What Is Mirror Hand Syndrome Ulnar Dimelia and Causes

by Mouli Chakraborty
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Recently, popular media is making polydactylism famous by presenting it as a distinguished genetic anomaly. Be it “Gravity Falls” or “The Princess Bride,” their fictional characters possess more than 5 digits on their hands/feet. Nevertheless, very few people know about a syndrome named Ulnar Dimelia or Mirror Hand Syndrome. 

This is because the syndrome is very rare; until now, only less than a hundred cases of mirrored hands have been diagnosed. In an ulnar dimelia-affected individual, their second hand usually remains attached to their wrist, which in turn mirrors the first’s movements. That’s why ulnar dimelia, colloquially, is named mirror hand syndrome. 

Many researchers are still trying to discover new facts about this syndrome. It seems that the disease is not hereditary. However, it may be the reason for a genetic mutation. Nonetheless, this is only an assumption or hypothesis.

This is because no one has exact knowledge about the originating factor of this rare hand condition. 

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What Is Mirror Hand Syndrome?

It’s an extremely rare kind of congenital disorder in which the radial ray remains absent, duplication of ulna happens, and also the duplication of the metacarpal, symmetric polydactyly, phalanx bones, and carpal happens.

Some cases need a surgical amputation to remove the duplicate phalanges, metacarpals, and carpals. 

Sometimes, your bone deformity also accompanies arterial as well as nervous anomalies. It happens because of ulnar nerve duplication, radial nerve shortening, and radial artery absence.

You can diagnose ulnar dimelia by doing lab tests of individuals’ frontal as well as sagittal planes in case of your suspicion of the condition. 

The Mirror hands deformity’s embryology was first interpreted by two experts, Saunders and Gasseling. They described it as an ectopic manifestation of the polarizing activity cells’ zone or the gene of sonic hedgehog (responsible for an anteroposterior axis’s limb patterning. 

According to them, the Hox genes, which give positional information during the period of embryogenesis, also play a secondary role. Actually, the etiology inferred is probably nothing but failure (loss) of differentiation of one portion of the ray instead of its pure duplication.

But, what are the characteristics of mirror hand syndrome ulnar dimelia? What are its types, and how can it be fixed? Come, Let’s see! 

Mirror Hand Syndrome Ulnar Dimelia – Types:

Mirror Hand Syndrome Ulnar Dimelia
Mirror Hand Syndrome Ulnar Dimelia

Medically, mirrored hands are of two types. In type 1, the disease entails a lunate, a trapezoid bone, and an index finger. In type 2, the mirrored hands possess two lunate as well as two trapezoid bones along with 2 index figures.

Ulnar dimelia has recently been classified in the 3rd group retaining congenital hand deformities. 

However, the Al-Qattan & Al-Thunayan proposed system of classification divides the mirror hand syndrome into 5 types.

  1. Type 1 refers to the ulnar dimelia that shows 2 ulnae with zero radius.
  2. Type 2 refers to an intermediate form of ulnar dimelia which comprises 2 ulnae along with 1 radius.
  3. The Type 3 also refers to an intermediate form of ulnar dimelia, which involves mirror hand polydactyly along with 1 radius and 1 ulna.
  4. Type 4 refers to a syndromal kind of mirror hand along with Laurin Sandrow syndrome’s fibular dimelia.
  5. Type 5 refers to ulnar dimelia in which the patient comprises multiple hands-on their forearms’ ends. 

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Radiographic Features of Mirror Hand Syndrome:

Mirror hand syndrome’s radiological traits are typical, and they are shown at:

Elbow Joint

Generally, the humerus articulates the elbow joint along with 2 ulnae. In this case, the articulation doesn’t happen accurately as it happens for a trochlea and ulna in an average population. The presence of 2 ulnar arteries may/may not occur. 

Wrist Joint

In this case, the radius and the thumb remain absent and the ulna, as well as carpals’/metacarpals’ ulnar halves, get duplicated. Besides, you will see the presence of 8 triphalangeal digits. 

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Characteristics Of Mirror Hand Syndrome/ Some Facts About Ulnar Dimelia:

Characteristics Of Mirror Hand Syndrome
Characteristics Of Mirror Hand Syndrome

Mirror Hand Syndrome Is A Very Rare Condition

Yes, this disease rarely happens in people. Till now, less than 100 persons have been diagnosed with this syndrome, and the disease has affected their arms and hands.

The first case was documented in 1587. And after that, only 72 cases of documentation of this syndrome have occurred in the medical literature. 

Also, there is a probability that some cases of this syndrome have gone unnoticed in this world’s underdeveloped areas. With the popping up of new cases, medical experts are continually trying to gather some extra information and data about this disease. Also, new studies on this syndrome are being published whenever possible. 

Duplication Of Fingers Or The Entire Hand

Persons suffering from ulnar dimelia may possess 2 hands-on 1 wrist. It will look as if the hands are joined at the person’s palm symmetrically. Also, the hand of the affected person will appear as if it is duplicated.

Again, a cleft may exist in their palm where their hands join. The additional fingers are observed as connected to the extra bones that elongate themselves down towards the carrier’s wrist, sometimes lengthening towards the elbow. 

