Ulnar Dimelia

Ulnar dimelia, also known as mirror hand, is one of the rarest hand deformities and occurs in approximately 1 in a million births. Normally, in the forearm, there is an ulna bone and a radius. However, in these cases, a baby is born with duplicated ulnar bones. Often, this results in extra fingers appearing symmetrically to the normal ones. Most of the time, there are around 6-8 fingers on one hand. 

Having 1-3 extra fingers can affect the function of the hand and wrist. It can cause problems with rotating the wrist and grasping objects.  In some cases, it can cause babies to be born without thumbs, affecting their pinching and gripping abilities. Babies typically undergo surgeries around one year old, but the timing depends on their size and development. Before surgery, doctors assess hand strength, which finger could be the best fit as a thumb, and nerve mapping.

The steps for surgery begin with imaging. This can be done with an X-ray, computed tomography (CT) scan, or even a magnetic resonance imaging (MRI). After imaging, extra fingers are removed or the thumb is reconstructed (pollicization). Surgeons may turn an index finger into a functioning thumb or even toes! Next, bone realignment occurs in the forearm. Because the ulna is duplicated, it needs to be adjusted for the forearm to fully function, such as rotations or elbow movement. Lastly, the surgeon adjusts the nerves and tendons to improve the movements in the wrists, fingers, or forearm. In some cases, robotic-assisted surgery is used to repair nerves. Recovery usually consists of 4 to 6 weeks in a splint or cast with occupational therapy. The occupational therapy teaches the kids how to work with their “new” hand.

After surgery, children usually end up with a fully functional and strong hand. To prepare for surgery, surgeons use 3-D printers to replicate the patient's hand, practice how the surgery should occur, and create a detailed plan for every cut and stitch. Ulnar dimelia is rare, but with the surgery and therapy, children gain better use in their hands and live more independently and confidently.

Written by Hadlie Darke-Schreiber at Incisionary

APA References

Al-Qattan, M. M. (2011). Mirror hand (ulnar dimelia): A case report and review of the literature. Case Reports in Orthopedics, 2011, 1–4. https://doi.org/10.1155/2011/302483

Boston Children’s Hospital. (n.d.). Thumb hypoplasia and pollicization. Boston Children’s Hospital. Retrieved July 17, 2025, from https://www.childrenshospital.org/conditions/thumb-hypoplasia

OrthoBullets. (n.d.). Congenital hand differences. Retrieved July 17, 2025, from https://www.orthobullets.com/hand/6023/congenital-hand-differences

American Society for Surgery of the Hand (ASSH). (n.d.). Congenital hand differences. Retrieved July 17, 2025, from https://www.assh.org/handcare/condition/congenital-hand-differences

Manske, P. R., & Oberg, K. C. (2009). Classification and developmental biology of congenital anomalies of the hand and upper extremity. The Journal of Bone and Joint Surgery. American Volume, 91(Supplement_4), 3–18. https://doi.org/10.2106/JBJS.I.00361