Ask Your Veterinarian Presented By Kentucky Performance Products: Conducting Lameness Exams

Veterinarians at Rood and Riddle Equine Hospital answer your questions about sales and healthcare of Thoroughbred auction yearlings, weanlings, 2-year-olds and breeding stock.

Question: Could you describe the process you go through to conduct a lameness exam?

Dr. Scott Hopper: Lameness exams are a subjective art form where we try to apply science and technology to identify the source or sources of the lameness. The goal of every lameness exam should be to come up with a definitive diagnosis. A definitive diagnosis is essential to proper treatment.

Lameness is described as any alteration in a horse's gait; this is often due to pain but can also be mechanical in origin. Lameness can be very subtle or manifest itself as an obvious limp. Often, lameness presents itself as a change in the horse's behavior or performance. The AAEP has set forth the following guideline when grading a lameness.

The AAEP Lameness Scale:

0: Lameness not perceptible under any circumstances.

1: Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g. under saddle, circling, inclines, hard surface, etc.).

2: Lameness is difficult to observe at a walk or when trotting in a straight line but consistently apparent under certain circumstances (e.g. weight-carrying, circling, inclines, hard surface, etc.).

3: Lameness is consistently observable at a trot under all circumstances.

4: Lameness is obvious at a walk.

5: Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move.

The lameness exam itself starts with a good history. It is important to know the breed and discipline of the horse, as certain causes of lameness are more prevalent in certain breeds and disciplines.

Once a history is obtained, the clinical examination begins. Most lameness exams are performed on a hard surface, as this will often exacerbate certain causes of lameness. The horse is typically trotted in a straight line and in circles both ways. Typically, the lame limb can be seen and heard by the difference in concussion. Horses land harder on the sound limb, creating an audible difference at the trot. Once the lame limb is identified, a hoof tester exam is performed followed by flexion tests. The horse is trotted after these tests to see if the horse's degree of lameness has worsened. Palpation of tendons, ligaments, joints, muscle, back, neck and sacroiliac ensue to further gather information to identify the source of the lameness.

Diagnostic nerve blocks are an important tool in obtaining a definitive diagnosis. Nerve blocks can be performed to isolate the lameness to a certain joint or region of the limb. If a horse's degree of lameness improves or switches to a different limb, we have identified the location of the lameness. Many horses are lame in more than one limb and blocking more than one limb during a lameness exam is common.

Radiographs are important to help identify any bone changes such as osteoarthritis, bone chips, or fractures. Certain views are taken of the bone or joints involved to allow full evaluation to identify any pathology.

Computerized Tomography (CT Scan) combines a series of X-ray images and uses computer processing to create cross-sectional images (“slices”) of the bones, producing very detailed images of bone.

Nuclear Scintigraphy involves injecting a radioactive isotope that binds to area of increased bone turnover such as a stress fracture or bone inflammation. The isotope emits gamma radiation and a gamma camera is used to create images of the skeletal system.

PET scan is similar to nuclear scintigraphy but has a better camera that is more sensitive and allows for cross sectional imaging. Currently, only areas from the carpus and tarsus distally can be evaluated.

MRI, or magnetic resonance imaging, is used to further evaluate bone and soft tissue injuries. Typically, MRI is used when the lameness has been isolated to a certain area of the limb and no significant pathology is present on radiographs or on ultrasound. MRI is very sensitive and obtains slices of information only millimeters thick.

Ultrasound is used to evaluate soft tissue structures such as tendons and ligaments. Ultrasound can also be used to evaluate the surface of bone and help identify problems such as pelvic stress fracture in racehorses.

Lameness examinations can vary from relatively straightforward to extremely complex and difficult puzzles to solve. The art of lameness examinations is the interpretation of the lameness after each block and the significance of diagnostic findings seen on radiographs, nuclear scintigraphy, ultrasound etc. There are many possible causes for lameness in horses and knowledge of the breed and discipline can be helpful. Lameness exams can vary less than an hour to several hours or couple days if advanced diagnostics such as MRI or scintigraphy are required. The goal of every lameness exam is to come up with a definitive diagnosis and advise the owner of the available treatment options to optimize the horse's ability to return to soundness.

Dr. Scott Hopper is a 1993 graduate of the University of Wisconsin College of Veterinary Medicine and a shareholder at Rood and Riddle Equine Hospital in Lexington, Ky. He completed a one-year hospital internship at Rood & Riddle in 1994, followed by a surgical residency at Washington State College of Veterinary Medicine in 1997. He became board certified in surgery in 1999. Dr. Hopper's interests include performance and sport horse lameness.