Using a block to diagnose equine musculoskeletal problems

Here  Dr Ed.A. Lyall, BVetMed, CertEM (StuMed) MRCVS of Sussex Equine Hospital explains about ways of diagnosing musculoskeletal problems in an equine.

Dr Ed Lyall of  Sussex Equine Hospital

AS humans when we have something in our musculoskeletal systam that is painful, we attend the doctor and tell him where it hurts and under what circumstances.

This instantly allows the doctor to know where to focus the diagnostic work up in terms of the clinical examination and then imaging.

This is not the case when we as vets are presented with a horse that has a problem with the musculoskeletal system.They may be lame, in which case we can work out which leg to concentrate on. However many horses are just not performing as well as they should or they have multiple limbs with pain resulting in a complex lameness.

Even if we know which leg is the problem by looking at the way the horse is moving, unless there is something wrong with a region of that leg on a clinical examination, we still do not not know where to focus our diagnostic imaging. We use a block to identify the site of the pain.

A block can either be a regional nerve block or a joint block. A regional nerve block involves placing a small volume of local anaesthetic around a nerve at a specific site, the nerve then, with time, become anaesthetised below that level and thus it loses its ability to transmit a pain response back to the brain.

There are many sites in a horse’s limb that can be blocked. Typically, if we do not know where the pain is coming from, we will work up from the lowest blocking site, the horse is trotted either on a straight line or on a circle on the soft or hard, whatever shows the lameness best, prior to blocking and then again several minutes later once the block has time to anaesthetise the nerve.

If the horse goes sound or the degree of lameness significantly improves, then we know the pain is coming from somewhere below that blocking site. If there is no improvement  we then move up to the next block and so on until the lameness improves, once improvement is made we know the pain is coming from a site between the previous two blocks.

The other block that is often carried is a joint block. This is where a specific joint is filled with local anaesthetic and it then becomes anaesthetised. A joint block has to be carried ut in as clean a manner as possible, prior to joint hibiscrub and then rinsed with surgical spirit- we then wear sterile surgical gloves to handle or syringes and needles. Often a joint block is carried out following oidentifistion of a egion of the limb by regional nerve blocks, to be more specific about what may be causing pain in that area.

Sometimes we will identify something on a radiograph such as close or overlappng doral spinous processes in the back. We may then infuse local anaesthetic around the affected bones to see if the horse moves better under saddle.

Basically I look at a block as being a question- we place the regional or joint block and we are asking does the pain come from here. If the horse goes sound or the lameness improves, then the answer is yes. If the lameness does not improve, the answer is no.

Dr E.A. Lyall, BVetMed, CertEM (StuMed) MRCVS

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