Estimation of the Fracture Toughness of Soft Tissue from Needle Insertion

A fracture mechanics approach was employed to develop a model that can predict the penetration force during quasi-static needle insertion in soft tissue. The model captures a mechanical process where the sharp needle produces a crack that is opened to accommodate the shaft of the needle. This process involves the interchange of energy between four distinct phenomena: the work done by the needle, the irreversible work of fracture, the work of friction, and the change in recoverable strain energy. From measurements made in vivo, porcine liver fracture toughness was estimated from the difference in penetration force between two consecutive insertions at the same location. The values obtained fall within a reasonable range and confirm the relevance of a computational model of needle insertion based on fracture mechanics.