A study of more than 2,000 people, published in the journal Arthritis and Rheumatism, suggests that people whose index finger is shorter than their ring finger are up to twice as likely to suffer from the condition, which is the most common form of arthritis.
Index to ring finger length ratio (referred to as 2D:4D) is a trait known for its differences between the sexes. Men typically have shorter second than fourth digits; in women, these fingers tend to be about equal in length. Smaller 2D:4D ratios have intriguing hormonal connections, including higher prenatal testosterone levels, lower oestrogen concentrations, and higher sperm counts. Reduction in this ratio has also been linked to athletic and sexual prowess.
Whether this trait affects the risk of osteoarthritis (OA), the most common form of arthritis that may associate with both physical activity and oestrogen deficiency, has not been examined — until now.
Researchers at The University of Nottingham conducted a case-control study to assess the relationship between the 2D: 4D ratio and the risk of knee and hip OA. Their findings suggest that having a relatively long ring finger to index finger ratio raises the risk for developing OA of the knee, independent of other risk factors and particularly among women.
For the study, 2,049 case subjects were recruited from hospital orthopaedic surgery lists and a rheumatology clinic in Nottingham. All had clinically significant symptomatic OA of the knees or hips, requiring consideration of joint replacement surgery. Recruited from hospital lists of patients who had undergone intravenous urography (IVU) within the past five years, 1,123 individuals with no radiographic evidence of hip or knee OA, no present hip or knee symptoms, and no history of joint disease or joint surgery served as a control group.
The study population was comprised of both men and women, with an average age of approximately 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. Researchers then assessed the 2D:4D length ratio from radiographs using three methods: a direct visual comparison of the two 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.
Hands radiographs were classified visually as either type 1, index finger longer than the ring finger; type 2, index finger equal to the ring finger; or type 3, index finger shorter than the ring finger. Not surprisingly, men were 2.5 times more likely than women to have the type 3 pattern.