Failure analysis of the tibial component baseplate after total knee arthroplasty

The present work was performed on a retrieved modular prosthetic tibial component, which presented a fracture in the medial portion of the baseplate. In order to understand the causes that led to the failure of the baseplate, the steel, the mechanical and structural characteristics and the fracture were analyzed and correlated with numerical studies related to the biomechanical loads and displacements transmitted to the knee joint during human gait. The results showed a set of adverse events that occurred before the fracture of the baseplate. The steel, used for the manufacture of tibial component, had a high ferrite content, low mechanical strength, and did not comply with standard specifications. Design errors of the baseplate and insert assembly were shown to be the cause for the damage to the polyethylene of the insert. This damage included wear, plastic deformation and plaque formation by delamination, which increased the gap between the fitting guides. These phenomena enabled the relative displacement between the components, and the misaligning of the mechanical axis, causing an increase of the bending moment in the medial region of the baseplate. The load peaks concentrated in the primary contact area with the medial femoral condyle exceeded the mechanical strength limits of the piece, causing the fracture of the metallic tibial baseplate.