A Zebra in a Stampede of Horses
The overwhelming majority of bone infections in diabetic feet are called contiguous spread osteomyelitis, meaning the bone infection began by spread from an area close by. There exists something called hematogenous spread osteomyelitis, meaning the bone infection began by spread from the bloodstream. Let me explain. When you get a cut, it would be anywhere on the body, bacteria can invade the skin and flesh. But sometimes it can sneak into our blood vessels and into the bloodstream. The bacteria usually gets destroyed by our immune system, but if the bacteria survives, it can land literally anywhere in our body including the foot, but this is EXTREMELY rare. So, let’s focus on understanding why contiguous spread osteomyelitis is so intimately associated with diabetic foot ulcers.
In the setting of diabetes and neuropathy, feet are prone to repetitive shear forces, which leads to calluses, blisters, and then foot ulcers. A foot ulcer (a break in the skin) is not painful in neuropathic feet, so it can go unnoticed, thus getting deeper and deeper until bone is exposed. Exposed bone is a free invitation for bacteria to invade, and bacteria love traveling the path of least resistance.
How They Feed Off of Each Other
It’s almost like how oxygen and fuel feeds a flame, it is the ulcer and bacteria that feeds bone infections. Infected bones have a lot of drainage. Think of dead pieces of bone fragments and pus continuously dripping out the ulcer. This continuous stream of drainage makes it impossible for the body to heal the ulcer, thus keeping the ulcer open. As long as the ulcer is open, the bone can keep getting infected. We need a plan that involves treating both the infection AND the ulcer. It doesn’t have to happen at the same time, but the concept is to first treat the infection, and then close the ulcer as soon as possible. We can talk about how we do this exactly by using examples in future posts.