Rod Fracture in Magnetically Controlled Growing Spine Rods

Area of Science:

• Spinal surgery
• Biomaterials science
• Orthopedic biomechanics

Background:

• Fracture mechanisms in magnetically controlled growing rods (MCGRs) and associated risk factors remain unclear.
• This study retrospectively analyzed explanted MCGRs to investigate fracture causes.

Purpose of the Study:

• To understand the failure mechanisms and identify risk factors for fractures in MCGRs.
• To compare fractured MCGRs with intact controls to determine differences in implant characteristics and surgical parameters.

Main Methods:

• Retrospective analysis of 120+ retrieved MCGRs, identifying 7 fractured and 15 intact single-rod constructs.
• Fractographic analysis to determine failure modes and implant functionality.
• Radiographic analysis of Cobb angle, rod contouring, and anchoring point distances.

Main Results:

• All 7 fractured rods failed due to bending fatigue, primarily in single-rod configurations.
• Fractured rods exhibited significantly greater contouring angles in both frontal and lateral planes (P=0.0407, P=0.0306).
• Greater distances between anchoring points were observed in fractured rods (P=0.0061, P=0.0074).

Conclusions:

• Fatigue fracture is the primary failure mode for MCGRs, particularly in single-rod constructs.
• Fracture initiation sites correlated with mechanical indentation from intraoperative contouring.
• Double-rod constructs are recommended for skeletally mature patients to mitigate fracture risk.