arachnoid: Thin membrane inside the spinal dura but outside the spinal fluid as well as small amounts of fibrous tissue within the spinal fluid space.

 

arbitration agreement: Agreement between a patient and a physician to settle disputes by arbitration rather than standard litigation.

 

Arnold-Chiari malformations: Congenital abnormality at the base of the skull and the posterior parts of the brain, that come in type 1, type 2 and type 3; with type 1 being mild, causing headache; type 2 causing significant abnormalities; and type 3 being in many cases, fatal near the time of birth.

 

arthritis: Inflammation affecting the joints.

 

arthropathy: Any degenerative abnormality affecting the joints.

 

arthroplasty: Replacement of a joint by an artificial material.

 

articular processes: A part of the vertebra, that extends from the lamina and supports a surface of a facet joint.

 

assignment of benefits: An agreement by a patient to allow any insurance payments for medical care to be paid directly to the doctor rather than to the patient.

 

atelectasis: Collapse of portions of the lung, that can take place during routine anesthesia.

 

autograft: An graft or implant or tissue taken from the patient's own body.

 

autologous: Blood transfusion using the patient's own blood.

 

autonomic nervous systems: A set of nerves in the body that control sweating, skin temperature and functions in the gastrointestinal system.

 

axis vertebra: The C2 vertebra.

 

axonal transport: A natural process whereby chemicals and proteins are moved along the length of a nerve.

 

axons: Elongated portion of a nerve cell that projects from the cell body out toward to the endpoint such as on muscle.