Damage analysis of the Harrington rod fracture after scoliosis operation.

Fracture of the distraction rod is one of the complications following operative treatment of scoliosis by the device of Harrington. It is reported to occur in about 7% of cases. We found this complication twice in our own number of 41 patients during a follow up period of 1 to 4 years. The rods had broken 18 and 23 months after operation, but we never saw a breakage in the 1st postoperative year during the time of cast fixation. The fracture surfaces of each rod were examined under the scanning electron microscope. In one case a fatigue fracture with two beginnings at the opposite sides of the rod was found in combination with a forced fracture in the middle. The number of alterations of load from the beginning of the fracture to the complete breakage was about 10,000. The X-ray showed a loss of correction in the curve of 20 degrees with a pseudoarthrosis visible in the fusion. In the other case a typical pure fatigue fracture was seen 23 months after the operation with 18,000 alterations of load. The X-ray showed only a slight loss of correction of less than 5 degrees and no pseudoarthrosis was visable, neither in the X-ray nor in the operative exploration of the fusion. The breakage of the distraction rod results not only from a pseudoarthrosis but also from other explained facts of the procedure. Further treatment depends on a proven pseudoarthrosis.