Stress fractures

Definition of stress fracture

A stress fracture is a crack in a bone caused by repeated stresses which are individually insufficient to fracture it. Stress fractures are not full-thickness breaks (although without correct management they may progress to become full-thickness breaks). They may involve the bony cortex only, and show up poorly on X-ray. They are sometimes referred to as hairline fractures.

Stress fractures may be overuse injuries. Bones constantly remodel and repair, particularly when stressed by impact in sport. Over time, repeat stress may exhaust the capacity of the osteoblasts to remodel. This may occur over quite a long period of repetitive, cyclic loading. This is sometimes known as a fatigue reaction stress fracture. The other type of stress fracture occurs when normal stresses and strains are applied to a bone where there is impaired formation. This is sometimes known as an insufficiency reaction stress fracture¹ .

Most stress fractures occur in the lower limbs. Typical presentation is with a history of exercise-related pain, often associated with a change in athletic activity. History and examination are often enough to make the diagnosis. Stress fractures are seen in otherwise healthy individuals, and whilst osteoporosis is a risk factor, they are not generally considered fragility fractures.

Epidemiology¹

Approximately 20% of all sports medicine injuries are due to stress fractures. Runners who average more than 25 miles a week are at particular risk. Members of the military are at risk of stress fractures due to the repetitive nature of their training. One study reported that from 2009 to 2012, US military members had 5.69 stress fractures per 1,000 person-years² .

In runners, stress fractures account for nearly 16% of all injuries. The most common stress fractures are the tibia (23.6%), tarsal navicular (17.6%), metatarsals (16.2%), femur (6.6%), and pelvis (1.6%)³ .

Risk factors

It is hard to predict specifically who will get a stress fracture, as runners vary with regard to biomechanics, training, general fitness, muscle strength and flexibility. Stress fractures often arise in those who are training when they suddenly increase distance or change running shoes. They also arise in sedentary people who suddenly start to exercise, and in elite athletes who exercise regularly and heavily.

Extrinsic risk factors¹

• High impact sports - eg running, jumping.

• Abrupt increase in physical activity.

• Irregular or angled running surface.

• Poor footwear.

• Running shoe wear older than six months.

• Deficient vitamin D and calcium intake.

• Smoking.

Intrinsic risk factors^{1 4}

• Factors affecting bone strength such as low bone density, lowered bone turnover rate (osteoporosis, osteomalacia).

• Skeletal alignment (leg length differences).

• In women, lower muscular strength and endurance.

• Hormonal abnormalities.

• Previous stress fractures.

• Female gender. Lower bone density, less lean body mass in the lower limb, a low-fat diet and a history of menstrual disturbance are all significant risk factors for stress fractures.

• Body mass index <19, late menarche (age ≥15 years) and previous participation in gymnastics or dance are also predictors in girls.

• For boys, prior fracture and increased number of seasons of athletics have been associated with an increased rate of stress fractures, whereas prior participation in basketball has been associated with a decreased risk.

• There is a relationship to eating disorders, amenorrhea and osteoporosis, which is also referred to as the female athlete triad.

• Those of black African ethnicity are at lower risk due to a generally higher bone mineral density (BMD).

• BMD - the incidence probably also increases with age due to age-related reductions in BMD.

• BMD - children may also be at risk because their bones have yet to reach full density and strength.

• Psychological factors are also likely to have a role. Those who run with pain or who cannot accept reductions or changes in training activity when tired or in discomfort are more likely to fracture.
  

Where do stress fractures occur?¹

The most frequent sites of stress fractures are:

• Tibia (23.6%)

• Tarsal navicular (17.6%)

• Metatarsals (16.2%)

• Femur (6.6%)

• Pelvis (1.6%)

The typical sites vary from sport to sport:

• Among track runners the navicular, tibia, and metatarsals are common. In women,pelvic fractures are also seen.

• In distance runners, the tibia and fibula are common. Femoral neck and pelvic fractures are also seen.

• Patellar fractures are common in hurdlers.

• In dancers, the metatarsals are typical.

• Gymnasts, female soccer players, American football linemen and linebackers, and Olympic style weightlifters are at increased risk of spondylolysis due to stress fracture related to repeated hyperextension of the spine.

• Stress fractures of the ribs are rare but are sometimes seen in rowers⁵ .

Presentation

Stress fractures are easy to miss as symptoms may be subtle. The pain source may not be immediately identifiable to the person affected, with the pain initially occurring in a diffuse area around the injury, localising later. Symptoms of a stress fracture are typically:

• Dull bone pain that worsens with weight-bearing or repetitive use. It is usually, but not always, well localised.

• Tenderness and localised swelling may occur at the pain site, which hurts to touch (apart from in femoral neck stress fractures, where the site is too well padded).

• Pain on activity may be worse to start with (but will not necessarily prevent the activity). It may ease during the activity then resume afterwards, leading some athletes to continue to run through it. It will start to occur progressively earlier in the workout regime, and is worse with weight-bearing. It generally decreases with rest.

• Pain may come on for the very first time during or after exercise.

• Pain may start suddenly, after impact, but may also come on more gradually.

