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Short Communication | DOI: https://doi.org/doi.org/10.31579/jsdr.2
*Corresponding Author:
Citation:
Copyright: © Wongelawit leul 2018 et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Received: 30 November -0001 | Accepted: 26 September 2018 | Published: 02 October 2018
Keywords: Low back pain, Osteoarthritis, Spine osteoarthritis, Disc space narrowing, Intervertebral disc degeneration
Lumbar spine osteoarthritis (OA) is very common, with estimates of prevalence ranging from 40–85 %. The process of degeneration of the spine has commonly been classified as OA (disc space narrowing together with vertebral osteophyte formation); however, anatomically, the facet joint is the only synovial joint in the spine that has a similar pathological degenerative process to appendicular joints. Low back pain (LBP) is also a common condition, with nearly 80 % of Americans experiencing at least one episode of LBP in their lifetime. The complex relationship between spine radiographs and LBP has many clinical and research challenges. Specific conservative treatments for spine degeneration have not been established; there has, however, been recent interest in use of exercise therapy, because of some moderate benefits in treating chronic LBP. An understanding of the relationship between spine degeneration and LBP may be improved with further population-based research in the areas of genetics, biomarkers, and pain pathways.
Osteoarthritis (OA) is the most common form of arthritis, affecting an estimated 27 million adults in the US [1]. The prevalence of OA has increased over the past two decades, and increases in life expectancy and obesity, both risk factors for OA, have led to concerns over the public health consequences of OA [1]. Arthritis in general is also a leading cause of disability and a significant cause of reduced quality of life [2, 3]. Commonly thought of as a disease of the peripheral joints (i.e., hips, knees, and hands), spine OA is often ignored in discussions of the prevalence and effect of OA on disability and function [4]. However, estimates of lumbar spine OA are high, ranging from 40–85 %, the large range being primarily because of study differences in definitions, distribution of age and other demographic factors, and recruitment of subjects [5].
Approximately 80 % of Americans experience at least one episode of LBP during their lifetime, making frequency of LBP second only to the common cold [6, 7]. Utilization of health care services resulting from LBP is high, and total social cost is estimated to be greater than 100 billion dollars per year in the United States [8]. Aside from prevalence and cost, the effect of LBP on the workplace is substantial. Approximately 149 million workdays per year are lost as a result of LBP [9], making it the most common reason for time off from work [10,11]. There is no doubt that LBP has a substantial effect on the US health care and workforce system, affecting more than 30 % of community-dwelling adults in a given year [12] and remaining one of the most common reasons for physician visits [13]. Because of its high prevalence and effect on health services, the spinal anatomical origins of LBP are of great interest to researchers and clinicians. To address prevention and treatment, understanding the etiology of LBP is important, because it may differ within the large majority of patients in whom we describe the etiology as mechanical or non-specific origin.
Pathophysiology and/or Anatomy
Individual radiographic features of the spine, commonly studied and referred to as the “three-joint complex”, are the structures of vertebral osteophytes (OST), facet joint OA (FOA), and disc space narrowing (DSN) from intervertebral disc degeneration [20]. All of these spinal structures have adequate nerve supply capable of generating LBP.
The vertebral facet joints (zygapophyseal joints) are synovial joints with the typical features of hyaline cartilage over subchondral bone, a synovial membrane, and a joint capsule [21]. Facet joint OA is a multifactorial process, and it has been thought that the presence of intervertebral disc degeneration leads to a greater load and motion at the facet joint, resulting in degenerative changes similar to those seen in other synovial joints [20]. However, the presence of facet joint OA has been found to be present even in the absence of intervertebral disc degeneration [22].
Situated between two vertebral bodies, the intervertebral disc is made up of two main regions: the soft inner nucleus pulposus and the firm outer collagenous annulus fibrosis [23]. The collagen content of the intervertebral disc consists of both type I and II collagen, with the nucleus containing only type II whereas the annulus contains both types I and II [24]. Changes to the disc collagen content can occur naturally with aging, a process commonly referred to as intervertebral disc degeneration. These aging-related changes include a decrease in aggrecan, water, and collagen content [25], resulting in DSN on plain film radiographs.
Prevalence: Gender and Race Differences
The presence of these radiographic spine features is quite common, as evidenced by community-based prevalence of lumbar spine DSN between 50 and 64 % and vertebral OST prevalence as high as 75–94 % [34–37]. Our recent work is the only study to quantify the prevalence of radiographic FOA in a community-based population, revealing the prevalence affecting at least one lumbar level to be 57.9 % [35**].
