Doctors have not determined exactly what causes Kienbock's disease. A number of factors seem to be involved. Usually the patient has injured the wrist. The injury may be a single incident, such as a sprain, or it can be from repetitive trauma. But the injury alone does not seem to cause the disease.
The way that blood vessels supply the lunate bone of the wrist is thought to play a role in Kienbock's disease. Some bones in the body simply have fewer blood vessels that bring in blood. The lunate is one of those bones. A bone with a limited blood supply may be more at risk of developing the disease after an injury. The reduced blood supply might be the result of a previous injury to the blood vessels
Other bones around the lunate may play a role in the disease, too. The length of the ulna, the bone of the forearm on the opposite side of the thumb, may be a factor. When the ulna is shorter than the radius, the lunate bone absorbs more force when the wrist is used for heavy gripping activities. Over time, this extra force may make it more likely for a person to develop Kienbock's disease, since the person may be more likely to injure the lunate or the blood vessels around it as a result.
Kienbock's disease is also sometimes found in people with other medical conditions that are known to damage small blood vessels of the body. Whatever the cause, the lunate bone develops a condition called osteonecrosis. In osteonecrosis, the bone dies, usually because it's not getting enough blood.