Pain in the knee associated with osteoporosis of the patella.

Four patients, all of whom complained of pain in the knee, were found to have radiological evidence of osteoporosis particularly marked in the patella. In 3 a neurological lesion at the appropriate spinal segment was present, and the fourth patient, who was frankly hysterical, had an autonomic disturbance. If radiological porosis is isolated to the patella a distant cause such as nerve irritation should be sought.