Computed tomography (CT) is a valuable imaging modality that provides diagnostic resolution often not achievable with other techniques. As a result of this clinical utility, the use of CT scans in the United States has been steadily rising; roughly 85 million CT scans were performed in this country in 2011, more than 4 million of which were performed on children. In fact, one recent study examining the use of CT scans in U.S. pediatric patients across a large network of health maintenance organizations found a nearly 3-fold increase in the use of CT from 1996 to 2010.

However, CT scans also carry a degree of risk. Namely, CT scans deliver a significantly higher dose of ionizing radiation than conventional radiography in ranges that have been associated with an increased probability for the subsequent development of cancer. Particularly concerning for pediatric orthopaedists are the facts that children are more sensitive than adults to the potential carcinogenic effects of ionizing radiation, and they have a longer life expectancy during which radiation-induced cancers may develop.

CT in pediatric orthopaedics
Diagnostic imaging modalities—including plain radiographs and CT scans—play a particularly important role in the diagnosis and management of many orthopaedic conditions. CT provides detailed imaging of bone and allows for multi-planar visualization of complex fractures and articular surfaces that are often not adequately evaluated with conventional radiographic techniques. For this reason, it may be the best choice when evaluating commonly occurring orthopaedic conditions and injuries in pediatric patients, such as tarsal coalition, congenital scoliosis, transitional ankle fractures, pelvic trauma, and even recurrent shoulder instability.

However, the pediatric orthopaedist must weigh the higher radiation doses associated with CT against the diagnostic advantages it delivers compared to other imaging modalities. This accompanying radiation dose depends at least in part upon the anatomic structure being imaged. In a retrospective review to estimate the effective radiation dose to adult patients associated with CT examination of the musculoskeletal system, researchers concluded that CT scans of both the axial and appendicular skeleton are accompanied by high radiation exposures, but the effective dose of radiation delivered declines as the distance of the imaged anatomic structures from the torso increases.

In the case of pediatric ankle and foot conditions, for example, a CT scan may provide clear diagnostic benefits with only a small associated increase in effective radiation exposure over plain radiographs. For triplane fractures of the ankle, the availability of a CT scan has been shown to have a substantial impact on surgical planning. Specifically, in one recent study, 10 orthopaedic surgeons were shown standard anteroposterior and lateral radiographs of triplane fractures and instructed to mark the positions they would place their fixation screws. They were subsequently shown the CT scan of the same fracture and asked if they would alter any of the screw positions or directions; all 10 did.

In a similar fashion, CT evaluation may be invaluable in the evaluation and surgical planning for tarsal coalitions, due to the complex orientation of the subtalar joint. Importantly, when the effective dose of radiation from CT performed in the foot and ankle is quantified, it is in range with doses typical of plain radiographs; thus, the information gleaned from CT scanning of the foot and ankle region may offset the risks of increased radiation exposure in this patient population.

Anterior shoulder instability in young patients is often accompanied by glenoid bone loss, and underappreciated damage to the glenoid rim has been described as a leading reason for recurrent instability after surgical stabilization. A recent retrospective study examined 48 patients with anterior shoulder instability for whom both preoperative magnetic resonance and CT images were available. When preoperative images were retrospectively compared to intra-operative findings, researchers found that MRI showed a low sensitivity in the detection of significant glenoid bone defects, while CT imaging provided an accurate prediction of the intra-operative finding in all cases.

Unlike distal extremity CT scans, however, CT scanning of the shoulder imparts a substantially higher effective dose of radiation than standard radiographs. It also involves radiation exposure to the thyroid, breasts, and lung parenchyma—organs that have been shown to be particularly radiosensitive. Thus, the clinical benefits that this imaging modality offers for optimizing surgical planning must be weighed against the substantial increase in radiation exposure and effective radiation dose delivered to vulnerable vital tissues, especially in young patients.

Radiation, cancer, and females
The association between radiation exposure and increased cancer risk in females is not a new issue, although the impact of CT scans is only recently being examined. Long-term cohort studies of infants irradiated for various conditions have shown the two most radiosensitive organ sites in children to be the thyroid gland and breasts. The U.S. Scoliosis Cohort Study, a retrospective study following females who received routine diagnostic radiographic examinations of the spine to monitor scoliosis curve progression, showed a 69 percent excess in breast cancer mortality, compared to expected mortality for this population. As the number of radiograph exposures and the cumulative radiation dose increased, so did the risk of breast cancer mortality for patients in this study.

