The thumb in a child with Apert syndrome provides the key to hand function. The characteristic "hitchhiker" posture or radial clinodactyly of these short but broad digits is caused by an abnormal proximal phalanx. Along with the shortened and radially deviated proximal phalanx, the first webspace (thumb-index) is always deficient. This article details the authors' anatomic observations of these abnormal thumbs and their rationale for treatment.