The Effect of Increasing Fracture Site Stiffness on Bone-Pin Interface Stress and Foot Contact Pressure within the Equine Distal Limb Transfixation Cast: A Finite Element Analysis.

The research investigates how modifying the stiffness of fracture site tissues near the pins in a horse’s lower limb influence the stress levels at the bone-pin interface, within the lower bones, and pressure between the foot and the cast. The team discovered that increasing tissue stiffness results in decreased maximum stress at the bone-pin interface, increased stress beyond the pins, and increased contact pressure between the foot and the cast, which could decrease complications in real and theoretical settings.

Research Method

• The research used a transfixation cast finite element model. This is a mathematical tool used to predict and simulate how an object might react to real-world forces, like heat, vibration, fluid flow, and other physical effects.
• The model was used to compare the stress at the bone-pin interface, the pin stress, the stress within the bones below the pins, and the contact pressure between the foot and the cast.
• Six different stiffness values were used for a composite tissue block, each representing a different stage of fracture healing.

Results

• The results indicated that as the stiffness of the composite tissue block increased, the maximum stress at the bone-pin interface decreased.
• While the stresses on the bones distal to the transcortical pins increased with heightened stiffness of the tissue block, the maximum pin stress was found to decrease.
• The study also revealed that with each increase in the tissue block stiffness, the contact pressure at the bottom of the block and the cast also increased. Additionally, the stress patterns around the pin holes became less focal.

Conclusions

• These findings suggest that effective contact between foot and cast in a transfixation cast can lead to decrease in bone-pin interface stresses as tissue stiffness increases due to progressive fracture healing. This also results in an increase of stress and loading at the fracture site.
• Enhancing the contact pressure between the foot and the cast could potentially lessen complications related to transfixation casting procedures such as pin loosening, pin hole fracture and poor fracture healing.
• The use of these results in real and hypothetical scenarios could provide more effective treatment plans.