A person had injury to right upper limb he is not able to extend fingers but able to extend wrist and elbow. Nerve injured is -

Posterior interosseous emerges from the supinator on the back of the forearm .Here it lies between the superficial and deep muscles.At the lower border of the extensor pollicis brevis, it passes deep to extensor pollicis longus.it then runs on the posterior surface of the interosseous membrane up to the wrist where it enlarges into pseudoganglion and ends by supplying the wrist and intercarpal joints.