Trussing beef before roasting helps retain its shape while it cooks in the oven and stops the meat from spreading. This method can also be used for stuffed and rolled joints of meat to hold them together.
The trussing method works by tying a series of interlinked knots to secure the meat in place. Regular knots won’t work as you cannot achieve the same amount of tension. You will need a roll of butcher's twine for this, which you should be able to pick up from your local butcher.