This foot problem, which is often progressive and chronic, affects the distal sesamoid bone (known as the navicular bone), the deep digital flexor tendon and their associated structures, usually in the front limbs. The horse presents with a progressive loss of movement and a decline in performance. It reduces its speed, starts to be lame (especially when cold and on hard surfaces). When resting, the horse often points the affected limb forwards. When working, cold or riding in circles, the horse is uncomfortable. Diagnosis is confirmed by a clinical examination.