Hitchhiker's thumb

Hitchhiker's thumb, also known as distal hyperextensibility of the thumb is the condition of having a thumb that has a distal phalange that bends backwards in an angle of 90°, it is thought to be inherited in an autosomal recessive manner, however, it presents on genetic disorders that are inherited in an autosomal dominant manner^[1] This condition is benign (when isolated) and does not cause pain or affect the thumb with the trait negatively.

Hitchhiker's thumb
Other names	Distal hyperextensibility of the thumb, thumb hypermobility, Z-shaped deformity,[2] duck-bill thumb [3]
Example of bilateral hitchhiker's thumb
Specialty	Medical genetics
Symptoms	A thumb that can bend backwards at more than a 90° degree angle
Complications	If it presents as an isolated trait, none
Duration	Life-long
Causes	May either present as an isolated trait, or be a symptom of a condition such as a hypermobility spectrum disorder[1]
Risk factors	Family history
Frequency	24-36% of the U.S. population [4]

If a person has the genes for this condition, it might present bilaterally, unilaterally, or on none of the thumbs.

Signs and symptoms[]

Symptoms vary among people with hitchhiker's thumbs, those who have it as an isolated trait aren't affected by any symptoms, however, this trait is sometimes a symptom of other conditions, such as a hypermobility spectrum disorder.

The signs of this trait are having a thumb with a distal phalange that is able to bend backwards beyond the normal range of motion. Some people with hitchhiker's thumb also have a Z-shaped deformity, named after the appearance of this deformity, which is that of the letter Z.

Example of a z-shaped deformity in a hitchhiker's thumb

Causes[]

The exact cause of isolated hitchhiker's thumb is not known, it is thought to be inherited in an autosomal recessive manner. ^[5][1]

However, this trait is often a symptom of an underlying condition, such as

• Diastrophic dysplasia
• Hypermobility spectrum disorder
• Rheumatoid arthritis

Diagnosis[]

The trait does not generally need a medical diagnosis, however, it can help with the diagnosis of an individual who is suspected of having a certain condition.

Treatment[]

If it is not associated with any condition, this condition doesn't need treatment.

Incidence[]

Hitchhiker's thumbs affect 24-36% of the U.S. population.^[4]

See also[]

• Hypermobility (joints)
• Ligamentous laxity
• Hypermobility spectrum disorder
• Ehlers-Danlos syndromes
• Diastrophic dysplasia
• Thumb

References[]