The effect of foot imbalance on point of force application in the horse.

Foot imbalance is believed to be a common cause of musculoskeletal injury in the horse; its biomechanical effects are, however, poorly understood. Wedges (angle 3.7 and 5 degrees) were attached to modified shoes to elevate one aspect of both front feet of Thoroughbred-type horses. The point of force application during weightbearing was determined at trot using a forceplate system. A total of 8 horses were studied with a minimum of 4 providing data for each wedge condition. The results demonstrated that application of a standard steel horse shoe to a balanced foot has minimal effect on the point of force trace through stance. Alteration of mediolateral hoof balance resulted in a displacement of point of force application by about 10 mm in the direction of the wedge throughout stance. Elevation of the heels delayed unloading of the heels and elevation of the toe advanced unloading. Reassessment 24 h after shoeing showed minimal change in the point of force trace. This work demonstrates that a horse is unable to compensate for an acute foot imbalance by redistributing the load under the foot. The higher loads in the elevated region are likely to have a detrimental effect on the hoof structure and horn growth in that part of the hoof.