A patient diagnosed to have leprosy with ulnar nerve involvement, presents with clumsiness of hand. Clumsiness is due to palsy of which of the following muscle?

All interossei muscles are innervated by deep branch of ulnar nerve. Palmar interossei adduct thumb, index, ring and little finger to the middle finger. Dorsal interossei are abductors of index, middle and ring finger. So clumsiness of hand in this patient is due to weakness of interosseus muscle innervated by ulnar nerve. Muscles innervated by ulnar nerve are: Flexor carpi ulnaris Flexor digitorum profundus III and IV Adductor pollicis Flexor pollicis brevis Palmar interossei Dorsal interossei Lumbricals III and IV Hypothenar muscles Features of ulnar neuropathy: Paresthesia and dysesthesia in the small finger and ulnar poion of ring finger Hand weakness and clumsiness Positive Tinel's sign: Exacerbation of paresthesias with light percussion over the ulnar nerve within the cubital tunnel. Clawing of ring and small finger Interosseus muscle wasting Froment's sign: substituting thumb IP joint flexion for thumb adduction due to weakness of adductor pollicis muscle. Ref: Turek's Ohopaedics: Principles and Their Application edited by Stua L. Weinstein, page 407. Anatomy and Human Movement: Structure and Function By Nigel Palastanga page 92.