Paediatric
Hypoplastic thumb
Thumb · reconstruction
What it is
A hypoplastic thumb is one that is underdeveloped at birth. The range is wide: from a thumb that is slightly small but fully functional, through an unstable thumb with a narrow web and absent muscles, to a floating remnant or no thumb at all.
It often accompanies an abnormality of the radius, and it is associated with syndromes that can involve the heart, the kidneys and the bone marrow. That is why a workup is arranged at diagnosis, even when the hand is the only reason for the visit.
Symptoms
The thumb is small, the web between thumb and index is narrow, and pinch is weak or impossible.
The most telling sign is behavioural: the child bypasses the thumb and pinches between the index and middle fingers, like a pair of scissors. That observation says more about real function than measuring the thumb does.
Non-operative treatment
Where the thumb is stable and only slightly small, no surgery is needed: occupational therapy encourages its use and function develops normally.
In more marked forms, therapy prepares for surgery and works on alternative grips, but it cannot create the stability that is missing at the base of the thumb.
Surgical treatment
The decisive question is whether the joint at the base of the thumb is stable. If that joint is present and stable, the thumb is reconstructed: widening the web, transferring a tendon to restore opposition, and stabilising the knuckle joint.
If the basal joint is absent, or the thumb is only a floating remnant, reconstruction in place would not produce a usable thumb. The standard operation is then pollicisation: the index finger is shortened, rotated and repositioned to become a thumb, keeping its own nerves, vessels and tendons.
Recovery expectations
A cast is followed by several months of occupational therapy. After pollicisation the child has to learn to use an index finger as a thumb — young children adapt remarkably quickly, the more so the earlier it is done.
Pinch and strength improve steadily over the first year after surgery, and follow-up then continues through growth.
These pages give general information for patients and referring physicians. They do not replace an individual assessment: the treatment plan is decided in consultation, based on your examination and your goals.