Subjective vs. Objective Lameness Identification Methods

Subjective clinical evaluation allows practitioners to detect mild lameness as well or better than objective methods.

Photo: Erica Larson, News Editor

Lameness evaluations can be extremely subjective. When examining a horse with a mild lameness, in particular, veterinarians often don’t agree on a diagnosis—some are prone to seeing a more sound horse, others a more lame one. To overcome such disparities, practitioners have turned to objective methods such as force plates and inertial sensor systems (e.g., the Lameness Locator). But which is superior: a subjective exam or one of these devices?

At the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah, Josh R. Donnell, DVM, equine sports medicine and rehabilitation resident at Colorado State University's Orthopaedic Research Center, in Fort Collins, compared the force plate to the inertial sensor system (ISS) and to two different forms of subjective evaluation: unblinded and blinded.

A force plate measures ground reaction forces that reveal how well a horse is loading the limb as he trots over the stationary plate. A horse loads a painful (lame) leg less than a sound leg. The force plate is limited, however, in that it only measures a single stride, said Donnell.

The ISS detects asymmetry of the head, pelvis, and limbs while a horse trots. The device's benefit is that it can be used on any surface in any environment or terrain and can record continuous strides, he said.

In the study Donnell and colleagues evaluated 16 horses for baseline soundness before surgically creating a cartilage defect in the middle carpal (knee) joint, which has been shown as a reliable way to induce lameness in research horses. They scored the horses—both blinded and unblinded—for lameness on Days 15, 42, and 72 after surgery.

In the unblinded subjective evaluation, a single clinician tried to identify the lameness with a hands-on musculoskeletal exam. In the blinded subjective evaluation four experienced clinicians watched videos and formed a consensus as to which limb was lame, but none performed a clinical exam.

Donnell said they determined that:

  • On Day 15, unblinded subjective evaluators identified the lame leg in 87% of the horses, whereas the blinded subjective evaluation identified it in 38% of horses;
  • Also on Day 15, the force plate identified the lameness in 63% of horses, and ISS in 50% of horses;
  • By Day 71, 50% of subjective evaluators identified lameness in the horses; and 
  • On Day 71, 80% of ISS exams identified lameness compared to 30% of force plate exams.

The study's results revealed some important points, said Donnell. First, all methods detected lameness on Day 15, and the blinded and unblinded studies “agreed” more often with the ISS. All systems detected the lame limb more easily as lameness worsened. There was, however, a big difference between the unblinded (83%) and blinded (38%) Day 15 evaluations, thereby demonstrating the importance of a clinical exam for mild forelimb lameness, said Donnell.

While the ISS identified lameness scores more frequently than the force plate, showing that the objective methods of evaluation are improving, Donnell said, “Practitioners are doing a good job with subjective clinical evaluation, which detects mild lameness as well or better than objective methods.”

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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