The research led by The University of Manchester and Boston found that across 12 trials, people who used so-called lateral wedge insoles rated their pain about two points lower on a 20-point scale than those who used flat insoles or none at all.
But when the study team looked only at higher quality trials, including ones that accounted for the placebo effect of simply having insoles, any significant benefit went away.
Heel wedges fit underneath the sole of the shoe and are thicker on the outside than the inside, tilting the foot inward. They are designed to relieve pain caused by a certain kind of knee arthritis by transferring loads to different parts of the joint.
The wedged insoles can be bought over the counter or can be specially made.
Because they are easy to use, heel wedges are “an attractive treatment,” Matthew Parkes from The University of Manchester’s Institute of Inflammation and Repair, who was part of the study team, said.
Mr Parkes said: “There’s a lot of promise to suggest that this should work but our results suggest that compared with control interventions, lateral wedges are not efficacious for the treatment of knee pain in people with medial knee osteoarthritis.”
For their analysis, published in the latest edition of JAMA (the Journal of the American Medical Association) the researchers reviewed 12 studies that looked at the effects of lateral heel wedge insoles or shoes.
Those included 885 people with knee osteoarthritis, 502 of whom were randomly assigned to use the wedges – which typically had an angle of five to six degrees. The other participants either used a flat insole or no insole.
Participants wore their assigned insole or shoe for anywhere from two weeks to two years, depending on the study.
The research, funded by Arthritis Research UK and the National Institutes of Health, found any benefits seen with the insoles were in studies that compared wedge insoles to a normal shoe alone.
“If you give one group nothing and one group something, then you see an effect,” Mr Parkes said.
However, the two-point improvement across all studies shrunk to a 0.1-point benefit in the seven trials that compared angled insoles to flat ones. Those studies are best able to account for a possible placebo effect of insoles, researchers said.
“It doesn’t mean there can’t be effective treatments that we put in shoes,” Dr David Felson, from the Boston University School of Medicine, said.
“There may be research which can identify for us those people who are likely to respond to this treatment, or that develops a newfangled approach to put a wedge in a shoe that might work a little better.”
Notes for editors
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