Hitchhiker thumb deformity, also known as Z-thumb, zig-zag deformity, or duckbill thumb, is a clinical and radiographic sign most commonly associated with rheumatoid arthritis (RA) 1,2 although is non-specific and can be seen in first carpometacarpal osteoarthritis 3 and pre-axial polydactyly of the thumb 4. The sign is also used in obstetric ultrasound and on radiographs to describe the appearance of the fingers in diastrophic dysplasia 8.
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Terminology
In relation to RA, zig-zag deformity more commonly refers to radiocarpal malalignment 5. It is equivalent to a type I (boutonniere) deformity in the Nalebuff classification of rheumatoid thumb deformities 7.
Clinical presentation
On examination, this thumb malalignment is similar to how a person would normally angulate and hold out the thumb with the intention to hitchhike.
Pathology
Subluxation at the first carpometacarpal joint results in proximal first metacarpal adduction, compensation develops in the form of 6:
hyperextension of the interphalangeal (IP) joint
hyperflexion of the metacarpophalangeal (MCP) joint
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