Observed Length Increases of Magnetically Controlled Growing Rods are Lower Than Programmed

Area of Science:

• Orthopedics
• Spinal Surgery
• Pediatric Orthopedics

Background:

• Magnetically controlled growing rods (MCGRs) are a key treatment for early onset scoliosis (EOS).
• Limited data exists on MCGRs' ability to achieve desired lengthening, especially with prior instrumentation or varying tissue depths.
• This study investigates factors influencing MCGR lengthening in EOS patients.

Purpose of the Study:

• To evaluate the actual lengthening achieved by MCGRs compared to programmed distraction in EOS patients.
• To determine if prior spine instrumentation affects MCGR lengthening.
• To assess the impact of tissue depth on MCGR distraction success.

Main Methods:

• Retrospective review of 31 EOS patients treated with single or dual MCGRs.
• Ultrasound measurement of rod distraction at each follow-up visit.
• Statistical analysis (t-tests, regression, correlation) to compare programmed vs. actual distraction and assess tissue depth impact.

Main Results:

• MCGRs achieved 86% of the programmed distraction (±21%), a statistically significant difference (P<0.001).
• Patients with prior spine instrumentation showed similar lengthening (87% ±23%) compared to those without (86% ±19%) (P>0.9).
• Increased tissue depth was inversely proportional to lengthening success, with a 2.1% decrease in achieved lengthening per millimeter of tissue depth (r=0.38, P<0.01).

Conclusions:

• MCGRs provide substantial lengthening but fall short of programmed distraction by approximately 14%.
• Prior spinal instrumentation does not appear to impede MCGR lengthening.
• Greater subcutaneous tissue depth is a significant factor limiting the effectiveness of MCGR distraction.