Smaller Interval Distractions May Reduce Chances of Growth Rod Breakage Without Impeding Desired Spinal Growth: A Finite Element Study.

Abstract

Growth rods allow regular distraction of the spine to compensate for growth. Traditionally such distractions are performed every 6 months via open surgery. However with the advent of minimally invasive techniques like magnetically controlled growing rods, the distractions can be performed non-surgically. This also implies that the interval of distraction could be changed or customized based on individual patient's need. In this study we have hypothesized that the distraction at shorter intervals reduces the stresses on the rods which in turn reduces the chance of rod failure. A finite element model of a juvenile spine was instrumented with growth rods and distractions were applied at different frequencies (2 months, 3 months, 6 months, and 12 months) for a period of two years to study the effects of frequency of distraction on maximum von Mises stresses on the rods for different loading conditions were studied. The stresses on the rods were highest for 12-month distraction (2 distractions in 2 years) and lowest for 2-months distraction (12 distractions in 2 years). It was found that the shorter intervals of distraction led to reduction of stresses on the rod for same spinal height gain in two years.