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

Abstract

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.

Finite element simulation of a scoliotic spine with periodic adjustments of an attached growing rod

“…The forces to effect the required Cobb angle changes appear to correlate well with patient data reported by Teli et al and Noordeen et al [19,20] . For instance, Teli [19] reported that the measured magnitude of force generated during the 5mm distraction process ranged from 172 N to 447 N. The force found in the FEM for the same 5 mm growing rod distraction is 362 N, which lies within this range. However, FEM force measured 669 N with growing rod distraction of 10 mm, which is slightly higher than Teli's [19] value of 500 N for the same amount of rod displacement.…”

“…For instance, Teli [19] reported that the measured magnitude of force generated during the 5mm distraction process ranged from 172 N to 447 N. The force found in the FEM for the same 5 mm growing rod distraction is 362 N, which lies within this range. However, FEM force measured 669 N with growing rod distraction of 10 mm, which is slightly higher than Teli's [19] value of 500 N for the same amount of rod displacement. From Table (II), we can seen clearly that distraction force is increasing significantly each time growing rod distraction is attempted.…”

Distraction magnitude and frequency affects the outcome in juvenile idiopathic patients with growth rods: finite element study using a representative scoliotic spine model

“…Differential distraction forces were also applied (eg, 50-25 denotes application of 50 N on left concave side and 25 N on right convex side). These distraction forces were selected based on the range of mean total distraction force data available in the clinical literature [27]. Along with it, we also applied a different distraction force in three of the six cases to incorporate differential distraction commonly seen (qualitatively) in clinical practice.…”

Is There an Optimal Time to Distract Dual Growing Rods?

“…For each procedure after the first surgery there was a 24% increase in likelihood of a perioperative complication. Sankar et al [16] found a statistically significant decrease in T1eS1 height gains with repeated distractions, and 2 other studies [17,18] showed a clinically significant increase in distraction forces across the spine and implants with repeated distractions. Repeated distractions can also lead to fracture of the rods, which are most likely to occur, on average, after the fourth distraction [19].…”