Lameness is a common reason horses present to equine practitioners. Federal researchers note that lameness has the highest annual incident density of all medical problems in horses — half of all horse operations with five or more horses experience one or more cases of lameness annually.1 Another report estimates lameness incidence at 7.5% to 13.7% annually.2
Assuming there are 9.2 million horses in the United States, at $432 spent on veterinary services per lameness incident, more than $500 million is being spent on lameness diagnosis and treatment per year. Horse owners’ annual total financial loss attributable to lameness — that is, the loss of use cost as well as veterinary spending — is estimated to exceed $1 billion.1
Fortunately, about 70% of all lameness incidents result in recovery. Successfully treating the 30% that won’t recover without proper diagnosis and treatment is the predicament. Aids in detecting and measuring lameness are most helpful in these cases.
Subjective classification and assessment
The American Association of Equine Practitioners’ lameness guidelines judge lameness according to a five-point scale, with zero noted as normal or sound and five representing maximum lameness.
> Grades 1 and 2, which are more difficult to observe or discern, are assessed while the horse is walking or trotting in a straight line with some difficulty.
> Grade 3 is further lameness, determined while the horse is trotting.
> Grade 4 lameness is detectable at the walk.
> Grade 5 is lameness so severe it causes the horse to bear minimal or no weight in motion or at rest, or to be unable to move.
Compensatory lameness involves asymmetric movement when the horse shifts weight from a painful to a normal limb. Over time this can lead to pain in an otherwise normal limb from overloading, a condition known as secondary lameness.
Subjective lameness evaluation, in which a clinician visualizes local, regional and whole-body movements, is the accepted standard for clinical lameness detection, says Josh Donnell, a veterinarian at Colorado State University and his colleagues.3 Unfortunately, there can be poor agreement among veterinary evaluators even about the same animal’s lameness. Therefore, more objective assessment measures have been sought.
Two objective assessment methods
Soundness and lameness in horses can be objectively quantified through biomechanics, using mechanical principles to observe the horse in motion. Video capture and other line-of-sight techniques are the most straightforward to understand, but for practical reasons they are difficult to implement routinely in over-ground situations. The other two objective potentially useful methods are the force plate or platform (FP) and the body-mounted inertial sensor system (ISS).
With a force plate, the horse strikes a flat piece of metal that measures force of weight-bearing. The FP can measure ground reaction forces in the three axes — X, Y and Z (three-dimensional space) — giving a reading of each. “It also tells you how much impulse the horse is going through, as well as how long the horse is putting weight on [an affected limb], or its stance duration,” says David Frisbie, a veterinarian and professor in the Department of Clinical Sciences at Colorado State University College of Veterinary Medicine.
1. USDA. Lameness and laminitis in U.S. horses. USDA:APHIS:VS, National Animal Health Monitoring System. Information Sheet. Fort Collins, Colorado: October, 2000. #N318.0400
2. USDA. National economic cost of equine lameness, colic, and equine protozoal myeloencephalitis in the United States. USDA:APHIS:VS, National Health Monitoring System. Information Sheet. Fort Collins, Colorado: October, 2001. #N348.1001.
3. Donnell JR, Frisbie DD, King MR, et al. Comparison of subjective lameness evaluation, force platforms and an inertial-sensor system to identify mild lameness in an equine osteoarthritis model. Vet J 2015;206:136-142.