Knee and hip osteoarthritis are widespread diseases seen in up to 6% of the population. The main goal of treatment is to improve pain control, according to a team of Danish reviewers, which included Bente Danneskiold-Samsøe, professor at The Parker Institute in Frederiksberg.

The aim of the systematic review was to determine the effectiveness of one form of such treatment aquatic exercise.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care.

Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.

Treating osteoarthritis typically includes a combination of medication, weight control, physical therapy and exercise. In aquatic exercise, also known as "pool therapy" or "hydrotherapy," patients perform tasks, such as aerobic activities or stretching and strengthening and range of motion exercises, in water heated to about 90 to 97 degrees Fahrenheit.

The Cochrane reviewers analyzed six trials that had 800 participants who all were living with osteoarthritis. Four studies included patients with osteoarthritis of either the knee or hip, one study followed patients with only hip arthritis and one included patients with only knee arthritis.

In the studies, some patients did aquatic exercises for different lengths of time and numbers of sessions per week, while other patients did no exercise or exercised on land. Most of the studies measured patients after 3 months of therapy.

Based on the studies' results, the reviewers said, "In people with osteoarthritis of the hip or knee, pain may decrease by 1 more point on a scale of 0 to 20 with aquatic exercise, and function may improve by 3 more points on a scale of 0 to 68."

"There is gold-level evidence that for osteoarthritis of the hip or knee, aquatic exercise probably slightly reduces pain and slightly improves function over three months," the reviewers wrote. "Based on this, one may consider using aquatic exercise as the first part of a longer exercise program for osteoarthritis patients."

The reviewers were unable to find evidence on whether aquatic exercise affected patients' walking ability or stiffness after treatment sessions.