I have done stress analysis by some softwares for approximately 10 years and familiar with the pros and cons of each of them. Engineering software like ANSYS and COMSOL which are good in the bio field and have better and more accurate results and convergence. Mathematical Softwares such as Matlab and MathCad are both good and strong in numerical methods and stress calculation, just they are not design specially for stress analysis or numerical simulation and takes time to write some code.
Also I have published some articles in international journals in bioengineering fields utilising COMSOL and MAtlab.
Some special algorithm should be used to solve the bio-material tasks as it is more complicated than the others. Also the convergency of the solution is an important parameter that should be considered and track in every steps. in some cases in biomechanical modelling, the results shows going toward the zero determinant and then by some automatic programming method, change the direction and makes better but in which side? coming close to zero is inevitable , that is the situation that the designer / programmer should understand what is going on and take decision. This decision is important to get right answer, because most of the time, he should come back some steps and change many things to make it correct not playing with the algorithm only.