Biomechanical testing of a novel, minimally invasive rib fracture plating system

BACKGROUND: A novel rib fracture repair plating system was developed to provide durable fixation with a shorter length than standard systems and thus facilitate minimally invasive repair. We hypothesized that U-plate fixation would be at least equivalent in durability to standard anterior fixation. STUDY: Twenty fresh frozen ribs (10 pairs) from two human cadavers were first tested for intact stiffness (force or deformation). A gap of 5 mm was then created in the middle of each rib with a saw. Each rib was reconstructed with either the U-plate (4.6 cm length, Acute Innovations, LLC, Hillsboro, OR) with four screws or a 2.4-mm anterior locking plate (9.5 cm length, Synthes, Paoli, PA) with six screws. The U-plates were placed on one rib and the anterior plates on the contralateral rib of the paired levels. 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. The stiffness of the construct was measured throughout the test. RESULTS: Stiffness decreased from the intact rib to the transected/plated rib for both types of fixation; however, a significant decrease in stiffness was observed only with the anterior repair (p = 0.03). After 50,000 cycles, the U-plated ribs lost 0.12 ± 0.03 N/mm (1.9%) stiffness, whereas the anterior-plated ribs lost 0.72 ± 0.13 N/mm (9.9%) stiffness (p = 0.001). CONCLUSIONS: In this simulation of an unstable rib fracture with a small bony gap, U-plate fixation was more durable than standard anterior fixation. The greatly diminished size of the U-plate compared with the standard may facilitate minimally invasive rib fracture repair.