The second pelvic pin has been placed towards the back of the pelvis. This area is called the ischium. In common with most parts of the pelvis the bone here is rather flattened. This makes it hard to place pins that will have good holding power. Careful positioning is vital. The third pin is placed in the femur. Note the so-called 'positive profile' pins used - these have a screw thread cut onto the outside profile of the pin. This gives increased holding power without weakening the pin with a cut-in thread.