Poster Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

THE BIOMECHANICAL VIABILITY OF FIXED HUMAN CADAVERS: CAN FIXED CADAVERS OFFER SCIENCE ONE MORE GIFT? (#30)

Noah Chow 1 , Sabrina I Sinopoli 1 , Mitchel C Whittal 1 , Diane E Gregory 1
  1. Wilfrid Laurier University, Waterloo, ONTARIO, Canada

Introduction: Human cadavers used for teaching anatomy are often fixed with a variety of preserving fluids through arterial embalming [1]. Because of the natural avascularity of the intervertebral disc, it is largely unknown how fixation fluids affect the biomechanics of the disc and specifically the annulus fibrosus [2]. This study aimed to compare the annular biomechanics from specimens fixed using various methods to determine if preserved human cadavers may be viable for annular mechanical testing.

Methods: Part A: In order to control for age, diet, activity, and environmental factors, a porcine animal model was used to examine the mechanical effects of four different fixation solutions. Ten porcine cervical spines were randomly assigned to one of the following conditions (2 per condition): fresh unfixed; ethanol fixation; Imperial College London fixation; saturated salt fixation; surgical reality fluid fixation. Intact cervical spines were submerged for 14 days [3]; figure 1. Post submersion, the C3/4, C4/5, and C5/6 discs were excised and subjected to three annular tests: single layer tensile test, 180° peel test, and bilayer tensile test. The single layer test was used to quantify the strength of the intralamellar matrix, the peel test was used to quantify the strength of the interlamellar matrix, and the bilayer test provided a holistic measure of the strength of the annulus [4,5]. Part B: Four human cadaver spines were obtained from a local anatomy school; each cadaver was fixed via arterial embalming using one of the solutions examined in Part A. The same annular tests were performed on samples obtained from the L1/2, L2/3, L3/4, and L4/5 discs. Note that no fresh human cadaver samples were tested.

Results: Part A: No significant (p>0.05) differences in annular mechanical properties were observed between the fresh (no fixation) condition and either the ethanol fixation, Imperial College London fixation, or surgical reality fluid fixation. However, significant differences were found with the saturated salt fixation; compared to fresh, saturated salt fixation resulted in reduced toe region strain (p<0.001) and reduced stress at 15% strain (p=0.031) in the bilayer test, and reduced average peel strength (p=0.017) in the peel test. Though not statistically tested due to sample size, mechanical data from the human samples in Part B showed similar findings to that in the porcine data (figure 2).

Discussion: The current study did not observe any significant differences in annular mechanical properties between the unfixed cervical spine and spines fixed with either the ethanol fixation, Imperial College London fixation, or surgical reality fluid fixation. Therefore, because of the rarity of human cadaveric tissue, cadavers embalmed in these particular solutions may be viable for biomechanical annular tissue testing. This would offer science one more gift before the donors are returned to their families. Further, based on the findings of this study, one should refrain from using tissues preserved in a saturated salt fixation for biomechanical testing of the disc.

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  1. Brenner E. (2014). Human body preservation - Old and new techniques. Journal of Anatomy, 224(3), 316–344.
  2. Jiang, L., Yuan, F., Yin, X., & Dong, J. (2014). Responses and adaptations of intervertebral disc cells to microenvironmental stress: A possible central role of autophagy in the adaptive mechanism. Connective Tissue Research, 55(5-6), 311–321.
  3. Wang, A., de Sa, D., Darie, S., Zhang, B., Rockarts, J., Palombella, A., Nguyen, L., Downer, N., Wainman, B., & Monteiro, S. (2023). Development of the McMaster Embalming Scale (MES) to assess embalming solutions for surgical skills training. Clinical Anatomy (New York, N.Y.), 36(5), 754–763.
  4. Gregory, D. E., & Callaghan, J. P. (2012). An examination of the mechanical properties of the annulus fibrosus: The effect of vibration on the intra-lamellar matrix strength. Medical Engineering & Physics, 34(4), 472–477.
  5. Gregory, D. E., Bae, W. C., Sah, R. L., & Masuda, K. (2012). Anular delamination strength of human lumbar intervertebral disc. European Spine Journal, 21(9), 1716–1723.