When Ahab leaves the deck of the Samuel Enderby, and half-jumps back onto the deck of the Pequod, he accidentally splinters his leg, forcing him to ask the ship’s carpenter to make a new one out of the remaining jaw-bone of one of the recently captured sperm whales. Ishmael reveals what he learned later about Ahab: that his unwillingness to see anyone at the beginning of the voyage was derived not just from his quest for the white whale, but from his embarrassment at a previous injury sustained while wearing his false leg. In that injury, the leg slipped and injured Ahab in the groin—and Ahab began cursing the ivory leg as an extension of the cruel animal, Moby Dick, who took away Ahab’s real leg in the first place.
It is interesting to note that Moby Dick took Ahab's leg and Ahab then built new false legs from whales he had killed. The novel is filled with these sorts of cycles or resonances. The injury that Ahab suffered to his "groin" is also of interest, as there is a hint here that part of Ahab's motivation for his mad quest against Moby Dick stems from the loss—both figuratively and, possibly, literally—of his virility.