Effect of young's modulus of porcine ligamentum flavum on the epidural needle insertion

In order to predict how much the human ligamentum flavum will be deformed and tented during insertion of an epidural needle, experiments with the porcine spines were done to check the effect of Young's modulus of the porcine ligamentum flavum. Porcine ligamentum flavums were harvested with vertebral bones and trimmed in rectangle shape. The epidural needle was inserted at 0.8 mm/s with a linear actuator from perpendicular to stretch direction of the specimens. Reaction force as insertion resistance with a load cell and side view of the specimen and the needle as deformation of the ligamentum flavum with a CCD camera were recorded synchronously. As results, width of vertebral bones related the maximum deformation, while no relation was observed between width of vertebral bones and the maximum insertion force. Young's modulus affected the maximum insertion force. Human ligamentum flavum has longer width of vertebral bones and larger Young's modulus. Thus, larger maximum deformation and higher maximum insertion force for the human ligamentum flavum were predicted.