What Is Thumb Hypoplasia?
The term hypoplasia refers to underdevelopment. Hypoplastic thumb refers to an underdeveloped or absent thumb finger. This condition occurs mainly as a part of radial longitudinal deficiency (in which the radius bone of the forearm is formed incompletely). The underdeveloped thumb is generally short and thin and sometimes is malpositioned. It often occurs in association with other syndromes.
The level of development of the thumb may vary for each individual with a hypoplastic thumb. The treatment for a hypoplastic thumb depends on the severity of the hypoplasia.
What Causes Thumb Hypoplasia?
The exact cause of the condition remains unclear, and it occurs to the malformation of the thumb during embryonic development. It is also seen in association with other conditions or syndromes. During embryonic development, the limb buds develop during the third to fourth weeks of gestation, followed by the development of the fingers of the hand during the fifth week of development. Any insult may result in malformation or an underdeveloped thumb at this stage.
Thumb hypoplasia is estimated to occur yearly in around one in one lakh children. Most cases have thumb hypoplasia in both hands, commonly occurring in the right hand. They occur in association with defects of the radial bone in most cases.
They also occur in conjunction with other conditions and syndromes, such as:
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Ulnar Longitudinal Deficiency: Ulnar longitudinal deficiency, also known as club hand, is a condition in which the affected child has a stiff and fixed wrist. On the affected side, the wrist is bent towards the hand's little finger.
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Transverse Limb Deficiency: A condition that involves the absence of the hand, leg, finger, or toe.
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Symbrachydactyly: A condition with abnormal short fingers which are fused or webbed.
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Cleft Hand Complex: A condition that causes an abnormal split or cleft appearance along the center portion of the hand.
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Brachydactyly: A genetic condition that involves the shortening of fingers and toes.
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Thumb Duplication: A condition with extra digits or toes in the hand or feet.
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Rubinstein-Taybi Syndrome: A genetic condition affecting learning abilities, facial features, and the thumb or fingers.
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Apert Syndrome: A rare genetic condition that causes deformities of the hand, skull, feet, and face.
Thumb hypoplasia is seen with various other syndromes such as VACTERYL (vertebral, anal, cardiac, tracheoesophageal, renal, limb), Holt-Oram syndrome, etc.
How Is Thumb Hypoplasia Classified?
Children with thumb hypoplasia have a non-functioning thumb. This results in difficulty with grasping or holding objects. Based on the Blauth system, the thumb is classified into five types.
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Type 1: Minor hypoplasia with stable surrounding components such as bones and muscles.
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Type 2: Bone structures are present but small in size. The thumb joint is unstable.
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Type 3: There is a deficiency of the bony structures and muscles. The jump joint is unstable.
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Type 4: Absence of bony structure and muscles. "Floating" thumb attached to the hand by the skin and soft tissues.
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Type 5: Complete thumb aplasia (absence of thumb).
How Is Thumb Hypoplasia Diagnosed?
Most of the time, thumb hypoplasia is identified during birth.
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Sometimes they are diagnosed even before birth with the help of an ultrasound (a diagnostic technique that uses sound waves to produce images of the internal organs and structures).
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The healthcare provider will perform a thorough and detailed physical examination of the patient.
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The doctor will also assess the surrounding structures for any associated developmental anomalies.
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The doctor will perform other radiographic examinations, such as X-rays, to evaluate the hands of the affected child. The radiographic examination may reveal an underdeveloped or hypoplastic first digit of the hand and the absence of a carpometacarpal joint (five joints located in the wrist that connects the bones of the wrist with bones of the hand),
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The affected child and the parents may require genetic testing for genetic-related conditions or syndromes.
How Is Thumb Hypoplasia Treated?
Treatment for thumb hypoplasia is completely dependent on the patient's functional abilities. The thumb finger plays a major role in day-to-day tasks. It is essential while holding or pinching objects. Some children might train and adapt with a missing finger. However, a missing thumb might affect the motor skills of the patient. Treatment for thumb hypoplasia depends on the severity of the condition. Surgical intervention is an effective method to treat a hypoplastic thumb.
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Surgical Reconstruction: Surgical reconstruction of the underdeveloped and hypoplastic thumb is recommended for thumb hypoplasia. It is recommended in cases where there is the presence of a carpometacarpal joint. The pediatric surgeon will rebuild the thumb's ligaments to stabilize the middle joint. They fix the tendons of the thumb by transferring them from another part of the hand. In cases with tight webspace (space between the thumb and the index finger), the surgeon will release the webspace using skin grafts. This surgery helps in improving the function and stability of the thumb finger. Post-operatively the patient may require a cast or splint to immobilize the thumb. Once the thumb is healed, the patients are referred to a physical therapist to improve the thumb finger's range of motion and functionality.
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Index Pollicization Surgery: This surgery is performed in severe cases of thumb hypoplasia with no carpometacarpal joint. This surgery is usually performed in children between six months to eighteen months. The surgeon will surgically remove the unfunctional thumb and reconstruct a functional thumb by transferring the other fingers, mostly the index finger, to the thumb position. This procedure might be followed by other procedures to increase the web space of the hand. Post-operatively the patient will be given splints and braces for two weeks. The patient will require intensive occupational therapy followed by surgery to improve the functions of the transferred finger.
Conclusion:
The hypoplastic thumb is a congenital condition that involves an underdeveloped or absent thumb finger. The affected child has difficulty grasping or holding objects. Most often, the hypoplastic thumb is associated with other genetic conditions or syndromes. They are accompanied by weakening and wasting of the surrounding muscles of the thumb finger. They are usually identified during the time of birth or sometimes even before birth. The effective treatment option for the hypoplastic thumb is surgical intervention. The surgical technique either involves reconstruction or pollicization, depending on the patient's age and the severity of the condition.
