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Effect of different full-limb casts on in vitro bone strain in the distal portion of the equine forelimb
S A Hopper1, R K Schneider, M H Ratzlaff
1Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman 99164-7060, USA.
Objective:
To determine the ability of a full-limb transfixation pin cast to protect the distal portion of the equine forelimb from weight-bearing forces by measuring bone strain in vitro on cadaver limbs loaded in a mechanical testing machine.
Sample Population:
6 forelimbs from 6 horses.
Procedure:
Each limb was instrumented with 3 unidirectional metal foil electrical resistant strain gauges. Gauges were placed on the dorsal aspect of the distal portion of the radius and the mid-dorsal portion of the cortex of the third metacarpal bone and the first phalanx. Each limb was tested 3 times, once supported with a transfixation pin cast, once supported by a standard full-limb cast, and finally, uncast. The limbs were tested in a mechanical testing machine under axial loads ranging from 100 to 1,000 lb, and bone strains were recorded at each load.
Results:
Compared with values for the uncast limb, the transfixation pin cast and the standard full-limb cast significantly (P < 0.001) reduced bone strain on the distal portion of the radius, third metacarpal bone, and first phalanx. Compared with the standard full-limb cast, the transfixation pin cast significantly (P < 0.001) reduced bone strain on the first phalanx.
Conclusion And Clinical Relevance:
Compared with the standard full limb cast, the full-limb transfixation pin cast is more protective of the first phalanx.