In vitro mechanical evaluation of three transfixation pin-cast constructs applied to equine forelimbs.

The research study compares three different types of pin-cast constructs used in treating bone injuries in adult horses with a focus on the strain occurring at the bone-pin and cast-pin interfaces. The findings suggest that the construct employing four pins was more efficient in reducing strain at the bone-pin interface, thus transferring more load to the cast, compared to the other two constructs using two pins each.

Study Overview and Methodology

• The study was conducted on 15 forelimbs from 15 adult horses.
• Three different pin-cast constructs were tested. The first and second constructs consisted of two centrally threaded positive-profile pins, differing only in the spacing between the pins (4 cm for the first construct and 5 cm for the second). The third construct used four pins spaced 2 cm apart.
• An osteotomy (surgical cutting of bone) was created in the proximal phalanx – the bone located between the hoof and the fetlock in the horses’ legs.
• Strain gauges were attached to the cast, the pins, and the bone to measure strain during compressive loading until failure.

Results and Findings

• The study findings showed no significant difference in strain between the first and second constructs.
• Compared to the two-pin constructs, the four-pin construct recorded less strain at the bone-pin interface, and more strain at the cast-pin interface. This finding suggested that a greater load was being transferred to the cast in the four-pin construct compared to the two-pin one.
• A simplified finite element model was created to further explore strain and load transfer between the bone and cast in the first and third constructs. The results of this model supported the recorded strain findings.

Conclusions and Clinical Relevance

• The study concluded that the four-pin construct effectively unloaded more of the fracture load onto the cast when compared to the two-pin constructs.
• This finding could potentially inform improvements to current equine fracture treatment techniques, as managing strain distribution is crucial to successful bone healing.