Objective: To evaluate the fatigue life of partially stacked and fully stacked (1.5/2.0 and 2.0/2.7 mm) veterinary cuttable plates (VCP) in a fracture gap model of the distal aspect of the radius.
Study design: In vitro biomechanical study.
Methods: Constructs (n=4/group) were assembled for each of 8 groups using 8-hole plates (1.5/2.0 and 2.0/2.7 mm VCP) in the following configurations: unstacked; 2-hole stacked centered over the gap (COG); 4-hole stacked COG; and fully stacked. Plate(s) were secured to 2 separate polyvinylchloride pipe lengths, mounted to a mechanical testing system with a custom jig, and were loaded in axial compression for 10(6) cycles at 10 Hz or until failure at 6-60 N for the 1.5/2.0 mm VCP and 10-100 N for the 2.0/2.7 mm VCP. Differences in number of cycles, stiffness, and failure mode were recorded.
Results: All construct failures occurred through a screw hole adjacent to the gap. Fully stacked and 4-hole stacked 1.5/2.0 and 2.0/2.7 mm VCP withstood 10(6) cycles. Fatigue life and stiffness of the 1.5/2.0 or 2.0/2.7 mm unstacked constructs were significantly less than the other constructs. Differences were identified in stiffness among the 1.5/2.0 mm stacked constructs and in fatigue life among the 2.0/2.7 mm VCP stacked constructs.
Conclusion: Four-hole partially stacked VCP (either 1.5/2.0 or 2.0/2.7 mm) have comparable mechanical properties to fully stacked VCP.
Clinical relevance: Partial stacking of 2 holes of VCP on both sides of the fracture gap may provide sufficient strength for healing, but this premise must be tested in vivo.