In A Handbook of Horse-Shoeing, published in 1898, Dr. A. W. Dollar described the correct manner for evaluating a horse prior to fitting shoes. "The horse must be seen both at rest and in motion," wrote Dollar, "the object being to form a clear idea of the conformation and action of the limb, of the form and condition of the hoof, of the way in which the horse brings the foot to, and lifts it from, the ground."

Until the last decade, this standard evaluation technique was taught and practiced largely unchanged since the days when Dollar was a veterinary surgeon and professor at the University of Edinburgh.

Evaluation of the movement of the horse was largely a matter of observation and experience and, eventually, according to Dollar, "the examiner makes up his mind whether the horse goes normally or not."

This new light opened many exciting areas of research that ultimately will yield information of benefit to the horse, but also called into question some of the concepts and practices veterinarians had previously thought to be true and valuable.

It is a long way from Dollar's visual evaluation of the moving horse, followed by a clinical interpretation/impression of the lameness or problem based on movement, to Dr. Andrew Clarke's Equine Studies Laboratory at the University Of Melbourne.

At the Equine Centre at Werribee, Australia, Clarke uses a system of dual cameras to record simultaneously each phase of a running horse's stride from the front and the side. These cameras can record up to 500 frames of film per second and advanced software then creates a three-dimensional analysis that can "more precisely evaluate lameness, gait abnormalities and specialized foot care and shoeing requirements," according to Clarke.

Seeing is believing, so there is no need for subjective clinical interpretation in this more modern approach to gait analysis.

Applying mathematics

Dr. Sion E. M. Lawson is the lead scientist for Horse Biomechanics, a company that specializes in the evaluation of equine motion. Lawson, who has a doctorate in biomechanics from Oxford University, explains that "Biomechanics is the study of the forces acting on a biological system and is the math behind the movement."

To evaluate equine kinetics, Lawson's company uses a method of placing reflective markers on the horse and then tracking the movement of those markers with infrared cameras. "Mathematical models are then applied (to the resulting data) to provide information that can be used to analyze existing movement theories," explains Lawson, "and to plan and assess clinical treatments" (such as joint therapy and shoeing applications).

His evaluation includes a look at the balance, symmetry, power, efficiency and coordination seen in a particular horse's movement. Parameters that are measured for such an evaluation include stride length, stride frequency, center of gravity placement (a recording of where the horse carries the majority of its weight, which can help evaluate equine athletes that may jump or spin), quality of movement in joint angles and hoof placements (which provides information relating to the potential for future arthritis or performance-stress injuries) and angular momentum on the ground and in the air.

Evaluation of this type of kinetic information quickly turns mathematic, but has allowed veterinary researchers to evaluate objectively the forces on all parts of the leg, joints and hoof, as well as on specific tendons and ligaments.

The results have both an academic appeal and a practical application. A look at what we now know about heel wedges, for instance, will illustrate newer biomechanical information put to clinical use.

Heel wedges have long been used to raise the horse's heel and reduce the pull or forces on the deep digital flexor tendon (DDF). Dr. Stephen O'Grady of Northern Virginia Equine addressed the use of heel wedges in a presentation at the 2006 American Association of Equine Practitioners meeting in San Antonio. "Elevation of the heels," he explained, "induces flexion of the distal interphalangeal joint, decreases tension in the DDF tendon, reduces pressure applied to the navicular bone and reduces stress on the hoof capsule."

The kinematic models, motion-capture data and force-gauge analysis allow researchers now to make these determinations and to provide objective proof to what had, until recently, been clinical supposition.