Finite element analysis of anterior spanning attachment devices for supporting biomechanical stability in diaphyseal femoral periprosthetic fracture fixation

Abstract

The incidence of periprosthetic femoral fractures has increased in recent years. Osteosynthetic stabilisation is challenging, particularly for UCS IV.3-C fractures. Lateral plate osteosynthesis is the gold standard; however, it allows excessive vibration, leading to plate breakage. Orthogonal double plate osteosynthesis has been established but requires considerable intraoperative dissection of the anterior extensor muscle. This work aims to analyse newly developed plate designs that demonstrate adequate vibration behaviour, which, in turn, promotes callus healing and causes less soft tissue trauma than the plate constructs used to date. A hip prosthesis geometry and a parameterised volume geometry of a UCS IV.3-C type periprosthetic femur fracture were simulated to generate a finite element model. Additionally, three alternative design studies were developed to optimise an LCP®, and the various constructs were then investigated using a finite element model concerning comparative stress and deformation under static and dynamic loading and their influence on fracture gap expansion. Isolated lateral plate osteosynthesis (V1) and double plate osteosynthesis (V2) served as references. The alternative plate designs include a ventral frame at the fracture level (V3) or spanning the length of the lateral LCP® (V4). The fifth variant is a fulcrum support attached to the existing LCP® at the fracture level (V5). Compared with V1, V3 and V4 yielded comparable results, presenting greater stiffness and increased survival. The functionality of V5 shows nearly identical outcomes to those of V1. Here, failure with plastic deformation is already observed under static loading, which does not occur with V2 even under dynamic loading, thus representing the most stable construct, albeit one that does not permit adequate vibration behaviour. For V3 and V4, optimal strain behaviour in the fracture gap is also evident after load application. Alternative implant design variants with an additional anterior frame lead to reduced deformation and failure of fixation in UCS IV.3-C periprosthetic femur fractures. In addition to double plate osteosynthesis, alternative plate constructs exhibit optimal strain behaviour conducive to callus fracture healing. Furthermore, the selected designs decrease the required dissection of the quadriceps muscle.