Background
The increase of elderly people has been occurring at unprecedented rates. There will be 2 billion people aged 60 or over worldwide, accounting for 21% of the world’s population by 2050 [
1,
2]. Along with these demographic changes, age - related diseases will bring a burden to society, for example, by an increase in demand for health services. However, the process of aging and the period of old age are still the least understood aspects of human development. Aging is defined as irreversible functional and structural changes in many organs and systems. These changes vary between individuals at different rates or extents. Deciphering the changes in body posture occurring with age is a current topic in the field of geriatrics which requires a great deal of study.
Body posture is a fundamental index for assessing health and quality of life, especially for elderly people [
3,
4]. Such index can provide information for targeted health promotion [
5], be used to assess healthy aging and for health abnormality alerts, such as osteoporosis [
6], sarcopenia [
7] and fall-risk estimation [
8], because falling is the most frequent cause of unintentional injuries and often leads to death in elderly people [
9]. As an aspect of body posture, maintaining proper sagittal alignment is an important determinant for proper spinal function [
10], and sagittal alignment is becoming recognized as an important predictor of a patient’s outcome after spinal surgery [
11]. Alterations in spinal alignment may serve as leading factor for diminished body biomechanics [
10]. Stress concentration in unbalanced sagittal spine can lead to functional and structural pathology, such as pain and degeneration of disc and facet joints [
12]. Recent studies support the idea that analysis of sagittal balance is a key point to optimize the management of spinal degenerative diseases [
13‐
15].
In the normal population a standard sagittal balance does not exist. Generally, researchers take healthy young adults as normal control, and the body posture differences are found between younger and older people [
16‐
19]. The sagittal alignment can be affected by aging related degeneration [
19,
20]. Aging has a number of inevitable consequences regarding the axial skeleton [
10], such as hypertrophic facet joints arthritis, degenerative disc disease, bone remodeling and atrophy of extensor muscles [
10,
14]. These pathologies lead to the risk to progressively develop a global sagittal unbalance [
21]. Spinal malalignment in elderly people greatly affects the quality of daily life [
22]. Describing the specific changes of body posture with aging would allow for the development of targeted rehabilitation programs, such as exercise-base interventions, surgical interventions, spinal orthotics and postural taping, etc., starting from no matter before or after 60 years of age, and help for improving life quality of elderly people [
18,
23].
Although aging is suggested to be associated with alterations in sagittal alignment, in turn body posture, changes of body posture occurring with aging is still a current issue in geriatrics needing further research. However, previous studies had some limitations as following: Firstly, most studies compared the body posture differences between populations only under 30 and over 60 years of age [
16‐
19]. More investigations on changes occurring with age are required to get close to decipher the beginning of the age-related changes on body posture, which will be helpful for intervention of aging process. Secondly, most studies focused on only one segment, such as cervical [
24], thoracic [
25] and lumbar spine [
10,
19]. As we have known, compensatory mechanisms contributing to keep the sagittal balance of the spine [
14] involve in different segments, especially the adjacent ones, for instance, cervical and thoracic, thoracic and lumbar spine. Full-body assessment of sagittal plane is necessary to get global and thorough characteristics of sagittal axis changes.
The aims of this study were to assess the parameters of body posture in the global sagittal plane - from head to legs – in men and women from 20 to 89 years of age, and to determine the dynamics of changes in standing body posture in sagittal plane occurring with age and differences between men and women.
Discussion
In the present study, we explored age and gender differences in relaxed standing body posture in the sagittal plane, with posture expressed as five angles derived from neck, thorax, waist, hip and knee, via a new photogrammetry. The results show significant changes with age in most parameters of body posture, including increasing cervical lordosis, thoracic kyphosis and knee flexion, especially starting from as early as around 50 yrs., and these changes were more marked among women than men. We believe that this paper present useful externally generalizable information not only for clinical purposes but also to inform further research on larger numbers of subjects, particularly to test angles of neck, thorax and knee.
