Effect of the Length of the superficial plate in stacked veterinary cuttable plate constructs: An in vitro study on the bending strength and stiffness, and on the strain distribution
This thesis investigated the effect of the length of the superficial plate on the mechanical properties of a stacked-plate construct made with 2.0-2.7 Veterinary Cuttable platesTM (VCP). Stacking VCP increases construct stiffness compared to using a single VCP but increases stress protection and concentrates stress at the extremities of the implants. We hypothesized that shortening the superficial plate would not reduce the stiffness of the construct, and would reduce stress concentration at the plate ends. A fracture gap model was created with a bone surrogate (copolymer acetal rods), stacked 2.0-2.7 VCP and 2.7 screws. The constructs consisted of an 11-hole VCP bottom plate and a 5-, 7-, 9- or 11-hole VCP superficial plate. In phase one, 5 of each construct were randomly tested for failure in 4-point bending and axial loading. Stiffness, load at yield, and work until failure were measured. In phase two, strains were recorded during elastic deformation for each configuration. During both testing methods, stiffness, load at yield and work to failure progressively decreased when decreasing the length of the superficial plate. No statistically significant differences were obtained for load at yield in 4-point bending and work to failure in axial loading. The strain within the implant over the gap increased as the length of the superficial plate decreased. Shortening the superficial plate reduces the stiffness and strength of the construct, and decreases stress concentration at the implant ends. As the cross section of the implant covering the gap remained constant, friction between the plates may play a role in the mechanical properties of stacked VCP.