Over the course of two days, I worked with Dr. Kinsley and Dr. Johnson on lameness cases. A family brought in a pony and a warmblood for soundness evaluations, and I was responsible for handling the horses during these exams. Lameness exams often take quite a long time, because locating the site of the lameness can be challenging. During a lameness exam, the horse is jogged in a straight line on hard pavement and lunged on a hard surface and in sand in order to try to isolate which limb the horse is lame on. When watching the horse track away from you, a hip drop is evidence of a hind limb lameness, while a head bob without a hip drop is evidence of a forelimb lameness. Once the lameness has been isolated to a limb, a series of flexion tests are performed. A flexion test is when the veterinarian holds the limb with a particular joint flexed for a particular period of time (30-60 seconds depending on the joint). Then, the horse is immediately jogged off in a straight line. If the flexion exacerbates the lameness, that is evidence that the joint that was flexed is involved in the horse's problem. Local nerve blocks are used to confirm the location of the lameness, as well as to rule out the possibility that other joints or limbs are involved. When this is done, the veterinarian starts by blocking the lowest area of the distal limb first, and working their way up the limb until the horse jogs off sound.
In the case of the pony, flexion isolated the lameness to the foot of the forelimb, with the right foot being worse than the left. Hoof testers were applied to the hoof and the pony had a small amount of reaction to pressure across the heel. A palmar digital nerve (PDN) block was applied, and the pony jogged sound. Heel pain/navicular disease was suspected, and radiographs confirmed this diagnosis. The pony was given a shoeing prescription that would provide support to the back of the hoof, and hopefully improve the pony's soundness.
The warmblood hunter was a more complicated case. Jogging and lunging isolated the lameness to the right hindlimb. Flexion tests did not isolate the lameness well, but flexion of the hock and stifle did make the lameness worse. Nerve blocks were utilized to attempt to localize the lameness. A plantar digital nerve block and a six point nerve block were each done individually, with neither nerve block resulting in any improvement. At this point, the horse was stalled and kept overnight, so as not to use too much lidocaine at one time. The next day, a joint block was done in the hocks, in which lidocaine and steroids were placed in the joint spaces. This procedure is both diagnostic and treatment, with the local anesthetic providing a nerve block and the steroid providing anti-inflammatory properties to the joint. After the lidocaine had been given ample time to work, the horse was jogged, and flexion tests were repeated. The horse was determined to be somewhat improved, but still not 100%. Dr. Kinsley had concerns that the problem may be in his pelvis as well as the hocks. He recommended to the owners that the horse may benefit from a bone scan. A bone scan, or nuclear scintigraphy, is a procedure in which a radioactive isotope is introduced into the horse's bloodstream via an IV catheter. This isotope has a high affinity for areas of bone turnover. Therefore, an area of injury shows up on the image. This can help to isolate areas of subtle or intermittent lameness. So, this was a very frustrating, and very time intensive case.
Another interesting case was a four year old Standardbred gelding that was used for racing and had a history of sudden exercise intolerance. The referring veterinarian suspected atrial fibrillation. This was a very interesting case for me because I worked on a mock case last semester that involved a horse with a-fib, and I was curious to see how this case would play out in real time. Atrial fibrillation is the most common equine cardiac condition. It is an electrical abnormality of the heart in which the atria fail to contract and instead quiver, and electrical impulses randomly travel through the A-V node to cause the ventricles to contract. The result is an irregular heart beat, and therefore lack of blood flow to the tissues causing the horse to struggle with intense exercise.
To confirm the diagnosis of atrial fibrillation, an electrocardiogram (ECG) was preformed. A picture of this ECG is included below. The ECG shows a lack of regular heartbeat, as well as a lack of distinguishable P wave that represents the atria contracting.
The cardiology team was called for a referral to perform an echocardiogram. This confirmed the ECG findings of atrial fibrillation, as well as ruled out any structural abnormalities that could be causing this conditions. Finding no structural abnormalities indicated that the horse was a good candidate for conversion to normal sinus rhythm. There are two options for conversion: 1. Pharmacological conversion via a drug called quinidine. 2. Transvenous electrical conversion (TVEC). Both options have their own inherent risks. Quinidine can cause colic in some cases, and can cause toxicity. TVEC requires general anesthesia and coordinated shock. Additionally, MSU cannot perform TVEC so the horse would have to be referred to another institution, and TVEC is quite costly. The owners opted to attempt to convert the horse using quinidine. The horse was placed on a Holter monitor to easily monitor his ECG. Quinidine was given orally every two hours. After a few doses, the horse converted to normal sinus rhythm, as shown below.
The summer is winding down here at the hospital. I only have a few shifts left until the end of my fellowship. I am now on nights, and will write about some of the interesting cases I see my last week and a half here. My time here has gone quickly, and I am not ready for the fall semester to start back!
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