04/09/2013 11:48 am ET Updated Jun 09, 2013

What Happens When Bones Are Stressed?

Last week, basketball fans shared a collective cringe while watching the horrific leg injury to University of Louisville basketball player Kevin Ware. And as the gruesome scene replays around the globe courtesy of YouTube, people everywhere are asking what could have caused the leg to break that way. There are a number of reasons why this could happen -- bone injuries we see frequently before they reach this level of trauma. First, I need to clarify that I am not involved in Ware's health care. I'm merely referencing his case to address bone injuries in athletes.

Patients often think of bone as an inanimate object, almost like a piece of wood. This couldn't be farther from the truth. Living bone in our body is quite a dynamic formation. Old bone cells are picked up and new bone cells are laid down by specialized cells 24 hours a day until we die. This flux of bone exists in a fairly balanced state until bone is stressed.

Bone has an incredible ability to adapt to mechanical loads or pressure we place upon it. According to Wolff's Law, a bone's internal framework (called trabeculae) is initially weakened when loaded by mechanical stress, thereby triggering a rebuilding process that eventually makes the bone denser. The hard outer shell of the bone also becomes a little thicker with time. This is how bone can become stronger.

When a load is placed on a bone from running, jumping, landing or direction changes, that process begins. Yet, if loaded again too quickly before the bone can rebuild, it begins to change in a different manner. This is what happens if athletes push themselves, or are pushed, to keep training. The cells that break down the trabeculae begin their work while cells that rebuild bone are delayed. Continued load causes a bone stress response, or weakening of the bone. This change, which is seen on MRI scans as a fluid accumulation in the stressed area, can be subtle, moderate or quite significant.

The bone stress response precedes what is commonly known as a stress fracture. A stress fracture does not occur from a singular traumatic event, but rather from continual loading of the bone that was not given the time and opportunity to recover or rebuild.

I have seen this pathology repeatedly in sports ranging from cross country, track and field (including the 100m and 200m sprints), boxing, basketball, volleyball and speed skating. During the early stage of the bone stress response, patients may not have any pain, and their injuries may not go beyond this point. Their training regimens often vary, and they have time to recover.

Yet, when the training continues without time to recover, bone weakens. Mild pain occurs in the early to middle stage, in most cases, and athletes may eventually find it quite painful to push off or land during a running stride or jump during later stages. The pain can eventually cause the athlete to stop competing or training.

MRI findings become more significant and reach a point that the radiologist could say that the bone may fracture any second. If we're lucky, we can catch the bone stress response before it fractures. The bone stress response and stress fractures can be seen in the ankle, the tibia (large bone of the lower leg), femur ("thigh bone"), pelvis and spine.

There is only one treatment: The patient must stop loading the bone and allow the bone building cells to take over and rebuild. If these changes have been monitored on MRI, we should see complete resolution of the bone stress response before the athlete can resume training. If the training continues without a recovery period, the bone may finally yield, resulting in a stress fracture. X-rays are typically only beneficial if the outer shell of the bone has fractured, or if we see extra bone forming around the area that we suspected was a problem. Unfortunately, by the time we see this bone formation/bone callous on X-ray, we learn the athlete already had a stress fracture.

Stress fractures and bone stress responses are not benign and are, unfortunately, often dismissed by athletes, parents, coaches and sometimes health care providers as insignificant until the stress fracture yields further and a complete, superimposed fracture occurs.

When this happens, the athlete is most likely facing surgical repair of the fracture, significant down time, and potential loss of a season or more. A very small percentage of chronic stress fracture cases require surgical debridement of weak or dead bone in the stressed area, with placement of bone grafts, and the use of bone stimulators to help the healing process.

Other pathologies that can weaken bone include tumors, osteoporosis (either from eating disorders or overtraining), which can suppress the endocrine system (hormones), or an unusual accident (often referred to as a "freak accident"). Sudden changes in training can also start the bone stress response.

Take bone pain seriously. Don't dismiss a potential stress fracture as a simple shin splint that requires nothing more than training through it. Muscles can become uncomfortable during hard training but usually recover rapidly. Bone pain that continues and/or is aggravated by minimal activity should be investigated by a health care professional, preferably someone who is board certified in sports medicine.

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