There are many reasons for nonunions to occur. In general, they fall into one of two broad categories, poor biology or poor biomechanics and sometimes both are the cause. Poor biology refers to how healthy the bone is; is the bone healthy enough to to allow the two bone ends to unite to each other. This is based mostly on if there is an appropriate enough blood flow to the bone ends. Many people do not know that bones have blood flow not unlike any other tissue in the body, skin, kidneys, etc. If the blood supply is damaged at the time of the injury, it may delay or even prevent the bone from going on to heal.

The next most common reason for a bone to not heal is that there is too much motion between the bone ends at the fracture site. This we refer to as poor biomechanics. This can occur in non operated fractures and operated fractures. In nonoperated fractures, the cast is unable to restrict the motion between the bone ends enough and it goes on to a nonunion. Alternatively, it can also happen with an operatively treated fracture. The two most common reasons for this are to much gap between the bone ends that you are trying to get to heal, or, destite using plates and screws to improve stability between the fractured (broken) bone ends, there is still too much motion between the two ends of the bones.

Many other factors can also delay the bone to healing also including but not limited to smoking, poor diet, steroids and Nonsteroidal antiinflamitory medications (such as motrin, Ibuprophen, aleve, etc.). These are all factors that the patient has some control over and make a huge contribution to their overall likelihood of fracture healing. One other factor that can significantly affect healing is infection. This is one factor that the patient has less control over. Even when everyone, patient, MD and healthcare workers take all of the appropriate precautions, infections do still happen. When and if an infection happens, it can make the nonunion even more difficult to treat. The patient below is an example of a nonunion with angulation and a broken rod. The final X-ray shows the bone healed and well aligned.


Tim Weber 2012