12.17 Stress fractures

Stress fractures represent excessive loading of bone, resulting in repetitive microtrauma that exceeds the bone’s ability to repair itself through osteoblastic remodelling. As the microtrauma continues, the rate of osteoclastic resorption of bone surpasses the reparative process, leading to failure of the bone. This process begins as a stress reaction, according to Wolff’s law, then progresses to a stress fracture. The fractures are generally symptomatic well before any displacement occurs. A strong index of suspicion, thorough history, and appropriate use of imaging can lead to early diagnosis before progression to a complete, displaced fracture.

Stress fractures have been reported in almost every bone. The relative frequency depends on the population studied, according to the age and the predominant activity in that population. The most commonly affected bones are the metatarsals, tarsals, tibia, femur, pelvis, and vertebrae. Although in the past there has been much emphasis on fatigue fractures in healthy individuals such as high-level competitive athletes or military recruits, insufficiency fractures are becoming more important as the population ages. Involvement in competitive youth sports is also increasing, resulting in the increased frequency of recognition of overuse injuries in the paediatric and adolescent populations. The female athlete has also been shown to be at increased risk of stress fractures compared to her male counterparts, which may be related to alterations in oestrogen levels and a resultant decreased bone mineral density.

While early literature focused on fatigue fractures in military recruits, there has recently been increased recognition of stress fractures in all age groups and activity levels. Many reports show that these fractures are related to an abrupt increase in the duration, intensity, or frequency of activity. It is felt that the microtrauma sustained with repetitive loading, without adequate rest, leads to an increase in osteoclastic activity that exceeds the bones inherent adaptability and ability to remodel. Experimental work also shows that normal bone can sustain stress fractures under the repeated application of submaximal loads.

With an active, aging population there has been an increased recognition of stress fractures. While in many cases there is no description of a history of change in activity level, many of the patients sustaining stress fractures have been shown to have decreased bone density. Older patients with no apparent musculoskeletal disease have thus developed stress fractures. Similarly, there are reports of insufficiency fractures in patients with decreased bone density as a result of rheumatoid arthritis, lupus erythematosus, osteoarthritis, chronic renal disease, osteomalacia, and osteoporosis. Insufficiency fractures can also occur adjacent to joint replacements and arthrodeses.

The reported incidence of stress fractures in the general athletic population is less then 1%. However, certain subgroups have much higher risk of developing stress fractures, such as runners with an incidence that may be as high as 20% (Table 12.17.1). One review of 370 athletes with stress fractures showed that the tibia was the most commonly affected bone (49.1% of fractures). Stress fractures of the tarsals (25.3%) and metatarsals (8.8%) were also commonly seen. This has been supported by subsequent studies, however one prospective study of 914 college athletes reported that the femoral shaft was involved in over 20% of stress fractures over a 2-year period. In this report, metatarsal fractures were shown to be more common in endurance runners, while tibial stress fractures were more common in sports with rapid decelerations such as tennis and basketball. Spondylolysis, a stress fracture of the pars interarticularis most frequently of L5, occurs in 3–6% of the general population, and is associated with activities such as weightlifting and gymnastics.

Many risk factors have been identified in the development of stress fractures. In competitive female track and field athletes, a history of menstrual disturbance, nutritional disturbance, and decreased bone mineral density have been identified as risk factors. In addition, anatomical variations such as leg length discrepancies, leg alignment, and bone geometry have also been shown to be related to stress fracture development. Insufficiency fractures in the elderly are clearly related to decreased bone mineral density.

Fatigue and insufficiency fractures can present with the clinical signs and symptoms of both benign and malignant skeletal disorders. There is commonly an insidious onset of pain over a variable period of time, from days to weeks. The pain is exacerbated by activity and relieved by rest, although some patients may continue to experience night pain. Although a careful history should elicit any recent trauma or changes in activity, the absence of such cannot rule out a stress fracture. The history should include general health, diet, occupation and activities, and a menstrual history in women, as well as more ominous features such as weight loss or constitutional symptoms.

Bone tenderness is the most obvious physical finding in superficial regions, while pain with a gentle range of motion or compression of the bone is also often useful. Stress fractures may cause local signs of inflammation such as local swelling or redness of overlying skin.

The differential diagnosis of stress fractures is varied, and depends largely on the location, signs, and symptoms. A stress reaction, where the bone is weakened in an area of bone remodelling, has no physical disruption. Other pathological entities in the differential include avulsion injuries, infection, muscle strain, medial tibial stress syndrome (shin splints), exertional compartment syndrome, nerve entrapment, periostitis, and neoplasm.

A careful history and physical examination can usually be suggestive of a stress fracture; however, imaging studies are imperative to confirm the diagnosis. Plain radiographs are the first studies to order for suspected stress fractures. Although they are more likely to be normal within the first 2–3 weeks following the onset of symptoms, later films often show periosteal reaction, cortical lucency, or a fracture line.

Radionuclide imaging, using technetium-99 diphosphonate bone scans, is highly sensitive for stress fractures; however, it is not specific as increased uptake will be seen with any insult causing increased osteoblastic activity. Acute stress fractures will exhibit increased uptake in all three phases of the bone scan, whereas soft tissue injuries will only show increased uptake in phases 1 and 2.

Computed tomography (CT) can show fractures that are not demonstrated on plain radiographs, and can be used to evaluate and document fracture healing. The axial image acquisition of CT, however, can fail to delineate many stress fractures, as they are usually transversely oriented in the appendicular skeleton. Compared with magnetic resonance imaging (MRI), CT is better at delineating the osseous changes with stress fractures.

