The upper limb above the carpus (knee) is composed mostly of the large forearm muscles. Under those muscles lie the radius (forearm) bone. Above this still is the elbow and shoulder joints. Bone, nerves and vessels are near the skin on the inside of the upper limb, whereas the front, back and outside of the upper limb are protected by heavy muscle. Due to this muscular protection, upper forelimb injuries are generally less serious and less common than lower limb injuries.

Swelling of the upper limb is usually caused by direct trauma such as a kick from another horse. However swelling of the upper limb can also occur as a result of injuries sustained nearby, on the forearm, the lower limb, the trunk, chest or armpit.

Bacterial infections in the chest or armpit (Pigeon Fever) can cause swelling of the upper front limb by extension. Pay special attention to any swelling right at or above the carpus and whether there is lameness associated with the swelling.