A 32-year-old man involved in a motor vehicle accident was brought to the ER with injury over the left arm. The patient gave the history that the truck hit the car from the side and the patient sustained injuries to the left arm. The doctor on duty performed an examination of the injured site and ordered an x ray of the injured site. He complains of an inability to open his left hand and loss of sensation to a poion of his left hand. What is the most likely injury