New physical examination tests for lumbar spondylolisthesis and instability: low midline sill sign and interspinous gap change during lumbar flexion-extension motion

The LS detection test is composed of both inspection and palpation. The patient is asked to stand with his/her feet shoulder-width apart facing the examiner. The examiner inspects the midline of the patient’s back composed of spinous processes of lumbar and sacral spine cephalad-caudal direction. The sign is considered positive if lumbar lordosis increases and a sill like a capital “L” is inspected 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). Following inspection, the midline of the patient’s back is then palpated. When an interspinous space is identified, the position of the upper spinous process in relation to the lower spinous process is evaluated. The sign is considered positive if the upper spinous process is displaced anterior to the lower spinous process and a sill like a capital “L” is palpated on the midline of the patient’s back. Tenderness is usually detected during palpation of the sill (Figure 1B).

The interspinous gap change during lumbar flexion-extension motion devised to detect LI is also performed in a standing position. The patient is asked to stand with his/her feet shoulder-width apart with the feet roughly leg-length from the examination table. Then the patient is asked to flex his/her back with both hands on the edge of the examination table. At flexion, the examiner inspects the patient’s back in a cranial-to-caudal direction, focusing on the gaps between the interspinous processes. If an interspinous space is bent or wider than the adjacent interspinous spaces, it is possible that this is an unstable level and particular attention should be paid to the area (Figure 2A). Following inspection, the examiner palpates the individual interspinous spaces of the patient’s back in a cranial-to-caudal direction and evaluates the width of individual interspinous spaces and the position of the upper spinous process in relation to the lower spinous process. 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 palpation in flexion (Figure 2B). Thereafter, the patient is asked to extend his/her upper body and push their buttocks toward the examination table with both hands on the table, which reproduces lumbar extension from a flexion state. During this motion, the examiner evaluates the change in the gap of the interspinous space that is suspected of being unstable. It is good to 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 examiner determines that 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 interspinous spaces with wide gaps, as the patient performs the 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 [12]. The type of spondylolisthesis was classified as proposed by Wiltse et al. using both lateral and oblique views [13].

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 [5]. 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).