A 45-year-old male is admitted to the hospital after accidentally walking through a plate glass door in a bar while intoxicated. Physical examination shows multiple lacerations to the upper limb, with inability to flex the distal interphalangeal joints of the fouh and fifth digits. Which of the following muscles is most likely affected

Loss of flexion at DIP (Distal Inter Phalangeal joint) occurs due to loss of function of FDP (Flexor Digitorum Profundus).Flexor digitorum profundus is dually innervated by the ulnar nerve to the medial phalanges (Finger 4 & 5) and the median nerve for the lateral phalanges (Finger 2 & 3). Because of the superficial course of the ulnar nerve, it is vulnerable to injury by laceration. Such an injury would result in an inability to flex the distal interphalangeal joints of the 4th and 5th digits. The flexor digitorum superficialis is innervated by the median nerve only, and the course of this nerve runs too deep to be affected by lacerations. The lumbricals function to flex the MCP (Metacarpophalangeal) joints and assist in extending the IP joints. The interossei adduct and abduct the fingers (along with MCP flexion).