By Shereen Lehman
(Reuters Health) - People whose parents had a total knee replacement due to osteoarthritis are more than twice as likely to develop knee pain in midlife as those with no family history of knee surgery, according to a new study.
The Australian authors say the link between parents and adult children shows that genetics may have much to do with knee problems and the pain that goes with them.
"It was abundantly clear that genes were a strong contributor to risk of osteoarthritis but there had been limited success in finding these genes," said Dr. Graeme Jones of the University of Tasmania in Hobart, the study's senior author.
"Thus, a better way may be to look at mechanisms by which genes lead to arthritis and the best way of doing this was to study the adult children of people who have had knee replacements for osteoarthritis," Jones told Reuters Health in an email.
By age 45, about one-quarter to one-third of adults have had knee pain that lasted for at least one week, the study authors write in the Annals of the Rheumatic Diseases .
The causes of knee pain aren't always clear, but previous studies have also suggested a genetic link.
The new study is the first to examine whether people who have a family history of osteoarthritis of the knee have a greater risk of worsening knee pain, according to the authors.
They enrolled 186 adults with at least one parent who had knee replacement surgery at one of the hospitals in Hobart, and an additional 186 adults whose parents had no history of knee arthritis or knee replacement surgery.
At the beginning of the study, participants answered questionnaires reporting any knee pain they had experienced over the past year, and had X-rays and MRI scans of their right knees. These measures were all repeated two years later and again 10 years after the initial enrollment.
The adults whose parents had knee replacement surgery tended to be heavier and there were more smokers compared to the control group, but there were no differences between the groups as far as visible damage to the knee joints at the beginning of the study.
After two years both groups had about the same number of participants with knee pain - just over half. But after ten years, 74 percent of the children of parents with knee replacements had knee pain compared to 54 percent of those with no family history of knee surgery.
Over those eight years there was also an increase in total knee pain in members of both groups, but the offspring of parents with knee surgeries tended to have a greater increase in pain.
Even after accounting for actual structural problems in the participants' knees, the researchers found that offspring of people with knee replacement surgery were 2.2 times as likely to report that their pain had worsened compared to the controls.
"I suppose there are many mechanisms by which genes lead to arthritis - some we can help, some we can't," Jones said. "Offspring have more pain, weigh more, are more susceptible to the effects of smoking, have weaker muscles, more splits in the cartilage and menisci and greater cartilage loss over time."
Since differences in arthritis and other structural knee problems did not explain the differences between groups in knee pain, Jones said that genetics most likely accounted for the outcomes - for instance, a greater sensitivity to pain that might be influenced by genes.
Still, other factors, such as aspects of the environment, that were shared by both parents and adult children could not be ruled out, he said.
To avoid knee pain, Jones suggests that people maintain an ideal body weight, minimize their risk of knee injury, exercise more when they're younger and refrain from smoking.
"Develop ways of decreasing pain severity, and manage stress better," he added. "Consider medications such as glucosamine if at high risk."
SOURCE: http://bmj.co/1zCnywT Annals of the Rheumatic Diseases, online December 4, 2014.