IDIOPATHIC SCOLIOSIS - Structural lateral curvature of an unknown cause.

ILIAC BONE - A part of the pelvic bone that is above the hip joint and from which autogenous bone grafts are frequently obtained.

ILIAC CREST - The large, prominent portion of the pelvic bone at the belt line of the body.

ILIOPSOAS MUSCLE - Large muscles starting at L-1 and becoming wider as it picks up segments from the lower lumbar spine; combines with the iliacus muscle before attaching to the lesser trochanter of the hip.

IMMOBILIZATION - Limitation of motion or fixation of a body part usually to promote healing.

INFANTILE SCOLIOSIS - Lateral curvature of the spine that begins before age 3.

INFRATENTORIAL - Beneath the tentorium.

INFUNDIBULUM - A stalk extending from the base of the brain to the pituitary gland.

INSTRUMENTATION - the use of instruments such as metal screws or braces during a surgical procedure to support bone as it heals.

INTERBODY - between the bodies of two adjacent vertebrae

INTERCOSTALS - The muscles between the ribs.

INTERNAL FIXATION - The immobilization of bone fragments or joints with implants in order to promote healing or fusion.

INTERSPINOUS LIGAMENT - Ligament between each of the spinous processes.

INTERSPINOUS PSEUDARTHROSIS - Formation of a false joint between two spinous processes.

INTERVERTEBRAL DISC - See Disc (Intervertebral).

INTERVERTEBRAL DISC NARROWING - Narrowing of the space between any two vertebral bodies.

INTRA-AORTIC BALLOON COUNTER PULSATION DEVICE - A pump which is inserted into the main vessel of the body, the aorta, to help the heart deliver blood to critical organs such as the brain or kidneys.

INTRACEREBELLAR - Within the cerebellum.

INTRA-ARTERIAL CATHETERIZATION ANGIOGRAPHY - An invasive study in which a catheter (a small tube) is placed in the artery and contrast material is injected to which makes the blood vessels visible on an X-Ray image. The catheter is inserted in the groin into the femoral artery (the artery to the leg) through a needle, and is guided into the arteries in the neck and head. This study is associated with a very small (less than 0.05 % chance of serious complications) and requires the patient to lie in bed for approximately six hours to allow the leg vessel to heal.

INTRACEREBRAL - Within the cerebrum.

INTRACEREBRAL HEMATOMA - A blood clot within the brain.

INTRACRANIAL - Within the cranium of the skull.

INTRACRANIAL PRESSURE (ICP) - The overall pressure inside the skull.

INTRAOPERATIVE CISTERNOGRAPHY - Administration of a contrast dye into the ventricles which are chambers in the brain that contain brain fluid.

INTRAMEDULLARY - Refers to medullaris, marrow; (1) withing the medulla oblongata of the brain, (2) within the spinal cord, and (3) within the marrow cavity of bone.

INTRINSIC - Situated entirely within or pertaining exclusively to a part.

IN VITRO - Describing biological phenomena that are made to occur outside the living body traditionally in a test tube. In vitro is Latin for in glass.

IN VIVO - Within a living body. In vivo is Latin for in life.

INFERIOR - Situated below or directed downward.

INFORMED CONSENT - Consent of the patient who has received sufficient information to have surgery, receive medication, or participate in a clinical study.

INSTITUTIONAL REVIEW BOARD (IRB) - A committee designated by an institution, such as a hospital, to review and approve research projects; e.g., clinical studies in that institution.

INVESTIGATIONAL DEVICE EXEMPTION (IDE) - A FDA regulatory status which permits the human use of an unapproved medical device for the purposes of collecting clinical data under strictly controlled conditions.

ISCHEMIA - Inadequate circulation of blood generally due to a blockage of an artery.

ISOLA - A posterior fixation device.

ISOMETRIC - Of equal dimensions. In physiology, denoting the condition when the ends of a contracting muscle are held fixed so that contraction produces increased tension at a constant overall length.

ISOTONIC - Relating to isotonicity or isotonia. Having equal tension; denoting solutions possessing the same osmotic pressure; more specifically, limited to situations in which cells can neither swell nor shrink.

ISTHMIC - The lesion is in the pars interarticularis. Three types occur: lytic, fatigue fracture of the pars interarticularis; elongated but intact pars interarticularis; and acute fracture of the pars interarticularis.

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