Volume VI, Number 2 | August 2022

The Effect of Formalin and Ethylene Glycol on the Biomechanics of the Human Distal Radius

The following abstract was selected by the JAOAO Editorial Board for publication in this journal issue.

1Memar S, 2Bledsoe G, 1Tersigni-Tarrant M

1Saint Louis University School of Medicine, St. Louis, MO, USA;
2Saint Louis University Park’s College of Aviation, Engineering and Technology, St. Louis, MO, USA

Biomechanical studies are important for understanding the mechanical and material properties of bone, fracture mechanics, and fixation techniques encountered in orthopedics. Fresh-frozen human bones are the gold standard; however, these specimens may be in limited supply and cost more to acquire and maintain. The precise effect on the cortical bone due to embalming solutions is unclear. It was hypothesized that the mechanical parameters of the human distal radius will be altered after a 10-week preservation period in either a neutral-buffered formalin (4% formaldehyde) or an ethylene-glycol solution, as compared to fresh-frozen specimens.

In one of the largest studies of its kind, 54 forearms, from fresh-frozen samples, were randomly chosen and equally assigned into fresh-frozen, formalin, or ethylene-glycol groups. Exempt from IRB status, this was conducted in accordance with standard operating procedures governing the use of specimens from the Saint Louis University Center for Anatomical Science and Education’s Gift Body Program. The cadavers had an average age of 80 years old, ranging from 48 years old up to 97 years old. The median age was 82 years old. T-scores and bone mineral density were measured with dual-energy X-ray absorptiometry before the radius was excised from the surrounding soft tissue. Each distal radius was cut with an autopsy saw at 13.0 cm and placed in a vacuumed sealed bag with 500 mL of fluid, according to its experimental group. Computed tomography and Horos v3.0.1 for Macintosh were used to calculate the cross-sectional areas. A pH analysis before and after preservation was completed with 1 mL of fluid per specimen using an ISFET pH meter, model IQ120. After 10 weeks, three-point bending to destruction was performed using a hydraulic powered MTS 858 Mini Bionix II with a load cell of 1,500 N, applied at a rate of 0.4 mm/s. The data was recorded at 15 Hz and exported into Microsoft Excel in order to compute the stiffness, maximum load, work to fracture, ultimate strength, and Young’s modulus. ANOVA statistical analysis was then performed with JMP 14 Statistical Software for Macintosh from SAS.

While general trends were observed, no significant differences existed when comparing embalmed bones of either type to fresh-frozen specimens, except in regard to their energy absorption; however, significant differences did exist when comparing the biomechanical parameters of bone embalmed in formalin to those of ethylene glycol.

Fresh-frozen bones should remain the gold standard for orthopedic research. Embalmed specimens are best served for pilot studies, as most of the preliminary data may not have significant differences compared to the fresh-frozen specimens. However, significant differences in parameters, such as stiffness and Young’s modulus, make comparing results and extrapolating information between projects which use different embalming solutions unreliable. Research studies on these topics should use a standardized embalming solution, if fresh-frozen specimens are not feasible. Further research is warranted with longer preservation times in order to see if the generalized trends become statistically significant at a later point in time.

The Journal of the American Osteopathic Academy of Orthopedics

Steven J. Heithoff, DO, FAOAO

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