Diagnosis and management of bone stress injuries of the lower limb in athletes

The role of sex and the female athlete triad

Retrospective and prospective observational studies have not found female sex to be a risk factor for running injuries other than for stress fractures,17 ^w6 and there are several contributing factors. Studies that showed lower bone mineral density, menstrual irregularity, and smaller lower limb mass as risk factors for injury led to the evolution of the term “the female athlete triad,” and presence of this triad (low bone mineral density or disordered eating, low body mass index (BMI), and menstrual irregularity or prolonged absence of menses) or any of its components increases the athlete’s risk of stress fracture.8 12 17 21 22 23 Two prospective studies also associated menstrual dysfunction and poor aerobic fitness with increased risk of stress injury to the lower limb in female military recruits.17 21 A retrospective study of 240 college athletes found that stress fractures occurred in 49% of female athletes who had fewer than five menses a year compared with 29% for those who had 10-13 menses a year.24 In addition, female runners who were taking oral contraceptives were half as likely to get stress fractures over the course of a year than those who were not taking oral contraceptives.24 A Finnish prospective study of female athletes found that those with a BMI of 20-25 had a lower risk of stress fracture than those with a BMI less than 20, although the difference was no longer significant after adjustment for confounding factors.25 This trend may be explained by a lower bone mass leading to more strain on the remaining bone, which further increases risk of fatigue. A systematic review of observational studies concluded that female athletes and military recruits who consumed more than 1500 mg of calcium daily were at lowest risk of stress fracture injuries.19

History

Patients with stress fracture usually have pain within the bone of the lower limb, which gradually gets worse and starts to present earlier in a training session. Progressive injury is likely when pain starts to be felt during day to day activities. It is important to locate the pain to help the radiologist interpret any investigations. Ask about the nature of the athlete’s training regimen, specifically about recent excessive or sudden increases in training and lack of rest days. Ask about risk factors for bony stress injury as outlined above. Remember that military recruits are also susceptible. Ask female athletes in particular about dietary intake. Information on menstrual function, history of bony injury, or family history of stress fracture can help the clinician assess the likelihood of stress fracture.

Although stress fractures mostly occur in bones of the lower limb, in athletes who throw or row, any upper limb pain or rib pain should increase suspicion of stress fractures in other bones.

Examination

Clinical examination of the affected limb will usually show localised bone tenderness. Later manifestations of the injury, usually caused by delayed presentation, include swelling, bruising, and warmth.

Imaging

Stress fractures are progressive, and their appearance depends on the timing of imaging. Early diagnosis through correct imaging will help to avoid unnecessary time out from training or participation in sport. If stress fracture is suspected on the basis of clinical findings, encourage the patient to avoid weight bearing—for example, by using crutches while waiting for imaging—to reduce the risk of propagation of the fracture. Plain radiography, radioisotope bone scanning, magnetic resonance imaging (MRI), and computed tomography are used most commonly in the diagnosis of stress fractures.

Magnetic resonance imaging

MRI is sensitive and specific for stress fractures (fig 4⇓) and patients are not exposed to radiation. The advantage of MRI over plain radiography is that it can detect bone changes—a “stress response”—earlier, often weeks before changes are apparent on radiographs, although experience is needed in interpreting the scan to reduce false positives. It is more sensitive than bone scintigraphy. MRI also provides information about surrounding soft tissues, which helps to exclude other potential causes of localised pain.28 Serial MRI scans are also used to monitor fracture resolution. The table⇓ shows a system for grading the severity of stress fractures on the basis of the results of imaging techniques.

Fig 4 T2 weighted magnetic resonance imaging scan with typical high signal appearance seen with a stress fracture of the tibia

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Grade of stress fracture based on results of plain radiology, bone scintigraphy, and magnetic resonance imaging²⁹

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A recent imaging study suggested that MRI may also show features consistent with an impending stress fracture of the hip before a cortical break has occurred.^w20 If true, this could lead to earlier diagnosis and possible intervention through modification of an athlete’s training programme.

