EFFECT OF DIFFERENT FULL-LIMB CASTS ON IN-VITRO BONE STRAIN IN THE DISTAL PORTION OF THE EQUINE FORELIMB

Objective-To determine the ability of a full-limb transfixation pin ca st to protect the distal portion of the equine forelimb from weight-be aring 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 me tal 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 phala nx. Each limb was tested 3 times, once supported with a transfixation pin cast, once supported by a standard full-limb cast, and finally, un cast. The limbs were tested in a mechanical testing machine under axia l loads ranging from 100 to 1,000 lb, and bone strains were recorded a t each load. Results-Compared with values for the uncast limb, the tra nsfixation 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-l imb cast, the transfixation pin cast significantly (P < 0.001) reduced bone strain on the first phalanx, Conclusion and Clinical Relevance-C ompared with the standard full limb cast, the full-limb transfixation pin cast is more protective of the first phalanx.