Study design. This is a cross-sectional study in a single hospital. This study was conducted with the approval of the institutional ethics committee of the Aizu Medical Center, Fukushima Medical University (approval number: general 29263). Then, only those who submitted written informed consent participated in the study. All methods were carried out in accordance with relevant guidelines and regulations.
Participants. Subjects were recruited from patients admitted to our hospital between December 2016 and April 2021. The inclusion criteria were as follows: those who complained of lower limb pain and/or numbness with neurogenic intermittent claudication, and had been diagnosed as having LSS by board-certified spinal surgeons approved by the Japanese Society for Spine Surgery and Related Research. Exclusion criteria were as follows: those with a history of cerebrovascular or cardiovascular disorders, those with an orthopedic history such as osteoarthritis, those with a history of dementia, and those with pain which makes it difficult to carry out the below-described experimental task.
QOL assessment. The ODI, a questionnaire that allows quantitative assessment of the degree of functional impairment in patients with low back pain 13, was used to assess QOL 14. The ODI rating scale consists of 10 items related to functional impairment. Each item is scored on a scale of 0 to 5, and the scores for all 10 items are summed. The summed score (0 to 50 points) is divided by the maximum score, 50, and multiplied by 100 to show the percentage. While 100% shows the highest degree of impairment, 0% shows the lowest degree of impairment. This evaluation was performed prior to the motion task.
Physical function evaluation. Trunk flexion / extension and hip extension / abduction muscle strength were measured using Mobie (Sakai Medical Co., Ltd.) which is a hand-held dynamometer (HHD). During measurement, the subject sat with the knee and hip joint flexed by 90° and both feet in contact with the floor. The subject's upper limbs were crossed in front of their chest, and the examiner pressed the device against the subject's sternum. Then, the subjects were instructed to hold the contraction against the HHD device, and peak isometric force of the trunk flexor was recorded 15. The device was then set against the subject’s back to measure trunk extension muscle strength 15. The hip extensor strength was measured by placing the device between the thigh and the seat, and pressing the thigh against the seat 16. The hip abductor muscle force was measured by applying the device to the lateral side of the thigh, and the examiner pressed the device against the subject's lateral thigh 16. Each measurement was performed twice, and the average value was used for later analysis.
Static alignment measurement. Spinal mouse® (Index Ltd., Japan), a device which can calculate the curvature and inclination of particular segments of the spine, was used to measure the static alignment of the spine. The subject first stood in an upright posture with the upper limbs dropped to the side of the body, and the feet were aligned shoulder-width apart. After that, the examiner held the device in one hand and moved it from the spinous processes of the seventh cervical vertebrae to the sacrum. This measurement was performed twice. The presence or absence of errors was checked for each measurement. The lumbar lordosis angle, thoracic kyphotic angle, and spinal tilt angle at the upright standing position were calculated automatically by supplied software, and the average value was used for later analysis.
Dynamic alignment measurement. A three-dimensional (3-D) motion analysis system, VICON MX (Vicon Motion Systems, Oxford, UK), and two force plates (AMTI, Watertown, MA, USA) were used to measure the dynamic alignment of the spine and pelvis during gait. Thirty-five reflection markers of 14 mm in diameter were attached on each of the following landmarks on the body surface according to the Plug-In Gait Full Body model; the forehead and occipital region, spinous process of the seventh cervical vertebra, manubrium sterni, xiphisternum, right shoulder blade, spinous process of the tenth thoracic vertebra, acromion, lateral epicondyle of humerus, ulnar styloid process, radial styloid process, second metacarpal head, anterior superior iliac spine, posterior superior iliac spine, lateral thigh, lateral knee epicondyle, mid-point between lateral knee epicondyle and lateral malleolus, lateral malleolus, second metatarsal head, and heel (Fig. 1). The experimental task and measurement were performed as follows. First, the subjects were asked to stand with the upper limbs down alongside the body, and the feet directed straight ahead, positioned waist-width apart. While the subjects held this posture for about three seconds, marker trajectory data were recorded. Next, a 1.5 × 5.0 m walkway was prepared, and eight cameras were mounted on the ceiling, focusing on the walkway. Two force plates were longitudinally placed on the walkway in the gait direction. The sampling frequency of each force plate was 1000 Hz. The subjects were then asked to walk, at their normal pace, on the walkway, and were instructed to step on each of the two force plates using the foot on the side with the more severe lower limb pain. The data were taken for one gait cycle which was defined as starting from heel contact to ipsilateral heel contact including two steps on the force plates. Prior to the actual measurement, each subject practiced the action multiple times so that the foot properly stepped on the force plate while they walked at their normal speed. After each gait, one gait cycle data was checked to ensure that they were completely recorded, and the task was repeated until the data for three gait cycles were recorded.
Data processing. Vicon Nexus software was used to analyze the gait data. Each segment used for analysis was composed of body surface marker sets. The thorax segment was defined by four markers on the manubrium sterni, xiphistermum, spinous process of the seventh cervical vertebra, and spinous process of the tenth thoracic vertebra. The pelvic segment was defined by four markers on the left and right anterior superior iliac spine and posterior superior iliac spine. The angles of the thorax and pelvis were calculated in a global coordinate system. The spine angle reflects the relative motion between the thorax segment and pelvic segment. The angles of the spine and pelvis during gait were calculated in three motion planes; sagittal, frontal and horizontal planes. The data throughout the gait cycle were analyzed, which was normalized to 100%. Segment data and one gait cycle were synchronized using the gait analysis software Polygon (Vicon Motion Systems) to obtain marker coordinate data. Those data and the analog data from the two force plates were filtered (Butterworth 4th order-low pass filter; 6 Hz). We used the maximum spinal and pelvic angles for analysis.
Statistical analysis. The items used for analysis were as follows: ODI score, trunk flexion / extension muscle strength, hip extension / abduction muscle strength, lumbar lordosis angle, thoracic kyphotic angle, spinal tilt angle, spinal and pelvic angle during gait on each motion plane. For statistical analysis, we examined the relationship between the ODI score and other items using two-tailed, correlation coefficient. The normality of all data was examined beforehand, and the Pearson's correlation coefficient was used for analysis when normality was observed, and the Spearman's rank correlation coefficient was used when normality was not observed. Furthermore, in order to investigate the influential factors on the ODI score, a stepwise multiple regression analysis was performed. SPSS statistics 26 (IBM, Chicago, IL, USA) was used for statistical processing. Statistical significance was set at p < 0.05.