"A small, sterile, threaded rod with a slotted head typically used for internal orthopaedic fracture fixation by being screwed into bone to hold plates or nails to bone or to provide direct interfragmentary stabilization of bone, or it may fasten soft tissue to bone; it is made of a material that cannot be chemically degraded or absorbed via natural body processes (includes implant grade metal such as surgical steel, titanium alloy, or carbon fibre). There are a number of kinds available: cortical, cancellous, malleolar, scaphoid, partially-threaded and fully-threaded, self-tapping, and cannulated. A ""lag screw"" can be any of these used to obtain compression across bone fragments."