Failure of a Knee Prosthesis Accelerated by Shedding of Beads From the Porous Metal Surface

A 61-year-old man who received a porous-metal-coated knee implant returned eight months later with chronic synovitis, instability, and loosening of his artificial joint. Subsequently, metal beads were detected in the joint space and soft tissues and were also embedded in the articulating surface of the tibial component. There was scoring of the tibial surface, and polyethylene wear particles were noted in the synovial and fibroconnective-tissue membranes, which had formed beneath the tibial component. Many particles were seen inside giant cells and macrophages. Failure in this case was probably accelerated by the granulomatous response in the soft tissue to wear particles. There was osteolysis rather than new bone growth at the interface with the tibial component. Analysis indicated that poor bead-bonding strength may have initiated the problem. Careful appraisal of the outcome from use of beaded porous-metal-coated devices and assurance of their adequate bonding strength are essential for further progress.