- Research article
- Open Access
- Open Peer Review
New physical examination tests for lumbar spondylolisthesis and instability: low midline sill sign and interspinous gap change during lumbar flexion-extension motion
© Ahn and Jhun; licensee BioMed Central. 2015
- Received: 23 October 2014
- Accepted: 13 April 2015
- Published: 22 April 2015
Lumbar spondylolisthesis (LS) and lumbar instability (LI) are common disorders in patients with low back or lumbar radicular pain. However, few physical examination tests for LS and LI have been reported. In the study described herein, new physical examination tests for LS and LI were devised and evaluated for their validity. The test for LS was designated “low midline sill sign”, and that for LI was designated “interspinous gap change” during lumbar flexion-extension motion.
The validity of the low midline sill sign was evaluated in 96 patients with low back or lumbar radicular pain. Validity of the interspinous gap change during lumbar flexion-extension motion was evaluated in 73 patients with low back or lumbar radicular pain. The sensitivity, specificity, and positive and negative predictive values of the two tests were also investigated.
The sensitivity and specificity of the low midline sill sign for LS were 81.3% and 89.1%, respectively. Positive and negative predictive values of the test were 78.8% and 90.5%, respectively. The sensitivity and specificity of the interspinous gap change test for LI were 82.2% and 60.7%, respectively. Positive and negative predictive values of the test were 77.1% and 68.0%, respectively.
The low midline sill sign and interspinous gap change tests are effective for the detection of LS and LI, and can be performed easily in an outpatient setting.
- Lumbar spine
- Physical examination
- Segmental instability
Spondylolisthesis is the anterior migration of a vertebra in relation to the vertebrae below. Low back pain, as well as pain, numbness, or weakness in the lower extremities, are symptoms clinically associated with lumbar spondylolisthesis (LS) . Prevalence estimates of spondylolisthesis among females range from 6% in Taiwan to 20–25% in the United States, whereas those among males range from 3% in Taiwan and 4–8% in the United States . Despite its common occurrence, few physical findings specific for the detection of LS have been reported . Kalpakcioglu et al.  compared clinical and radiological findings from 100 patients with, and 30 patients without, LS and reported that clinical findings, such as increased lumbar lordosis and signs of slipping, were positively correlated with radiological findings. However, the validity (i.e., sensitivity and specificity) of the clinical findings of LS detection were not presented.
Lumbar instability (LI) is presumed to be a major cause of low back pain and is often an important factor in determining the surgical indications for spinal fusion with decompression . It is associated with pathological mechanisms of various spinal disorders, such as spondylolisthesis , peridural fibrosis , and failed back surgery syndrome . Several clinical findings have been described as symptoms and signs of LI, including patient reports of “giving away”, “locking”, and pain exacerbation with transitional activities or sustained postures . Physical examination tests for LI detection have been proposed, including a prone instability test, instability catch sign, and passive lumbar extension test . However, the majority of these clinical findings and tests have demonstrated a limited ability in LI diagnosis, and only a few have investigated the diagnostic accuracy of the measures .
In the study described herein, new physical examination tests for LS and LI were devised, and the validity of these tests was evaluated. The test for LS was designated “low midline sill sign” and that for LI was designated “interspinous gap change” during lumbar flexion-extension motion.
Validity of the two physical examination tests was evaluated at two interventional pain management clinics in the Republic of Korea. Validity of the low midline sill sign for LS was evaluated by the corresponding author of this article (HJJ) at an interventional pain management clinic in Daejeon, Korea (Clinic A). Validity of the interspinous gap change for LI was evaluated by the first author of this article (KA) at an interventional pain management clinic in Seoul, Korea (Clinic B).
Subjects recruited to evaluate the validity of the low midline sill sign for LS detection (group A) included 96 patients with low back or lumbar radicular pain that visited Clinic A. Subjects recruited to evaluate validity of the interspinous gap change during lumbar flexion-extension motion for LI detection (group B) included 73 patients with low back or lumbar radicular pain that visited Clinic B. We excluded those who had a contraindication for a radiological evaluation, such as pregnancy; who had a history of lumbar spinal surgery; who had difficulty in standing on his/her feet; and who were unable to flex and extend the spine due to pain or muscle spasm.
The subjects were asked to rate their pain severity on a 10-point numerical rating scale (NRS), where 0 was the absence of pain and 10 was the most severe pain.
