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Hardware: What is an IM Rod?

The IM part stands for Intra-Medullary.
The medulla is the hollow cavity inside a long bone.
The "nail" part is really the same as "rod"
Most IM Nails are themselves hollow rods of varying lengths and diameters. The ones for the femur have a slight curve to them because the femur is a curved bone.
To put them in the surgeon first has to line up the bone accurately -which is called reducing the fracture. Then a small hole is made at the top of the bone and a thin guide wire is slid down inside the bone, across the fracture and into the next fragment. A flexible reamer is used to make sure that the rod will be a tight fit to the inside of the bone. If I ream to 13 mm and find that it takes some force to pass the reamer up and down I know that a 12 mm rod will be a snug fit. Once the reaming is done we measure the length of rod which is needed then slide it down over the guidewire, across the fracture and into the other end of the bone. Because it is a tight fit it lines up the fragments correctly and holds them immobile. To make sure there is no further shifting of the position we put in transverse screws at the top and bottom.
Rods and nails are the same. The originator of the technique was a German surgeon called Kunshner and the original implant was called a Kunschner Nail - used up to the 1970s. The Brits and the US noticed that German soldiers were getting back into battle a few months after fractured femurs whereas the Allied soldiers were out for the duration. (they were treated in traction) So there was great interest after WW II in finding out what the German OS did differently. The term nail stuck but rod is really more descriptive of the implant. Describing the operation as "nailing" is also standard usage. Kunschner used an open technique putting the IM rod in through the fracture itself. "Closed Nailing" as described above was first done in the 1970's in Seattle and is now the standard technique for broken femoral shafts.
Rods can be made of stainless steel or titanium and there is no detectable difference in healing rate or outcome.

Myles Clough MD OS Jan 11 2002


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