Measurement of forces generated during distraction of growing-rods in early onset scoliosis

AIM: To measure the forces applied during distraction of growing-rods in early onset scoliosis (EOS), aimed at developing a motorized elongation device. METHODS: A consecutive series of measurements were carried out to analyze the forces applied by the surgeon during distraction of single growing-rods in 10 patients affected by EOS (mean age 8.3 years; range 6 to 10 years) undergoing the first distraction 6 months following implantation of the rods. For each measurement, output from the transducer of a dedicated pair of distraction calipers was recorded at zero load status and at every 1 mm of distraction, up to a maximum of 12 mm for each of the two connected rods. RESULTS: Twenty measurements were obtained showing a linear increase of the load with increasing distraction, with a mean peak force of 485 N at 12 mm distraction and a single reading over 500 N. We did not observe bone fractures or ligament disruptions during or after rod elongations. There was one case of superficial wound infection in the cohort. CONCLUSION: The safe peak force carrying capacity of a motorized device for distraction of growing-rods is 500N.