Design and In Vitro Evaluation of Five Epiphyseal Plate Fracture Stabilization Methods in Canines

Abstract

Epiphyseal growth plate fractures of the distal femur are commonly seen in young canines that have not completed full ossification of the growth plate. Current treatment techniques involve the use of crossed Kirschner wires and commercial stainless steel plates. This raises concerns of either providing not enough stability or providing too much to the point where stress shielding is observed in the surrounding tissues or the full growth potential of the bone cannot be realized. To prevent this, a second surgery must be performed to remove these stabilization implants after proper healing of the fracture. Currently, resorbable polymers have been used to treat fractures, primarily in the cranio-maxillofacial area. This study aimed to mechanically evaluate the effectiveness of custom designed polycaprolactone (PCL) resorbable bilateral bone plates and lateral titanium plates to the current epiphyseal plate fracture repair techniques of crossed Kirschner wires and lateral commercial stainless steel bone plates. Forty identical models of the distal femur with pre-designed epiphyseal plate fractures were produced for the fixation of these five repair methods. The model constructs underwent nondestructive cranio-caudal bending, medio-lateral bending and torsional loading tests as well as destructive cranio-caudal bending and torsional loading failure tests. The study showed no statistically significant differences among the constructs for the destructive tests, suggesting the models failed prior to reaching the yield and ultimate strengths and torques of the actual constructs. However, from nondestructive tests, the constructs repaired with custom designed titanium plates displayed comparable mechanical properties to the commercial stainless steel plates. Structural stiffnesses of the titanium plate repaired constructs were not statistically significant from the commercial plate repaired constructs for nondestructive cranio-caudal bending medio-lateral bending and torsional loading tests.

The study also displayed excellent mechanical properties of the two thicknesses (4mm and 2mm) of custom designed resorbable PCL plates. Results showed both 4mm and 2mm resorbable plates were statistically more structurally stiff when responding to cranial forces compared to Kirschner wire repaired fractures. Both 4mm and 2mm resorbable plates were also more structurally stiff when responding to medial forces compared to Kirschner wire repaired fractures and due to their bilateral attachment, also provided a marginally greater stability than the laterally attached metal plates. The resorbable 4mm and 2mm plate constructs were also marginally better in structural stiffness in response to torsional loading than the Kirschner wire constructs. Additionally, results indicated that the 2mm resorbable plate was statistically comparable to the thicker 4mm plate, in cranial bending, medial bending, and torsional bending. Custom designed titanium plates could be an effective alternative to commercial stainless steel plates for fractures observed by more mature canines, and both resorbable 4mm and 2mm PCL plates could be a more effective alternative to Kirschner wire epiphysis plate fracture repair techniques in young canines.