Is Dynamic Spino-Pelvic Alignment During Gait Associated with Quality of Life in Patients with Degenerative Lumbar Spinal Canal Stenosis?

Takuya Miura (  takuya-m@fmu.ac.jp ) Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center) Ryoji Tominaga Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center) Keita Sato Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center) Tatsuya Endo Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center) Masumi Iwabuchi Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center) Toshikazu Ito Hokkaido Chitose College of Rehabilitation Osamu Shirado Departments of Rehabilitation / Orthopaedic and Spinal Surgery, AMEC (Aizu Medical Center)


Introduction
The prevalence of lumbar spinal stenosis (LSS) in the Japanese population over 40 years of age was 5.7% which was estimated to be 3,650,000 1 . Patients with lumbar spinal stenosis (LSS) complain of various symptoms such as leg pain, numbness, paresthesia, and intermittent claudication 2, 3 . These symptoms are caused by compression of the nerve roots due to narrowing of the spinal canal and/or intervertebral foramen. Previous studies have reported that approximately 80% of patients with LSS experience lower extremity pain 4 . In addition, Otani et al. 5 reported the prevalence of lower limb neuropathy by age group, which was 19% in their 60s, 27% in their 70s, and 38% in their 80s. Previous studies using the Oswestry Disability Index (ODI) 6 or Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) 7 as a measure of quality of life (QOL) have reported low QOL in LSS patients. As the most important goal of rehabilitation for patients with LSS is to improve their QOL, it is necessary to examine the factors that contribute to the decline in QOL in such patients.
In patients with LSS, postural collapse has been observed in many cases, and its relation to QOL has been pointed out. Lafage et al.,8 found that pelvic tilt and stooped posture were associated with lower QOL and another study 9 demonstrated that LSS patients with a positive sagittal vertical axis preoperatively had a signi cant negative effect on health-related QOL. Although previous studies have examined the relationship between the parameters measured from X-ray images in a static standing position and QOL, it must be taken into account that symptoms in patients with LSS often occur in a dynamic state such as gait. Although previous studies have measured the gait ability of LSS patients using several gait tests 10,11 and accelerometers 12 , no study has measured the alignment of the spine and pelvis during gait and further examined the relationships between that and QOL.

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The purpose of this study was to investigate the relationship between dynamic alignment of the spine and pelvis during gait and QOL in LSS patients.

Materials And Methods
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 boardcerti ed 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 di cult 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 exion / 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 exed by 90° and both feet in contact with the oor. 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 exor 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 rst 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-ve re ection 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, midpoint 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 de ned 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 de ned 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 de ned 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 re ects 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 ltered (Butterworth 4th order-low pass lter; 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 exion / 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 coe cient. The normality of all data was examined beforehand, and the Pearson's correlation coe cient was used for analysis when normality was observed, and the Spearman's rank correlation coe cient was used when normality was not observed. Furthermore, in order to investigate the in uential 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 signi cance was set at p < 0.05.

Results
Thirty patients with LSS (17 men and 13 women) participated in this study. The demographic data of the subjects are shown in Table 1. The ODI score had a signi cantly negative correlation with trunk extension strength (r = -0.559, 95% CI; -0.765, -0.249, p = 0.002, Table 2) and hip extension strength (r = -0.473, 95% CI; -0.712, -0.136, p = 0.011, Table 2). There was no signi cant correlation between the ODI score and static alignment. In the dynamic alignment, a signi cant negative correlation between the ODI score and  (Table 3).

Discussion
The current study showed that spinal and pelvic alignment during gait in LSS patients was signi cantly correlated with the ODI score. Furthermore, trunk and hip extension strength also showed a signi cant relationship with the ODI score. The current study is the rst to investigate the relationship between dynamic spinal and pelvic alignment and QOL in LSS patients. Our study suggests that both physical function and dynamic spinal/pelvic alignment are important factors for QOL in patients with LSS.
Previous studies have reported that LSS in the elderly is triggered by age-related degenerative changes, resulting in progressive worsening of symptoms and decreased activity [17][18][19] . The results of the current study extend the evidence of these previous studies, and suggest that muscle weakness associated with reduced activity may lead to a lower QOL. If hip extensor strength is reduced, compensatory movements such as excessive anterior tilt of the pelvis and excessive lordosis of the lumbar spine may occur.
Repeated gait with increased load on the pelvis and lumbar vertebrae due to weakening of the hip and/or trunk extensor muscles can lead to exacerbation of symptoms such as intermittent claudication, which may result in a lower QOL.
The relationship between QOL and the static alignment was not observed in the current study. However, a previous study using the ODI reported that a decrease in lumbar lordosis angle (OR = 1.02) and an increase in sagittal vertical axis (OR = 1.09) signi cantly increased the odds ratio of low QOL 6 . While this previous study radiologically measured lumbar lordosis, thoracic kyphosis and sagittal vertical axis, the present study measured them from the body surface using a Spinal Mouse. Due to the difference in assessment method, we believe that no association between the static alignment and QOL was found in our study.
In another previous study, lower limb pain, numbness and intermittent claudication caused by LSS have been reported to reduce QOL 20 . The novelty of our study is that we calculated the spinal and pelvic alignment during gait, and investigated how the dynamic alignment correlate to QOL. It was shown that patients with LSS who routinely walk in an inappropriate posture that tends to exacerbate their symptoms may have a poorer QOL. The results of multiple regression analysis showed that the trunk extensor strength, maximum spinal exion angle and hip extensor strength had an effect on ODI score. Therefore, it is important to evaluate and to examine these factors postoperatively or before and after rehabilitation interventions such as conservative therapy, as changes in these factors can lead to changes in ODI score.
There are several strengths to this study. Firstly, gait analysis of LSS patients was performed using a 3-D motion analysis system. Until now, gait analysis in clinical practice has generally been based on the physical therapists' visual or subjective perceptions. However, gait analysis based on these conventional methods has no guarantee of reliability or validity, and there was a large reliance on empirical evidence.
The 3-D motion analysis system is a tool to solve such a problem, and for this reason, it is widely used for people with musculoskeletal diseases. Our study provides valid and objective data on the gait of LSS patients. The second strength is that we used data obtained in the dynamic environment to investigate the relationship of spinal and pelvic alignment with QOL, which has not been investigated previously. The results obtained from the gait analysis in the present study allow us to better characterize the real-life problems and concerns of LSS patients, and can provide useful insights for appropriate medical interventions.
Our study has several limitations. First, there may be a selection bias. Since all of the subjects were patients who were to undergo surgery, their physical function, ADL and QOL were quite low. Therefore, the results of this study may be different from those obtained from relatively mild LSS patients who would be followed up with conservative treatment. Secondly, although we used the ODI as a QOL indicator in this study, we did not consider other evaluation batteries such as JOABPEQ and SF-36. These assessment batteries are widely used worldwide and should be used in the future to examine QOL in more detail. Thirdly, only the spine and pelvis were analyzed as dynamic alignment, and other distal joints such as the hip and knee joints were not evaluated in this study. In order to evaluate the gait dynamics of LSS patients in more detail, future studies should include an assessment of lower limb function.
In conclusion, the patients with LSS who walked with a more anteriorly tilted pelvis and a more extended spine were found to have a lower QOL, and such patients also had lower trunk and hip extension strength.  Values are the mean (SD). a) HHD, hand-held dynamometer; b) ODI, Oswestry Disability Index.
* indicates a signi cant correlation with ODI score at p < 0.05.