• Specific features depend on site - features of some high-risk stress fractures are described below.

Diagnosis^{1 6}

• A high index of suspicion is needed in order to consider the diagnosis on the basis of the history.

• Particular care is needed with atypical stress fractures and those with a high risk of progression to complete fracture or to non-union, particularly the neck of femur, middle third of tibia, medial malleolus, talus, tarsal navicular and fifth metatarsal.

• As the clinical symptoms of stress fracture may mimic other less severe musculoskeletal injuries, the diagnosis of stress fracture can often be delayed.

• Plain X-rays have low sensitivity for the detection of stress fractures. Plain radiography may not detect stress fracture injury until fracture healing is well underway. In some cases this delay in diagnosis can lead to catastrophic fracture.

• Radionuclide bone scanning is highly sensitive, although it does not allow visualisation of fracture lines. Bone scintigraphy has long been recommended for the diagnosis of stress fracture,. However, as bone scintigraphy involves ionising radiation it should not be used when there is an alternative.

• Computerised tomography (CT) provides fine osseous detail, but also involves ionising radiation.

• Magnetic resonance imaging (MRI) is highly sensitive and specific, showing bone marrow oedema and periosteal reaction as well as detection of fracture lines. MRI is the method of choice whenever it is available.

Management^{1 7}

Management depends upon whether the stress fracture is low or high in risk of developing complications due to compromise of the blood supply. Low-risk and high-risk stress fractures both require a period of immobilisation to allow the fracture to heal. However, whilst most low-risk fractures heal with conservative treatment, surgery is usually required for high-risk injuries. An orthopaedic surgeon should be consulted at an early stage.

Low-risk fractures

Low-risk stress fractures include the posterior tibia, 2nd to 4th metatarsals, femur, inferior and superior pubic rami, sacrum, and fibula.

The principles of conservative treatment are rest from the aggravating activity and removal or modification of the risk factors, usually for at least 4-8 weeks. Patients can maintain fitness by working out on fitness machines, water running and cycling.

• Prompt diagnosis is important as continuing the aggravating activity will make things worse.

• Sometimes symptoms occur as the bone is under strain and remodelling is beginning to fail but before a true stress fracture has occurred. Intervention at this point may be preventative.

• Where there is a true stress fracture prompt intervention helps prevent progression to displaced fracture. Options for intervention include rest, casting, splinting and internal fixation.

• Management should begin at the point of suspicion. Once a stress fracture is suspected, a cyclic management programme should be initiated. This should allow the person to remove the source of the stress to the bone, maintain fitness, promote a safe return to activity and permit full healing.

Phase 1 (1-3 weeks)

The first priority is a period of rest from the activity that is causing the symptoms. Rest is not absolute - allowing the athlete to exercise in a pain-free manner prevents muscle atrophy. The goals of active rest are described by the acronym REST:

• Removal of the abnormal stress.

• Exercise to maintain fitness and prevent atrophy.

• Safe pain-free return to usual activity.

• Time for maturity of healed bone to catch up with increased bone remodelling.

Phase 1 focuses on removing the stress from the injured area, controlling pain and preventing de-conditioning until acute symptoms no longer occur with normal activities.

• Casting may be indicated when the individual cannot avoid the stressor. Casting is not used routinely as it may contribute to further weakening of bone and muscle.

• Crutch walking is an alternative, allowing for non-stressful exercise and weight-bearing.

• Pneumatic splints may reduce abnormal tibial loading, provide support around the fracture site and reduce the length of the rehabilitation process.

• Ice is used to decrease swelling.

• Anti-inflammatory medication may help with pain.

• Ambulation should progress to full weight-bearing as soon as this is painless. In the meantime physiotherapy for muscle strengthening is advisable.

Phase 2 (typically 2 weeks)

• Patients increase exercise but stay within what they can do without pain.

• Walking for at least thirty minutes three times a week, pain-free, is needed before progression to Phase 3.

• If pain recurs, go back a step.

Phase 3

• Introduction of running or jogging.

• Running should start slowly in a programme based on the patient's ultimate goals.

• Increase activity no more than 15-20% per week.

• A walk-jog, in which the person jogs the straight sections and walks the curves of a track for 0.80 km (0.5 miles), followed by a day of rest, is a good starting point for a person who hopes to return to a running or field sport.

• Once that distance is completed without pain, the person can begin walk-jogs three times per week. Distance is added in 0.80-km (0.5-mile) increments per week until the athlete can complete 3.2 km (2 miles).

• At this point, jogging begins for 1.6 km (1 mile) and increases by 0.80 km (0.5 miles) per week until 5 km (3 miles) or a distance commensurate with the person's activity is reached.

• During this phase, the athlete continues physiotherapy to strengthen leg muscles. Once they can squat 1½ times body weight, training involving jumps may begin.

• Failure of treatment is most likely to occur in stage 3.

• The running should be in a cycle of two weeks on, one week off, for 3-6 weeks, to allow bone to remodel. As the running programme progresses to sprinting and sport-specific activities, the rest days decrease.

