A horse becomes lame when there is a source of pain in one of its legs during locomotion, leading to an unwillingness of the horse to fully use that leg. Lameness is first noticed when the gait becomes uneven. In the case of a forelimb lameness the horse is seen to nod its head. Typically the horse will put more weight on the opposite unaffected limb during exercise, therefore it is said that the horse nods to the good leg.

When the horse is lame behind, the same principle applies and the hips of the horse are seen to move unevenly. When the movement of the hips is examined closely while the horse is trotted it is possible to detect the affected hindlimb.

A diagnosis of the cause of lameness is often not straightforward. Initial examination of the leg by your veterinary surgeon will involve detection of any obvious area of heat or swelling. A foot examination will also be performed given that the majority of lameness cases involve structures within the foot. Subsequent investigation may involve nerve blocks which aim to narrow down the area of pain using local anaesthetic. Additional diagnostic techniques may also be required including radiographs (X-rays), nuclear scintigraphy and CT or MRI.

Given the large number of separate tissues and structures that make up the horses functional limb there are numerous conditions which may cause pain and therefore lameness. The specific occurrence of any of these varies according to breed, conformation, the type and intensity of activity as well as the surface upon which they are worked. Many horses will respond initially to rest and anti-inflammatory treatment, but this section goes on to discuss some of the more serious common causes of lameness.