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Objective—To evaluate mediolateral, axial, torsional, and craniocaudal bending behavior of 6 distal ring-block configurations commonly used to stabilize short juxta-articular bone segments in small animals.

Sample Population—8 circular external skeletal fixator constructs of each of 6 distal ring-block configurations. The distal ring-block configurations were composed of combinations of complete rings, incomplete rings, and drop wires.

Procedure—Constructs were nondestructively loaded in axial compression, craniocaudal bending, mediolateral bending, and torsional loading by use of a materials testing machine. Gap stiffness was determined by use of the resultant load displacement curve.

Results—Circular external skeletal fixator configurations and constructs significantly affected gap stiffness in all testing modes. Within each loading mode, gap stiffness was significantly different among most configurations. In general, complete ring configurations were significantly stiffer than similar incomplete ring configurations, and addition of a drop wire to a configuration significantly increased stiffness of that configuration.

Conclusions and Clinical Relevance—When regional anatomic structures permit, the use of complete ring configurations is preferred over incomplete ring configurations. When incomplete ring configurations are used, the addition of a drop wire is recommended. (Am J Vet Res 2004;65:393–398)

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in American Journal of Veterinary Research


Objective—To determine relative effects of ring diameter and wire tension on axial biomechanical properties of 4-ring circular external skeletal fixator constructs.

Sample Population—4-ring circular external skeletal fixator constructs and artificial bone models.

Procedure—4-ring constructs were assembled, using 50-, 66-, 84-, or 118-mm-diameter rings. Two 1.6-mm-diameter fixation wires were attached to opposing surfaces of each ring at intersection angles of 90o and placed through a gap-fracture bone model. Three examples of each construct were loaded in axial compression at 7 N/s to a maximum load of 400 N at each of 4 wire tensions (0, 30, 60, and 90 kg). Response variables were determined from resulting load-displacement curves (construct stiffness, load at 1 mm of displacement, displacement at 400 N).

Results—Ring diameter and wire tension had a significant effect on all response variables and had a significant interaction for construct stiffness and displacement at 400 N. Significant differences within all response variables were seen among all 4 ring diameters and all 4 wire tensions. As ring diameter increased, effect of increasing wire tension on gap stiffness and gap displacement at 400 N decreased. Ring diameter had a greater effect than wire tension on all response variables.

Conclusions and Clinical Relevance—Although effects of wire tension decrease as ring diameter increases, placing tension on wires in larger ring constructs is important because these constructs are inherently less stiff. The differential contribution of ring diameter, wire tension, and their interactions must be considered when using circular external skeletal fixators. (Am J Vet Res 2001;62:1025–1030)

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in American Journal of Veterinary Research