A subluxation may have different meanings, depending on the medical specialty involved. It implies the presence of an incomplete or partial dislocation (Latin: luxatio) of a joint or organ. The World Health Organization (WHO) defines both the medical subluxation and the chiropractic subluxation. It contrasts the two and states in a footnote that a medical subluxation is a "significant structural displacement, and therefore visible on static imaging studies."
An orthopedic subluxation of any joint will usually need medical attention to help relocate or reduce the joint. Nursemaid's elbow is the subluxation of the head of the radius from the annular ligament. Other joints that are prone to subluxations are the shoulders, fingers, kneecaps, and hips affected by hip dysplasia. A spinal subluxation is relatively rare, but can sometimes impinge on spinal nerve roots, causing symptoms in the areas served by those roots. In the spine, such a displacement may be caused by a fracture, spondylolisthesis or severe osteoarthritis.
An ophthalmologic subluxation is called ectopia lentis, an ocular condition characterized by a displaced or malpositioned lens within the eye. Although a relatively rare disorder, subluxated lenses are frequently found in those who have had ocular trauma and those with certain systemic disorders, such as Marfan syndrome, Ehlers-Danlos syndrome and homocystinuria. Some subluxated lenses may require removal, as in the case of those that float freely or those that have opacified to form cataracts.