Letters to the editor

Some finite element programs which are widely used to solve orthopaedic biomechanics problems have default finite elements which fail to pass the requirements for solution convergence. In particular, prior to the release of version 4.3 of ANSYS the default continuum finite elements of this program were incompatible and did not pass the convergence requirements. These elements also are included in the libraries of the programs SAP and SAPIV. When used incorrectly these elements can cause significant errors in the calculated stresses. The finite element patch test can help the user to avoid this problem by determining when a collection of finite elements can cause large errors.