Bead loosening in porous metal coated orthopaedi implants: a case study

Abstract This paper describes our clinical observations and the results of an analysis of the biomechanical parameters affecting bead loosening. A PCA-Howmedica porous coated tibial plateau was retrieved during revision arthroplasty, and loose beads were observed in the synovial fluid. One bead had migrated and was embedded in the high density polyethylene (HDPE) articulating tibial surface. Only soft tissue was observed in localized areas of the interface between prosthesis and bone. The tibial prosthesis was visually examined by stereoscopic magnification and with the scanning electron microscope (SEM). The componentwas then sectioned to study the microstructure of the beads, and their bonding to each other and to the substrate. Energy dispersive scanning revealed large localized deviations from the standard composition of cobalt chromium alloy. The embedded bead, the HDPE and the femoral articulating surface were badly worn.