Tibial stress fractures

Conservative treatments include rest, ultrasound therapy, extracorporeal shock wave therapy, and, recently, the use of a pneumatic lower leg brace. The more common posterior stress fractures respond well to non-surgical treatment, probably because of improved vascularity posteriorly and reduced compressive loads.31 ^w24

A small prospective randomised controlled trial of low intensity ultrasound therapy for posterior tibial stress fractures found a significant decrease in healing time in the treatment group,^w25 but it is not clear whether this treatment would be efficacious for chronic anterior tibial stress fractures. Observational studies of extracorporeal shock wave therapy report that it is beneficial, although again no good data support the use of this treatment for more difficult to treat anterior stress fractures.^w26

Anterior tibial stress fractures are more likely than posterior ones to be complicated by delayed union or non-union, and non-operative management normally takes longer than six months.^w27 For athletes and military recruits such a long time away from training and usual physical activity may be psychologically unacceptable, detrimental to fitness, and a financial burden. It may represent the end of a career. Surgical intervention, specifically minimally invasive tibial nailing, has been described in several case series with promising results (radiological union at three months and return to play at four months).^w28 However, 60% of patients may experience anterior knee pain, especially when kneeling, or extensor mechanism disruption. These side effects may be considered unacceptable outcomes in elite athletes and need to be discussed carefully with the patient.^w29

Anterior tension band plating has been proposed as a more biomechanically sound intervention. In a case series of four patients who underwent this operation, fractures went on to unite at a mean of 10 weeks, after an average delay in operative intervention of 13 months. One patient had symptomatic irritation from the plate, which was subsequently removed. All returned to previous levels of sporting participation, which was Olympic level for two.^w29

Metatarsal stress fractures

Most of these fractures occur in the distal second to fifth metatarsal and if undisplaced can be managed conservatively with rest and the wearing of a hard soled shoe or walking boot. The rate of non-union of proximal second and fifth metatarsal fractures is high, with proximal fifth metatarsal fractures failing to unite in 20-67% of cases.^{w30 w31} Expert advice varies. One group recommended that non-sclerotic fractures of the fifth metatarsal can be treated conservatively with a non-weight bearing cast for six to eight weeks, but that any sign of sclerosis on imaging indicates the need for operative intervention, with medullary curettage and bone grafting followed by non-weight bearing for six weeks.^w3 Another group that reported on the use of intramedullary screw fixation in a series of 22 patients achieved 100% union at six to eight weeks. Athletes returned earlier to sport, albeit with a complication rate of 9%.32

Femoral shaft and neck fractures

Femoral shaft fractures are considered low risk compared with femoral neck fractures and are usually treated conservatively. Return to play is guided by pain during activity. A conservative management algorithm for femoral shaft stress fractures is shown in fig 5⇓.4 However, the algorithm is based on findings from a small case series of high level athletes with an age range of 17-21 years. It is not clear whether this algorithm should be used for people in different age groups and with different sporting abilities, and more research is needed into the optimal management of femoral shaft stress fractures.

Fig 5 Algorithm for management of femoral shaft fractures4

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The diagnosis of femoral neck fractures is often delayed and serious complications can occur. The biomechanics underpinning stress injuries to the femoral neck are complex.

If late diagnosis and undertreatment occur, patients with resulting displacement of the femoral head are at high risk of avascular necrosis, arthritis, non-union, or mal-union.^w32-w35 Displaced fractures must be managed surgically. For undisplaced stress fractures of the femoral neck, avascular necrosis and osteoarthritis are unlikely after conservative treatment according to the findings of a Finnish prospective study that followed up 66 military recruits with undisplaced fracture for an average of 18 years.33 Femoral neck fractures that are treated conservatively should be regularly monitored radiographically to assess progression, displacement, and complications. A graded return to sports may be considered when there is radiographic evidence of a healed fracture and no pain on walking.

In summary, management depends on the risk of non-union. High risk fractures are managed by surgery or non-weight bearing pending imaging results, whereas low risk fractures are managed clinically, depending on symptoms during activities or training.