The flip test: a reappraisal

Diagnostic study.

To assess the construct validity of the flip test as a sign of nerve root tension.

The flip test is commonly performed in patients with sciatica to confirm or otherwise nerve root tension evidenced by a restricted supine straight leg raise (SLR). Passive extension of the knee with the patient in the erect position and the hip flexed is reported to cause a sudden falling or flipping back of the trunk. Although widely known there are no research articles validating this test.

Sixty-seven patients with sciatica and magnetic resonance imaging scans confirming disc protrusion and nerve root compression underwent the flip test. The response of the patient was recorded, compared with the supine SLR, and subjected to statistical analysis.

Thirty-three percent of patients felt no pain, 39% felt pain on full extension of the knee, and 28% resisted full extension of the knee due to pain. Only one-third of patients demonstrated a "flip." The response was related to the supine SLR, such that patients with high SLRs tended not to show a painful reaction whereas all patients with a supine SLR below 45 degrees showed a painful response.

We consider that the flip test has been substantially misinterpreted in the past. However, it remains a useful check of nerve root tension but only for patients with supine SLRs below 45 degrees . The most reliable response was not a flip but the demonstration of pain on extension of the knee. We would recommend the term "sitting SLR test," as a more accurate and less misleading name.