However, it is not the only aspect of the manifestation of mirror hand syndrome. Such cases are also observed where a person possesses extra fingers in a single hand, which just looks like multiple hands’ molding.

Besides, a few other cases also involve multiple fingertips that branch off from only one finger. It all depends on which classification or group the specific case is falling.  

Absence Of Thumbs

In the case of mirror hands syndrome, the hands don’t comprise any thumb, even though the person’s hand appears duplicated right down the middle.

Instead, you will see that the ulnar dimelia hands possess either 2 index fingers placed centrally or a single index finger on a shared basis. In such a type of hand, zero thumb bone exists. 

Unison Movement Of The Connected Hands

The mirror hands affected people usually cannot move their coalesced appendages independently from one another. Instead, most individuals with ulnar dimelia confessed that whenever they tried to move their hands’ one half, the other half automatically mimicked the motion of the first half. 

Also, the mirror hands struck a person’s hand while grabbing things and opening and shut in the manner of a Venus fly trap. The fingers are curled inwards towards one another.

In case some of the fingers get extended, it becomes impossible for the others to flex. Again, in the case of mirror hands, the person’s nerves react in unison apart from their digits mirroring symmetrically. 

Impeding Of The Range Of Motion Of Your Whole Arm

The problem of ulnar dimelia never remains restricted to a person’s hands. Its effects spread throughout his entire arm and impede the range of motion of their whole arm. Such person would find it hard to flex/move their elbow.

This is because his arm may be missing the radial bone. Certain bones duplication would limit his arm’s spectrum of motion. Besides, ulnar dimelia can weaken the muscles of the person. Because of these detrimental effects, people look for corrective surgery. 

The Disease Is Not Hereditary

It has been researched that mirror hand syndrome has never been genetic. Though its actual cause is not very forthcoming, it has been confirmed after intense research that people suffering from ulnar dimelia hardly retain a familial record of congenital deformities. 

The Syndrome Rarely Happens In Both The Arms; It Happens Or Spreads To One Arm Only:

It’s a highly perplexing condition in which most symptoms perceive chaotically disparate. They do not confirm the medical world’s perceived order. The majority of cases with this syndrome have occurred unilaterally.

Different case studies tell us that the other arm of an affected individual remains absolutely normal. Nonetheless, only rare instances happened in which both of a person’s arms exhibit signs of mirror hands. 

Though Not Sure, Sonic Hedgehog Gene May Cause Mirror Hands:

A few people hypothesize that 2 genes are responsible for Mirror Hands. They are a sonic hedgehog, which helps monitor your limb and digit growth, and Hox genes, which informs the configuration of embryonic stage developing bodies. Nevertheless, there’s no definitive link between these genes with mirror hand syndrome. 

Sometimes, Multiple Surgeries May Be Needed For Treating The Syndrome:

At times, the last way to correct ulnar dimelia is none other than undergoing multiple surgeries. The surgeries will be complex, as they will address the issues of the wrist and elbow movement.

The doctor may, again, remove on-demand some of the digits of the mirror hands. Further, the muscles or tendons are strengthened in high-stress regions. 

Surgeons from utilitarian and cosmetic backgrounds frequently strive to establish a person’s thumb out of their extra fingers. Surgeries often successfully create people’s usable and conventionally aesthetic hands.

However, not treating the syndrome for fear of undergoing multiple surgeries might only enhance further issues or abnormalities of the limb (for example, the person’s posture or range of motion). 

No Definitive Cause About The Syndrome Is Identified 

As only a few records exist until now, some experts are yet to provide you with a full awareness regarding ulnar dimelia. Though it happens randomly, both sexes- boys and girls- would equally display this unusual condition. 

Treatment of Mirror Hand Syndrome

Mirror hands can only be treated using the surgical reconstruction intervention method. In general, a doctor always recommends their patients go for this surgery before their baby turns 2. This is because the surgery must be done only after the parents observe their child at the time of playing to establish the promising radial digit required for pollicising.   

Wrapping Up

So, in case you find that your newborn child is a victim of this rare disease, mirror hand syndrome, don’t break down. First, consult your doctor and discuss with him patiently how you can make your child get out of it and give him a normal healthy life like other children. In case he assures you that surgery can bring a difference in your child’s life in a positive direction, trust him and just go for it. The surgery will give your baby a new life and free them from mirror hand syndrome. 


Q.1. How common is mirror hand syndrome?

Answer: The prevalence of mirror hand syndrome is supposed to be slightly less than one if estimated in one million people. However, the researchers confided that a few mildly affected persons may never get diagnosed.

Also, some people don’t like to report the problem to their children officially. So, there’s no record of mirror hand syndrome in such children in an official manner; hence, no counting of them in the list of estimated persons who are suffering from this syndrome. 

Q.2. What causes ulnar dimelia?

Answer: No specific cause of mirror hand syndrome has been diagnosed or specified till now by the researchers. However, research is going on to discover the actual reasons for ulnar dimelia. The pathogenesis of this syndrome is associated with the embryology of the upper limb. In this case, the 1st stride of limb formation is the surge of limb buds (known as Wolff crest) that arise on the embryo’s ventrolateral side. Besides, the buds are shaped by mesenchyme shrouded with a membrane of ectoderm.

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