The biomechanics of four guided growth plates

Background: Guided growth using the eight-plate is the most common method to correct angular deformities in children. We compared the properties of four plate constructs (two-hole guided-growth plates, four-hole guided-growth plates, locking guided-growth plates, and one-third tubular plates) using a three-point bending model. Methods: A three-point bending model was constructed to test strength of four plates. An osteotomy was made in a Sawbones Cylinder. The plate was then fixed across the osteotomy site using the appropriate screws designed for the plate. A 5 N preload was applied, and a linearly applied force was applied under displacement control. Constructs were loaded to failure. Results: For an angular correction of 8.5 degrees, the four-hole guided-growth plates required the most force (40.9 N) followed by two-hole guided-growth plates (36.6 N). Locking plates and one-third tubular plates required less force to achieve the same correction (28.0 N and 23.0 N P<0.001), respectively. The four-hole plate was the stiffest construct (1.87 N/mm). Load to failure for the four-hole plates (46.0 N), two-hole plates (42.8 N). locking plates (32.1 N), and one-third tubular plates (25.5 P<0.001) followed similar trends as the force required for angular correction, with the four-hole plate requiring the most force. Conclusions: Despite the addition of two extra screws in the four-hole plate, this construct was only 10% stiffer than the two-hole plate. There is limited benefit to the use of a four-hole plate over a two-hole plate. The one-third tubular plate had the lowest load to failure of the four tested constructs. Level of Evidence: NA (biomechanical)