When it comes to easing the pain of arthritic knees, footwear choice matters, new research shows.

And the findings suggest that flatter shoes with more flexible soles are easier on the knees than clogs or walking shoes. “It may not be the supportive, stable shoes that we just thought would be shock-absorbing for them that they should wear,” Dr. Najia Shakoor of Rush Medical College in Chicago, one of the study’s authors, told Reuters Health.

Past injuries, overuse, excess weight and aging all contribute to osteoarthritis, or breakdown of cartilage within the joints. Knee osteoarthritis is particularly common, and can be disabling.

The “loading” of a person’s weight onto the knee joint is a key factor in the development of arthritis, Shakoor and her colleagues note. Abnormal loading can worsen wear and tear and add to joint pain, while reducing joint loading can help ease pain.

Currently, the standard treatment for knee osteoarthritis includes giving a person painkillers, Shakoor said, which can actually worsen the problem because when a person feels less pain they tend to walk in a way that loads the knee more heavily. “Pain can be protective,” she noted.

In a previous study, Shakoor and her team found that people walking barefoot had less loading on their knees than people wearing shoes. To investigate further, Shakoor and her colleagues analyzed the gait of 31 people with knee osteoarthritis as they walked barefoot and then as they wore four different types of shoes.

They looked specifically at the forces acting upon the inner, or medial, side of the knee joint, which typically carries three times as much load as the outer, or lateral, side of the knee. “That’s why we see a lot more people with medial knee osteoarthritis,” Shakoor explained.

She and her colleagues tested the type of slip-on clogs often worn by doctors, nurses and others who need to spend a lot of time on their feet; walking shoes designed to maximize foot stability; flat sneaker-type shoes with flexible soles; and flip-flops.

Clogs and stability shoes produced the highest knee loading, while knee loads were lightest with barefoot walking, flip flops and flexible-sole sneakers. The reduction in loads with the latter shoe type was comparable to that produced by therapies designed to reduce knee loading such as braces and shoe inserts called orthotics, the researchers note.

While the Osteoarthritis Research Society International recommends that people with knee osteoarthritis get advice on appropriate footwear, Shakoor and her colleagues say, there is “scant evidence” that recommended footwear actually reduces impact loads. The new findings can help provide an evidence base for footwear recommendations, they add.

But for now, according to Shakoor, it’s too early to make blanket recommendations on the best footwear choice for people with osteoarthritis of the knee. “Everyone’s different, so we’ll have to take into account those people’s feet and the rest of their anatomy,” she said. For example, it may be difficult for older or weaker people to wear flip flops without slipping, tripping and falling.

“Flat, flexible footwear could be beneficial, but still further long term studies are necessary,” she said.

SOURCE: Arthritis Care & Research, online February 26, 2010.