The Effect of Reducing the Bone to Cast Distance in an Equine Transfixation Pin Cast: An Ex Vivo Biomechanical Study.

This research investigated the effect of decreasing the distance between the bone and the cast in an equine transfixation pin cast on the pin’s resistance to repeated loading. The findings showed a significantly higher load levels and number of cycles until failure in the group where the bone-cast distance was reduced, indicating the padding under the cast can affect the overall stability and longevity of such constructs.

Methods

• Eleven pairs of cadaveric equine third metacarpal bones were used in the ex vivo study. Each bone had a 6.3/8.0mm transfixation pin inserted in a standard fashion 10mm above the distal physeal scar.
• The study was divided into two groups. The first had a 10mm bone-cast distance (10mm group) and the second had a 20mm bone-cast distance (20mm group).
• The pins were secured at both ends to polyoxymethylene-copolymer sleeves in a simplified test setup in eight pairs. The remaining three pairs of bones had the pins incorporated into a fibreglass cast.
• All samples were tested under repeated loading until the pin failed in axial compression.

Results

• All pins failed either on one or both sides at clinically relevant load levels.
• The 10mm group withstood significantly higher loads and total number of cycles until failure compared to the 20mm group.

Conclusions

• The study concluded that the distance between the bone surface and the cast at the location of pin insertion significantly impacts the pin’s resistance to repeated loading.
• Therefore, the padding applied underneath an equine transfixation pin cast can significantly affect the overall stability and longevity of the construct.