title: Effect of Distraction Force on Growth and Biomechanics of the Spine: A Finite Element Study on Normal Juvenile Spine With Dual Growth Rod Instrumentation.
abstract: BACKGROUND
  Growth rods are used to limit the progression of scoliosis without restraining the opportunity for the spine to grow. The growth is sustained by consecutive distraction at intervals of 6 months. The optimal distraction force for a scoliotic patient is not defined adequately and rod breakage, screw loosening, stimulation of growth and altered sagittal contour has been observed.
  
  
  OBJECTIVE
  The hypothesis of this study is that for every patient with dual growth rods treatment there exists a distraction force that will sustain the growth of that patient's spine equal to normal growth with minimum changes in sagittal contours, results in lower von Mises stresses on the rods and minimum force at the pedicle screw-bone interface at 6 months.
  
  
  OBJECTIVE
  In this finite element study, we undertook an objective to identify the effect of magnitude of distraction forces on the T1-S1 growth, maximum von Mises stresses on the rods, sagittal contours, and the load at the pedicle screw-bone interface.
  
  
  RESULTS
  An optimal distraction force exists for which the growth is sustained with minimum stress on the rod, lower loads at screw-bone interface and unaltered sagittal contours. Another observation was that higher distraction forces (in the given range) didn't produce stresses on rod or load on screw that could result in failure of the implant.
  
  
  CONCLUSIONS
  Restoration of sagittal contour along with height restoration could guide the clinical practice, for the given range of distraction force.
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, Department of Bioengineering and Orthopaedics Surgery, Colleges of Engineering and Medicine, University of Toledo, 5051 Nitschke Hall MS 3032801 W. Bancroft St., Toledo, OH 43606-3390, USA.
authors.forename: Aakash
authors.initials: A
authors.lastname: Agarwal
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, Department of Bioengineering and Orthopaedics Surgery, Colleges of Engineering and Medicine, University of Toledo, 5051 Nitschke Hall MS 3032801 W. Bancroft St., Toledo, OH 43606-3390, USA.
authors.forename: Anand K
authors.initials: AK
authors.lastname: Agarwal
authors.affiliation: Department of Orthopaedics, All India Institute of Medical Sciences, Ansari Nagar East, Gautam Nagar, New Delhi, DL 110029, India.
authors.forename: Arvind
authors.initials: A
authors.lastname: Jayaswal
authors.affiliation: Engineering Center for Orthopaedic Research Excellence, Department of Bioengineering and Orthopaedics Surgery, Colleges of Engineering and Medicine, University of Toledo, 5051 Nitschke Hall MS 3032801 W. Bancroft St., Toledo, OH 43606-3390, USA. Electronic address: Vijay.Goel@utoledo.edu.
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
keywords: Distraction; Finite element study; Growth rods; Juvenile scoliosis; Rod fracture