Hitchhiker's Thumb

What is hitchhiker's thumb?

Hitchhiker’s thumb means your thumb joint, closest to your nail, is hypermobile. Hypermobile means you can move your joints beyond the normal range of motion. If you can move your thumb joint backward more than 50 degrees, you may have hitchhiker’s thumb. It’s called hitchhiker’s thumb because it resembles what your thumb looks like if you’re trying to hitch a ride on the side of the road.

Hitchhiker’s thumb is also known medically as distal joint hyperextensibility. One or both of your joints may be involved. For example, one may be a hitchhiker’s thumb, and one may be straight. Hitchhiker’s thumb typically isn’t painful and usually doesn’t cause any complications or problems with using your hand. However, hitchhiker’s thumb can be associated with various genetic diseases and conditions.

What causes hitchhiker's thumb?

Many scientists believe hitchhiker’s thumb is an inherited condition, meaning it's passed down from your parents.

In 1953, two researchers performed a study on 450 families. The researchers used a protractor to measure the angles of the study participants’ thumbs. If the participants could bend their thumb joints backward greater than or equal to 50 degrees, they were labeled hitchhiker’s thumbs. As a result of the study, the researchers determined hitchhiker’s thumb is genetic and passed on as a recessive trait, which is explained below.

Your DNA contains genes that determine specific traits, such as your height, weight, skin color and eye color. You receive two genes for each trait from your parents. Each gene contains a specific pattern called an allele. If these alleles are different, the dominant (stronger) gene masks the recessive gene. The dominant gene will take over and you’ll have that trait. If you receive two recessive genes, the recessive gene will take over and you’ll have that trait — in this case, a hitchhiker’s thumb.

Therefore, if your mother and father both have hitchhiker’s thumb, you should have it too. However, if one of your parents passes on the dominant gene for a straight thumb, and your other parent passes on the recessive gene, you won’t have hitchhiker’s thumb, as the dominant gene masks the recessive one.

What health conditions or disorders are associated with hitchhiker’s thumb?

Hitchhiker’s thumb is commonly seen in several genetic conditions and disorders. These include:

• Joint hypermobility syndrome: Joint hypermobility syndrome is a connective tissue disorder. If you have this disorder, your ligaments are loose and weak, causing your joints to be more flexible than normal.
• Diastrophic dysplasia: Diastrophic dysplasia is a rare genetic disorder present at birth (congenital). This disorder affects bone and cartilage development. Diastrophic dysplasia is a type of skeletal dysplasia.
• Atelosteogenesis type 2: A rare genetic disorder that affects bone and cartilage development. It’s similar to diastrophic dysplasia but more severe.
• Atelosteogenesis type 3: A rare genetic disorder affecting bone development throughout your body.

What are the symptoms of hitchhiker's thumb?

If you have very flexible (hypermobile) thumb joints, you may have hitchhiker’s thumb (distal joint hyperextensibility). Hitchhiker’s thumb could also be a symptom of another condition or disorder, as mentioned above. The symptoms of these conditions include:

If you have any of the above symptoms, you should let your healthcare provider know.

What can I expect if I have hitchhiker's thumb?

The outlook of hitchhiker’s thumb depends on the reason or cause for it. Many people have hypermobile thumb joints. Hitchhiker’s thumb alone causes no pain and usually doesn't affect the use of your hands. Hitchhiker’s thumb doesn’t cause any other diseases or conditions but may mean you're more likely to have arthritis. If hitchhiker’s thumb is related to another disease or condition, the outlook may vary, depending on the disease.

If you have joint hypermobility syndrome, you may find your symptoms will decrease as you get older and develop arthritis. For some people, symptoms are mild. For others, pain can be severe. Symptoms can oftentimes be managed by protecting your joints and taking over-the-counter or prescription pain medication.

If you have diastrophic dysplasia, you can lead a normal life with the appropriate treatment. Treatments depend on the symptoms and body systems affected. They may include nutritional therapy, respiratory therapy, physical therapy, hand surgery, dental treatments and steroids.

Atelosteogenesis type 2 and atelosteogenesis type 3 can cause serious health issues. Most infants with these conditions are stillborn or die shortly after birth due to respiratory failure. However, some infants survive with intensive medical support and treatment.

When should I see my healthcare provider?

If you believe that you have hitchhiker’s thumb, or any of the other conditions discussed, schedule a visit with your healthcare provider. Specifically, you should seek medical attention if you develop:

• Change in the function of your hand or specific joint.
• Change in the mobility of your hand or specific joint.
• Swelling and/or change in the appearance of your hand or specific joint.
• Increasing pain in your hand or specific joint.

Is hitchhiker's thumb a myth?

Some people believe hitchhiker’s thumb is a myth. There’s been very little research done on the trait since the first study was done in 1953. Some scientists believe there are more than simply two kinds of thumbs — not just hitchhiker’s thumb and straight (non-hitchhiker’s) thumb. They believe hitchhiker’s thumb is more complex and isn’t a genetic trait controlled by a single gene with two recessive alleles. They believe thumb bendability varies greatly, from having no bendability in your thumb joint to having extreme bendability. They don’t believe thumbs only fall into one category or the other, and more research needs to be done on this matter.

A note from Cleveland Clinic

If you’re able to bend your thumb joint backward more than 50 degrees, you may have hitchhiker’s thumb. For most people, this trait simply means you have highly flexible thumb joints. Sometimes, hitchhiker’s thumb is associated with a rare genetic disease or condition. If hitchhiker’s thumb is related to a disease or condition, your healthcare provider will work with you to manage this condition, help correct the issue and determine your outlook.