Equine Lameness Evaluation

Further Diagnostic Procedures

Another strategy that is useful in many cases is to perform flexion tests. Either the lower limb or the upper limb is held in flexion for a period of time (usually between 30 and 90 seconds), and then the horse is trotted off in a straight line. If the lameness is exacerbated by the flexion, it is an indication that the source of the lameness is in the region that was flexed. If the limb that is the source of the lameness was easily determined by the visual exam, flexion tests can be performed on this limb to isolate the region of the limb that is the source of pain. If the primary limb is still in question after the visual exam, all four limbs can be flexed to try to exacerbate the lameness enough to make a diagnosis.

Once the primary limb which is the source of lameness has been identified, the next step is usually to perform nerve blocks. This procedure involves injecting a small volume of local anesthetic (freezing) under the skin directly over the nerve that allows the horse to feel certain parts of its limb. This local anesthetic takes away the sensation to the portion of the limb below the injection. The horse is trotted away after the nerve block has taken effect. If the source of the lameness is in the region below the injection, we would expect the lameness to be improved. If this is the case, we have successfully narrowed down the options to isolate the region that is the source of the lameness. In general, we will start with nerve blocks in the lower limb, and work our way up the limb.

In certain cases, local anesthesia can also be injected directly into the joint in question to allow a more specific joint block. This technique carries a very small risk of introducing infection, so nerve blocks are often utilized first. However, joint blocks do not diffuse up the limb as nerve blocks do, so it is possible to isolate a more specific region of pain. Depending on the type of local anesthesia used, the lack of sensation in the area blocked lasts several hours.

It is important to note that the horse must be consistently lame in order to perform nerve or joint blocks, so that the examiner is able to tell whether the block has resulted in significant improvement. However, if this is the case, nerve blocks are a valuable phase of the examination. The results of a nerve block allow the examiner to image a specific area and know definitively that any changes seen on radiographs or ultrasound are truly the cause of the horse’s current lameness. Otherwise, it is possible that a lesion identified on radiographs was preexisting and is not actually causing the horse a problem at this time.