Biomechanical Comparison Between 2 Guided-growth Constructs

Background: Correction of deformity using guided growth with plate and screw constructs has shown good results in the correction of angular deformities in children. Some recent reports have shown device failure, perhaps because of increased patient weight as seen in Blount disease. The purpose of our study was to compare the strength to failure between 2 similar devices, the Orthofix 8-plate manufacturer 1 (M-1) and Biomet Peanut plate manufacturer 2 (M-2), using 2 different screw types: solid and cannulated. Methods: A model of bone was developed using 30-pcf solid polyurethane foam as cancellous bone and high-density polyethylene as cortical bone. A 10.0-mm defect was created through the polyurethane foam and was spanned by a plate and screw system. Under the assumption that device failure is caused by cyclical loading, each device underwent fatigue testing on an MTS Bionix machine with a 4-Hz micromotion of 5.0 mm at -500-N compression, and the number of cycles to failure was recorded. Results: All devices failed at the screw shaft; plates did not break under any circumstances. The highest mean number of cycles to failure was seen with the M-2 device using solid, stainless-steel screws (22,614 cycles; SD, 6885). On comparing with titanium screws, solid screws were significantly stronger in both the M-1 (P = 0.002) and M-2 devices (P = 0.013). The M-2 device with cannulated screws was noted to be significantly stronger than the M-1 device with cannulated screws (P = 0.036). Conclusions: This study reveals a significant increase in strength in one titanium cannulated guided-growth system over another. Solid screws are also shown to be significantly stronger than cannulated screws. Long-term clinical data will be required to determine whether this difference results in lower failure rates. Clinical Relevance: Use of a stronger guided-growth device may be of benefit for correction of deformity in children who are heavier, such as those with Blount disease. Comparative clinic trials will be needed to confirm the advantage of one device over another.