Mirror Hand
Also known as: Mirror hand deformity, mirror hand syndrome, ulnar dimelia.
Mirror hand is a very rare congenital difference. In most cases, there is mirrored symmetry of the hand with a central digit and 3 digits on either side and no thumb. There are usually 7 or 8 digits, with middle, ring and small fingers seen on either side of the central digit.
Differences are often seen in the forearm and elbow as well. Movement in the fingers, forearm and elbow may be limited.
Why Choose US
Education Experience
I earned my MD in Surgery from Huazhong University of Science and Technology in Wuhan, China, in 2003. Later, I completed my PhD at Katholieke Universiteit Leuven in Belgium in 2008.
Professional Experience
I am currently an Associate Professor and Chief Physician of Hand Surgery at Wuhan Union Medical College Hospital. I supervise master's students and serve on the editorial boards of several journals, including the Chinese Journal of Experimental Surgery, the Journal of Foot and Ankle Surgery, and the Chinese Journal of Microsurgery.
Expertise
My expertise includes performing syndactyly release using the Pelnac artificial dermal substitute, which eliminates the need for skin grafting. This work was published in the Journal of Plastic, Reconstructive & Aesthetic Surgery in September 2023.
What Causes Mirror Hand
Ulnar dimelia, also referred to simply as mirror hand, is a very rare congenital disorder characterized by the absence of the radial ray, duplication of the ulna, duplication of the carpal, metacarpal, and phalanx bones, and symmetric polydactyly. In some cases surgical amputation is performed to remove the duplicate carpals, metacarpals and phalanges. As of 2015, approximately 70 cases have been recorded in the medical literature.
The cause is thought to be an error during embryonic development and typically only one arm is affected.
Bone deformity may also accompany nervous and arterial anomalies in some cases due to the duplication of the ulnar nerve, the presence of abnormal arterial arches, the duplication of the ulnar artery, the shortening of the radial nerve, and the absence of the radial artery. The diagnosis of ulnar dimelia is based on laboratory tests of frontal and sagittal planes in individuals suspected of the condition. There are two types of ulnar dimelia noted in medical journals: Type 1 ulnar dimelia entails one lunate and one trapezoid bone as well as one index finger, while type 2 ulnar dimelia has two lunate and two trapezoid bones as well as two index fingers.
The exact cause is not known, though the genes responsible for positional information during limb development are likely involved. Mirror hand is diagnosed on prenatal ultrasound or at birth.
What are the symptoms of mirror hand?
Along with the physical appearance of the upper arm, hand and fingers, mirror hand is also characterized by limited range of motion of the affected limb.
What are mirror hand care options?
Surgery can help improve appearance and function of mirror hand in affected patients.
Your child will need reconstruction surgery to fix the physical appearance as well as the function of the affected hand. This may include multiple surgeries.
Usually, the surgeon will wait until your child is between 18-24 months to perform this surgery. That's because this allows the hand to grow almost twice the size it was at birth.
During the surgery, they'll remove additional fingers and most likely pick one of the digits to use as a thumb. The doctor will reposition it where the thumb would have naturally developed. This is known as pollicization. The aim of the surgery is to rebuild their hand with five digits including a thumb.
They also try to keep as much muscle, tendon, and growth plates on their hand as possible and reconstruct their wrist. This will help your child to develop hand movement, growth, and function as they grow up.
If mirror hand syndrome affects their elbow joint or forearm, they'll need surgery to fix their ability to bend and rotate it.
They might need motion exercises and physical therapy for the hand to improve function as it grows. Speak to your doctor, physical therapist, or an occupational therapist about it.
How Is Mirror Hand Syndrome Diagnosed
Mirror hand syndrome, also known as ulnar dimelia, is an extremely rare congenital (meaning it's there from the time you're born) birth defect that affects your hand. In some cases, your forearm and elbow might be impacted, too. The first case was seen in 1852. Since then, there have been fewer than 100 cases reported.
If your child has this condition, they're typically born with 7-10 fingers on one or both hands.
This means from the midpoint of their hand, their fingers look like mirror images. Usually, there's no thumb.
Instead, in most cases, they'll have a central finger. And on either side, they'll have a mirrored symmetry of three fingers - the middle finger, the ring finger, and the little finger.
Studies show it affects men and women equally.
Usually, you have two bones in your forearm - the ulna and the radius. Both bones lend to different hand and finger growth and function.
But when you have mirror hand syndrome, typically there are two ulna bones, and the radius is missing. This tends to happen when your limb is still in the developing stages as an embryo. Your wrist bones might duplicate, too. This then causes your forearm and hand to look like mirror images.
There are experts who believe there are different types of mirror hand syndrome. In some cases, it's possible for you to develop two ulnae along with a radius bone. If the bones develop differently, it can affect how your hand appears physically. For example, it could cause you to have more than five fingers (polydactyly). It's also possible to develop multiple hands at the end of your forearm.
Besides the physical appearance of multiple fingers and no thumb, the condition may cause the wrist to be bent slightly. Your child might be able to bend their elbow regularly. But in some cases, the elbow might be straight and difficult to bend or rotate.
Mirror hand syndrome can cause you to have a limited range of motion in your wrist and hand. This can lead to dexterity issues, which means it may be hard to use your hand and fingers to perform certain day-to-day tasks such as grasping or picking things up.
