NEW YORK - Strengthening the thigh muscle is generally thought to help arthritic knees, but a new study suggests that strong thigh muscles may hasten arthritis in those with certain joint or leg characteristics.

The results do not mean that exercise is harmful for those with arthritis, but does suggest more research is needed on whether or not special exercise programs need to be tailored for patients, according to the report, released Monday.

An estimated 12 percent of Americans aged 65 and older have osteoarthritis of the knee, and experts often recommend strengthening of the quadriceps muscle in the thigh as a treatment. Osteoarthritis occurs when the cartilage that cushions joints breaks down, often leading to pain, swelling and loss of mobility.

In an 18-month study, Dr. Leena Sharma of Northwestern University Medical School in Chicago, Illinois and colleagues, evaluated 171 men and women with an average age of 64 who had knee arthritis.

Patients with the strongest thighs at the beginning of the study who had leg bones that did not line up correctly or had a "loose" knee joint, were more likely to show signs of disease progression compared to those with weaker quadriceps.

The study did not specifically look at patients who performed exercises to strengthen their leg muscles. However, the findings could indicate that such exercises may not help everyone, according to the report.

"Our results raise questions about the use of quadriceps strengthening," the authors write in Tuesday's issue of the journal Annals of Internal Medicine.

The results are "interesting" and "hypothesis generating" but are not solid evidence that the standard leg-strengthening exercises are detrimental for some patients, according to an editorial by Dr. Kenneth D. Brandt of Indiana University School of Medicine, in Indianapolis.

Brandt adds that more research will be needed before a definite conclusion can be drawn.

The researchers only looked at the thinning of knee cartilage on an x-ray and did not ask patients about their pain or knee function, he notes. Patients with stronger thigh muscles may have less pain and better function, but more study is needed to determine this. Of the 328 knees evaluated in the study, 78 were considered to be misaligned, meaning the two bones that meet in the knee joint were not perfectly in line according to x-rays. Overall, 110 of 328 knees were considered to be more lax or "loose" than other knee joints. (Reuters)