Published in the January 2008 edition of Arthritis and Rheumatism, a study conducted at the University of Nottingham suggests that people whose index finger is shorter than their ring finger are up to twice as likely to suffer from osteoarthritis (OA), which is the most common form of arthritis. The study team was led by Professor Michael Doherty.
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, while in women these fingers tend to be about equal in length. Research also shows that smaller 2D:4D ratios have intriguing hormonal connections, including higher prenatal testosterone levels, lower oestrogen concentrations, and higher sperm counts.
Researchers at The University of Nottingham conducted a case-control study to specifically assess the relationship between the 2D:4D ratio and the risk of knee and hip OA. For the study, 2,049 case subjects were recruited from hospital orthopedic surgery lists and a rheumatology clinic in Nottingham. All had symptomatic OA of the knees or hips. 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. Hands radiographs were classified visually as: 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. Confirming previous research, men were 2.5 times more likely than women to have the type 3 pattern.
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, researchers assessed the relationship between 2D:4D length ratio and OA. Compared with the other finger types, the type 3 finger was associated with an increased risk of OA involving any part of the knee or the hip, and including the presence of arthritic finger nodes. Of particular note, the risk of knee OA in participants with the type 3 finger pattern 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 in this study admit that the underlying mechanism of the risk is unclear and that further study is necessary.
To read a news article on the study, or the findings themselves, click on one of the links below:
Radiographic assessment of the index to ring finger ratio (2D:4D) in adults, site accessed on 02/11/08