The anatomical description of the human hand having 27 degrees of freedom is a standard didactic fact of everyday biomechanics and requires no citation.
The claim states an anatomical and biomechanical fact about the human hand (27 degrees of freedom, encompassing the wrist and fingers). While various biomechanical models might approximate or simplify this number for specific simulations (e.g., 25 degrees of freedom in paper [1]), the standard anatomical breakdown (8 carpal bones interacting, metacarpals, and phalanges contributing to total kinematic degrees of freedom) is a classic matter of common knowledge and everyday anatomical description, making citations unnecessary.