Formaldehyde embalming alters biomechanical strain of human cervical spinal dura mater: quantification and implications from paired fresh-frozen and embalmed specimens.

PURPOSE: This study aimed to quantify the biomechanical strain of the human cervical spinal dura mater in fresh-frozen versus embalmed (formalin-fixed) states, elucidate the impact of formaldehyde fixation on its mechanical response, and provide evidence-based guidance for specimen selection in spinal biomechanical research. METHODS: A paired repeated-measures design was employed using 20 fresh cadaveric specimens (10 male, 10 female; 35-40 years). After initial testing in the fresh-frozen state (- 20 °C storage, slow thawing), specimens were fixed in 20% neutral buffered formalin. Standardized head-neck positions (neutral, flexion, extension, right rotation) were applied, and the posterior surface length of the C1-C7 dura mater was measured using a digital caliper. Spinal cord strain (ε) was calculated as (L-L₀)/L₀, where L₀ was the neutral-position length. Statistical analyses included one-way/two-way repeated measures ANOVAs and paired t-tests. RESULTS: Embalming significantly reduced the neutral-position dura length (79.90 ± 11.02 mm fresh vs. 63.56 ± 11.09 mm embalmed, p < 0.001) and amplified strain magnitudes: flexion (7.75%→13.13%), extension (- 6.46%→-9.75%), and right rotation (- 1.86%→-2.17%). Paired t-tests confirmed significant increases in absolute strain for flexion (Δ = 5.39%, p < 0.001) and extension (Δ = 3.29%, p <0.001), with no significant change in right rotation (p = 0.172). A two-way ANOVA revealed significant main effects of state (F = 63.87, p < 0.001) and position (F = 726.73, p <0.001), and a strong interaction effect (F = 673.40, p < 0.001), indicating position-dependent embalming artifacts. CONCLUSION: This study demonstrates that formaldehyde embalming significantly alters the biomechanical properties of the human cervical spinal dura mater, increasing tissue stiffness and reducing strain tolerance under load. These findings emphasize the importance of native viscoelasticity in fresh tissue and caution against directly extrapolating biomechanical data from embalmed specimens to living humans. The results provide a critical reference for interpreting existing literature and selecting appropriate specimen models in future spinal biomechanical research.