Which type of nerve injury causes an inability to extend the thumb in a hitchhiker's sign?

The hitchhike sign represents the extension of the thumb and it is used to identify two different conditions: radial nerve or posterior interosseous nerve palsy and diastrophic dwarfism.
If there is radial nerve lesion then weakness of brachioradialis and finger flexion occurs. If there is a posterior interosseous nerve lesion then weakness of finger extension occurs.

The basic processes of life include organization, metabolism, responsiveness, movements, and reproduction. In humans, who represent the most complex form of life, there are additional requirements such as growth, differentiation, respiration, digestion, and excretion. All of these processes are interrelated.