Lameness assessment and investigation for the horse
Following our first article looking at how to spot lameness in the horse, we delve further into Lameness assessment and investigation with the Animal Health Trust.
About the AHT Equine Clinic
The Animal Health Trust (AHT) Equine Clinic is made up of world specialists that treat a variety of injuries or conditions, but their greatest area of expertise lies in orthopaedics and, in particular, lameness.
No horse or injury is ever the same and it’s up to their Clinicians to solve these mysteries on a daily basis, helping hundreds of horses each year (putting Sherlock Holmes to shame!) Many horses are suffering from long-term problems which their owners may have noticed months ago and have exhausted every other option without a clear diagnosis. Or, the horse has attempted to get through its daily life or work by compensating for the issue, preventing the owner from noticing it sooner.
Top athletes, such as the thoroughbred racehorses, are kept in peak condition throughout their lifetimes. Horses are prey animals, they cannot afford to look weak in turn giving them a high pain threshold. Unfortunately, this not only gives the problem more time to develop but makes identifying and diagnosing lameness particularly tricky. This is why vets turn to specialists in their field, like those at the AHT, for their expert help.
Some owners tell the Clinicians that “not knowing” is one of the hardest things they have to deal with because, without a clear diagnosis, they can’t help their horse get on the right track to recovery. It’s the AHT Clinicians’ mission to uncover the mystery of lameness, back problems or tendon injuries. They work like detectives in gathering evidence from the owner and referring vet; following clues in how the horse moves and analysing the data to determine the culprit of the problem.
There are three main stages in lameness investigation: clinical assessment, nerve blocking and diagnostic imaging.
There are three main stages in lameness investigation: clinical assessment, nerve blocking and diagnostic imaging.
Clinical Assessment – the first step towards solving the mystery
The principles of any lameness investigation are to determine which is the lame limb or limbs and where is (are) the source or sources of pain. What a rider feels as the lame limb is not always correct. A detailed clinical examination – looking at and feeling the limbs, the neck and back and assessment of the horse moving under a variety of circumstances, combined with flexion tests – is the basic and fundamental start point.
The horse’s gait will be assessed in a straight line (forwards and backwards), on a tight circle and on a lunge. The Clinicians will observe the horse from the front, back and side, and on both a hard and a soft surface to gain a full picture of when the lameness is at its worst. The Clinician will be watching for irregular limb placement, the height of the limbs in flight and even for any signs of pain in the horse’s facial expression.
Nerve blocking – the mystery unfolds
After watching a horse move in hand, on the lunge and often ridden, Clinicians can start to hone in on which limb or limbs is the source of pain causing lameness. To help narrow down even further to a specific region of the limb they can use local analgesia (nerve blocking) to eliminate regions from the diagnosis.
Using local analgesia to numb each region in turn, if a horse’s movement is then improved, we know that area was the cause of pain. Nerve blocking is initiated at the base of the limb and then blocking upwards at each crucial point of the limb. Once local anaesthetic is injected into the area you must wait several minutes for numbing to occur, before the horse is then worked again on the trot-up or lunge.
Diagnostic imaging – confirming suspicion
Having identified the regions of pain, diagnostic imaging technology can be used to identify the causes of pain resulting in lameness. The AHT are privileged to be able to offer radiography (X-ray), ultrasonography, magnetic resonance imaging (MRI) and scintigraphy services to provide a detailed diagnosis.
Nerve blocks tell us about the general region from where pain is coming; frequently a combination of x-rays and ultrasonography is ideal to establish the precise cause of pain. With digital technology the standard of x-rays has risen enormously, and x-rays remain the number one technique for investigation of bone injuries and identification of osteoarthritis. However, interpretation is not always straightforward.
Very early on in injury x-rays may be negative, but a bone scan may identify a ‘hot spot’ indicative of bone injury. Ultrasonography is invaluable for assessment of soft tissues – tendons, ligaments, muscles, joint capsules, tendon sheaths.
MRI or CT – further investigations
If x-rays and ultrasonography are negative then the use of MRI or CT may be indicated. MRI in particular has to be targeted on a specific area because image acquisition is time-consuming and expensive. MRI provides images of both soft tissues and bones and allows us to identify some types of damage in bone that cannot be detected by either x-ray or CT. It is therefore superior to CT.
Both MRI and CT are particularly valuable for foot-related lameness, because some of the soft tissue structures within the hoof capsule cannot be assessed using ultrasonography.
Interpretation is not always straightforward because there is not necessarily a correlation between the degree of lameness and what is found using MRI. Not all abnormalities necessarily cause pain.
As with all imaging techniques, anomalous results may reflect the way in which the image was acquired or the presence of adjacent blood vessels, resulting in alteration in signal intensity that may mimic a genuine injury. So once again, knowledge and experience are required for accurate interpretation.
To find out more about the AHT Equine Clinic and the services available for your horse, visit the AHT website.
