Jan. 7 (HealthDay News) -- Women whose index finger is shorter than their ring finger are at greater risk of osteoarthritis of the knee, researchers report.

In fact, having a shorter index finger may double the risk of osteoarthritis for all people, the British team of scientists said.

The ratio of index finger length to ring finger length has been widely studied. Men are more likely to have a ring finger that is longer than their index finger, while women's second and fourth fingers are usually similar in length.

Previous studies have also shown that people whose index fingers are shorter than their ring fingers have higher prenatal testosterone levels, lower estrogen concentrations and higher sperm counts.

Osteoarthritis is associated with physical activity and a lack of estrogen, so researchers at the University of Nottingham decided to test for any correlation between finger length and the risk of knee or hip osteoarthritis.

Writing in the January issue of Arthritis & Rheumatism, the researchers analyzed data from more than 2,000 patients on hospital orthopedic surgery lists and at a rheumatology clinic in Nottingham. Each participant suffered from osteoarthritis and was under consideration for joint replacement.

The researchers established a comparison group using more than 1,100 similar individuals with no history or symptoms of osteoarthritis. All participants were between 63 and 67 years old.

The team took X-rays of the knees, pelvis and hands of all participants. They then measured their finger lengths using a visual estimation, a measure from the base to the tip of the upper finger joints and the measure of the metacarpal bone lengths.

They classified the hands in three categories: type 1 was hands with the index finger longer than the ring finger; type 2 ,where the index and ring fingers were of equal length; and type 3, with the index finger shorter than the ring finger.

In keeping with previous research, men were 2.5 times more likely than women to fall into the third category.

Compared with hands in the other two groups, type 3 hands were correlated with osteoarthritis of the knee and hip, and often included arthritis in the fingers. The researchers noticed that people with type 3 hands were two times more likely to have osteoarthritis of the knee. Women with type 3 hands were at greater risk than men.

The researchers also found that the smaller the upper finger joint ratio between the index and ring fingers, the greater the risk of osteoarthritis of the knee, particularly in the tibiofemoral knee joint. This relationship remained even after other arthritis risk factors such as age, gender, weight, injury and sedentary lifestyle were taken into consideration.

"Specifically, women with the 'male' pattern of 2D:4D length ratio -- that is, ring finger relatively longer than the index finger -- are more likely to develop knee osteoarthritis," lead author Dr. M. Doherty, professor of rheumatology at the university, said in a prepared statement.

SOURCE: Arthritis & Rheumatism. news release, Jan. 2, 2008