Fatigue fracture of the femoral component in total knee replacement.

BACKGROUND

Fracture of femoral component in total knee arthroplasty (TKA) has become a rare complication with improvements in metal alloy manufacturing technology.

METHODOLOGY

We report two cases of fracture of femoral components 9 and 10 years after primary TKA. The Buechel-Pappas (BP) knee system used in our two cases were designed by the same team who designed the LCS TKA implants. The femoral component is made of cobalt chromium alloy. The break in the femoral component noted in both the cases were at a similar site, at the distal medial flange just posterior to the peg of the femoral component.

RESULT

Both these cases underwent revision surgery using stemmed implants with good results. Implants retrieved were analysed with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) to study the fracture pattern and material properties respectively. Fractography analysis of both our cases showed that the crack initiated laterally from the thin edge (1mm) around the sharp angulated corner of the medial femoral condyle and spread medially towards the thicker segment.

CONCLUSION

We feel two fractures of femoral component out of 9000 TKA in ten years is significant. We recommend a re-evaluation of the femoral component of the BP knee system to ensure that the edges, specifically the sharp corners, have adequate thickness to avoid a fatigue fracture.