Written by: Susan Stafford-Pooley

Cutting-edge technology for pinpointing often elusive unsoundness

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Occasional bouts of lameness are inevitable when you own horses – not surprising when you look at their anatomy and the stress under which we put their limbs during the concussive forces of training and competition. Horses carry 60-65% of their body weight on their forelegs, which are the site of most common lamenesses (90% in or below the knee). The hind limbs are taxed during jumping, galloping and various dressage manoeuvres, with 80% of hind limb injuries occuring in the stifle and hock.

Veterinarians have commonly relied on diagnostic aids such as radiographs, ultrasound, nerve blocking, computer tomography (CT), and magnetic resonance imaging (MRI) to assess lameness. Now, their toolbox is a bit fuller with the help of some new technology.

Wireless Objective Gait Analysis

Gait analysis is a rapidly-growing field in both human and animal medicine. Wireless inertial sensor-based technology is at the forefront of lameness evaluation and research and is fairly reasonable, starting at about $200-250 per assessment.

An example is the Equinosis Lameness Locator, which allows the vet to determine whether the horse is lame, the severity of the lameness, the limb or limbs involved, and the segment of the motion cycle at which peak pain is occurring. The portable unit employs wireless microelectronic sensors that are placed on the horse’s head, pelvis, and pastern and are able to sample up to 20x faster than the human eye, tracking head and torso movement accurately to less than one millimeter at 100 meters. Data is sent to a tablet for immediate on-board analysis. The system allows objective comparison of improvement at recheck evaluations after treatment or during rehabilitation.

EquiMoves is another equine gait analysis system which uses sensor nodes attached to the legs, withers, and head as mobile measuring units. The movement coordination, temporal and spatial gait parameters at all gaits are retrieved, allowing responses to training, shoeing, nerve blocking, medication, etc, to be measured.

Nuclear Scintigraphy

Nuclear scintigraphy is a bone scan that can identify areas where the bone is undergoing renovation or inflammation because of disease or injury. This is particularly helpful in identifying hairline or stress fractures, sclerosis, or bone infections, and is considerably more sensitive than x-rays for detecting bone inflammation.

At the clinic, the horse is injected intravenously with a short-acting radioisotope which for the next two to six hours circulates through his body. During that time he is sedated and scanned with a gamma camera – either full-body or targeted, such as the front or hind legs. Any areas where the bone is undergoing ‘remodeling’ will absorb larger quantities of the radioisotope, showing up on the gamma camera image as “hot spots.” Once the location is pinpointed, other imaging techniques such MRI may be able to determine the cause more clearly.

Scintigraphy, while expensive (a scan can run well over $2,000) can be a useful tool for unearthing the cause of hard-to-detect lameness and enabling treatment to begin sooner, often ensuring a better outcome.

PET Scan

Another new diagnostic imaging option for horses is the positron emission tomography (PET) scan, first performed on an equine last August at the University of California, Davis. While PET technology has been used to diagnose human conditions from cancer to heart problems, the development of an equine scanner now allows veterinarians to diagnose lower limb injuries in horses.

Similar to scintigraphy, a small amount of radioactive tracer is injected into the horse. Rather than a single two-dimensional image, however, the scan provides a series of images and can pick up lesions and changes at the molecular level that aren’t visible using other imaging modalities. The PET scan can also distinguish the difference between an old lesion and an active one. The modality is so new that costs for horses are not yet available; for human patients it runs about $1,000-$1,200 per scan.

Which Leg is Lame?

A brisk trot is generally the best gait for a lameness exam because of the symmetry of the movement. Watch the horse travel from the front, from the side, and from behind on a hard surface. Circling can accentuate lameness, as can being ridden under saddle as opposed to hand-walking.

Clues to look for include:

  • head bobbing
  • shortness of gait
  • different foot heights during the arc
  • joint flexion angle
  • foot placement

If the horse is lame in front:

  • the head drops when the sound leg hits the ground and rises when the lame leg hits the ground as the horse attempts to minimize the weight on the affected limb.

If the horse is lame behind:

  • the hip rises as the lame leg hits the ground
  • there will be a downward head bob when the contralateral forelimb (opposite side front) hits the ground
  • the affected toe may drag or the arc of the foot’s path may be lower

For comprehensive info explaining why horses go lame, what lameness looks like, and even a video challenge to see how good your “eye” is, visit Equine Guelph’s Lameness Lab Healthcare Tool at equineguelph.ca/Tools/lameness_lab.php