Presence of the low midline sill sign in group A was compared with lumbar lateral radiographs from the patients. An independent radiologist who was not informed of the physical findings evaluated the radiological findings from group A. The grade of spondylolisthesis was measured on the lateral view according to the Meyerding classification; grade I indicates a translation of the upper vertebra of up to 25% and grade II indicates that of up to 50% of the lower vertebra . The type of spondylolisthesis was classified as proposed by Wiltse et al. using both lateral and oblique views .
The presence of an interspinous gap change during lumbar flexion-extension motion in group B was compared with lumbar flexion-extension radiographs from the patients. Another independent radiologist who was not informed of the physical findings evaluated the radiological findings of group B. Forward or backward translation of one vertebra over the other and angle of a motion segment was evaluated using flexion-extension lateral views. The cut-off between normal and abnormal movement of the spine is difficult to determine; several radiographic criteria have been proposed for LI, although there is no consensus on this issue. However, values of 10° for sagittal rotation and 4 mm for sagittal translation are typically used to infer instability . Therefore, these cut-off values were used in this study.
Radiographic findings other than lumbar spondylolisthesis and instability were also reported by the radiologists at the two clinics.
The sensitivity, specificity, and positive and negative predictive values of the low midline sill sign and interspinous gap change tests for LS and LI, respectively, were investigated. For data analysis, 2 × 2 tables were created from the data obtained and used to calculate sensitivity, specificity, and positive and negative predictive values.
As this study used data obtained from standard clinical and radiological examinations and no foreseeable harm was expected when obtaining data from the study subjects, written informed consent was not required from the subjects. We obtained consent for photograph from the people appearing in the photographs of this study. The study protocol was reviewed and approved by the institutional review board of Wooridul Spine Hospital (WRDIRB-Ext-2014-02).
Clinical data of study subjects
Low midline sill sign group (Group A, n = 96)
Interspinous gap change group (Group B, n = 73)
Age (years, mean ± SD)
52.8 ± 13.9
56.2 ± 12.4
31 / 65
19 / 54
Pain level (mean ± SD)
5.3 ± 1.3
7.1 ± 2.0
Radiographic findings other than spondylolisthesis and instability (%)
Disc space narrowing
Diagnostic validity of the “low midline sill sign” for the detection of lumbar spondylolisthesis
Radiographic lumbar spondylolisthesis
Low midline sill sign
Diagnostic validity of the “interspinous gap change” during lumbar flexion-extension motion for the detection of lumbar instability
Radiographic lumbar instability
Interspinous gap change
In the study described herein, new physical examination tests for LS and LI were devised and their validity was evaluated. Validation studies revealed that the low midline sill sign showed 81.3% sensitivity and 89.1% specificity for the detection of LS. Another validation study revealed that the interspinous gap change test showed 82.2% sensitivity and 60.7% specificity for the detection of LI. We believe the low midline sill sign is highly sensitive and specific for the detection of LS and the interspinous gap change test is highly sensitive but moderately specific for the detection of LI. Therefore, these two tests are effective for LS and LI detection, and can be performed easily in an outpatient setting.
The two tests introduced in this study were devised to detect changes in the interspinous space associated with LS and LI by both inspection and palpation. Any conditions that cause difficulties in the detection of changes in the interspinous space may lead to an inaccurate physical examination. We believe disc-space narrowing and obesity are important conditions that can disturb an accurate physical examination by the two tests. Disc-space narrowing leads to a reduction in the height of the interspinous space. Obesity may also lead to disturbances by making it difficult to find interspinous spaces and any associated changes. We recommend that examiners who intend to perform these tests accumulate clinical experience through comparison of physical examination findings with radiographs and beware of conditions that may disturb an accurate physical examination.
We developed two new physical examination tests for lumbar spondylolisthesis (LS) and instability (LI), and evaluated the validity of these tests. The test for LS was designated “low midline sill sign”, and that for LI was designated “interspinous gap change” during lumbar flexion-extension motion. Ninety-six patients with low back or lumbar radicular pain were recruited to test the validity of the low midline sill sign and 73 patients with low back or lumbar radicular pain were recruited to test the validity of the interspinous gap change test. The sensitivity and specificity of the low midline sill sign were 81.3% and 89.1%, respectively, whereas those of the interspinous gap change were 82.2% and 60.7%, respectively. We believe these tests are effective for the detection of both LS and LI.
We thank Ms. Jung-Mi Yu for her advice on research ethics.
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