Stress Fracture

A fracture is simply a break in the continuity of bone. Lay people often refer to 'just a fracture' but the term refers to any broken bone from a small crack to a high-energy multi-fragment injury. 

Usually a fracture is caused by abnormal loading of bone, such as falls from a height, motor vehicle accidents etc where the bone is normal, but the loads are abnormal. There may be other situations where the loads are less than one would normally expect to cause a fracture, but the bone is weakened by a pathological process such as osteoporosis, bone metastasis from tumour etc. These are referred to as pathological fractures. 

A third type of fracture is where the bone is normal, and the loads would not normally cause fracture, but repeated so frequently that the bone cannot recover and fails by fatigue, similar to metal fatigue. This is called stress fracture.

Normal bone is constantly changing. It remodels throughout life to reinforce areas that are increasingly used, and diminishes when not used (the reason people on prolonged bed rest, or astronauts without gravity tend to develop osteoporosis). When loads are increased microscopic cracks form in the structure of bone, which heal with laying down new tougher bone, and overall the strength and density of bone increases. 

If the rate of formation of these cracks exceeds the rate of healing, then these cracks progress from microscopic to frank visible cracks on xray, and are accompanied by pain.

Classic sites for stress fractures are the tibia, the metatarsals of the foot and the neck of femur. 

Tibial Stress Fracture:

  • Classically mid-upper tibia

  • Crest or posterior cortex

  • Pain constant, severe with exercise

  • Unable to run due to pain

  • Endorphins may allow completion of a run    

  • Can be warm in area

  • Very tender when acute

Treatment consists of rest and immobilisation either in a cast or removable boot, with crutches if painful.

Causative factors are assessed such as osteoporosis due to hormonal causes, vitamin D deficiency etc.
In recurrent stress fractures tibial nailing is occasionally necessary.

Medial Tibial Stress Syndrome (MTSS) is a condition similar to tibial stress fracture, and may be a precursor to it.

Pain is typically felt at the subcutaneous border of the tibia on the medial side.

AN MRI may reveal fluid under the periosteal layer.

Treatment is rest, attention to biomechanics with orthotics if necessary, and in severe cases subperiosteal injection of a sclerosing agent to stick the periosteum down and thus obliterate the space ('prolotherapy')
 

Tibial Stress Fractures can show only cortical thickening (left) or visible cracks (right)

Medial Tibial Stress Syndrome (MTSS) is a condition similar to tibial stress fracture, and may be a precursor to it.

Pain is typically felt at the subcutaneous border of the tibia on the medial side.

AN MRI may reveal fluid under the periosteal layer. If there is doubt, a technetium bone scan is very sensitive.

Treatment is rest, attention to biomechanics with orthotics if necessary, and in severe cases subperiosteal injection of a sclerosing agent to stick the periosteum down and thus obliterate the space ('prolotherapy')

MRI showing a white band of subperiosteal fluid

Diffuse bone scan uptake of MTSS (left) vs localised uptake in stress fracture (right)

Metatarsal Stress Fracture:

Stress fractures of the second and third metatarsal necks are common in army recruits who do a lot of unaccustomed marching and are hence often referred to as 'March Fracture'. They are also common in runners, particularly those increasing their regular distance, or running on harder surfaces.

Stress fractures of the 5th metatarsal tend to occur at the base, and are notorious fo being slow to unite, and occasionally going on to nonunion.

Presentation is with pain, commonly of several weeks' duration, X-rays may show a slowly healing fracture, or occasionally nothing at all, but with a high signal on MRI.

Treatment is rest, usually with an immobiliser boot for 6 to 8 weeks before a gradual return of impact activity.

Second metatarsal neck showing callus with incomplete healing.

Femoral neck stress fracture:

Stress fracture of the femoral neck occurs mainly in distance runners, and is commonly associated with hormonal abnormalities causing osteoporosis. 

It presents with pain in the groin, particularly on impact, and may rapidly progress to pain on walking.

It should be considered an emergency, and non weightbearing with crutches essential until the degree of involvement diagnosed by CT scanning. If severe, femoral neck fracture may occur. To prevent the risk of this surgical fixation is common, since displaced fracture in this area can be disastrous.

Superior cortex stress fractures occupy the 'tension side' of the bone and may fracture completely. They should be fixed with screws.