This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': 'Which among the following is TRUE regarding mallet finger? \nSelect and explain. \nA. Avulsion of tendon at the base of the middle phalanx, B. Avulsion of extensor tendon at the base of the distal phalanx, C. Fracture of distal phalanx, D. Fracture of the proximal phalanx', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The mallet finger deformity is characterized by a loss of full active distal interphalangeal joint extension with full passive ROM evident. The mallet finger reflects the loss of normal extensor force transmission the terminal tendon inseion onto the distal phalanx. The unopposed flexor digitorum profundus pulls the distal joint into flexion. The usual mechanism of injury involves sudden passive flexion of the actively extended distal interphalangeal joint. Disruption of the terminal tendon may be entirely confined to the tendon or may involve an avulsed fracture fragment from the dorsal lip of the distal phalanx proximal aicular surface. Ref: Bednar M.S., Light T.R. (2006). Chapter 10. Hand Surgery. In H.B. Skinner (Ed), CURRENT Diagnosis & Treatment in Ohopedics, 4e.', 'role': 'assistant'}]