A positive Lasegue's test, specifically in the context of a crossed straight leg raise, is when a patient reports pain in their involved limb at just 40 degrees of hip flexion while the examiner passively flexes the uninvolved limb and maintains the knee in extension.
Understanding Lasegue's Test (Straight Leg Raise)
The Lasegue's test, commonly known as the straight leg raise (SLR) test, is a physical examination technique used to assess for nerve root compression in the lower back, often related to conditions like sciatica. The basic test involves passively raising the patient's leg, while they lie supine, with the knee in full extension. The angle at which pain is elicited and the location of that pain are important factors in determining whether the test is positive or negative.
Crossed Straight Leg Raise (Crossed Lasegue)
The crossed straight leg raise test (or crossed Lasegue test) builds on the basic test to add specificity. The examination involves the following steps:
- The patient lies on their back (supine).
- The examiner passively flexes the uninvolved limb, while keeping the knee extended.
- The test is considered positive when the patient reports pain in the involved limb (the one suspected of having nerve compression) at a relatively low degree of hip flexion – specifically at 40 degrees when flexing the uninvolved leg.
Why is a Positive Crossed Lasegue Significant?
A positive crossed Lasegue test suggests a higher likelihood of nerve root compression compared to a positive straight leg raise test conducted only on the affected limb. Here's why:
- Nerve Root Irritation: The crossed leg raise places mechanical stress and tension on nerve roots in the lower spine. Pain in the involved limb when flexing the uninvolved leg points to a significant irritation of the spinal nerve root.
- Specificity: Pain experienced when flexing the uninvolved leg is more specific for nerve root involvement than pain elicited during the regular SLR, especially when positive at a low degree like 40 degrees.
- Diagnosis: A positive crossed Lasegue test combined with other clinical findings helps health care professionals to diagnose spinal nerve root compression, which helps with subsequent treatment planning.
Key Features of a Positive Crossed Lasegue Test:
| Feature | Description |
|---|---|
| Patient Position | Supine (lying on the back) |
| Limb Being Raised | Uninvolved limb (the limb not initially suspected to have the problem) |
| Knee Position | Extended (straight) |
| Positive Test Result | Pain reported in the involved limb at just 40 degrees of hip flexion while raising the uninvolved leg. |
Conclusion
In summary, a positive crossed Lasegue test indicates a heightened likelihood of nerve root compression when pain is elicited in the involved limb at 40 degrees of hip flexion while flexing the uninvolved leg. This is different from the standard straight leg raise test and is more specific to nerve root pathology.