As this condition can happen when the limbs are forming during the embryo's developing stages, mirror hand syndrome is often diagnosed at the prenatal ultrasound screening during pregnancy. It can also be diagnosed at birth.
Mirror hand, also known as ulnar dimelia, is an extremely rare condition with reported incidence of 70 cases in the last 300 years. It is characterized by the presence of duplication of the ulna. There is no radius and almost symmetrical duplication of the ulna digits around a central digital axis producing seven or more digits. This patient had two ulna bones in the left forearm and eight fingers in the left hand.
Anatomically, the carpus appears symmetric with a large lunate surrounded by triquetrals on either side. There are two capitates, two extensor tendons to the central digit and a duplicated ulna nerve. Arterial supply is through a lateral vessel supplying the radial two and a half digits and a medial vessel supplying the ulnar four and a half digits.
These included patients with two ulnae and one radius, two radii and one ulnae; and ulna dimelia with other congenital malformations. The patients had multiple fingers in which: type 1 is ulnar dimelia (two ulnae), type 2 is intermediate with two ulnae and a radius, type 3 is intermediate with one radius and ulna, type 4 is syndromal mirror hand; and type 5 is multiple hand. The case we are presenting is type 1A in which the two ulnae are fully developed. type 1 is the most common with type 1B being more commonly reported than type 1A.
Who produced mirror image digit duplications in chicks by grafting a small piece of posterior border mesoderm into an anterior position . This is the zone of polarizing activity (ZPA) and is regulated by the sonic hedgehog (Shh) gene, which is responsible for limb patterning on an anteroposterior axis. Ectopic expression of the zone of polarizing activity cells or the sonic hedgehog gene can therefore produce mirror image deformities. Secondary signaling molecules such as the Hox genes have been implicated in the embryogenesis of mirror image deformities. Hox genes encode positional information during embryogenesis. Hox b-8 is thought to be important in the specification of the zone of polarizing activity cell positioning, ectopic expression of which has experimentally resulted in mirror image duplication.
The management of the ulnar dimelia deformity involves treatment of the elbow, wrist and hand. The limitation of motion in the elbow is treated by extra-periosteal resection of the proximal part of the duplicated ulna. This improves forearm rotation and elbow flexion. Severe rotational deformities may require derotational osteotomy. The wrist is usually in flexion and is treated by releasing the wrist to allow extension. This may involve Z-plasty of the palmar skin, flexor tendon lengthening, volar capsulotomy or proximal row carpectomy. Flexor tendon transfer to the dorsum and wrist flexion may be required. The hand is treated by pollicization of one of the radial digits and amputation of the adjacent redundant digits. The radial index finger was of good function, size and with adequate radial index-ulna index web space. It was therefore pollicized. The ulnar small finger was of good function and position and was therefore retained. The radial small, ring and long fingers were amputated. The wrist was normal in this patient while the elbow will need a proximal ulna resection later.
Preoperative Modeling for Mirror Hand
A computed tomography (CT) scan of the hand and forearm was utilized to generate a 3D computer model of the left forearm and hand soft tissue using segmentation software. A negative mold of the soft tissue computer model was created using 3D modeling software. The molds were then 3D printed using a fused-deposition modeling printer. The hand soft tissue was then casted with silicone. The material cost of making the molds was under $30, and mold printing time was approximately 8 hours. The computer modeling to prepare the molds took approximately 1 hour.
The resulting silicone hand model was then used for preoperative marking, planning, and trial surgery. The surgeons marked planned incisions and incised the silicone hand using surgical instruments to perform trial procedures to determine the optimal surgical approach. Preoperative visualization of the nerves was not possible. The bony portion of the reconstruction was considered using the 3D computer model rendered from the preoperative CT.
Operative Procedure
Utilizing the preoperative bony and vascular imaging in conjunction with the 3D silicone model, the overall reconstructive plan included removing the first, second, and fourth digits and retaining and pollicizing the second digit of the mirrored hand. The first, third, and fourth digits were amputated through their metacarpal bases. A mid-shaft osteotomy of the second digit metacarpal was then performed. A K-wire was then placed through the proximal phalanx through a hyperextended metacarpal head onto the proximal metacarpal stump. The abductor pollicis brevis, located during the dissection of the first digit, was transferred to the base of the proximal phalanx of the second digit. The interosseous muscles of digits 2 and 3 were combined and transferred to the ulnar base of the proximal phalanx of the second digit to recapitulate adductor pollicis function. A web space between the new thumb and index finger was developed from a dorsal triangular flap at the base of the second digit. Release of the simple syndactyly of the second and third digits was done using a zigzag incision. Finally, the web space skin between the third and fourth digit were preserved.
The silicone hand provided excellent real time, 3-dimensional preoperative visualization of the deformity. The model allowed for preoperative trial markings and the ability to practice the procedure using surgical instruments. By incising and manipulating the silicone, the surgical team was better able to visualize the deformity to determine the most optimal surgical plan.
Surgery can help improve appearance and function of mirror hand in affected patients.
Though the hand of a person with Ulnar Dimelia may appear to be duplicated down the middle, this usually does not include the thumb. Instead, hands affected by Ulnar Dimelia have either two index fingers in the center or a single, shared index finger. In such cases, no thumb bones are present in the affected individual's hand.
When this condition is repaired via surgery, the procedure usually involves creating a thumb using one of the extra fingers. This is not just for cosmetic purposes, as it's a lot easier to navigate the world with working thumbs.
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