Interspinous Gap Change | Radiographic Lumbar Instability & Spondylolisthesis

The Interspinous gap change is an orthopedic test to assess for lumbar spondylolisthesis and radiographic lumbar Instability.
Ahn et al. (2015) report a sensitivity of 82% and specificity of 61% when compared to lumbar flexion-extension radiographs using a cut-off value of 10° for sagittal rotation and 4mm of sagittal translation. As there is no consensus on the classification of lumbar instability and this is the first study to evaluate this test the clinical value is at most moderate.

To conduct the test the patient stands approximately one leg-length away from the treatment table with the feet shoulder-width apart.
The patient is asked to flex the back forward with both hands on the edge of the treatment table.
Examine the patient’s spine from top to bottom and pay attention to the gaps between the spinous processes. If one level appears bent or the interspinous gap appears wider, focus on that region in the following step. Continue by palpating the spine in cranial-to-caudal direction and evaluate the spaces between the spinous processes and the position of the upper compared to the lower spinous processes.  If during inspection and palpation an area appears to have a wider superoinferior or anterioposterior gap, place one thumb on each of the spinous processes. Then ask the patient to extend the spine by pushing the pelvis towards the treatment table while the examiner palpates the spinous processes.

The test is considered positive if the interspinous space abruptly becomes narrow compared with those of other levels or if the position of the upper spinous process in relation to the lower spinous process changes anteriorly or posteriorly from its original state. Furthermore, tenderness is usually detected during the flexion-extension motion when palpating interspinous spaces with wide gaps.

There are several other orthopedic tests for the diagnosis of radiographic lumbar instability:

• Prone Instability Test
• Passive Lumbar Extension Test
• Low Midline Sill Sign

Ahn, K., & Jhun, H. J. (2015). New physical examination tests for lumbar spondylolisthesis and instability: low midline sill sign and interspinous gap change during lumbar flexion-extension motion. BMC musculoskeletal disorders, 16(1), 1-6.