Degenerative skeletal disorders are common and serious problems worldwide, particularly in the aging populations. These disorders are classified as polygenic diseases because they are developed as a consequence of the interaction between an individual's genetic, lifestyle, and environmental factors. Degenerative disease of the spine is a common manifestation of the degenerative process, with the earliest spinal lesions thought to occur in the intervertebral discs. Intervertebral disc degeneration (IDD) typically appears in the second decade of life in men and in the third decade in women, with more than 50% of middle-aged adults showing some evidence of spinal spondylosis [1].

The human spine is subjected to large compressive preloads during activities of daily living. Depending on the position of the spine, the axial load exerted on the lumbar intervertebral discs can increase to magnitudes of up to three times the body weight. Age, individual somatotype, and environmental factors, such as activities of daily living and occupation, are the most important etiological factors of IDD [2]. Although not completely understood, genetic factors are increasingly being considered in the etiology of IDD. There is emerging evidence that gene polymorphisms in disc components, such as proteins, proteoglycans, cytokines, enzymes, and vitamin D receptor, play significant roles in the pathology of IDD, possibly by altering the normal homeostasis of the intervertebral disc and/or influencing the effects of environmental factors [34567].

Although IDD is common, clinical diagnosis and treatments are complicated because patients frequently present with complex neurogenic patterns of pain and impairment related to degenerative changes at multiple spinal levels. In these cases, assessment and treatment are often focused on the spinal region associated with the patient's primary complaint. For instance, a clinician may associate complaints of gait disturbances reported by patients with radiological evidence of lumbar spinal canal stenosis to cauda equina syndrome, focusing the neurological examination on the lower extremities, such as assessment of deep tendon reflexes, without considering the contribution of upper spinal lesions. An issue limiting the assessment and treatment in these cases is the absence of information regarding the relationship between degenerative changes at different levels of the spine.

Numerous studies investigating the degenerative processes of the human spine have reported the results of diagnostic imaging for the assessment and identification of spinal degeneration, as well as the resulting effects of the degeneration on the kinematics of the spine [891011121314151617]. However, to the best of our knowledge, few reports have so far investigated the correlation between degenerative changes of the cervical and lumbar spine. The aim of our study was to elucidate the prevalence of degenerative changes in the cervical and lumbar spine and estimate the degenerative changes in the cervical spine based on lumbar disc degeneration through a retrospective review of positional magnetic resonance imaging (MRI) scans.

This study included 152 patients (81 men and 71 women; age, 20–62 years; mean age, 46.9 years) with symptoms related to cervical and lumbar spondylosis with or without a neurogenic component and who had not undergone prior spinal surgery.

This study was approved by the Institutional Review Board at University of Southern California Health Science Campus (IRB protocol no., HS-1400397).

A high level of agreement (κ=0.674) was noted among three independent observers who graded IDD. The distribution of IDD grades is reported in Table 1. The average disc grades for each segment and DDSs for the cervical and lumbar spine are shown in Tables 2 and 3, respectively. The highest IDD grade in the cervical spine was identified at C5–6, followed by C6–7 and C4–5 segments. The IDD grade in the lumbar spine progressively increased from a minimum at the L1–2 segment to more extensive evidence of degeneration in the lower lumbar segments.

There were positive correlations between age and DDSs (cervical spine: p<0.01, r=0.25, r²=0.06; Fig. 1; lumbar spine: p<0.01, r=0.25, r²=0.06; Fig. 2). In addition, DDSs for the cervical and lumbar spine were positively correlated (p<0.001, r=0.44, r²=0.2) (Fig. 3).

The average cervical DDSs for each lumbar segment are shown in Table 4. We observed significant differences in cervical DDSs between the groups with normal and degenerative intervertebral disc in all lumbar segments. Although there were no significant differences in cervical DDSs in the degenerative lumbar segments, the cervical DDSs at the L1–2 and L2–3 segments tended to be higher than those at the L3–4, L4–5, and L5–S degenerative segments.

The range of motion among the different spinal segments has largely been characterized based on functional plain radiographs obtained in non-weight-bearing positions. This provides evidence of a progressive, cephalad-to-caudal increase in the segmental range of motion, with greater magnitudes of motion in the lower segments of the lumbar spine, L4–5 and L5–S, compared with the upper lumbar segments [1213]. Weight-bearing alters the biomechanical state of intervertebral discs, with reported 5%–15% decrease in the height and volume of lumbar spine discs in the weight-bearing compared with the non-weight-bearing positions [1415]. Therefore, imaging studies using non-weight-bearing positions may not accurately reflect the functional kinematics of the human spine. Using positional MRI to investigate the effects of degenerative changes in the lumbar intervertebral discs on the kinematics of the lumbar spine, Lee et al. [1617] reported a significantly larger range of motion at the L2–3, L3–4, and L4–5 segments compared with the L1–2 and L5–S segments [111617]. Our results demonstrated that degenerative changes in the lumbar intervertebral discs are largest in the lower lumbar segments (L4–5 and L5–S segments), with lower evidence of degenerative changes in the upper lumbar segments (L1–2 and L2–3 segments). This lack of concordance between the range of segmental motion, weight-bearing disc volume, and IDD grade may be explained by the findings of Nachemson et al. [18] that the degree of degenerative changes in the lumbar segments does not correlate with the segmental range of motion. The progressive increase in degenerative changes from the upper to the lower segments of the lumbar spine agrees with our predicted pattern of IDD based on the weight-bearing function of the lumbar spine. In particular, the lower lumbar spine is the mechanical fulcrum between the spine and the pelvis. Therefore, the lower lumbar segments might be subjected to the highest magnitudes of mechanical stress during activities of daily living and, as a result, would also be the most influenced by somatotopic, genetic, and environmental factors.

In our study, age reflected the grade of degenerative changes in the cervical and lumbar spine, and there was a significant positive association of the degenerative changes between the cervical and lumbar spine. In particular, we found that participants with degenerative changes in the upper segments of the lumbar spine (L1–2 or L2–3 segments) were more likely to have a higher DDS of the cervical spine. Based on our study results, we propose the need to consider the presence of cervical spine disorders in patients being evaluated and treated for lumbar spine disorders. A prognostic determination of degenerative changes in the cervical spine based on the assessment of IDD of the spinal segments in the upper lumbar spine could lower the incidence of missed diagnosis of cervical spine disorders in patients presenting with lumbar spine symptomology.

The limitations of our study need to be considered in the application of its outcome to practice. Foremost, only IDD in the cervical and lumbar spine was assessed, without consideration of neurological symptoms and impairments, such as the degree of spinal cord or cauda equina entrapment. Therefore, our results proof-of-principle data to support the development of a larger, population-based study to establish the prevalence of degenerative changes for all segments of the spine, as well as to clarify the relationships between the degenerative changes at multiple spinal levels.

Our study showed that patients with degenerative changes in the upper lumbar segments are more likely to have certain degree of cervical spondylosis. This information could lower the incidence of missed diagnosis of cervical spine disorders in patients presenting with lumbar spine symptomology.