Optimum energy on the fragmentation of kidney stones by direct impact

摘要

Purpose - This paper aims to describe a numerical approach to the fragmentation of kidney stones by direct impact. Design/methodology/approach - The numerical approach consists of a Lagrangian finite element formulation with dynamic insertion of cohesive-free surfaces. Cohesive free surfaces are governed by a damage constitutive model whereas the continuum part of the mesh remains linear elastic. The impact of the metallic probe of the medical device is modeled with a displacement control of the nodes inside the area of impact on the stone. Findings - The results show the relation between the total energy transmitted during the impact with the damage and the fragmentation (number of fragments and number of microcrack clusters) of the kidney stone. The paper establishes the existence of both, an activation and saturation energy level, that delimit a range optimum working energy transmitted during the impact. In particular, the computations show that, for the calcium oxalate monohydrate stone, the maximum energy supplied by the medical device (Lithoclast) coincides with the saturation energy level. Originality/value - In medical investigations, the experimentation is always restricted to the availability of patients or specimens. In the particular case of the elimination of renal calculi, the literature exhibits an extensive number of works reporting the practical experience of medical doctors. However, there is still a lack of information that might help to understand and to improve the comminution of kidney stones.