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Thumb Hypoplasia

What is thumb hypoplasia?

Inadequate growth and development of thumb is called thumb hypoplasia.

Are these children prone for other deficiencies?

Thumb hypoplasia is commonly associated with radial club hand. Other syndromes associated with it are Holt-Oram syndrome, thrombocytopenia–absent radius (TAR) syndrome, the VACTERL association, and Fanconi‚Äôs anaemia.

Systemic evaluation of the child by a paediatrician needs to be done to assess status of other systems.

What causes thumb hypoplasia?

The aetiology of thumb hypoplasia is not known but many factors including genetic, teratogens, and environmental may contribute.

There are many associations of this condition and usually a paediatric / paediatric surgery consultation is given for evaluation of other systemic involvement.

What investigations are required for diagnosis?

The most important factor in management is assessment of the deformity. Stability of the thumb, mobility at each joint, sensation, assessment of individual muscle function, various grips and pinches and condition of the web space are important considerations.

X rays are taken to evaluate the status of skeleton. Other investigations may be required to rule out other systemic illness (as per the advice of paediatrician). Just before operation, some blood tests and chest X-ray may have to be taken to evaluate fitness for anaesthesia.

How do we decide upon the treatment?

Depending upon stability of the thumb, mobility at each joint, sensation, assessment of individual muscle function, various grips and pinches and condition of the web; one easy way of classification puts them into two broader classes as 'adequate' and 'inadequate'.

In general, these deformities are divided into five classes. Most simple deformity (class I) has mild hypoplasia with near normal function while in the most severe deformity (class V) the thumb is absent.

Treatment varies depending upon the severity of the deformity.

What is ideal age for treatment?

The ideal age for treatment in these children is between 6 months to 1 year. We attempt to provide thumb by one year so that the child learns to use his new thumb.

What are the treatment options?

Of the adequate thumbs (Class I, II, and III A); in milder deformities if the thumb is functional it can be left alone. While more deformed ones may need simple operations to adjust the muscle pull and stabilisation of joints. Increasing the span of the first web also is frequently required.

In little more severe deformities when the thumb is unstable but present, few options like bone grafting, vascularised joint transfer from the foot and pollicisation are present. Parents need to understand the advantages and problems associated with each before deciding upon the operation.

In most deformed cases pollicisation of the index finger is currently the best possible option. In this the index finger is transferred in the position of thumb so that it will act like a thumb. The overall result will depend upon the status of index finger as in some cases the index itself may be hypo-plastic.

Toe transfer is normally not an option in these patients as the muscles of the thumb required for moving the transferred toe are absent (hypo-plastic).

Few details of pollicisation surgery.

Pollicisation of index finger

This operation transfers the index finger of the involved hand to thumb. Though it is the best possible options for these hands; due to differences in the configuration of thumb basal joint and the index finger joint and lack of normal muscles of thumb the function is not as perfect as normal thumb.

This operation involves multiple steps

Incision planning: the incisions are planned in such a way that the vascularity of the skin is preserved and in the end adequate flap tissue is available for formation of the first web space.

Dissection: the dissection involves careful separation of the palmer and dorsal skin preserving the circulation of the skin and the index digit. The tendons, nerves and vessels are dissected out and kept ready for transfer.

Shortening: as the index digit is much longer than thumb and has an extra bone it is shortened by removing the basal bone but preserving the joint. This new joint will become the basal joint of thumb.

Transfer: the index finger is then switched in place of thumb and the bones are fixed in this new place.

Muscle balancing: Then the native muscles of thumb and the muscles of index finger are adjusted for their length, tension and orientation so that they will function to simulate movements of a thumb.

Skin closure: After controlling all the bleeding and checking the skin blood supply the incisions are closed taking care to have adequate space between the long finger and the new thumb (new Ist web).

Postoperative: A POP slab will be applied and will be kept in place for 3-4 weeks. Patient will be discharged at the end of first week after dressing and will be seen periodically as outpatient.

After removal of cast parents will be taught to splint it for few more weeks. Parents are taught regarding physiotherapy, application of compression bandage, wound care and other necessary care.

Complication: Infection, bleeding, haematoma (collection of clot in the wound) are rare complications. The new digit is stabilised with K wires and rarely especially after removing the plaster the wire may come out. Other few rare complications are skin necrosis (might require minor surgical procedures). A very rare complication in expert hands is injury to the blood vessels of index finger that may result in necrosis of this transferred digit.

Case 1: Hypoplastic thumb is transferred to its normal position for better function and appearance

Before After
Thumb Duplication Thumb Duplication