Simple Tests for Lumbar Spondylolisthesis and Instability Show Efficacy
Commentary by Kang Ahn, MD and Silvano Ferrari, PT
Despite the frequent occurrence of spondylolisthesis and lumbar instability in the United States, few physical examination findings have shown accuracy in detecting this condition. Two physical examination tests—the low midline sill sign and interspinous gap change tests—demonstrated sensitivity and specificity in the detection of lumbar spondylolisthesis and instability in a recent study published in BMC Musculoskeletal Disorders.
“A variety of tests are used to detect spondylolisthesis or lumbar instability, but we perceive patients can benefit from these physical tests since they can be performed more easily and fast,” said lead author of the study Kang Ahn, MD, Founder of Ahnkang Pain Free Hospital, CHA University, Seoul, Korea.
Dr. Ahn noted that many patients with low back pain show no abnormalities on magnetic resonance imaging, computed tomography, or X-ray scans due to patients’ positioning during the scan. On the other hand, abnormalities may be found on examinations among patients with no specific symptoms. “Therefore, physical examination tests need to be conducted, and then the findings should be confirmed with radiographic evaluation,” Dr. Ahn said. He added that despite how common lumbar instability is in patients with back pain, there are still cases in which lumbar instability is not correctly diagnosed or is overlooked.
Study Inclusion and Exclusion Criteria
Test validity was assessed in 96 patients with low back or lumbar radicular pain for the low midline sill sign test and in 73 patients with low back or lumbar radicular pain for the interspinous gap change test. (See below for details on how the tests were performed.)
The study did not include pregnant women, patients with a history of lumbar spinal surgery, or patients who had difficulty standing or flexing/extending the spine. Radiological findings were used to analyze the sensitivity, specificity, and positive/negative predictive values of the tests.
The low midline sill sign showed a sensitivity of 81.3%, specificity of 89.1%, and positive and negative predictive values of 78.8% and 90.5%, respectively. The interspinous gap change tests showed a sensitivity of 82.2%, specificity of 60.7%, and positive and negative predictive value of 77.1% and 68.0%, respectively.
Low Midline Sill Sign Test for Lumbar Spondylolisthesis
- The patient stands with feet shoulder-width apart.
- Examine the spinous processes of lumbar and sacral spine cephaladcaudal direction.
- Look for increased lumbar lordosis and if the spinous processes form a sill like a capital “L” on the midline of the patient’s back. The skin around the sill is usually wrinkled and thick compared with the surrounding skin (Figure 1A).
- Palpate the intraspinal space in the area of the sill, and note the position of the upper spinous process in relation to the lower spinous process (Figure 1B).
- The test is positive if the upper spinous process is displaced anterior to the lower spinous process and a sill like a capital “L” is plapated in step 3.
Figure 1 (above). The low midline sill sign test for lumbar spondylolisthesis. The test is positive if lumbar lordosis increases and the spinous processes form a sill like a capital “L” on examination (A), and the upper spinous process is displaced anterior to the lower spinous process on palpation (B). Reprinted from Ahn K, Jhun JH. BMC Musculosekelet Disord. 2015;16(1):97.
Interspinous Gap Change Test for Lumbar Instability
- The patient stands with feet shoulder-width apart in front of an examination table.
- The patient is asked to flex his/her back with both hands on the edge of the examination table.
- At flexion, inspect gaps between the interspinous processes in a cranial-to-caudal direction.
- An interspinous space that is bent or wider than the adjacent interspinous spaces may indicate an unstable level and should be evaluated further (Figure 2A).
- Palpate the individual interspinous spaces of the patient’s back in a cranial-to-caudal direction.
- If an interspinous space has a wider supero-inferior or antero-posterior gap between the upper and lower spinous processes than the adjacent interspinous spaces, it is suspected to be an unstable level. The interspinous space that is suspected of being unstable is selected through inspection and palplation in flexion (Figure 2B).
- Ask the patient to extend his/her upper body and push their buttocks toward the examination table with both hands on the table to reproduce lumbar extension from a flexion state.
- Evaluate the change in the gap of the interspinous space that is suspected of being unstable. Use both thumbs, with one placed on the interspinous space suspected of being unstable and the other placed on the interspinous space above or below that level to compare the changes in gap of the two spaces (Figure 2C).
- The test is considered positive if the width of an interspinous space abruptly becomes narrow compared with those of other interspinous spaces, or the position of the upper spinous process in relation to the lower spinous process is changed anteriorly or posteriorly from its original state during the lumbar flexion/extension motion.
- Tenderness is usually detected during palpation of the interspinous spaces with wide gaps, as the patient performs the flexion/extension motion.
Figure 2 (above). The intra-interspinous gap change test for lumbar instability. Inspect the patient’s back at flexion, focusing on the gaps between interspinous processes (A). Palpate the interspinous spaces of the patient’s back and evaluate the width of individual interspinous spaces and the position of the upper spinous process in relation to the lower spinous process (B). Palpate the interspinous gap change while the patient extends his/her upper body and push their buttocks toward the examination table as both hands are on the examination table, to reproduce lumbar extension from the flexion state (C). Reprinted from Ahn K, Jhun JH. BMC Musculoskelet Disord. 2015;16(1):97.
The Findings Add to Current Knowledge on Detecting Spondylolisthesis in Clinical Practice
“The lumbar spinous palpation to detect the low midline sill sign in patients with low back pain should be done when the clinician suspects the presence of spondylolisthesis,” said Silvano Ferrari, PT, adding that technique is frequently used by clinicians and taught in professional education courses. “The positivity of the test is not needed for a diagnosis, but the execution of X-ray to confirm this hypothesis is suggested. Of course, only the imaging can make a diagnosis of spondylolisthesis (gold standard),” said Dr. Ferrari, who is a physiotherapist in Milan, and Lecturer of Master of Manual Therapy and Musculoskeletal Rehabilitation, Department of Molecular Medicine, University of Padova, Padova, Italy.
Dr. Ferrari agreed also noted a need for tools to detect clinical instability that is not necessarily related to radiological instability. “Regarding the utility of interspinous gap change to detect a lumbar instability, I would be cautious, firstly, because the accuracy of this test has been performed only on specific types of patients. In fact, subjects unable to flex and extend the spine due to pain or muscle spasm (as patients in acute phase and/or with high irritability) were excluded from the study, and the authors report that it also may be difficult to assess interspinous space in obese subjects.”
“Secondly, no clinical test can detect lumbar instability alone,” Dr. Ferrari said. “Our experience suggests the use of a cluster of tests. The interspinous gap change could be one of these, together with the aberrant movements, passive lumbar extension test, prone instability test, and active straight leg raise test,” Dr. Ferrari said.
In a recent study by Dr. Ferrari and colleagues, all of these 4 tests except the active straight leg test were significantly associated with disability in patients with symptomatic spondylolisthesis (n=119). Only the passive lumbar extension test was significantly associated with findings on dynamic radiographs (P=0.017) in the study.
Dr. Ferrari noted that Dr. Ahn’s study detected the accuracy of these tests and that more research is needed to assess the reliability of the tests. This need to examine the tests’ reliability “isn’t secondary, because we know well the poor interexaminer reliability of all tests that use palpation and palpation movement,” Dr. Ferrari said.
Overall, the study by Dr. Ahn “adds to our knowledge about the possibility to detect a lumbar spondylolisthesis and lumbar instability in clinical practice,” Dr. Ferrari concluded. “I think these tests are useful in clinical practice,” he added.