The risk of developing thyroid cancer is another area previously evaluated in studies of pediatric radiation exposure. Significantly, females are known to be more sensitive than males to the carcinogenic effects of radiation to the thyroid. In a pooled analysis of seven major studies examining ionizing radiation exposure and thyroid cancer, the carcinogenic effects of radiation demonstrated a strong linear dose-response down to 0.1 Gray. Strikingly, the risk of thyroid cancer was three times higher in females than in males, according to researchers.

The previously mentioned study examining pediatric CT use from 1996–2010 also found that the risk of a malignancy developing following CT exposure was significantly higher for females than males. These authors projected the occurrence of one radiation-induced solid cancer for every 300 to 390 abdomen/pelvis scans performed in females (versus one for every 670 to 760 abdomen/pelvis scans for males). The malignancy risk for females was also substantial for those who had chest and spine scans, with one malignancy projected to result from every 330 to 480 chest scans and from every 270 to 800 spine scans, depending on age.

Additionally, among children who had CT examinations, those younger than age 5 years had significantly higher rates of future cancer development than older children. The children at highest risk were those who had undergone CT scan of the abdomen and pelvis. Because abdomen/pelvis and cervical spine CT scans are common components of the initial evaluation for pediatric trauma patients, it is essential that the risks of CT exposure in young patients be weighed against the potential diagnostic benefits that may be obtained.

Ultimately, determining both who is most at risk for developing radiation-induced malignancy and which musculoskeletal conditions are best evaluated with CT will help in the development of clinical guidelines for the safe and effective use of CT in pediatric patients. Despite increasing data demonstrating that the risks of radiation-induced cancer are disproportionately greater for females, no data suggest how to integrate this information into clinical practice.

Conclusions
CT use in the assessment of pediatric patients has increased dramatically in the past several decades and continues to play an essential role in the evaluation and management of numerous pediatric orthopaedic conditions. Because children, both male and female, have a risk of developing radiation-induced cancers later in life, efforts to limit imaging radiation exposure in children have increased.

One example is the Image Gently campaign, begun in 2007 by the Alliance for Radiation Safety in Pediatric Imaging. This campaign encourages the use of the minimal radiation dose and elimination of unnecessary scans to reduce exposure, especially CT scans of the pelvis and spine that may result in substantial radiation exposure. That said, the data are sparse as to what makes a scan unnecessary; information about the clinical outcomes of pediatric patients with different imaging modalities and quantities of radiation exposure is limited and the actual risk imparted by performing CT scans in the distal extremities is poorly understood.

An additional confounding factor is that the risk of developing radiation-induced cancer from imaging studies seems to be notably higher in females than in males. Currently, there are limitations to using this information to inform clinical decision making in pediatric orthopaedics. Inclusion of this sex-based difference in future studies of radiation-induced cancer risk may yield valuable information on how to apply these data systematically to improve the safety and value of orthopaedic care for all pediatric patients.

Hannah Dzimitrowicz, BS, is a medical student at the Yale School of Medicine. Cordelia W. Carter, MD, is an assistant professor in the Yale Department of Orthopaedics and Rehabilitation and a member of the AAOS Women’s Health Issues Advisory Board.

Bottom Line

• CT scans are used commonly for evaluation of numerous pediatric orthopaedic conditions, including tarsal coalition, transitional ankle fractures, shoulder instability, and pelvic trauma, and their use in the pediatric population has been steadily increasing.
• CT scans performed on sites in the distal appendicular skeleton are associated with lower radiation doses to vulnerable tissues than those performed on the axial or proximal appendicular skeletons.
• Breast and thyroid tissues are particularly sensitive to the ionizing radiation associated with CT.
• Females (particularly young females) exposed to this type of radiation have a higher risk of cancer development later in life than their male peers.
• Because young males and females are both at risk for developing radiation-induced malignancy, the pediatric population as a whole should be “imaged gently.”
• More research is required to best understand how this information should be integrated into clinical decision making.

Putting sex in your orthopaedic practice
This quarterly column from the AAOS Women’s Health Issues Advisory Board and the Ruth Jackson Orthopaedic Society provides important information for your practice about issues related to sex (determined by our chromosomes) and gender (how we present ourselves as male or female, which can be influenced by environment, families and peers, and social institutions). It is our mission to promote the philosophy that male and female patients experience and react to musculoskeletal conditions differently; when it comes to patient care, surgeons should not have a one-size-fits-all mentality.

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