2. DISCREPANCY BETWEEN PROGRAMMED AND OBSERVED DISTRACTIONS IN MAGNETICALLY-CONTROLLED GROWING ROD TREATED PATIENTS
María del Mar Pozo-Balado, PhD; Noelia Domingo-Montesinos, MD; Francisco José Lirola-Criado, MD; José Manuel Martínez-Salas, MD; David Farrington, MD.

3. INTRODUCTION Magnetically-controled growing-rods (MCGR)
Allow distractions without the need for additional surgeries.
The use of ultrasonography reliably documents rod distractions:
Reduces the number of radiographs.
Minimizes ionizing radiation exposure in early-onset scoliosis (EOS) patients.
However, there is a discrepancy between the distraction programmed on the external adjustment control (EAD) device and that which actually occurs in vivo.

4. OBJECTIVE
Objective
Our aim was to analyze the discrepancy between Programmed Distractions (PD) and Observed Distractions (OD) measured by ultrasonography, and to analyze associated clinical factors.

5. METHODS
Study design
A retrospective medical record review was performed of all children with EOS treated for scoliosis with MCGR at our institution from March 2014 to January 2016.
PD and OD values were recorded at each distraction, and differences between them were also calculated.
Correlations between PD and OD with clinical parameters (gender, age, weight, Cobb angle and rod position in relation to the curve) were also investigated.
Statistical Analysis
Friedman test was used for multiple longitudinal comparisons and the Willcoxon paired test for longitudinal comparisons between two groups.
Correlations were explored by using the Spearman test.
For all test, p<0.05 was considered stitistically significant.

6. RESULTS I
Patients
17 patients with at least 6 months of follow up met the inclusion criteria and were finally included in the study.
Patients underwent rod distraction at 2 month intervals.
Characteristic
Value
Male Sex (%)
10 (58.8)
Age at MCGR insertion, mean months [max-min]
90 [60-115]
Number of elongations, mean [min-max]
6 [3-10]

7. RESULTS II PD and OD values Parameter Left rod Right rod
Total PD, mean mm
15.1
15.9
Total OD, mean mm
14.9
16.5
PD/OD ratio
1.01
0.96
No significant differences were found between total PD and OD values, or PD/OD ratio between rods.

8. RESULTS III
High correlation between total PD and total OD values in both rods.
Left Rod
Right Rod

9. RESULTS IV
Negative correlation between PD/PO ratio values and Cobb angles along the follow up time.

10. CONCLUSIONS
There is a discrepancy between PD and OD values along the time that seems to be related with the Cobb angle, being the amount of distraction reduced in patients with higher Cobb.

11. SIGNIFICANCE
Even though our results are preliminary, and should be supported with larger series, we consider the discrepancy between the Programmed Lengthening and Obtained Lengthening measured with ultrasonography
should be taken into account when calculating the amount of distraction applied to MCGR.