Pain is usually an indication that the level of activity is too high, and activity should be dropped back to the previous stage. Compliance is critical and is most difficult during the rest phase of Phase 3. Because the treated person has been predominantly pain-free up to this point, stopping a pain-free functional activity is difficult to accept and athletes may overdo things and slip backwards.

High-risk stress fractures^{1 8 9}

Tibial stress fracture

This typically presents with gradual onset of localised pain on the inner aspect of the shin bone. Fractures of the middle third of the anterior cortex are prone to non-union, in which case internal fixation may be needed to prevent acute transverse fracture of the tibia.

Talar stress fracture

Presents with a deep ankle pain that increases with weight-bearing activity. Other symptoms may include night ache, pain during movements of the foot and ankle or pain on firmly touching the talus. Treatment typically involves an initial period of rest with crutches or a protective boot. Exercises to maintain flexibility, strength and balance are also important to ensure the ankle is functioning correctly.

Calcaneal stress fracture

Patients typically experience pain on either the inner or outer aspect of the heel bone that increases with impact activity. Treatment typically involves an initial period of rest, which may include the use of crutches or a protective boot.

Fifth metatarsal stress fracture

Patients typically experience pain in the forefoot that increases with impact activity and may decrease with rest. Symptoms may also radiate to other areas of the foot. Occasionally there is swelling or discolouration at the stress fracture site. In more severe cases, standing or walking may be enough to aggravate symptoms (often causing a limp) and patients may experience rest pain. Fifth metatarsal stress fractures are prone to non-union and to progression to full fractures. Patients are frequently treated with non-walking short leg casts for six weeks, after which activity is gradually resumed. Most patients make a full recovery but occasionally internal fixation is needed.

Tarsal navicular stress fracture

These are common in runners, jumpers and basketball players, and usually present with insidious onset of foot pain along the medial arch or long the dorsum. Without treatment recovery is poor, and even with rest and gradual return to activity the risk of delayed union and non-union is high. Immobilisation in a cast is therefore recommended for at least six weeks, followed by a six-week rehabilitation programme.

Medial malleolar stress fracture

These occur in distance runners, and typically cause medial ankle pain. The fracture line is often vertical. Most respond to immobilisation for six weeks, but some require internal fixation.

Femoral stress fracture

These are uncommon but they can have serious consequences, particularly of progression to full femoral neck fracture. They should be in the differential diagnosis when an athlete has groin pain and reduced range of movement in the hip. Patients typically experience a poorly localised pain in the front of the thigh that increases with impact and decreases with rest. Pain may cause the patient to cease activity and may eventually be present when lying on the affected leg, and at night, although tenderness cannot be clinically detected.

When a femoral neck stress fracture is suspected, an MRI should be obtained as this will help to differentiate a tension (superior side) stress fracture from a compression (inferior side) fracture. Tension fractures usually require surgery. If the MRI shows a compression fracture with a fracture line less than 50% of the width of the bone, this can be initially managed non-operatively. In any case, all femoral stress fractures should be followed up closely, and if the pain increases or the fracture increases in size, then a surgical opinion should be obtained. If the fracture becomes displaced, it should be treated rapidly as there is a high risk of avascular necrosis to the femoral head

Most patients with a femoral stress fracture make a full recovery in a period of 3-12 months, but in more severe cases, recovery may take 1-2 years and some patients may experience ongoing symptoms or complications which require further management.

Prevention

Stress fracture prevention involves attention to preparation and technique, as well as general health measures to improve bone strength.

Preparation for exercise

• High-impact exercise should be increased gradually, as moderate stress applied to the bone in a controlled manner can strengthen the bone and make it less susceptible to a stress fracture. Increasing distance by no more than 10% per week allows the bones to adapt.

• Building muscle strength in the legs increases shock absorption and prevents them from becoming fatigued quickly.

• Warm up appropriately before exercise, including stretches.

• Seek training advice if developing pain during running.

• Minimise changes in shoes and running surfaces by making these changes gradually.

• A continuing controversy is whether running shoes reduce the risk of stress fracture or whether in fact this is reduced by running barefoot. A systematic review was unable to reach a definitive conclusion¹⁰ .

Exercise technique

• Running on smooth, level surfaces such as a treadmill carries a lower risk.

• Pain or swelling developing during sporting activity should be reviewed, and resting until diagnosis/resolution is advisable. Avoid running on an injury, particularly on an undiagnosed injury.

• Bone is the weakest in the third week after the initiation of a stressful activity. By altering training intensity during the third week of workouts (for example, a change from higher- to lower-impact aerobic activity during the third week) the stressors associated with stress fractures may be reduced.

General measures

• Measures that prevent osteopenia and osteoporosis are beneficial - eg, avoidance of smoking, avoidance of excessive alcohol, and good calcium and vitamin D intake.

Complications

• If not treated properly stress fractures may progress to a complete - and therefore more serious - fracture. This is particularly true in the higher-risk fracture sites detailed above.

• Other possible complications include delayed union and non-union, with resulting disabling complications and need for internal fixation.

Dr Mary Lowth is an author or the original author of this leaflet.