INVESTIGATION OF FAILURES IN STAINLESS-STEEL ORTHOPEDIC IMPLANT DEVICE

Failure investigation was carried out on a failed orthopaedic total kn ee prosthesis removed from a patient. In this prosthesis the weld join t between two sections was found to be weak and hence its capacity to withstand the load bearing forces are not completely balanced and even ly distributed. As a result bending and torsional stresses due to dyna mic and cyclic loading had been concentrated on the welded section of the prosthesis. Moreover, the welded construction contained deficienci es such as delta ferrite, heat affected zone and macro cavities. Howev er, the grain size, inclusion content and chemical composition of the prosthesis were within the limits recommended by ASTM standard. Theref ore, the failure of the total knee prosthesis was a result of improper welding at the critical site.