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Abstract

Objective—To determine the effect of differences in structural and mechanical tendon properties on functionality of the passive stay apparatus in horses.

Sample—5 forelimbs each from nondwarf Friesians, dwarf Friesians, and ponies.

Procedures—Harvested forelimbs were loaded to test the passive stay apparatus. Tendons that stabilize the distal portion of the limb (superficial digital flexor tendon, deep digital flexor tendon, and tendo interosseus [suspensory ligament]) were isolated, and force-elongation data were obtained. Bone lengths, initial tendon lengths, and initial tendon cross-sectional areas were measured, and Young moduli were calculated. A model was used to determine whether joint angles could be explained by these 4 factors only.

Results—Dwarf limbs were unable to stand passively under loading because tendons that prevent overextension of the distal limb joints were too long and compliant to prevent over-extension. Tendon properties of limbs of nondwarf Friesians appeared to be intermediate between those of ponies and dwarf Friesians.

Conclusions and Clinical Relevance—Dysfunction of the passive stay apparatus in dwarf Friesians could be related to differences in structural and material properties of the tendons that result in hyperextension of the joints under loading. Nondwarf Friesians had intermediate tendon properties, which might be a breed-specific variation. Results indicated that certain tendon properties were associated with load failure of the stay apparatus and provided additional information about the functionality and requirements of the passive stay apparatus.

Full access
in American Journal of Veterinary Research

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)

Free access
in American Journal of Veterinary Research