Why is it almost impossible to abduct the fingers when they are flexed at the metacarpophalangeal joints, especially in the context of wrist drop?

When the fingers are flexed at the metacarpophalangeal (MCP) joints, the interossei muscles, which are responsible for abducting the fingers, are unable to function effectively. This is because the flexed position changes the angle of pull of these muscles, making it difficult for them to generate the necessary force for abduction. In the case of wrist drop, the fingers are often flexed due to the loss of extensor muscle function, making it essential to correct this position by resting the hand in the prone position on a flat surface before attempting finger abduction.