Risk of disc degeneration not linked to heavy lifting

Study shows it is also not related to back pain

Despite legitimate concerns about the impact of heavy lifting on back health, occupational health professionals can rest a bit easier about one aspect of perceived occupational risk factors. A recent study indicated that heavy lifting, traditionally associated with back pain, is not necessarily linked to spinal disc degeneration. Furthermore, the study noted, the risk of disc degeneration is not necessarily linked to back pain at all.1

A Swiss research team used magnetic resonance imaging (MRI) scans to look for evidence of lumbar disc degeneration in 41 adults who were initially free of back pain. Follow-up scans showed that disc degeneration had developed or progressed in 41% of the subjects.

A wide range of possible risk factors for disc degeneration were evaluated, focusing on work- and sports-related factors. After adjustment for other factors, there were just three significant risk factors found: the presence of disc herniation, lack of sports activities, and night-shift work. Heavy lifting, carrying, twisting, and bending were not found to be significantly related to disc degeneration.

Results not surprising

The findings of this study came as no great surprise to Scott D. Boden, MD, professor of orthopedics and director of The Emory Spine Center at Emory University School of Medicine in Atlanta. "It has been very difficult to make direct associations between disc degeneration and many environmental/occupational exposures that one might assume would be risk factors," he asserts. "This difficulty likely stems from the fact that disc degeneration is common as the population ages, and it can be increased to varying degrees depending on the interplay between many different factors that are difficult to control in studies, such as genetic predisposition, environmental exposures, diet, physical loads, smoking, and injuries." Even studies in identical twins have had difficulty finding major risk factors for disc degeneration, he adds.

The notion that disc degeneration may not correlate with low back pain also is not new, says Boden. "In 1990, my group published a paper in the Journal of Bone and Joint Surgery reporting on MRI scans in asymptomatic (no low back pain history) volunteers. By age 60, 92% had at least one level of disc degeneration (dehydration) on MRI scans even though they had no back pain," he reports.

The mystery of shift work

The authors of the study had a harder time explaining why there was a correlation between shift work and risk degeneration. "The cause for this negative effect remains speculative," they wrote. "An alteration of the diurnal fluid shift in the disc required for normal disc nutrition might be a contributing factor. A disturbance of normal sleep is among the most commonly reported problems among shift workers. In addition, sleep quality, physical fitness (maximum oxygen consumption and muscle strength) and musculoskeletal problems are shown to be associated in shift workers. On the other hand, the negative influence of night shifts might be caused by adverse working conditions associated with night shifts." 1

For additional information, contact: Scott D. Boden, MD, Professor of Orthopaedics, Director, The Emory Spine Center, Emory University School of Medicine, Atlanta, GA. E-mail: Scott_Boden@emoryhealthcare.org.

References

1. Elfering A, Semmer N, Birkhofer et al. Risk factors for lumbar disc degeneration: A 5-year prospective MRI study in asymptomatic individuals. Spine 2002; 27:125-134.