Ring finger link to arthritis

Women with long ring fingers could be at greater risk of arthritis, according to the Daily Mail . Usually, women have a shorter ring finger than index finger (the opposite pattern to men). However, “women with uncommonly long ring fingers had almost double the risk of osteoarthritis in the knee”, the newspaper said.

The story is based on research by scientists in Nottingham, which reported that women with long ring fingers had three times the risk of osteoarthritis in the knee when compared with those women with ring and index fingers of similar length or those where the ring finger was shorter than the index finger. The researchers suggest that this type of finger pattern is a new risk factor for the development of osteoarthritis. However, as the underlying mechanism is unclear, more research is needed before this can be used a useful indicator of arthritis risk for patients.

Where did the story come from?

Dr Weiya Zhang and colleagues from the University of Nottingham conducted this research. Some of the data was supplied by a study supported by the drug company AstraZeneca. It was published in the peer-reviewed medical journal: Arthritis and Rheumatism .

What kind of scientific study was this?

In this case-control study, the researchers contacted 3,475 people from a previous study who were known to have arthritis and asked them if they would agree to participate. Baseline tests were carried out to assess if the patients were eligible for inclusion, and the final number of participant was 2,049 (1,042 records from people with knee arthritis and 1,007 from those with hip arthritis). These records were then compared with 1,123 controls who did not have arthritis. These people were selected from hospital patients undergoing kidney X-rays.

Hand X-rays were examined for all study participants and these were classified into three groups, each with different finger patterns:

• 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.

The researchers used statistical methods to adjust for known factors that may also put people at risk of developing osteoarthritis, or that are already linked with finger length. They made adjustments for age, sex, body mass index, bone mineral density, joint injury, energetic activity from age 20–40 and acne from the ages of 30–39.

What were the results of the study?

When they compared the 2,049 cases with the 1,123 controls, the researchers found that the patients with the type 3 finger pattern (who had a smaller index to ring finger length ratio) were associated with about a doubling of the odds of having arthritis in the knee, compared with people with a type 1 or 2 finger pattern. This increase in odds was greater in women (roughly tripled) than in men (roughly one and a half times the odds). Any difference in the risk of hip arthritis was inconsistent.

People with the type 3 finger pattern were also at increased risk of having the combination of nodules in the joints of the hand which are characteristic of osteoarthritis, together with knee or hip osteoarthritis.

What interpretations did the researchers draw from these results?

The researchers conclude that the smaller index to ring finger length ratio (type 3, as assessed from hand radiographs) is associated with an increased risk of knee osteoarthritis. It is also associated with the combination of signs of hand osteoarthritis, together with knee or hip osteoarthritis. They go onto say that the association is independent of other established osteoarthritis risk factors. They also warn that the “underlying mechanism of the risk is unclear and merits future exploration”.

What does the NHS Knowledge Service make of this study?

This interesting study has provided further data on the expanding list of conditions associated with the index to ring finger length ratio. Although it is tempting to speculate about the mechanisms and particularly the part that hormones may play in determining the differences found between the sexes, the authors are cautious about these interpretations. They list several limitations to the study.

• The study was conducted in selected patients attending a hospital, so the results may not apply to people living in the community.
• As the groups were not randomised (the study was a case-control design) there may be unknown differences between the groups which may account for the associations found.
• More than half of the patients with hip arthritis also had knee arthritis, which may have reduced the ability of this study to detect any links between finger length and those with hip arthritis alone.

Arthritis is a common condition and finger length is relatively easy to examine. Before accepting this as an important risk factor, it will be important to know exactly how finger length is linked with an individual’s chance of developing arthritis.

Sir Muir Gray adds...

It is an old proverb that association is not necessarily causation. Namely, the fact that A and B are found together does not prove that A causes B.