The prevalence of these radiographic features has been found to differ by gender and race. Most recent studies agree that OST is more prevalent [34, 35, 37] and severe [35, 37] in men whereas prevalence of DSN is greater in women [34, 35, 37]. Our recent work is the first to describe these features across a sample of African Americans (AA) and Caucasians [35]. We found the prevalence of all these radiographic features was significantly lower for AA than for Caucasians, most notably in the odds of FOA (OR = 0.45; 95 % CI 0.32, 0.62). The reason for this may be related to racial differences in occupational exposure, BMI, physical activity demands, or anatomical differences. As such, there is still much to be learned about the reasons for these race and gender differences and radiographic changes in the lumbar spine.
Associations With Low Back Pain
An topic that is particularly understudied is the association between spine radiographic features and physical function. de Schepper et al. [34**] found, in some instances, stronger associations between reduced physical function and disability and DSN (OR = 1.9; 95 % CI 1.4, 2.6) as measured with the Health Assessment Questionnaire. In this same cohort, Scheele et al. [40**] recently found a strong association among those with both morning stiffness and LBP with DSN (OR = 2.5; 95 % CI 1.9, 3.4). Our findings with regard to physical function are similar to those of de Schepper et al., measured by use of a condition-specific questionnaire (Roland-Morris Back Pain and Disability Questionnaire). We have found, using data from the Johnston County OA Project (n = 1,633), that after adjusting for age, BMI, and gender, mean levels of perceived disability because of LBP increase significantly.
Current Conservative Treatment Options
Given the effect of LBP on the US healthcare system, workplace, and individual quality of life, there is great need to better understand predictors and etiologic factors of LBP. Most research has focused on treating symptoms and functional impairment of LBP rather than on understanding the mechanisms underlying the anatomic and functional changes we currently call spine degeneration and their relationship to symptoms and functional impairment. Currently, our understanding of the treatment for LBP is, stated simply, that some activity is better than no activity [43, 44]. Exercise therapy is an activity which has long been a treatment option for LBP, with Cochrane and other reviews indicating some effectiveness for treating chronic low back pain [45]. Specifically, treatment of LBP with yoga has attracted substantial interest in recent years [46–48]. A recent randomized clinical trial by Sherman and colleagues [47**] found that outcomes for the yoga intervention group were superior to those for the self-care group, but no significant difference was found from the stretching group for chronic LBP. The functional outcomes found in the yoga and stretching group remained statistically superior to those for the self-care group after a follow-up of 26 weeks. These findings suggest it is the physical rather than psychological aspect of yoga that has moderate benefits for chronic LBP. This trial did not specifically target patients with intervertebral disc degeneration and excluded patients with severe intervertebral disc degeneration, because some patients with severe disc degeneration may not tolerate exercise therapy [48]. The use of conservative treatment to prevent spine degeneration or conservative treatment for spine degeneration as a primary technique for treating LBP has not yet been reported in the literature. Reasons for this may be the small number of longitudinal studies, inconsistencies in predictors, and weak risk factors.
The radiographic features of spine degeneration are common and are associated with LBP and reduced physical function. Therefore, facet joint OA and degeneration of the spine resulting in DSN and OST formation should not be overlooked in the discussion of OA and population estimates of prevalence and disease burden. This is particularly true of the facet joint, which may follow an OA-related degenerative process similar to that of appendicular synovial joints. However, recent population-based studies have been unable to link FOA with LBP and the multidimensional nature of LBP may cloud these associations. In recent years population-based studies have consistently demonstrated that DSN is associated with LBP, and recent longitudinal evidence suggests it may be a risk factor for LBP. Current treatment has not focused on primary or secondary prevention of LBP resulting from intervertebral disc degeneration, but evidence suggests that exercise therapy in general, including stretching and yoga, are good treatments for LBP. The different associations of LBP, physical function, and radiographic features in the spine are indicative of the importance of individual assessment of radiographic features and measured outcomes in future studies. Given the multidimensional nature of LBP, determining the association between spine degeneration and both LBP and reduced physical function may prove more worthwhile and clinically applicable in understanding the burden of spine degeneration than self-reported LBP alone. Finally, the role of genetics, biological markers, and understanding pain pathways in spine degeneration and LBP may be crucial to understanding the complex relationship between these two conditions.