Date Published: January 25, 2019
Publisher: Public Library of Science
Author(s): Gentaro Kumagai, Kanichiro Wada, Hitoshi Kudo, Toru Asari, Daisuke Chiba, Seiya Ota, On Takeda, Kazushige Koyama, Shigeyuki Nakaji, Yasuyuki Ishibashi, Nicole C. Wright.
The physical and biochemical factors related to cervical disc degeneration (CDD), which is involved in several spinal disorders, remain uncertain. We investigated associations between CDD and muscle strength in a general Japanese population. We used mid-sagittal-plane MRIs to assess CDD in 344 subjects recruited from participants in our community health-check project, and measured body mass index (BMI), skeletal muscle index (SMI), and muscle strength in the neck, trunk, hands, and legs. CDD was scored based on the prevalence and severity of intravertebral disc degeneration. Spearman correlation coefficients were used to evaluate whether the SMI or muscle-strength values were correlated with the disc degenerative score. Stepwise multiple linear regression analyses were then conducted with the CDD score as the dependent variable, and age, sex, BMI, and muscle strength as independent variables, for each gender. These analyses used the muscle-strength parameters that were found to be correlated with the CDD scores in the single correlation analyses. The CDD scores were similar in men and women. Men had significantly more muscle strength in the neck, trunk, hands, and legs. There was a significant negative corelation between the CDD score and the trunk strength in both sexes, handgrip in men, and leg strength in women in the single-variable correlation analysis. Including age and the limb- or trunk-muscle strength comprehensively, multiple linear regression analyses showed that age was the strongest factor that was independently associated with CDD in both sexes, and that the effects were attenuated by limb and trunk muscle strength.
Chronic neck pain and neck shoulder stiffness are common symptoms in the general population . One study showed that radiographic degenerative changes in the cervical spine were associated with the severity of neck pain in a general population . However, degenerative changes in the cervical spine are also common in asymptomatic individuals, challenging the simple concept of cause and effect . The number of subluxations and the incidence and severity of degenerative changes in the cervical spine increase with age [4, 5]. Typical changes include osteoarthritis of the facets with reduced joint space and disc narrowing. Cervical myelopathy, a common degenerative spinal disease that interferes with normal activities , partly involves compression of the cervical spinal cord by spinal canal stenosis. Cervical spinal canal stenosis can arise from developmental canal stenosis, intervertebral disc protrusion into the spinal canal, or thickening of the ligamentum flavum . Degenerative cervical changes can also appear in the intervertebral discs, and these changes progress with age  . Epidemiologic studies have shown that the prevalence of cervical canal stenosis increases with age  . Reported risk factors for cervical disc degeneration (CDD) include age   , genetics , bone metabolism , smoking , metabolic syndrome , manual labor , and lumbar spinal disorders  .
Among the volunteers from our public health-project population, 151 men (mean age 54.2) and 193 women (mean age 55.5) were enrolled in the study. The youngest of the 344 participants was 20, and the eldest was 86 years old (Table 1). Table 1 summarizes the participants’ age, smoking, exercise habits, BMI, SMI, degenerative score, and muscle strength. There was no significant difference in age between the men and women. The men had a significantly higher prevalence of smoking (P < .0001) and a higher BMI (P < .001). Although there was no significant difference in mean degenerative score between the men and women, the men had a significantly higher mean SMI and had significantly more strength in the neck, trunk, hands, and legs (Table 1). To our knowledge, this is the first community-based survey of associations between CDD and muscle strength in a rural Japanese population. We showed that the strength of trunk flexion in men and women, hand grip in men, and leg strength in women were negatively correlated with CDD scores in single-variable correlation analyses. Multiple linear regression analyses that comprehensively included age and limb or trunk muscle strength showed that age was the strongest independent factor associated with CDD in both sexes, while the associations of limb and trunk muscle strength were attenuated. Source: http://doi.org/10.1371/journal.pone.0210802