Hypoplastic thumb, also known as thumb hypoplasia, is a birth defect in which a child’s thumb is underdeveloped (hypoplasia) or missing (aplasia).
There are five types of thumb hypoplasia and aplasia which are:
- The thumb is slightly smaller than normal; all structures are normal but undersized
- The thumb is smaller than normal and there are abnormalities in the tendons and muscles. Movement is restricted and unstable because of a tight web space between the thumb and index finger.
- There are abnormalities in the thumb's muscles and joints. There is also a tight web space between the thumb and index finger.
- The thumb is floating and has no bone support, only skin and soft tissue.
- The thumb is missing.
Diagnosis and Treatment of Hypoplastic Thumb
An orthopedic doctor may diagnose thumb hypoplasia based on a physical exam of the hand. To determine which type of hypoplastic thumb a child has the doctor will check the width of the web space, presence or absence of the thumb, and the joint functioning. Tests to confirm the diagnosis often include a hand x-ray.
Treatment for hypoplastic thumb depends on the type, functionality, and stability of the thumb and hand. The most common treatment for severe hypoplastic thumb is pollicization of the index finger. Pollicization is a procedure where a thumb is created from an existing finger, usually the index finger.