MRI is well documented to be superior for imaging and diagnosis of stress fractures. It is sensitive for detecting bone marrow oedema that occurs with stress reactions and stress fractures, and has the potential to demonstrate the presence of a fracture before changes are visible on plain radiographs or CT. However, oedema is somewhat non-specific and is also seen with both infection and neoplasm. The characteristic pattern of a stress fracture is a linear abnormal signal involving both the cortex and the medullary canal. Grading systems have been developed based on MRI or bone scan findings, with significant differences in time from diagnosis to return to sport according to the fracture grade (Table 12.17.2).

The majority of stress fractures are singular and oriented in the transverse plane, though multiple fractures in the same orientation may occur. Uncommonly a stress fracture may run in a longitudinal direction in long bones, typically in the anterior cortex of the distal tibia. These fractures have a confusing appearance on MRI, but have a characteristic pattern on several consecutive CT images, with a small cortical break and both endosteal and periosteal reaction.

The key to the treatment of stress fractures is timely identification and diagnosis. Any intrinsic (hormonal, nutritional, etc.) or extrinsic (training regimen, activity level) factors must be assessed and corrected. Most fractures can usually be treated by analgesics, activity modification, and occasionally orthoses or casts. Stress fractures can broadly be divided into either low-risk or high-risk injuries. Low-risk stress fractures are often diagnosed on the basis of a thorough history, physical examination, and plain radiographs, without the need for advanced imaging modalities. A period of rest and restricted activities is usually adequate, with possible supplementation with bracing or cast immobilization. This period of relative inactivity is followed by a rehabilitation program with low-impact activities such as cycling or swimming, until the patient can perform without discomfort. The athlete can then gradually progress to higher impact activities and increase the intensity before returning to sport-specific exercises. In general, operative intervention for low-risk stress fractures is limited to those fractures that have failed non-operative management, non-unions, and malunions. Electromagnetic field therapy has been tried, but a recent prospective study failed to show a difference in time to healing between placebo and treatment groups.

High-risk fractures are those that have a tendency to progress to displaced complete fractures, and those with a propensity to go on to delayed union or non-union. Also of consideration is the morbidity of the development of a complete fracture. For this reason, stress fractures of the tension side of the femoral neck and fractures of the anterior cortex of the tibia are considered to be high risk. Other bones occasionally considered high risk include the patella, medial malleolus, talus, and fifth metatarsal. Because of the high complication rate, these fractures should be treated as acute fractures. Algorithms for the evaluation and treatment of suspected high-risk fractures have been developed.

Although uncommon, stress fractures of the proximal femur have a high rate of complications if the patient is not appropriately managed. Osteopenia and coxa vara may predispose the femoral neck to fracture. These fractures can occur on either the tension side, or more commonly, on the compression side of the neck. Compression side fractures of the inferior neck are stable injuries, and hence non-operative management is appropriate. In contrast, tension side fractures of the superior neck have a much higher risk of propagation across the neck, and are more likely to become complete and displaced. Complications of delayed or inadequate treatment include avascular necrosis, non-union, and delayed union. Given the significant morbidity of these outcomes, aggressive treatment including surgical intervention is indicated. Once a fracture has become displaced, many patients are unable to return to pre-injury activities, despite appropriate surgical intervention. Percutaneous cannulated screw fixation will prevent completion of a tension side stress fracture and thus avoid the significant sequelae of a displaced fracture. As stress fractures take longer to heal than acute traumatic injuries, the patient with a displaced fracture needs to be kept non-weight bearing for 6 weeks, followed by 6 weeks of partial weight bearing.

The most common location of stress fractures in athletes is the tibial shaft. The incidence has been reported as 20–75% depending on the study group. Most frequently these fractures occur along the compression side of the tibia, the posteromedial cortex. These are seen more commonly in distance runners, and generally heal with activity modification alone. Less commonly, a stress fracture occurs on the tension side of the tibia at the anterior cortex of the mid-third. These fractures are more frequently seen in athletes with repetitive jumping activities Stress fractures in this area have the potential to progress to complete fracture. Initially rest and immobilization can be tried. The recalcitrant stress fracture of the anterior tibial cortex is best treated with reamed unlocked intramedullary nailing of the tibia.

Other fractures that the clinician must be aware of include those of the patellar, medial malleolus, talus, navicular, fifth metatarsal, and great toe sesamoids. Fractures at each of these sites have the tendency to progress delayed union or non-union, and must be treated appropriately to permit a return to sport and to avoid poor long-term outcomes. Frequently a high-risk stress fracture in one of these bones necessitates aggressive management and surgical intervention.

Fractures of the pars interarticularis are the most frequent. Repetitive hyperextension places stress on the lumbar spine, predisposing certain athletes (ballerinas, gymnasts, and football lineman) to developing stress fractures of the lumbar spine, usually of the pars of L5. Spondylolysis, a stress fracture of the pars, is a result of mechanical failure. It is seen in 4–6% of the general population, but has been reported to be much higher (11%) in the previously-mentioned groups. Though there is a lack of consensus regarding the best management for spondylolysis, the most appropriate treatment plan starts with a removal from sports. Physical therapy to promote peripelvic flexibility and core strengthening to counter lordosis should then be undertaken. Stationary cycling and swimming are the only activities that should be allowed. Bracing may be indicated to decrease lumbar lordosis. After a 6-week period to allow healing, if the athlete is asymptomatic they may begin a return to sport programme. If symptomatic, ongoing physical therapy and bracing are indicated. For the athlete that fails non-operative management, surgical intervention such as a posterolateral transverse body fusion is indicated. Postoperative bracing is then continued for several months before sports are allowed.