An anomaly of the shape or form of the proximal phalanx of the thumb.
Comment:
In contrast to the proximal phalanges of the digits 2-5, the proximal phalanx of the thumb is embryologically equivalent to the middle phalanges of the other digits, whereas the first metacarpal is embryologically of phalangeal origin and as such equivalent to the proximal phalanges of the other digits. {xref="HPO:probinson"}
Synonyms:
exact_synonym:
Abnormal innermost thumb bone; Abnormality of proximal thumb phalanx