Abstract
BACKGROUND:
Prospective study.
OBJECTIVE:
To determine the change in spinal sagittal parameters which may occur throughout the day in healthy population.
METHODS:
Thirty-five healthy hospital employees were enrolled in the study. Two standing left lateral orthoroentgenograms were obtained at 8.00 a.m and at 6.00 p.m. Six spinopelvic parameters were measured on the X-rays. Thereafter, the subjects were divided into two cohorts according to their BMI as low BMI and high BMI.
RESULTS:
Thirty-five subjects with a mean age of 25.97
CONCLUSION:
Routine workload in a hospital environment does not cause significant change in the spinopelvic parameters throughout the day.
Introduction
Optimal sagittal balance ensures that we spend minimum effort to stand upright [1]. The vertebral body and disc complex acts to resist the forces of physiological compression and sustains an erect posture [2]. A degenerated disc or loss of anterior bone support may cause deformation, thus leading to flexion (kyphosis) and lateral bending (scoliosis), usually coupled with torsion (rotation) [3]. Therefore, during the course of aging it is likely that one will encounter a gradual loss of spinal alignment. As new data highlights the importance of sagittal vertebral balance for better outcomes of spinal deformity surgery, research concerning spinal sagittal parameters has become more popular among spinal surgeons [4, 5]. The amount of correction in sagittal parameters has been found to be directly related to clinical improvement [6, 7]. Therefore, understanding anatomical and physiological properties along with compensatory mechanisms which allow for the maintenance of sagittal balance has become more important than ever before. Previous literature contains a great deal of research which focuses on the determination of compensatory mechanisms and classification of sagittal imbalance [8, 9]. Currently, we know that an increase in thoracic kyphosis is compensated by an increase in lumbar lordosis, or anterior shift in the center of gravity is compensated with by retroversion of the pelvis [1, 10]. Most sagittal parameter research has focused on surgical goals for the treatment of degenerative spine cases or other special conditions that cause sagittal imbalance, such as idiopathic scoliosis and Scheuermann’s disease [11, 12]. To our knowledge, there is no study which has focused on physiological sagittal changes which may occur throughout the day as a probable result of working and muscle fatigue. As a result of this deficit, we endeavored to determine the change in spinal sagittal parameters which may occur throughout the day by comparing spinal sagittal measurements made early in the morning to measurements made in the evening in healthy hospital workers.
Materials and methods
Thirty-seven operating room nurses who had no back pain at the time of the study, with no known spine, hip or pelvic disorders and without any contraindications for radiographic exposure were enrolled in the study. Among them two subjects with previous spinal surgery were excluded. The participants were mainly operating room nurses who work actively throughout the entire day. All participants provided informed consent and the study was approved by the ethical committee of Acibadem University (ATADEK 2016/1).
The radiographic protocol was standardized for all participants. For each subject, two standing left lateral orthoroentgenograms including the whole spine and pelvis were obtained, with the subject standing 72 inches away from the X-ray tube. The participants were instructed to stand straight and relaxed, with their knees fully extended. The elbows were parked in 90 degrees flexion, with both elbows resting on a horizontal bar at the level of their shoulders. The first X-ray was obtained at 8 o’clock in the morning just before the work shift. The second X-ray was obtained at 6 o’clock in the afternoon at the end of the work shift. Six spinopelvic parameters were measured on the X-rays: thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI) and sagittal vertebral axis (SVA) [13]. The definition of the aforementioned study variables are provided in Fig. 1 to provide better apprehension. All radiographs were analyzed by the same surgeon and checked by two other surgeons with the aid of digital graphics software (The Surgimap software New York, NY, USA).
Thoracic kyphosis (TK), the angle between the superior endplate of T4 and the inferior endplate of T12; lumbar lordosis (LL), the angle between the superior endplate of L1 and the superior endplate of S1; sacral slope (SS), the angle between the superior endplate of S1 and the horizontal line; pelvic incidence (PI), the angle between the line perpendicular to the superior endplate of S1 and the line connecting the midpoint of the superior endplate of S1 to the hip axis (HA, the midpoint of the line connecting the centers of two femoral heads); pelvic tilt (PT), the angle between the vertical line and the line connecting the midpoint of the superior endplate of S1 to HA (considered positive if angulated behind the vertical line and otherwise negative); sagittal vertebral axis (SVA), the distance between the C7 plumb line and the posterosuperior corner of S1 in the sagittal plane.
