Biomechanical considerations of multiple-component hip prostheses. Analysis of three failures of the Lippman...

Three cases are presented and analyzed in which a Lippman Transfixion Hip Prosthesis had to be replaced because of the discomfort of the patient. In each case, there was evidence of wear between the head of the prosthesis and the flange. The different wear patterns indicated problems which exist in the alignment of component parts of the prosthesis. In each case there was low grade sepsis to which the debris may have contributed. Because of phagocytosis, amount of debris accumulation was difficult to evaluate. The factors which appear to have contributed to the amount of debris accumulation were: the length of time the prosthesis had been used; the degree of alignment and amount of debris which may be formed and is phagocytized; the degree of manufacturing control. The design of this prosthesis incorporated mechanical problems which are generally undesirable because of: the eventual deformation of the end of the pivot rod or hole in the head of the prosthesis: progressive loosening of the movement due to this and inherent malalignment; the difficulty in fabrication, assembly and installation of the prosthesis because of the multiplicity of parts; the difficulty in maintaining adequate control of surface finishes.