AC Joint: Acromioclavicular joint; joint of the shoulder where acromion process of the scapula and the distal end of the clavicle meet; most shoulder separations occur at this point.

Achilles Tendinitis: Inflammation of the Achilles tendon.

Achilles Tendon: One of the longest tendons in the body, it attaches the calf muscles to the heel bone.

Anterior Compartment Syndrome: Condition in which swelling within the anterior compartment of the lower leg jeopardizes the viability of muscles, nerves and arteries that serve the foot. In severe cases, emergency surgery is necessary to relieve the swelling and presure.

Anterior Cruciate Ligament (ACL): A primary stabilizing ligament within the center of the knee joint that prevents hyperextension and excessive rotation of the joint. A complete tear of the ACL necessitating reconstruction could require up to 6 months of rehabilitation.

Anterior Talofibular Ligament: A ligament of the ankle that connects the fibula (lateral ankle bone) to the talus. This ligament is oft times subject to sprain.

Arthritis: Inflammation of joints.

Arthroscopy: A surgical examination of the internal structures of a joint by means of viewing through an arthroscope. An arthroscopic procedure can be used to remove or repair damaged tissue or as a dagnostic procedure in order to inspect the extent of any damage or confirm a diagnosis.

Anti-Inflammatory: Any agent which prevents inflammation, such as aspirin or ibuprofen.

Avasular Necrosis: Death of a part due to lack of cirulation.

Avulsion: The tearing away, forcibly, of a part or structure.

Axilla: The armpit.