Disc degeneration potentially delayed through increased body mass, study says

The body’s capacity to adapt to the load directly affects whether the effects are harmful or beneficial.

Cumulative or repetitive loading due to routine physical loading with higher body mass may slightly delay disc desiccation, according to an investigator from Canada.

The findings were discussed by Tapio Videman, MD, PhD, at the 24th Annual Meeting of the North American Spine Society in San Francisco.

Videman also added that the body’s capacity to adapt directly impacts whether physical loading has harmful or beneficial effects.

The paper won The Spine Journal Outstanding Paper Award for Medical and Interventional Science.

Tapio Videman

Videman said the purpose of the study was to investigate the associations of routine physical loading from body weight with quantitative measures of disc degeneration. Previously, disc degeneration’s cause has been related to either genetic influences or the cumulative and repetitive injury model, which emphasizes physical loading or biomechanical forces.

“There is an interesting paradox, here,” Videman said. “In the cumulative repetitive injury model, physical loading at work is the main suspected risk factor for disc degeneration. However, in exercise physiology, frequent, repetitive, and progressively greater physical loading increases the strength of bones, ligaments, muscles and tendons.”

According to Videman, the most prevalent source of physical loading is what each individual is carrying around on a daily basis: their own body weight.

“Body mass loads the lumbar discs from an early age,” he said. “Body weight is a continual factor in loading exposure in work and leisure time. As an adult, body weight is typically the largest mass handled.”

Parameters

Videman’s study involved 44 pairs of healthy male monozygotic twins with 8 kg or more discordance in body weight (mean of 13 kg), with lumbar MRIs and bone density measurements available.

Quantitatively measured disc height, disc signal intensity and signal variation, adjusted by the intrabody reference of adjacent cerebrospinal fluid signal, were used to assess the main outcome of disc degeneration.

“To verify effective loading and discordance, we also had data on bone mineral density in the lumbar spine,” Videman said.

He added that data on suspected constitutional and environmental risk factors were available for control of possible confounding factors.

Surprising results

According to the study results, higher body weight was associated with a 6.2% higher bone density in the spine – confirming an effective discordance. Disc signal variation was 5.4% higher among the heavier monozygotic co-twins, but the 2.6% higher disc heights and 2.9% higher adjusted disc signals were not statistically significant.

“Regular, repetitive loading is known to be beneficial for muscles, tendons and bones — which we confirmed with respect to bone in this study,” Videman said. “Our findings provide evidence that more cumulative and repetitive physical loading in the form of body weight appears to delay this degeneration slightly.”

Videman referred to the study’s design as “very strong,” citing its elimination of confounding factors and large sample size. Still, he said there was a limitation in that his team was unable to measure instances of extreme loading.

“The take-home message is that the disc is not an exception in the musculoskeletal system with regards to adaptation to loading,” he said. “These findings have immediate implications for preventative strategies and patient education. Heavy loading is not necessarily bad for a disc – within limits. Adaptation may be important.” – by Robert Press

References:

• Videman T, Gibbons LE, Kaprio J, Battié MC. Challenging the cumulative injury model: Positive effects of greater body mass on disc degeneration. Outstanding Paper – Medical and Interventional Science. Presented at the 24th Annual Meeting of the North American Spine Society. Nov. 10-14, 2009. San Francisco.
• Videman T, Gibbons LE, Kaprio J, Battié MC. Challenging the cumulative injury model: Positive effects of greater body mass on disc degeneration. Spine J. 2010;10:26-31.
• Tapio Videman, MD, PhD, is a member of the faculty of rehabilitation medicine with the University of Alberta, Edmonton. He can be reached at 3-48 Corbett Hall, University of Alberta, Edmonton, AB, Canada T6G 2G4. E-mail: tapio.videman@ualberta.ca.

Eugene J. Carragee

Obviously the difference in weight that you have here goes from 12 to 15 kilograms, with sufficient numbers. There must be a limit to this. If the loading difference was 100 pounds or 150 pounds, eventually it will have a bad effect – won’t it? Or can you get used to anything?

Videman replied with an acknowledgement that extreme cases of obesity were not investigated, but also pointed out that such an investigation was not the purpose of the study.

“This was not really a study in obesity, but rather a study of the effects of the differences in routine and continuous loading as experienced through body weight,” he said. “The mean BMI of these subjects was 26. It is a limitation.”

According to Videman, twin pairs with extreme weight discordance, such as 100 pounds, would likely be associated with other co-morbidities, which could confound the study results.

– Eugene J. Carragee, MD
Orthopaedic Spine Center, Stanford University,
Stanford, Calif.