Knee arthri­tis rates have spiked, and re­searchers don’t know why

Newsweek - - NEW WORLD -

RATES OF

knee os­teoarthri­tis, a painful and dis­abling con­di­tion in which car­ti­lage wears down and bones rub against each other, have dou­bled in the past 50 years, ac­cord­ing to new re­search. The cause of this spike is a mys­tery—which raises the tan­ta­liz­ing pos­si­bil­ity that when the trig­gers are found, the pain can be stopped.

Ian Wal­lace, a pa­le­oan­thro­pol­o­gist at Har­vard Univer­sity, and col­leagues ex­am­ined sev­eral thou­sand skele­tons of peo­ple who died dur­ing three eras in Amer­ica: pre-in­dus­trial (300 to 6,000 years ago), early in­dus­trial (1800s to early 1900s) and post-in­dus­trial (late 1950s on­ward), tal­ly­ing cases of knee os­teoarthri­tis in each group. They also noted the age and body mass in­dex of the ca­dav­ers, when avail­able.

Ac­cord­ing to the study, re­ported Au­gust 14 in Pro­ceed­ings of the Na­tional Academy of Sciences, 18 per­cent of the skele­tons from the post-in­dus­trial pe­riod had signs of ad­vanced knee arthri­tis, ver­sus up to 8 per­cent of the older bones. The dis­ease was more than twice as com­mon among mod­ern bones com­pared with ei­ther of the older two.

The pri­mary risk fac­tors for knee os­teoarthri­tis were long thought to be ag­ing and obe­sity, but re­searchers found no sta­tis­ti­cal re­la­tion­ship be­tween ei­ther fac­tor and the rise in arthri­tis. Even among skele­tons of sim­i­lar ages and weights from the dif­fer­ent eras, knee arthri­tis was more com­mon among the post-in­dus­trial skele­tons. Some un­known cause or causes must be at play.

Iden­ti­fy­ing those miss­ing risk fac­tors could lead to bet­ter preven­tion and re­duced arthri­tis preva­lence, Wal­lace says.

Study co-au­thor David Fel­son, a physi­cian at Bos­ton Univer­sity, says phys­i­cal in­ac­tiv­ity likely plays a part. “Our joints don’t do well when they aren’t ac­tive much of the time.” In­flam­ma­tion due to hy­per­ten­sion or di­a­betes could con­trib­ute, says Fran­cis Beren­baum, a physi­cian at Pierre & Marie Curie Univer­sity. A diet high in pro­cessed sug­ars and grains may also lead to in­flam­ma­tion­driven arthri­tis, says Wal­lace.

The re­sults sug­gest arthri­tis may not be “an in­evitable as­pect of ag­ing,” Wal­lace says. That’s the good news be­hind the bad news here.

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