A person is not able to extend his metacarpophalangeal joint. This is due to injury to which nerve?

Ans. is 'd > b' i.e., Post. Introsseus nerve injury > Radial nerve injury Extension of MP joint is caused by muscles supplied by posterior interosseus nerve. Posterior interosseus nerve is a branch of radial nerve, so radial nerve palsy also results in loss of ability to extend MP joint. However, for single answer, the best option is posterior interosseus nerve because the only finding in PIN palsy is inability to extend MP joint of thumb & fingers, and inability to do radial abduction of thumb. In radial nerve palsy other findings will also be there. Clinical features of radial nerve palsy Clinical features depend upon the site of lesion. 1. If lesion is high Wrist drop, thumb drop and finger drop. Inability to extend elbow, wrist, thumb & fingers (MP joint) Patient can extend interphalangeal joints due to action of lumbricals and interossei. Sensory loss over posterior surface of arm & forearm and lower lateral half of forearm. 2. If lesion is low A. Type 1 Wrist drop, thumb drop and finger drop. Elbow extension is preserved. Sensory loss over the dorsum of first web space. B. Type II Thumb drop and finger drop Elbow and wrist extension is preserved Sensory loss over the dorsum of first web space Clinical features of posterior interosseus nerve It is prone to be injured in injury & operations of radial head- neck. There is no sensory deficit as it is a pure motor nerve. Wrist extension is preserved (i.e. no wrist drop) due to spared extensor carpi radialis longus . Presents with loss of extension of metacarpophalangeal (MP) joints i.e., thumb & finger drop.