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The effect of simulated microgravity on lumbar spine biomechanics: an in vitro study

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Abstract

Purpose

Disc herniation risk is quadrupled following spaceflight. This study tested the hypothesis that swelling-induced disc height increases (comparable to those reported in spaceflight) stiffen the spine and elevate annular strain and nuclear pressure during forward bending.

Methods

Eight human lumbar motion segments were secured to custom-designed testing jigs and subjected to baseline flexion and compression and pure moment flexibility tests. Discs were then free-swelled in saline to varying supraphysiologic heights consistent with prolonged weightlessness and re-tested to assess biomechanical changes.

Results

Swelling-induced disc height changes correlated positively with intradiscal pressure (p < 0.01) and stiffening in flexion (p < 0.01), and negatively with flexion range of motion (p < 0.05). Swelling-induced increases in disc height also led to increased annular surface strain under combined flexion with compression. Disc wedge angle decreased with swelling (p < 0.05); this loss of wedge angle correlated with decreased flexion range of motion (R 2 = 0.94, p < 0.0001) and decreased stiffness fold change in extension (p < 0.05).

Conclusion

Swelling-induced increases in disc height decrease flexibility and increase annular strain and nuclear pressure during forward bending. These changes, in combination with the measured loss of lordotic curvature with disc swelling, may contribute toward increased herniation risk. This is consistent with clinical observations of increased disc herniation rates after microgravity exposure and may provide the basis for future countermeasure development.

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Acknowledgments

This work was supported by the National Aeronautics and Space Administration (NASA), Grants NNX10AM18G and NNX13AM89G.

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Authors and Affiliations

  1. University of California, Box 0514, 513 Parnassus Avenue, Medical Sciences Bldg., San Francisco, CA, 94143-0514, USA

    Cory J. Laws, Britta Berg-Johansen & Jeffrey C. Lotz

  2. UCSD Medical Center, University of California, 350 Dickinson St., Suite 121, Mail Code 8894, San Diego, CA, 92103-8894, USA

    Alan R. Hargens

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  1. Cory J. Laws
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Correspondence to Jeffrey C. Lotz.

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Conflict of interest

The authors do not have any financial relationship with the organization that sponsored the research (NASA), and have full control of all primary data that the journal is free to review if requested.

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Laws, C.J., Berg-Johansen, B., Hargens, A.R. et al. The effect of simulated microgravity on lumbar spine biomechanics: an in vitro study. Eur Spine J 25, 2889–2897 (2016). https://doi.org/10.1007/s00586-015-4221-6

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  • DOI: https://doi.org/10.1007/s00586-015-4221-6

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