A Man Falls Forward and to One Side, but Manages

A man falls forward and to one side, but manages to break the fall to some degree by putting out his hand on the side toward which he is falling. Although he lands on his hand and knees, causing some abrasion, and he feels shaken and somewhat sore overall, no other injuries are noted at the time. However, a few hours later, he complains of severe pain in the area of the shoulder and upper chest region. What has most likely happened, and how could a knowledge of surface anatomy help