Aging of the cervical spine in healthy volunteers: a 10-year longitudinal magnetic resonance imaging study
From: Spine. 2009 Apr 1;34(7):706-12
Prevalence of back and neck problems is high among general populations, and it has been estimated that neck pain is recognized in 9,000,000 and both neck and low back pain in 19,000,000 people in the United States. The total cost for the treatment of neck pain in Netherlands in 1996 was estimated to be US $686 million.
Aging of the cervical spine can inevitably occur in anyone. Recent advances in basic researches on disc degeneration have revealed its possible mechanisms including a decrease in proteoglycan contents and water concentration, involvement of inflammatory cytokines such as interleukin-15 and iTNF-α, and some genetic factors. Since the intervertebral disc is one of the tissues subject to early aging processes starting as early as 20 years of age, and is often the source of cervical spinal disorders causing neck pain and related symptoms, it is important to ascertain the processes of aging when considering treatments for age-related cervical spinal diseases. There have been a few studies on aging of the cervical spine in healthy subjects using plain x-ray, computed tomography, or magnetic resonance imaging (MRI). In particular, MRI has excellent tissue resolution and can sharply visualize degeneration of the intervertebral discs. However, the majority of these studies were cross-sectional, and have only been able to determine the prevalence of age-related degenerative changes in the cervical spine, but failed to clarify the sequential processes of aging. Thus, long-term longitudinal studies following the same individuals are necessary to elucidate the accurate aging processes of the cervical spine.
We conducted a cross-sectional study of MRI findings of the cervical spine in 497 asymptomatic healthy subjects between 1993 and 1996,11 and showed that the incidence of degenerative changes in the cervical spine increased with age; the incidence of degenerative findings on MRI was 17% and 12% in male and female teenagers, respectively, and was 86% and 89% in male and female subjects in their 60s, respectively.
In the present study, which was conducted approximately 10 years after the previous study, a part of the same cohort was recruited and underwent follow-up MRI. The objectives of this longitudinal study were to investigate the processes of the progression of intervertebral disc degeneration and to clarify correlations between the progression of intervertebral disc degeneration and the development of clinical symptoms.
Previous cross-sectional studies have demonstrated that age-related changes of the cervical spine are widely present even in asymptomatic healthy subjects. Boden et al, who conducted MRI of the cervical spine in asymptomatic healthy subjects, reported that degenerative MRI findings were recognized frequently in subjects 40 years and older despite the absence of symptoms. Lehto et al conducted MRI of the cervical spine, using a 0.1-T MRI imager in 89 healthy subjects. Some sorts of abnormal findings were recognized in 62% of the subjects 40 years and older, whereas abnormal findings were rare in those younger than 40 years.
Although these several cross-sectional studies have been reported, the longitudinal studies on the aging processes of the spine are very scarce. However, this kind of study is necessary as a control when assessing the outcomes of various surgical and nonsurgical interventions against various cervical spinal diseases. Once surgical intervention for serious cervical intervertebral disc herniation and cervical spondylotic myelopathy, secondary to disc degeneration, is warranted, anterior cervical discectomy with fusion is the usual procedure and the gold standard. It is widely and anecdotally believed that degeneration of the intervertebral discs adjacent to the fusion level are accelerated by fusion, thereby causing later problems, Yue et al investigated 71 patients who underwent anterior cervical fusion, and found progression of disc degeneration at the adjacent intervertebral levels in 73% of the patients after a long-time follow-up. They reported that reoperation was required in 17% of the 71 patients. To solve adjacent segment deterioration, attempts to develop and clinically apply artificial intervertebral discs and homologous intervertebral disc transplantation that preserves physiologic motions of the cervical spine have been carried out. However, at present, it is unknown whether anterior fusion truly accelerates degeneration of the adjacent segment or whether motion preservation technique can really prevent degeneration, because there has been few longitudinal study on the normal aging processes of the disc that can serve as an appropriate control. Borenstein et al followed 31 of 67 asymptomatic healthy subjects (follow-up rate, 46%) longitudinally for 7 years and repeated MR studies of the lumbar spine, and found that low back pain appeared in 42.0% and progression of degenerative findings on MRI was recognized in 74.2% of the subjects.
The report by Gore et al is the only longitudinal study of the cervical spine in healthy subjects. They performed a 10-year longitudinal follow-up study of healthy subjects without cervical spine-related symptoms, using plain x-ray, and found that, at follow-up, neck pain was recognized in 15% of their subjects, who had no symptoms at the time of initial imaging, and that changes in x-ray findings were recognized in 63% of the subjects.
The present longitudinal 10-year follow-up study revealed that degeneration of the cervical intervertebral discs progressed in 81.1% of the initially asymptomatic subjects. According to the evaluation in the different age groups, progression of disc space narrowing and foraminal stenosis was observed more frequently in subjects 50 years and older than those under 50 years of age, while the proportions the subjects with progression of decrease in the signal intensities of the intervertebral disc, anterior compression of the dura and the spinal cord, and PDP were higher in subjects 20 to 49 years old than in those older than 50 years. The differences in the degree of progression in the different MR findings among the different age groups may reflect the presence of different stages in the degeneration processes of the intervertebral discs. Our results suggested that biochemical changes in the intervertebral disc represented by the decrease in the signal intensity on MRI and early structural changes of the disc represented by anterior dural compression and posterior disc protrusion occur in the younger age groups (20-50 years) and more advanced structural changes in the intervertebral disc represented by disc space narrowing and foraminal stenosis occur in the older age groups (older than 50 years).
Smoking habit, labor, history of lumbar surgery, etc. were suggested as factors accelerating the aging process of the cervical intervertebral discs in several previous studies. The subjects of most of these studies were patients with serious cervical spinal disorders requiring surgery and few such studies dealt with healthy subjects, as this present study. The proportion of the subjects with progression of degeneration of the intervertebral disc during 10-year study period was higher in the elderly than in the young age groups. However, there was no significant correlation between progression of disc degeneration and the parameters, including gender, smoking, alcohol, sport and BMI, which have been reported to be related to disc degeneration in the previous studies.
Most cross-sectional studies on asymptomatic volunteers conducted to date have shown that degenerative changes in the intervertebral discs are frequently observed on MRI, suggesting that such degenerative changes on MRI are often not associated with clinical symptoms. However, in the present longitudinal study, patients who developed clinical symptoms during 10 years, including neck pain and stiff shoulder demonstrated significantly more frequent progression of structural disc degeneration on MRI including anterior compression of dura and spinal cord, posterior disc protrusion, disc space narrowing, and foraminal stenosis than those without development of clinical symptoms. Thus, unlike the results of the previous cross-sectional studies, progression of structural changes of intervertebral discs on MRI during a long-time period is likely to correlate significantly with clinical symptoms.
The present study is the first large-scale longitudinal study, in which the degree of degeneration of the cervical spine was investigated using MRI, demonstrating progression of disc degeneration in initially asymptomatic healthy volunteers. The result of the present study can serve as a useful control for the evaluation of the postinterventional course in patients with various cervical spinal disorders.
