A rare condition can leave people with a symmetrical hand, sometimes with three digits on either side matching up.
It’s called mirror hand, but the scientific name for it is ulnar dimelia.
Mirror hand is an incredibly rare congenital condition, and for the most part it leaves people with mirror symmetry on their hand with a digit in the middle and usually three digits on the side, but no thumb.
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When it is seen, the person usually has seven or eight digits, with the middle, ring and smaller fingers on either side of that central finger.
It can also cause limited movement in the fingers, forearm, and hand, as well as causing differences in the forearm and elbow.
We should stress, this is an extremely rare condition, but the exact cause is not known.
It’s something to do with genetics, and occurs during development in the womb.
Mirror hand can be diagnosed either at birth or on an ultrasound before the birth.
If someone is born with mirror hand, it can be treated with surgery, but only to improve the function or change the appearance of the hand.
In one case documented by the US National Library of Medicine, a two-month-old girl was brought to the doctor for the reason of polydactyly - extra digits - and had some of the fingers amputated.
As you can see from the pictures, she had several surgeries which resulted in her having the ordinary number of fingers on her hand.
This is interesting, as the library states that there are - or were at the time of writing in February 2018 - only 70 documented cases of ulnar dimelia.
They wrote: “Ulnar dimelia is a very rare developmental anomaly of the upper limb.
“There are only approximately 70 cases described in the literature.
“Ulnar dimelia, called also the mirror-hand, is classified to the 3rd group of congenital hand malformation, according to the classification proposed by Swanson [Swanson 1976] and adopted by the American Society for Surgery of the Hand (ASSH) and the International Federation of Societies for Surgery of the Hand (IFSSH).”
In this instance, they noted: “In the presented case of type II ulnar dimelia an anatomical correction of the hand was possible.
“The result of surgical treatment in both functional and cosmetic aspects was, in authors' opinion, good.”
Given that there’s so few cases of this particular condition, it’s very unlikely that you’ll ever hear about it again.
It’s definitely interesting though.
Tom Wood