Today's artificial hip joints last longer than those made from older materials, so now joint wear is less likely to be a factor in how long an artificial hip will last after hip replacement surgery. Instead, say Japanese researchers in the April 29 Lancet, a patient's own bone quality and structure determine an artificial joint's longevity. Age-related bone loss, vitamin D deficiency and a lack of estrogen after menopause may contribute to poor bone quality and play a role in joint failure, according to an accompanying editorial. Nevertheless, many older synthetic joints may last for decades. A 25-year study of 51 patients who had hip replacements in the early 1970s found that 97 percent were satisfied with the outcome of their surgery. Of the 62 total hip replacement procedures in this group, 77 percent of the original prostheses were still in place after 25 years, according to the report in the April Journal of Bone and Joint Surgery.