Effect of aging on body posture
There have been little data regarding the normal physiological sagittal changes with aging for the cervical and thoracic alignment before the current study. Subjects enrolled in the previous aging-related cervical alignment studies were usually before 80 yrs. [
16,
24,
32] or were divided into old group after 60 yrs. [
16,
33]. The previous aging-related thoracic alignment studies are in similar situation, since the researchers compared elderly people after 60 yrs. with young subjects aged 20-25 yrs., or only investigated elderly people [
17,
18,
34]. In our study, we assessed the posture parameters in population covered from young to old age sequentially. Although Fon et al. measured thoracic kyphosis in subjects aged 2-77 yrs. [
25], they reported only the mean degree of each decade of life and analyzed the correlation on age as linear regression. However, usually, the naturally dynamic changes with aging are not simply in linear. We applied GAM and got fitting-curve which presented the changes with aging closer to the true nature of the population compared to linear regression. Through these fitting-curves, we found that the tendency and degree of changes had discrepancy at different age stages.
The neck angle in this study gives a measure of the cervical lordosis, which is a useful clinical indicator of mid and/or lower cervical spine dysfunction. In general, cervical lordosis observed in the neutral position increases with aging [
16,
32,
33,
35,
36]. Our research is the first report about the starting period of cervical lordosis development. Furthermore, we found for the first time in the asymptomatic subjects, the degree of cervical lordosis reduced from about 70 yrs., particularly in men. Similar to this, in a study of cervical spondylotic myelopathy patients, the lordotic angle measured by Cobb method also decreased in men and increased little in women after the decade of 80′ compared to before 80′ [
35]. However, in another study, the cervical lordosis developed gradually from the 6th to 10th decade [
36]. The discrepancy maybe because in the latter study, they enrolled much more women than men, since the lordosis angle of women is greater than men.
The thorax angle in this study gives a measure of the thoracic kyphosis. A decrease in this angle is considered to result in a ‘poking chin’ posture and hunchback. In previous studies, the deepening of thoracic kyphosis with age is seen in both men and women [
17,
18,
25,
34]. In our study, we also found the thoracic kyphosis developed, especially deteriorated from around 50 yrs. Fon et al. reported that the thoracic kyphosis increase appears to be more obvious after 40 yrs. by means of a modification of the Cobb technique [
25]. This discrepancy is maybe because of the difference of the methods, population selection, etc. However, both of these studies indicated thoracic kyphosis developed far earlier than 60 yrs.
In previous studies about changes of knee during aging, researchers usually investigated parameters of gait or walking ability [
37‐
39], or in patients with deformity or after surgery [
31,
40]. There are little studies assessed the knee posture when standing still in normal aging population. In the current study, we reported the flexion tendency of knee with aging in standing position, especially in women. Knee flexion is considered to be the last compensatory mechanism in case of sagittal imbalance [
31,
40].
In consistence with our study about the middle segments of the body, waist and hip, some studies also found no significant difference in lumbar lordosis between younger and older volunteers [
19,
23,
41]. However, many other studies reported a flattening of lumbar lordosis with aging [
10,
34,
42,
43]. The possible reasons of this discrepancy include: since the middle segments of the body are relative stable and change in a narrow range, the assessment needs more accurate and more sensitive methods, such as radiographs; second, different parts of lumbar spine have different change tendency. For example, Dreischarf et al. reported that the lower lumbar spine retains its lordosis and mobility, whereas the middle part flattens and becomes less mobile in the older (> 50 yrs) compared to the younger age cohort (20–29 yrs) [
42]. It suggests that different part of lumbar should be investigated separately. In study by Lee et al., although there was no significant difference in lumbar lordosis between the younger and older groups, when they separately analyzed lumbar lordotic angle as upper and lower lumbar lordosis, the distribution was different [
19]. These findings suggest that the lumbar sagittal profile in a standing position is not affected by aging, but components of the lumbar spine with distinct anatomical and biomechanical functions do appear to be affected by aging.
Effect of genders on body posture
We found that, although overall, both cervical lordosis and thoracic kyphosis were more accentuated in men than in women. However, the differences between men and women mainly occurred in younger ages - before 60 yrs. for neck angle and before 70 yrs. for thorax angle. After this age, the angles of two genders are close, while before this age, the younger, the bigger is the difference between two genders. Thus, both previous studies and the present study demonstrated that women had a greater tendency of accentuation of both cervical lordosis [
24,
32,
36] and thoracic kyphosis [
17,
25] than men during aging. Therefore, women developed greater compensatory lordosis of the cervical spine with age. Since the age-related progression of sagittal malalignment relates to some adverse effects [
17,
44‐
46] and affects the quality of life [
3,
4], the problem induced by deteriorating body posture relates to women significantly more often [
47,
48]. Furthermore, the present study suggests that men and women have different normal body posture parameters and it is important to take the change tendency into account.
