Coat a 4-quart Dutch oven or pot with nonstick cooking spray. Brown shank bones and round steak in pot.
Carefully add beef stock, tomatoes, catsup, sugar, and sour salt to meat in pot; stir. Bring to boiling; reduce heat. Cover; simmer for 1 hour.
Remove meat and bones from the mixture; cool slightly. Remove and discard the skin, bones, and any fat from the meat. Cut the meat into bite-size pieces. Return the meat to the pot.
Stir in the cabbage. Bring the mixture to boiling; reduce heat. Cover and simmer for 10 minutes or until cabbage is crisp-tender.
Ladle the borscht into warm soup bowls. Makes 6 main-dish servings.
Reduce the sodium by using low-sodium broth.