Biomechanical Evaluation of a Growth-Friendly Rod Construct

Sarah Galvis, Josh Arnold, Erin Mannen, Benjamin Wong, Hadley Sis, Eileen Cadel, John Anderson, Dennis Anderson, Paul Arnold, Elizabeth Friis

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)11-17
Number of pages7
JournalSpine Deformity
Issue number1
StatePublished - Jan 1 2017
Externally publishedYes


  • Autofusion
  • Biomechanics
  • Intradiscal pressure
  • Scoliosis

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine


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