system
Given the following post, respond as if you're commenting on Reddit:
human
How do they put a rod into a broken femur?

I know someone who broke their femur in half while skiing.  I saw their x-ray and the doctors put a rod actually inside the bone to hold the two halves together while it healed.  How would they do this?
gpt
Ortho resident here.

Lets start with some anatomy. Like others have said, long bones have two parts, a cortex and a medullary canal. The cortex is the outside of the bone and is what is usually seen on X-rays. It contains cortical bone which is arranged in a way that it is very strong. This is where most of the bending and compressive strength of bone is and is what most of the shaft portion of long bones (femur, tibia, humerus, etc) are made of. The medullary canal contains a combination of bone marrow and what is called cancellous bone, which is bone that does not contribute as much to the strength of the long bone, but is important part of bone health.

We place a rod down the femur by taking advantage of the medullary canal. You can place a rod in the femur by going in from the top or the bottom of the femur. First a hole is drilled in line with with medullary canal either through the greater trochanter (the large bump at the top of the femur) or through the knee. This is all done under X-ray guidance (called fluoroscopy). We then line up the fracture fragments, place a long wire in the medullary canal and then ream. These reamers start out small and get larger. This helps remove any of that cancellous bone and medullary contents that would get in the way of the rod we place in. We ream until the reamers start to "chatter" on the cortical bone. We then place a rode slightly smaller than the final reamer down the canal. This is all done under imaging guidance through the hole in the bone we made at the top or the bottom of the femur. The rod is hammered to the appropriate depth. Finally screws are placed at the top and the bottom of the rod to hold it into place. These are placed perpendicular to the bone and the rod in order to "lock it" into place so it doesn't move up or down.

We do rodding or "nailing" of long bones because it does not require large incisions and it is what we call a load sharing construct so patients can weight bear the next day.