Proximal anchor fixation in magnetically controlled growing rods (MCGR): preliminary 2-year results of the impact of anchor location and density.

STUDY DESIGN

Multicenter, retrospective cohort study.

OBJECTIVES

Analyze the impact of MCGR proximal anchor location and density on radiographic outcomes and complications. Magnetically controlled growing rods (MCGRs) reduce the need for repeat operations for lengthening when treating spinal deformity in children. The evidence behind choosing the location and density of proximal anchors comes from the traditional growing rod and rib-based distraction technique literature. Thus, there is much debate regarding the optimal quantity and location of proximal anchors.

METHODS

This study included early-onset scoliosis patients treated with MCGR with a minimum 2-year follow-up. Comparisons of 2-year correction in the coronal and sagittal planes, complication rates, and patient-reported outcomes were made based on proximal fixation type, proximal anchor density, and type of case (primary, conversion).

RESULTS

This study included 155 MCGR patients. Spinal deformity correction at 2 years was significantly higher in spine-based than rib-based constructs, in terms of both the major (23.9° vs. 17.1°, p = 0.05) and minor curves (10.0° vs. 4.5°, p = 0.03). Greater proximal anchor density, regardless of location, was also associated with better major curve correction at 2 years (25.0° vs. 18.2°, p < 0.05). There was a trend towards higher risk of device migration with rib-based fixation (13.8% vs. 4.1%, p = 0.06) and rod breakage with spine-based fixation (10.3% vs. 3.4%, p = 0.21). Having 5+ proximal anchors did not significantly decrease the risk of complication, including device migration (8.4% vs. 7.7%).

CONCLUSIONS

When using the MCGR, proximal spine anchors and greater anchor density impart superior deformity correction but do not significantly impact the risk of device complications. Although rib-based constructs afford less rigidity than spine-based constructs, there is a similar risk of rod breakage and device migration. This study suggests that having 5+ MCGR proximal anchors does not protect against proximal anchor complication.

LEVEL OF EVIDENCE

Level III-therapeutic.