The lameness examination commences with the horse walking and trotting in straight line. This allows us to assess lameness evident in a straight line as well as the symmetry of your horses’ movement. We will assess the foot flight of each limb, and the movement of the head, neck and pelvis. At this point, we will also often perform flexion tests. Then we will decide which is the most appropriate way to proceed with the examination. Sometimes we will ask you to lunge your horse because some lameness will only become evident on the circle. Equally, sometimes lameness may become evident in both legs depending on which rein the horse is working. If the complaint has only been noticed under saddle then we may ask you to ride the horse so we can accurately assess the problems that you have noticed. The aim of the clinical examination is get as much information as possible before deciding where to direct further efforts towards isolating the cause of the lameness.
The next step in the lameness examination is often the use of nerve blocks. Flexion tests are the not the only method for isolating the site of lameness, and can sometimes be misleading, so we often combine flexion tests with the use of peri-neural (around the nerve) nerve blocks. A peri-neural nerve block involves injecting local anaesthetic around nerves in the leg in a certain commonly accepted pattern. A knowledge of anatomy allows us to understand the path of the nerves as they travel down the leg and by injecting local anaesthetic at certain sites we can dull pain originating from areas below the sites of local anaesthetic placement. After waiting a certain amount of time for the local anaesthetic to take effect, we trot the horse again. If the lameness has been abolished by the nerve block, we have a very strong indication that the lameness is originating from a site below the level of the block. We can then use diagnostic imaging modalities in a targeted and strategic manner to diagnose the problem. If the lameness is not abolished, the next appropriate step is to administer another nerve block at a point higher in the leg and assess the lameness again. This process can be time consuming, but it will often allow us to definitively isolate the site of the lameness.
In some cases, instead of performing peri-neural nerve blocks, we will elect to perform intra-articular (joint) nerve blocks. This is when local anaesthetic is injected into a joint such as the fetlock in a sterile fashion. One of the main benefits of an intra-articular nerve block, is that it does allow us to make an assessment of whether the lameness is isolated to a joint or whether there may also be some soft tissue involvement. Another benefit, is that a positive response to an intra-articular nerve block is often a good indication that the horse will respond to intra-articular therapy.
Once the site of soreness has been isolated, we will discuss with you the most appropriate imaging modality or modalities to use to reach a final diagnosis. It is very important to work through the process of lameness isolation instead of just simply jumping to diagnostic tests. The reason for this is that many horses will have radiographic changes in multiple areas that may or may not be causing lameness. In other words, they may or may not be clinically significant. However, if we have isolated the site of lameness and there are radiographic changes in that area we can be quite certain that those radiographic changes are clinically significant.