Hitchhiker thumb deformity
Hitchhiker thumb deformity, also known as Z-thumb or duckbill thumb, is used to both describe the appearance of the thumb on physical examination and also the corresponding radiographic appearance. It is similar to how a person would normally angulate and hold out the thumb with the intention to hitchhike. It is one of the musculoskeletal manifestations of rheumatoid arthritis in the hand although not entirely specific for this diagnosis.
The sign is also used in obstetric ultrasound and on pediatric radiographs to describe the appearance of the fingers in diastrophic dysplasia.