The value of another centimeter: assessing the impact of magnetically controlled growing rod replacement in thoracic height gain and scoliosis correction.

Abstract

Purpose: Magnetically controlled growing rods (MCGR) enable scoliosis correction and height gain with minimum surgeries; however, the risk of extension failure increases with repeated lengthening, potentially necessitating rod replacement. This study aimed to investigate the benefits of replacing MCGR for additional lengthening before definitive fusion compared with direct transition to fusion without replacement.

Methods: This single-center retrospective study included patients with early-onset scoliosis who were treated with MCGR and underwent definitive fusion. Achieved rod length, T1-T12 height gain, and major curve correction were compared between patients with and without MCGR replacement. Additionally, achieved length of first and second rods was compared among patients who underwent MCGR replacement.

Results: Of 39 patients (56% female) meeting inclusion criteria, 13 underwent MCGR replacement. Patients who had replacement achieved greater total lengthening (37 vs. 20 mm, P < 0.001) over a longer period (6.2 vs. 3.5 years, P < 0.001). The replacement group also showed higher T1-T12 height gain after definitive fusion than the control group (61 vs. 47 mm, P = 0.011), although most height gains occurred during the index surgery. In contrast, the major curve correction rate was significantly lower in the replacement group (51% vs. 65%, P = 0.033). The initial MCGR achieved more lengthening than the secondary in 11/13 replacement patients.

Conclusions: MCGR replacement leads to additional lengthening and T1-T12 height gain but is associated with diminished scoliosis correction. These findings question the value of the modest 14-mm increase in thoracic height from MCGR replacement considering the decreased deformity correction and the additional time and cost.

Level of evidence: Retrospective Cohort, Level III.