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

Harold Brommer From the Departments of General and Large Animal Surgery (Brommer, Back, Rijkenhuizen, Barneveld) and Veterinary Anatomy (Schamhardt), Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

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Wim Back From the Departments of General and Large Animal Surgery (Brommer, Back, Rijkenhuizen, Barneveld) and Veterinary Anatomy (Schamhardt), Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

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Henk C. Schamhardt From the Departments of General and Large Animal Surgery (Brommer, Back, Rijkenhuizen, Barneveld) and Veterinary Anatomy (Schamhardt), Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

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Astrid B. M. Rijkenhuizen From the Departments of General and Large Animal Surgery (Brommer, Back, Rijkenhuizen, Barneveld) and Veterinary Anatomy (Schamhardt), Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

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Ab Barneveld From the Departments of General and Large Animal Surgery (Brommer, Back, Rijkenhuizen, Barneveld) and Veterinary Anatomy (Schamhardt), Faculty of Veterinary Medicine, Utrecht University, Yalelaan 12, NL-3584 CM Utrecht, The Netherlands.

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Abstract

Objective

To improve fracture treatment, in vitro experiments were performed to study the influence of a full limb cast and a walking cast on the loading regimen of bones in the distal portion of the equine forelimb.

Animals

6 forelimbs of 6 Shetland ponies.

Procedure

Loading of the third metacarpal bone was considered a representative measure for distal limb loading. Electrical resistance rosette strain gauges were attached to the dorsal, palmar, medial, and lateral surfaces of the midshaft of this bone in 6 forelimbs of 6 Shetland ponies. The limbs were tested in a pneumatic loading device to a maximal load of 1,500 N.

Results

Both casts decreased the amount of compressive forces acting on the metacarpal bone. Application of a full limb cast resulted in a variable and eccentric decrease, remaining strains ranging from 84 to 7% of the baseline value. A walking cast was superior in that it gave a centric and more uniform reduction of compressive loading to <11 % of the baseline value. Moreover, a walking cast neutralized the bending and torsion components of the loading.

Conclusion

This study confirmed the clinical experience that a walking cast creates more reliable and favorable conditions for healing of fractures than does a full limb cast. (Am J Vet Res 1996;57:1386-1389)

Abstract

Objective

To improve fracture treatment, in vitro experiments were performed to study the influence of a full limb cast and a walking cast on the loading regimen of bones in the distal portion of the equine forelimb.

Animals

6 forelimbs of 6 Shetland ponies.

Procedure

Loading of the third metacarpal bone was considered a representative measure for distal limb loading. Electrical resistance rosette strain gauges were attached to the dorsal, palmar, medial, and lateral surfaces of the midshaft of this bone in 6 forelimbs of 6 Shetland ponies. The limbs were tested in a pneumatic loading device to a maximal load of 1,500 N.

Results

Both casts decreased the amount of compressive forces acting on the metacarpal bone. Application of a full limb cast resulted in a variable and eccentric decrease, remaining strains ranging from 84 to 7% of the baseline value. A walking cast was superior in that it gave a centric and more uniform reduction of compressive loading to <11 % of the baseline value. Moreover, a walking cast neutralized the bending and torsion components of the loading.

Conclusion

This study confirmed the clinical experience that a walking cast creates more reliable and favorable conditions for healing of fractures than does a full limb cast. (Am J Vet Res 1996;57:1386-1389)

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