Samartzis and his colleagues report on a cross-sectional study of Chinese youth, aged thirteen to twenty years. Out of a larger cohort of 1989 Southern Chinese volunteers, they identified eighty-three individuals in this particular age group who did not have spinal deformity. Fifty-four of them, twenty-two males and thirty-two females, had no evidence of disc degeneration on a T2-weighted sagittal magnetic resonance imaging (MRI) of the lumbar spine. Twenty-nine, sixteen males and thirteen females, did exhibit MRI evidence of juvenile disc degeneration. Statistical analysis showed no significant difference in age or sex between the two groups. However, weight, height, and body-mass index (BMI) were all significantly higher in the group with juvenile disc degeneration. The odds ratio for having disc degeneration was 14.19 (95% confidence interval [CI], 1.44 to 140.40) if an individual was overweight or obese compared with underweight. Interestingly, it was a remarkable 11.70 (95% CI, 1.34 to 102.37) even if the BMI was normal; again, note that the risk was relative to being underweight. The broad confidence intervals are also important to note. The odds ratio for having juvenile disc degeneration was 6.57 (95% CI, 1.96 to 22.02) for subjects who recalled sustaining a lumbar injury. Cigarette usage, exercise level, and Schmorl nodes did not predict juvenile disc degeneration. MRI findings in the group with juvenile disc degeneration were disc bulges or extrusions and high-intensity-zone lesions. The number of levels involved ranged from one to three, with a mean of 1.3 levels, and the average disc degeneration score was 2.9 (range, one to nine).
Within the group with juvenile disc degeneration, increasing BMI was associated with more severe disc degeneration. Elevated BMI together with a history of lumbar injury was associated with having juvenile disc degeneration.
Furthermore, some individuals in the normal juvenile group as well as the group with juvenile disc degeneration had low back pain, with or without sciatica. The prevalence was higher among those with juvenile disc degeneration, and on average, the symptoms were of greater severity. It is important to note that back and leg pain occurred in both groups. Disc degeneration is one, but not the only, cause of such symptoms. Conversely, disc degeneration can be asymptomatic, as was shown in this study and in many other investigations. Thus, disc degeneration is an important, but not the sole, marker of individuals with (or at risk for) back and leg problems. Disc degeneration is not always a disease. One could counter that in this particular age group it is pathological, but in the absence of signs or symptoms, do we wish to label these individuals as having disease?
One strength of the study is that it consisted of a group of volunteers drawn from a general population. The authors do not provide information about the stability of that population, but characterize it as Southern Chinese. The methodology for identifying disc degeneration was similar to that employed by other investigators. The authors add to the growing appreciation of lumbar spinal complaints among the young. Given the rise of obesity in many parts of the world, and its association with both a greater severity of disc degeneration and lumbar symptoms, the authors provide yet another reason to seek strategies to attain ideal body mass early and throughout life. This would be true even if the disc degeneration were silent, since symptoms could develop during adulthood. Indeed, even if the disc degeneration is not the cause of such later symptoms, its presence could lead to expensive diagnostic and therapeutic interventions that are only marginally effective, especially in the case of lumbalgia. It is sobering to note that the definition of obesity in this ethnic group is lower than that used in North America.
There are some weaknesses to the study. The sample is relatively small (eighty-three subjects); this is reflected in the broad confidence intervals and large standard deviations. One wonders whether a larger sample might demonstrate an association between disc degeneration and tobacco use or physical inactivity. Physical activity was characterized on the basis of a very modest threshold of twice-a-week exercise. Assuming a stable population with a stable gene pool, the investigators’ claims regarding this group may be reasonable. However, their results are not necessarily generalizable to other populations with different gene pools and with different environmental conditions, since nature and nurture both play roles in lumbar spinal disorders, including disc degeneration. The study shows association, but not necessarily cause and effect. As a cross-sectional study, it elucidates prevalence, not incidence. The link to previous lumbar injury is subject to recall bias, although the authors did query relatives to corroborate the data. There was also no way to quantify the amount of previous lumbar trauma experienced, much less determine if it actually caused the development of disc degeneration that in turn produced or could produce symptoms sufficient to interfere with the activities of daily living. The data are tantalizing but leave us with many unanswered questions.
The authors are to be congratulated on their study. They add to the massive, but still incomplete, database concerning the prevalence of disc degeneration in the young. They are quite correct that disc degeneration may be associated with debilitating symptoms that could limit the ability of affected individuals to engage in life for the many decades ahead of them. I would encourage the authors to seek to enlarge their sample and to follow their subjects over time to gain additional data and insights.