Biomechanical comparison of monocortical and bicortical plate fixation for rib fractures in a cadaveric model using a locking plate system

Abstract

Background: Surgical stabilization of rib fractures is an established form of treatment for complex rib fractures. Plate fixation with bicortical screws placement can cause injury to intra-thoracic organs and pleural irritation from protruding screw tips. The aim of this study is to compare the biomechanical properties of monocortical and bicortical plate fixation for rib fractures using a locking plate system. Methods: Ten pairs of fresh-frozen cadaveric ribs were harvested. Native ribs were mounted onto a biomechanical tester and statically loaded to failure to induce a rib fracture. The native stiffness of the rib was measured. Next, the ribs were stabilized using the Synthes MatrixRIB (Johnson & Johnson, USA) locking plate. Left-sided ribs were fixed in a bicortical manner and right-sided ribs were fixed in a monocortical manner. The repaired ribs were subjected to cyclic loading of 50,000 cycles between 2 to 6 N to simulate physiological respiration, followed by static loading at a rate of 10 N/min until failure. The pre and post-repaired stiffness were measured. A high-speed camera was used to record the mechanism of failure. Results: One left-sided rib was omitted from the study because the fracture occurred at the drill hole site. Left-sided ribs demonstrated a mean native stiffness of 10.0 N/mm (SD 3.71) and right-sided 11.92 N/mm (SD 3.57). After plate fixation, pre and post cyclic stiffness was 3.32 N/mm (SD 1.21) and 4.41 N/mm (SD 3.59) for the bicortical group; 3.14 N/mm (SD 1.24) and 3.91 N/mm (SD 1.98) for the monocortical group. There is no statistical difference found between the two groups (P=0.872). Conclusions: Our results show that there is no difference in stability between monocortical and bicortical fixation for rib fractures using a locking plate system. Monocortical fixation is recommended to avoid potential complications.