Fatigue failure of an orthopedic implant – A locking compression plate

In the present work, the fatigue failure of a locking compression plate (LCP) fixed across a transverse fracture (8-mm gap) at the midshaft of femur was experimentally evaluated. The complete fracture of LCP occurred after 42,000 cycles of loading, i.e. equivalence to about 8 days of walking. The fatigue failure of LCP was possible before the adequate healing of fracture, and the full load of walking should not be allowed for the patient with the present fracture condition. The fatigue crack firstly initiated from a subsurface inclusion embedded under the surface of compression hole. After some cycles of loading, another fatigue crack also initiated from the surface of locking hole, and then both cracks propagated inside the LCP. As an evidence of the propagation of fatigue crack, the striations were observed on the fracture surface of the LCP. The striation spacing was long when observed far from the crack initiation site, and became shorter when observed around the crack initiation site. Based on the striation spacing, the number of cycles for the propagation of fatigue crack from the initiation site to the bottom part of LCP was estimated to be approximately 5000 cycles.