interpretation of the test can vary widely among clinicians, with significant differences in the angle at which the test is considered positive (range 10-90 degrees) 8
• Many clinicians incorrectly interpret what constitutes a positive test, with only a minority correctly recognizing that reproduction of leg pain (not back pain) indicates a positive test 8
• The CSLR test should be performed alongside the standard SLR test to improve diagnostic accuracy, as they complement each other with their different sensitivity and specificity profiles 1, 4