Evaluate equine lameness objectively

How to judge a tricky problem with objective tools.
Dec 01, 2009

Figure 1: Stankey, a 5-year-old Quarter Horse gelding, being evaluated for lameness with the Lameness Locator by Dr. Brittany Hager, house officer intern at the University of Missouri College of Veterinary Medicine's Veterinary Medical Teaching Hospital. The system consists of 1) a head accelerometer sensor attached to the felt head bumper, 2) a right forelimb gyroscopic sensor in the pastern pouch, and 3) a pelvic acceleration sensor attached between the tubera sacrale with tape. Data are collected live as the horse is trotted in hand or ridden past the examiner.
As a young veterinarian with an interest in equine lameness, I looked up to, sought out the advice and direction of, and worked for equine practitioners seasoned in lameness detection and evaluation. Over the years, I learned many things, some from my colleagues and some just by plugging away, looking at as many lame horses as possible and following up with them as well as I could.

Along the way, a few things became apparent to me. First, it was rare that two experienced practitioners observed a horse in motion the same way, and they often had difficulty expressing exactly what they were observing. Second, disagreement on selection of the affected limb between my mentors was frequent enough to be confusing, at least to me.

Given the dedication and experience of my mentors, I knew the reasons for these observations were not likely due to deficient skills. Many veteran lameness veterinarians have since confided to me that they have made the same observations. They all reported having their share of confusing cases and believe there must be a better way.

The art of lameness detection

Lameness detection in horses is difficult to master, and, until recently, the lack of ability to objectively measure lameness's effect on movement prevented standardization. Thus, when veterinarians were taught lameness detection in veterinary school or by mentors in their first years of practice, they were likely taught one of a myriad of different ways proposed either in text or tradition.

The human eye also has its physical limitations. Small changes in the movement of a body part due to lameness may be missed or misinterpreted by the limited spatial and temporal resolution of the human eye. And, as humans, we subjectively express how the lameness appears to us and can be biased. This is the art of lameness detection. But our art is more properly directed to unraveling the complexities and interconnectedness of anatomy, pathology, imaging, treatment and prognosis—in other words, the skills and knowledge that separate equine practitioners from the crowd.

The search for objectivity begins

Figure 2: A Lameness Locator report with graphical display (top of report) and calculated lameness variables (bottom of report). The arrows on the left point to the forelimb evaluation. The arrows on right point to the hindlimb evaluation.
A search for a method of objective measurement began at the University of Missouri in 1993. We chose to study motion analysis with cameras and the treadmill. A wealth of information on the technique was already available from pioneers in equine motion analysis.

However, distilling the published research down did not point to a reliable set of measures. An unreasonably large number of possible measures needed to be studied: stride length, stride timing, limb swing patterns, head and hip motion, and so on. What exactly were the best motion parameters to measure to detect lameness?

Table 1
We marked horses at every joint and prominent body part possible and collected motion data with high-speed cameras from large numbers of horses that were sound or lame, either naturally or from one of several different experimental models of lameness induction. We determined through analysis of these large data sets that vertical movement of the torso was the best approach for detecting lameness in horses. It was reassuring that others had suggested the same from earlier studies. But this was the first step.