Which option best describes a blemish of the leg?

A blemish of the leg refers to a superficial abnormality that does not necessarily affect the horse's performance or soundness. A capped elbow is a specific type of blemish characterized by a fluid-filled swelling that results from inflammation or irritation in the elbow area, often caused by trauma or repeated pressure. This condition is primarily cosmetic, meaning it may alter the appearance of the leg but does not inherently affect the horse's ability to move or perform.

In contrast, conditions like osteoarthritis, splints, and mud fever refer to issues that can involve pain, inflammation, or infection. Osteoarthritis is a degenerative joint disease that leads to chronic pain and mobility issues. Splints are bony growths on the leg that can indicate underlying injury and may affect performance. Mud fever, also known as pastern dermatitis, is an inflammatory skin condition that can cause discomfort and lameness. Thus, while these conditions are significant health concerns, they do not fit the definition of a blemish, making capped elbow the most suitable choice for describing a blemish of the leg.