Optimising the surgical treatment of distal femur fractures

Abstract

Distal femur fractures are severe injuries that require surgical treatment. In young patients, most distal femur fractures are high-energy, while in elderly patients, they can be caused by low-energy trauma.

These fractures can have a gap between fragments or be reduced (fragments put back in the position).

Simple fractures, including transverse and oblique, are common distal femur fractures. The AO classification is a well-recognized standard to categorize fracture patterns. However, this classification does not distinguish between fractures occurring at different angles. Previous research has also not considered how fracture angles can influence optimising treatment options.

Locking plates are commonly used in the treatment of distal femur fractures. The treatment is expected to promote healing and provide appropriate stability depending on whether there is a fracture gap or if it has been fully reduced. Weight bearing by the patient is expected after surgery. However, inter-fragmentary motions at the fracture site due to loading caused by physiological activities are key factors that affect both primary and secondary healing. Treatments can be optimised if the mechanical behaviour of the bone-implant construct can be predicted. This thesis aimed to employ finite element simulation for response prediction.

The boundary conditions with the human femur are complex. An approach with novel constraints was employed to represent a single-legged stance. The load distribution at the condyles was used to verify the boundary conditions used.

In the presence of a fracture gap, the overall stiffness of the construct would clearly be independent of the fracture pattern if the fracture gap does not close and if identical treatment configuration is employed.

However, the normal and shear components of interfragmentary motions were found to be affected by the fracture angles, which have consequences with regard to healing. If full weight bearing is achieved, the fracture gap can close. This closure was found to occur at different load levels for different fracture angles. After closure at the fracture gap, the stiffness of the construct and the interfragmentary motions were found to be drastically affected by the fracture pattern.

For fully reduced fractures, total stability results in primary healing. Simulations showed that fracture angles significantly influence the normal and shear interfragmentary motions. Contrary to common intuition, the shear interfragmentary motions do not always increase with the fracture angle due to load sharing between the implant and the fractured bones.

Also, on load application, the fragments do not remain in contact, and an opening occurs at the far cortex. Interfragmentary friction at the fracture surface also influences the relationship between the fracture angle and interfragmentary motions. This interesting pattern of construct behaviour was verified by using simple two-dimensional models.

Pretensioned cerclage cables have been used as a supplementary device to stabilise fixation with locking plates. No clear guidance is available on how much pretension to apply and how it affects stability. This study analysed the stabilizing effect of cerclage cables by comparing the interfragmentary motions for a range of different cases.

Different magnitudes of pretensions were considered.

The change in tension and the slippage of the cerclage cables as load was applied were examined. It was found that even small pretensions effectively reduce shear interfragmentary motions. Both application of pretension and load result in cable slippage over the bone, with post pretension slippage reducing with increase in pretension.

In conclusion, fracture patterns have a significant effect on interfragmentary motions.

Cerclage cables reduce the risk of implant failure and increase the stability of the fixation construct for reduced fractures. In the treatment of distal femur fractures fracture pattern should be considered to optimise treatment. Both fracture patterns and fixation techniques have a significant effect on interfragmentary motions. Cerclage cables reduce the risk of implant failure and increase the stability of the fixation construct for reduced fractures. In the treatment of distal femur fractures, the fracture pattern should be considered to optimise treatment.