Multidirectional in vivo strain analysis of the equine radius and tibia during dynamic loading with and without a cast.

Rosette strain gauges were applied to the equine radius and tibia. Three sites were examined on each bone on separate occasions (proximal metaphysis, middiaphysis, and distal metaphysis). At each site, 4 rosette gauges were applied around the bone (ie, cranial, caudal, medial, and lateral). Strain recordings were made while walking the horse with and without a full-limb plaster cast. The principal axis of tensile strain was on the craniolateral aspect of the radius. Distally, on the radius, the largest strains were torsional. The cast changed the principal axis of tensile strain on the radius from the craniolateral surface to the caudal surface. The principal tensile strain of the tibia was just to the lateral side of cranial in the proximal and diaphyseal regions. Distally, the principal axis of tensile strain was craniolateral; however, the largest strains measured here were torsional. The cast changed the principal axis of tensile strain on the distal metaphysis of the tibia, but it did not reduce the magnitude of the strains measured. Casts may not aid stabilization of radial or tibial fractures repaired with internal fixation and may in fact place additional stress on the fracture site.