Radiculopathy: Any physical condition of the nerve roots, commonly expected to radiate pain.

Radiograph: Proper terminology for an x-ray film after it has been exposed to radiation (x-ray).

Radiolucent: An object/item/mass that appears on a radiograph that allows the x-ray to pass through it. (e.g., air pockets are radiolucent and appear dark on an x-ray. The bone, which has more density, appears whiter.)

Radiopaque: An object/item/mass that appears on a radiograph that does not allow the x-ray to pass through it. (e.g. surgical implants made of metal are bright white as they are denser than bone.)

Range of Motion: The limit of normal movement, measured in degrees of a circle, through which a joint may be moved. Active range of motion is how far the patient can move by contracting the muscles voluntarily; passive range of motion is how far the joint can be moved by the doctor or therapist.

Raynaud’s Phenomenon: A vascular disorder marked by recurrent spasm of the capillaries, especially those of the fingers and the toes upon exposure to cold. Characterized by pallor (loss of color), cyanosis (bluish skin tint), and redness in succession which is usually accompanied by pain.

Referred Organ Pain: Some organs, such as the gall bladder, kidneys, prostate or conditions thereof as kidney infections, ulcers, gallstones, or prostate disease, can cause pain in the low back. Since the area in which pain is experienced is not the dysfunctional site, the pain is deemed as referred.

Reflex Sympathetic Dystrophy (RSD): Sometimes called causalgia, RSD is an ill defined source of pain, experienced as both a painful and often burning sensation in an extremity; it has been described as minor to debilitating. While the exact cause is not clearly understood, it often responds to early controlled movement of the affected extremity, or a selective pharmaceutical blockade of the sympathetic nervous system. RSD is usually brought on by a trauma of some sort, and may contain an emotional component. http://www.rsdfoundation.org/en/en_clinical_practice_guidelines.html