Descriptive values for all parameters
Correlation matrix between parameters and their related P values for all subjects
Correlation matrix between parameters and their related P values for low BMI group
Correlation matrix between parameters and their related P values for high BMI group
Thereafter, the subjects were divided into two cohorts according to their body mass indexes (BMI) as low BMI (
Data were analyzed using SPSS 14.0 software (SPSS Inc., Chicago, IL). Application of the Kolmogorov-Smirnov test showed no normal distribution of data sets, thus Wilcoxon test was utilized and median and range values were calculated and used instead of mean values. The Independent Samples test was utilized to assess comparison of the parameters. Relationships were assessed using Pearson’s coefficients. A significance value less than 0.05 was considered to be significant.
Thirty-five subjects: 16 males (45.7%), 19 females (54.3%) with a mean age of 25.97
The values of TK, LL, SS, PI, PT and SVA were not normally distributed in both cohorts. All spinopelvic parameters were measured twice from X-rays obtained in the morning at 8 o’clock and in the evening at 6 o’clock. Descriptive values of all parameters are shown in Table 1 for better comprehension. No significant change was found between morning and evening measurements for any of the parameters. The evaluation of the study parameters gathered from the morning X-ray revealed a significant relationship between thoracic kyphosis and lumbar lordosis (
When results are grouped for BMI, the value of morning SVA was found to be 5.50
As a result of the correlation of daily changes for study parameters in the low BMI cohort, we found a significant direct relationship between SVA and PI minus LL, TK and LL, PT and PI; on the other hand, a significant inverse relationship between TK and PI minus LL, LL and PI minus LL, SVA and LL, SS and PT (Table 3). The same comparison for the high BMI cohort showed significant direct relationship between SS and PI, LL and SS, LL and PI and an inverse relationship between LL and PI minus LL, SS and PI minus LL (Table 4).
Discussion
In recent years, understanding the importance of sagittal balance, which significantly affects quality of life, has led to the identification of new targets in deformity surgery [4, 6, 14, 15, 16]. Bess et al. defined new values for correction such as: PT
When spinopelvic parameters were considered in a study by Mac-Thiong and colleagues [10] on 709 volunteers without any spinal symptoms, they declared the PI value range to be 32
It has been well defined by a number of studies focusing on relations of sagittal vertebral parameters that the thoracic kyphosis is balanced with hyperlordosis of the cervical or lumbar region and global kyphosis can be compensated with an increase of the pelvic tilt due to pelvic retroversion [9, 10, 17, 23, 24, 25]. Among these, Mac-thiong and colleagues [10] have demonstrated a direct relation between C7 translation amount and other spinopelvic parameters such as PT, SS and PI. Ghandhari and colleagues [26] have found a direct relationship between TK-LL, LL-PI and LL-SS and an inverse relationship between LL-SVA and PT-PI. In our study, we have found a direct relationship between TK-LL and SS-LL and an inverse relationship between SS-PT.
Furthermore, when the relationship between sagittal vertebral alignment, PI, TK and LL were investigated we discovered that only LL was inversely related to sagittal vertebral alignment. This finding supports previous studies proposing lumbar osteotomies to correct severe thoracic kyphosis [27, 28]. Further analysis revealed that PI minus LL values were related to SS with a 39% effect. Likewise, the direct relationship between SVA and PI minus LL had a 50% effect.
In this study, our main aim was to investigate change of sagittal balance between morning measurements and evening measurements, thus making inferences concerning compensation mechanisms to spinopelvic balance. When the measurements for the main cohort were taken into account, it was shown that there is no significant change in sagittal spinopelvic parameters throughout the day, but the PI minus LL were decreased from
This is the first study focusing on sagittal vertebral alignment changes throughout day in the literature, so we think that the results we have produced are important for the spinal research community. However, our study has its own limitations. Firstly, the number of participants is limited, but given that both morning and evening measurements of our study are parallel to the recent literature findings we find this to be of little concern. Secondly, the measurements made with computer software may have their own measurement faults. We attempted to address this problem by repeating measurements multiple times with multiple surgeons. Finally, we believe that the change of spinopelvic parameters throughout the day or by specific professional work scenarios should be further investigated with well-planned cohorts for age and body mass index with more subjects.
Conclusion
In the light of all this information, we observed no significant change in the spinopelvic parameters throughout the day. This showed that compensatory mechanisms will work to prevent collapse of spinal sagittal balance. Nevertheless, one should keep in mind that in extremely overweight patients these mechanisms might become insufficient.
Footnotes
Acknowledgments
We thank Funda H. Sezgin for her statistical analysis.
Conflict of interest
We all certify that there is no conflict of interest with any medical and financial organization regarding the manuscript. We all state that there is no funding received for this study.
