Finite element modelling of the feline antebrachium - Comparison of stress in the intact bones and after extramedullar bridging of a mid-diaphyseal fracture

Application of an interlocking nail (IN) was analyzed to stabilize a simple diaphyseal feline antebrachial fracture. The purpose was to investigate stress distribution during static weight bearing using a finite element model (FEM). A regularly shaped radius and ulna from a cat of a body mass of 5 kg was used to create a FE foreleg model. A vertical load of 15 N was used for the simulation of a 4-leg static loading. The modulus of elasticity (E) of the bones was assumed 10,000 MPa. A simple and not dislocated fracture was simulated in the middle third of the antebrachial diaphysis. An IN with a length of 68 mm and a diameter of 4 mm was chosen for the stabilization of this fracture. Von Mises stress and strain in the FEM of the intact and fractured bones and the implant respectively were used to compare the selected situations. For better analysis both antebrachial bones were divided into their anatomical regions. In the intact feline radius, diaphyseal stress values changed from 1.56 MPa to 6.87 MPa from proximal to distal. Ulnal diaphyseal stresses ranged from 0.0811 MPa to 0.0356 MPa (proximal), from 0.0356 MPa to 0.746 MPa (middle) and from 0.746 MPa to 0.356 MPa (distal). In the fractured and stabilized radial diaphysis, values in the proximal third increased from 2.75 MPa to 6.87 MPa and decreased to 0.176 MPa at the location of the second proximal screw. In the middle third of the tended radius where the fracture was located the values were negligibly small (0.0706 MPa) and increased to 6.87 MPa where the proximal of the 2 distal screws was located. In the distal third constant values of 6.87 MPa were found. In the fractured ulna, peak stresses were located in the fractured area in the middle third of the ulna with values between 0.176 MPa and 0.441 MPa. This FEM may be expected to be the basis for future studies into biomechanics of the feline antebrachium. An extramedullarily applied IN might be a usable tool to treat simple not dislocated diaphyseal fractures of feline radius and ulna.