Clinical implications
Considering the tight relationship between sagittal plane deterioration and quality of life measures [
3,
4], there is growing interest of analyzing the sagittal plane and the non-deformity patients. Following a mild positive sagittal malalignment, the patient often begins recruiting mechanisms to compensate. Compensatory mechanisms are the patient’s progressive response to sagittal plane deterioration. Generally, elderly people exhibit greater thoracic kyphosis. The consequence of an accentuated thoracic curvature is mirrored in the cervical region with compensatory adjustments to head posture required to preserve forward gaze [
14,
49]. In our study, we did find that greater accentuation of both cervical lordosis and thoracic kyphosis occurs with aging. Moreover, correlation between neck and thorax angles has been found and neck and thorax have similar change tendency with aging. Age-related progression of thoracic kyphosis may affect the quality of life in elderly people most profoundly. In osteoporosis patients, the lower quality of life, including physical and emotional roles, such as bodily pain and general health, are associated with increased thoracic kyphosis [
50]. Extend adjacent segments of the kyphotic spine allowing for compensation of the sagittal unbalance but potentially inducing adverse effects [
14,
17,
45]. Furthermore, considering the gender differences, the problem induced by deteriorating cervical lordosis and thoracic kyphosis relates to women significantly more often [
47,
48]. On the other hand, assessment of the lower limbs is part of a full body sagittal plane analysis, including knee flexion angle. Knee flexion is another well-known compensatory mechanism for patients with severe degenerative spine and has already been widely reported [
14,
51]. This report confirms the close interaction between spine and lower extremities.
For the aging population, comprehensive geriatric assessment (CGA) provides substantial insight into the comprehensive management of elderly people [
52]. Developing concise and effective assessment instruments is helpful to carry out CGA widely to create a higher clinical value. CGA concerns the general health of elderly people and multidimensional and comprehensive scientific assessment of health status [
52]. Physical health is one of the main domains of CGA. Since body posture is a fundamental index for assessing health and quality of life, it has potential to be involved in CGA. This can be applied to the elderly people in the community and in a variety of care settings.
The advantages of this sagittal posture photogrammetry
Due to its non-invasive, reproducible, and sensitive testing characteristics, we decided to use the photogrammetry, which has been widely using in observational studies for body postural evaluation. Its use undoubtedly contributes to reducing exposure to radiation and thus enables the monitoring of postural treatment [
18,
53]. Specifically regarding the application of photogrammetry in spinal evaluation, many studies have performed procedures to validate the technique [
53‐
56]. However, the application of photogrammetry in postural evaluation is directly dependent on both the collection procedures and the mathematical methods used to provide measurements and postural diagnoses. In the current study, the five posture angles are considered useful and easily attained postural outcome measures. Besides the above advantages, our photogrammetry is simple and needs no special software. So it is appropriate for application to clinical studies, self-evaluation, intervention monitoring, population epidemiology survey etc.
Limitations
As with any study, this investigation has some limitations. Firstly, the study sample was small. However, we endeavored to minimize distortion and generalization of the data by using various statistical tests. Further testing with larger subject numbers is required to be certain of these findings. Secondly, all the subjects are from Han Chinese and majority of them are mental workers. However, the height, body weight and BMI of our sample did not have significant influence on these body posture parameters, and these data are useful to help people of other background, who would prepare for an aged society, to understand age-related change. Thirdly, we evaluated body posture only in sagittal plane, not in coronal plane. Fourthly, as discussed above, we didn’t find significant changes of waist and hip, alterations of which have been reported during aging.
Conclusions
The presented results showed changes in the parameters describing body posture throughout consecutive ages and emphasized that for an individualized functional analysis, it is essential to consider age-and gender-specific changes in the neck, thorax and knee, including increasing cervical lordosis, thoracic kyphosis and knee flexion, especially starting from as early as around 50 yrs., and these changes were more marked among women than men. This paper presents useful externally generalizable information not only for clinical purposes but also to inform further research on larger numbers of subjects.