What is a stress fracture?
How does a stress fracture present, how is it diagnosed, and how is it treated? What are the consequences of ignoring and not treating a stress fracture?
Stress fractures are overuse injuries. They occur when a cycle of repetitive forces, none on their own sufficient to cause injury, is applied such that tissue eventually fails.
A common example of a cycle of repetitive forces, none on their own sufficient to cause damage, leading to fracture is how one breaks a paperclip. One can bend a paperclip repeatedly and at first it holds its shape, but it will eventually break it in two.
The damage inflicted on the clip is akin to a stress fracture: not one single bend was enough to overwhelm the strength of the metal, but the cumulative effect of the cycle of bending was.
Of course, a paperclip is not a living thing, and therefore does not benefit from remodeling as bone does. Therefore, the time course of applying a cycle of repetitive forces is a primary consideration in bone (unlike that of a paperclip). If an individual is given enough time to “ramp up” his or her activity, the bone will remodel, and become stronger. Recall Wolff’s law: bone grows in response to load. If the remodeling process is given adequate time to compensate, a stress fracture will be avoided.
For example, to break a normal metatarsal bone with a single load one might have to apply a force of, 20 times body weight** (as seen when jumping to the ground from a height). Nevertheless, the metatarsal might fail from a load of 5 times body weight, if that smaller force were applied 20,000 times over a single day (a forced march of 20 miles, for example). Yet even that 20,000 cycle load might be insufficient to break the bone if the individual were allowed to gradually acclimate to it by loading 5,000 times per day, followed by 2 days of no loading, over a course of two months.
How does a stress fracture present and how is it diagnosed?
Patients with stress fractures will classically present with a history of overuse and pain of insidious onset that acutely worsens with high impact activity and improves with rest.
For example, runners who recently increased their training from 5 to 10 miles per day may present with new symptoms. Stress fractures often have no objective findings on exam, though subjective point tenderness or swelling may be present.
At first, patients with stress fractures will have normal radiographic findings. Positive findings are more likely to be found several weeks after symptom onset and may include small cracks in the bone or signs of healing, such as a periosteal reaction (Figure 1).
MRI and technetium (Tc99m) bone scans are the best diagnostic imaging tests for the identification of occult stress fractures (i.e., those that are not apparent on plain radiographs).
How is a stress fracture treated?
The mainstay of treatment of stress fractures (an overuse injury) is relative rest (“underuse”). For some cases, simply cutting back on activity is sufficient.
Stress fractures of the metatarsals, femoral shaft, and tibial shaft might require partial weight bearing. Fractures in the calcaneus and navicular may require a more strict non-weight bearing status.
Surgery, namely open reduction and internal fixation (ORIF), may be considered in elite or professional athletes who require a faster recovery and are at a higher risk of complications such as displacement or nonunion. Operative treatment is also indicated for fractures in locations at high risk of fracture propagation or poor healing such as fracture on the tension side of the femoral neck or anterior cortex of tibia, Jones' fracture of the 5th metatarsal, and navicular stress fracture. Lastly, surgery is indicated when non-operative measures have failed.
What are the consequences of an untreated stress fracture?
Athletes are counseled to not return to play until pain subsides, tenderness has resolved, and radiographic findings are negative. They don’t always listen.
Persistent weight bearing on a stress fracture might cause an overt (grossly apparent) fracture (recall our friend the paperclip, above). This is particularly catastrophic in the case of a stress fracture of the superior femoral neck. That’s because propagation and displacement of the fracture can disrupt the blood supply to the femoral head and lead to osteonecrosis.
** The numbers used in this example are not exact. (Dr. Google could not provide exact numbers so none are provided here.) Nonetheless, the general point is certainly valid: a long march may lead to fracture if there is insufficient acclimation. Indeed, “march fracture” is the eponym for a stress fracture from walking long distances with insufficient acclimation.