Effect of different full-limb casts on in vitro bone strain in the distal portion of the equine forelimb

Scott A. Hopper From the Departments of Veterinary Clinical Sciences (Hopper, Schneider, White), Veterinary Comparative Anatomy, Pharmacology, and Physiology (Ratzlaff), College of Veterinary Medicine, and the Department of Mechanical Engineering (Johnson), Washington State University, Pullman, WA 99164-7060.

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Robert K. Schneider From the Departments of Veterinary Clinical Sciences (Hopper, Schneider, White), Veterinary Comparative Anatomy, Pharmacology, and Physiology (Ratzlaff), College of Veterinary Medicine, and the Department of Mechanical Engineering (Johnson), Washington State University, Pullman, WA 99164-7060.

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Marc H. Ratzlaff From the Departments of Veterinary Clinical Sciences (Hopper, Schneider, White), Veterinary Comparative Anatomy, Pharmacology, and Physiology (Ratzlaff), College of Veterinary Medicine, and the Department of Mechanical Engineering (Johnson), Washington State University, Pullman, WA 99164-7060.

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Karl K. White From the Departments of Veterinary Clinical Sciences (Hopper, Schneider, White), Veterinary Comparative Anatomy, Pharmacology, and Physiology (Ratzlaff), College of Veterinary Medicine, and the Department of Mechanical Engineering (Johnson), Washington State University, Pullman, WA 99164-7060.

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Craig H. Johnson From the Departments of Veterinary Clinical Sciences (Hopper, Schneider, White), Veterinary Comparative Anatomy, Pharmacology, and Physiology (Ratzlaff), College of Veterinary Medicine, and the Department of Mechanical Engineering (Johnson), Washington State University, Pullman, WA 99164-7060.

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SUMMARY

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. (Am J Vet Res 1998;59:197–200)

SUMMARY

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. (Am J Vet Res 1998;59:197–200)

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