In vitro determination of equine third metacarpal bone unloading, using a full limb cast and a walking cast.

The research article presents a study conducted on equine forelimbs to assess the effects of a full limb cast and a walking cast on the load-bearing properties of the third metacarpal bone.

Objective and Methodology

The aim of this study was to understand how different casting methods influence the weight-bearing capacity of bones in the forelimb of a horse, specifically the third metacarpal bone. The researchers chose this particular bone as it was deemed representative for measuring distal limb loading (the weight borne by the lower part of the limb).

• The study used six forelimbs from Shetland ponies, with electrical resistance rosette strain gauges attached to different surfaces of the midshaft of the third metacarpal bone.
• A pneumatic loading device was used to apply a maximum load of 1,500 N, and the strain experienced by the bone was analyzed under different conditions: without a cast, with a full limb cast, and with a walking cast.

Findings

The study found that both casting methods reduced the compressive forces (the force resulting from an applied load) on the third metacarpal bone, but the effects varied depending on the type of cast used.

• The application of a full limb cast led to a variable and eccentric decrease in force, with residual strain ranging from 84% to 7% of the original or baseline value.
• The walking cast provided a more effective and uniform reduction in compressive loading, reducing it to less than 11% of the baseline value.
• Additionally, the walking cast neutralized bending and torsion elements of the load, which could have potential benefits in supporting bone healing.

Conclusions

The study confirmed that a walking cast is better suited for the healing of fractures in the third metacarpal bone, compared to a full limb cast. The walking cast not only provided a more uniform reduction in loading but also mitigated any bending or torsional elements, offering more stable conditions for fracture healing.