An animal uses certain muscles more than others. Muscles in the legs, belly, and neck of a four-legged animal do more work than those located along the mid-backbone. The least exercised, and therefore the most tender, primal is the short loin, followed by the sirloin and rib primal cuts. The degree of toughness even varies within each primal.
As a general rule, the closer the meat is to the hoof or horn, the tougher it will be. Therefore, the portion of the chuck (or round) that lies closest to the mid-carcass will be more tender than the part situated near the head (or rear leg) of the animal. It follows that not all cuts of beef marketed under the same primal designation possess equal tenderness. The sirloin primal is a good case in point. Certainly, the sirloin steak that is cut from next to the short loin is much more tender than one taken from the area bordering the round. In order of their proximity to the short loin, the three basic steaks of the sirloin primal are the pin bone, flat bone, and wedge bone. They derive their names from the cross-section configuration of the one bone they all share, which is the hip bone.
Unfortunately, most stores market sirloin steaks simply as "sirloin steak" rather than sub-classifying them. Should your butcher not give you complete information, look for the shape of the hip bone. If the hip bone cross-section is flat like a bar, the steak is a flat bone sirloin. If the cross-section is triangular, your have a wedge bone steak.
Sometimes the difference between the pin bone and wedge bone isn't obvious. When confronted with that situation, remember that the steak will be a pin bone sirloin if the overall piece of meat has a configuration slightly resembling that of a porterhouse steak, the cut that lies immediately next to the pin bone sirloin. The difference between these two cuts is the thickness of a sharp butcher knife.
** Asian Meat Recipes **