Retrieval and analysis of intramedullary rods. A follow-up study.

From 1980 to 1983, 16 AO intramedullary femoral rods were retrieved and analyzed clinically, radiographically, and metallurgically. Cracking and/or fracture was observed in four of the 16 specimens. All cracks occurred at the point of maximum stress at the end of the slot. In two cases a structurally weaker weld zone coincided with this location. The weld zone and slot were also found to coincide in five of the uncracked rods. Two of the four cracked rods were removed because of pain, while only three of the 12 uncracked rods caused pain. Structural and material characteristics (i.e., the location of the weld at a point of maximum stress and significant variability in microstructure), rather than surgical technique or time in situ, were found to be responsible for the implant mechanical failures. Improvements should be made in fabrication techniques and material properties. For the present, careful assessment of a painful intramedullary rod and routine removal after healing are advisable.