Researchers at the University of Nottingham in the UK done a study on index to ring finger length ratio (2D:4D). They observed that having uncommonly long ring fingers raises the risk of developing osteoarthritis, the most common form of arthritis that results in severe pain in the joints.
They also added that their finding is particularly applicable to women with long ring fingers.
For their study, the researchers recruited 2,049 case subjects, all of whom had clinically significant symptomatic OA of the knees or hips, requiring consideration of joint replacement surgery. The study also involved 1,123 controls who neither had OA nor a history of any joint disease.
The study population was comprised of both men and women, with an average age of roughly 67 years for cases and 63 years for controls.
Radiographs of both knees and the pelvis were obtained for all participants. Every participant also underwent separate radiographs of the right and left hands.
The researchers assessed the 2D:4D length ratio from radiographs using three methods—a direct visual comparison of the 2 finger ends, the measured ratio from the base to the tip of the upper finger joints, and the measured ratio of the metacarpal bone lengths.
They found that men were 2.5 times more likely than women to have the index finger shorter than the ring finger.
The relationship between 2D:4D length ratio and OA was then assessed using blind comparisons of hand radiographs with both knee and hip radiographs from random case and control samples, combined with statistical analysis and odds ratios.
It was found that people with index fingers shorter than the ring fingers had an increased risk of OA involving any part of the knee or the hip, and including the presence of arthritic finger nodes.
The risk of knee OA in participants with index fingers shorter than their ring fingers was nearly double that of the risk for participants without this pattern. Women with this finger pattern had a greater risk of knee OA than men.
The researchers also found that the smaller the 2D:4D upper finger joint ratio, the greater the risk of OA of the tibiofemoral knee joint, among participants of both sexes.
Finally, after adjusting for established OA risk factors—age, sex, body mass index, joint injury, and lack of physical activity—the strong association of smaller 2D:4D length ratio with the risk for knee OA was deemed independent.
"The 2D:4D length ratio appears to be a new risk factor for the development of OA. 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 OA," said Dr. M. Doherty, the study's leading researcher.
He, however, admits that the "underlying mechanism of the risk is unclear, and merits further exploration."
Published in the journal Arthritis & Rheumatism, this is the first study to examine the relationship between 2D:4D length ratio.