Interspinous Gap Change | Radiographic Lumbar Instability & Spondylolisthesis

The Low Midline Sill Sign also known as Slipping Palpation or Step-Off Sign assesses for lumbar spondylolisthesis and radiographic lumbar Instability.
Petersen et al in 2017 reviewed the literature on assessments used to classify patients with low back pain, which included spondylolisthesis. They report a sensitivity ranging from 60-88% and specificity ranging from 87-100% for the slipping palpation. These ranges and their sometimes-large confidence intervals as well as real-life disturbances such as obesity make it at least moderately useful in the assessment of spondylolisthesis.

Conducting this assessment is pretty simple. The patient stands upright with their back exposed. Observe the midline of the back and see if you can spot a sill like a capital “L”. Here is a picture of what it looks like. Then run your thumb down the midline of the spine. In case of a positive test, you would feel that the superior spinous process is displaced anteriorly to the inferior spinous process. Hence the appearance of the sill, which will usually be painful to the touch.

21 OF THE MOST USEFUL ORTHOPAEDIC TESTS IN CLINICAL PRACTICE

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

• Prone Instability Test
• Passive Lumbar Extension Test
• Interspinous Gap Change

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.

Petersen, T., Laslett, M., & Juhl, C. (2017). Clinical classification in low back pain: best-evidence diagnostic rules based on systematic reviews. BMC musculoskeletal disorders, 18(1), 1-23.