title: Biomechanical Evaluation of a Growth-Friendly Rod Construct.
abstract: BACKGROUND
  Distraction-type rods mechanically stabilize the thorax and improve lung growth and function by applying distraction forces at the rib, spine, pelvis, or a combination of locations. However, the amount of stability the rods provide and the amount the thorax needs is unknown.
  
  
  METHODS
  Five freshly frozen and thawed cadaveric thoracic spine specimens were tested for lateral bending, flexion/extension, and axial rotation in displacement control (1°/sec) to a load limit of ±5 Nm for five cycles after which a growth-friendly unilateral rod was placed in a simulated rib-to-lumbar attachment along the right side. The specimens were tested again in the same modes of bending. From the seven Optotrak Orthopedic Research Pin markers (Northern Digital Inc., Waterloo, Ontario, Canada) inserted into the top potting to denote T1, and the right pedicles at T2, T4, T5, T8, T9, and T11 and the Standard Needle Tip Pressure Transducers (Gaeltech, Isle of Skye, Scotland) inserted into the T4/T5 and T8/T9 discs, motion, stiffness, and pressure data were calculated. Parameters from the third cycle of the intact case and the construct case were compared using two-tailed paired t tests with 0.05 as the level of significance.
  
  
  RESULTS
  With the construct attached, the T1-T4 segment showed a 30% increase in neutral zone stiffness during extension (p = .001); the T8-T12 segment experienced a 63% reduction in the in-plane range of motion during flexion (p = .04); and the T8/T9 spinal motion unit had a significant decrease of 24% in elastic zone stiffness during left axial rotation (p = .04).
  
  
  CONCLUSIONS
  It is clear the device as tested here does not produce large biomechanical changes, but the balance between providing desired changes while preventing complications remains difficult.
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Galvis
authors.affiliation: Tufts University, 419 Boston Ave, Medford, MA 02155, USA.
authors.forename: Josh
authors.initials: J
authors.lastname: Arnold
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Mannen
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Wong
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA.
authors.forename: Hadley
authors.initials: H
authors.lastname: Sis
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA.
authors.forename: Eileen
authors.initials: E
authors.lastname: Cadel
authors.affiliation: Children's Mercy Hospital, 2401 Gillham Rd, Kansas City, MO 64108, USA.
authors.forename: John
authors.initials: J
authors.lastname: Anderson
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, USA.
authors.forename: Dennis
authors.initials: D
authors.lastname: Anderson
authors.affiliation: University of Kansas Medical Center, 3901 Rainbow Blvd, Kansas City, KS 66160, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Arnold
authors.affiliation: University of Kansas, 1450 Jayhawk Blvd Mechanical Engineering and Bioengineering, 1530 W. 15th St., 3138 Learned Hall, Lawrence, KS 66045, USA. Electronic address: lfriis@ku.edu.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Friis
keywords: Autofusion; Biomechanics; Intradiscal pressure; Scoliosis