Background:
Children with spinal muscular atrophy (SMA) frequently develop neuromuscular scoliosis at an early age, requiring surgical treatment with growth-friendly spinal implants (GFSI), such as magnetically controlled growing rods. This study investigated the effect of GFSI on the volumetric bone mineral density (vBMD) of the spine in SMA children.

Methods:
Seventeen children (age 13.2 & PLUSMN;1.2 y) with SMA and GFSI-treated spinal deformity were compared with 25 scoliotic SMA children (age 12.9 & PLUSMN;1.7 y) without prior surgical treatment as well as age-matched healthy controls (n=29; age 13.3 & PLUSMN;2.0). Clinical, radiologic, and demographic data were analyzed. For the calculation of the vBMD Z-scores of the thoracic and lumbar vertebrae, phantom precalibrated spinal computed tomography scans were analyzed using quantitative computed tomography (QCT).

Results:
Average vBMD was lower in SMA patients with GFSI (82.1 & PLUSMN;8.4 mg/cm(3)) compared with those without prior treatment (108.0 & PLUSMN;6.8 mg/cm(3)). The difference was more prominent in and around the thoracolumbar region. The vBMD of all SMA patients was significantly lower in comparison with healthy controls, especially in SMA patients with previous fragility fractures.

Conclusions:
The results of this study support the hypothesis of reduced vertebral bone mineral mass in SMA children with scoliosis at the end of GFSI treatment in comparison with SMA patients undergoing primary spinal fusion. Improving vBMD through pharmaceutical therapy in SMA patients could have a beneficial effect on the surgical outcome of scoliosis correction while reducing complications.