Biomechanical Testing
Biomechanical testing showed that the U-shaped plate with locking screws maintained better fixation after 50,000 breathing cycles [1].
Study Design:
Twenty fresh frozen human cadaver ribs were first tested for intact stiffness (force/deformation). A fracture was created in the middle of each rib and was reconstructed with either the U-plate (4.6 cm length) with four screws or an anterior locking plate (9.5 cm length) with six screws. The reconstructed ribs were cycled 50,000 times with a load of ± 2N at 1 Hz in a simulation of the repetitive loading of deep breathing (Figure 1). The stiffness of the construct was measured throughout the test.
Results:
After 50,000 cycles the U-plated ribs lost a mean 2% of stiffness, while the anterior-plated ribs lost a mean 10% of stiffness (p=0.001, Figure 2).
Conclusions:
The U-plate construct retained more stiffness after repetitive loading than a standard anterior plating system with twice as much length. A loss of stiffness correlates with motion at the screw/bone interface, which ultimately leads to loss of fixation. If durable fixation can be achieved with a shorter plate, minimally invasive repair may be facilitated.
Testing Images
