The Straight Leg Raise (SLR) test is used during physical examinations to help pinpoint the cause of a patient’s lower back and leg pain. This maneuver is classified as a neurodynamic tension test, designed to place mechanical stress on the nerve structures of the lower spine and leg. By stretching these tissues, the test helps a clinician determine if a person’s discomfort originates from the nervous system or from other tissues like muscles and joints. The way the body reacts to the passive movement of the leg provides important clues about the underlying source of the pain.
The Primary Diagnostic Purpose
The most significant purpose of the Straight Leg Raise test is to identify irritation or impingement of the lumbosacral nerve roots, particularly L4, L5, and S1, which combine to form the sciatic nerve. This nerve root compression is a common cause of pain that travels from the back down into the leg, a condition known as radiculopathy. A positive result strongly suggests that a space-occupying lesion is interfering with the nerve’s normal function.
The mechanism relies on the fact that the sciatic nerve is a continuous structure running from the spinal cord down the back of the leg. When a clinician passively raises the extended leg, the movement pulls on the nerve, increasing tension along its entire length. If a herniated intervertebral disc is pressing on a nerve root, this stretching motion tugs on the inflamed and compromised nerve, sharply recreating the patient’s familiar radiating leg pain.
A positive SLR test is highly indicative of a lumbar disc herniation pressing on the nerve root, often occurring at the L4/L5 or L5/S1 levels of the spine. The mechanical compression causes inflammation, and the stretching of the nerve during the test increases the pressure on this already sensitive area. This diagnostic finding is a strong signal for the clinician that the patient’s symptoms are nerve-related, guiding the necessary steps for further imaging or treatment.
Test Procedure and Interpreting Results
The Straight Leg Raise test is performed with the patient lying flat on their back (supine), while the examiner slowly raises the affected leg. The knee must remain fully straightened throughout the entire movement to ensure maximum tension is placed on the sciatic nerve pathway. The clinician carefully monitors the patient’s reaction, noting the exact angle at which the familiar pain is reproduced and the specific location of that discomfort.
Interpretation of the results is dependent on the angle of leg elevation and the quality of the pain experienced. The test is considered truly positive for nerve root tension if the patient reports pain that radiates below the knee when the leg is raised between approximately 30 and 70 degrees. Pain felt in this specific range is significant because it correlates with the point at which tension on the nerve roots reaches its maximum.
It is crucial to differentiate between simple hamstring tightness and true nerve root radiculopathy. A positive test must reproduce the shooting, electrical, or tingling pain that radiates down the leg, which is characteristic of nerve involvement. If the patient only reports a dull ache or pulling sensation in the hamstring or posterior thigh, and the pain does not travel below the knee, the test is considered negative for nerve root compression. Furthermore, if the patient only reports pain localized to the lower back, the result is typically not classified as a positive test for sciatica.
Distinguishing Musculoskeletal Sources of Pain
While the Straight Leg Raise test is primarily a neurological assessment, the results also help to rule out or identify other non-nerve causes of lower extremity discomfort. The angle at which pain occurs often helps to distinguish between nerve tension and purely musculoskeletal issues. Pain that only occurs when the leg is raised above 70 degrees is generally considered less indicative of nerve root pathology.
Discomfort in this higher range is most often attributed to mechanical stretching of the muscles along the back of the thigh, such as hamstring or gluteal muscle tightness. Musculoskeletal pain from these sources typically presents as a localized, pulling sensation that does not have the sharp, radiating quality of nerve pain. This distinction guides the clinician to focus treatment on muscle stretching and physical therapy rather than on spinal decompression.
Additionally, the SLR test can provide clues about conditions in the hip or sacroiliac (SI) joints. If pain is elicited at a very low angle, such as less than 30 degrees, it may suggest pathology in the hip joint or an acute inflammatory process in the buttock area. In these cases, the pain is usually localized to the back or hip and does not follow the distinct radiating path of the sciatic nerve. By observing the pain’s location and the angle of onset, the Straight Leg Raise test assists in narrowing down the broad possibilities of lower back and leg pain.