Original contributions
Performance of a decision rule for radiographs of pediatric knee injuries

Presented at the Pediatric Academic Society’s Annual Meeting in Baltimore, Maryland, May 4–7, 2002.
https://doi.org/10.1016/j.jemermed.2004.09.010Get rights and content

Abstract

Although decision rules for radiographs of pediatric knee injuries have been suggested from retrospective studies, prospective evaluations of such rules have been limited. We sought to prospectively assess the performance of a rule in children presenting with acute knee injuries. Eligible participants were children aged 3–18 years with an acute knee injury. The settings for the study were a tertiary pediatric emergency department (ED), a community hospital ED, and a pediatric urgent care center. All of the participants received standard knee radiographs. Before radiography, each patient was assessed by a pediatrician or pediatric emergency physician for presence of the following: 1) inability to bear weight, 2) inability to flex the knee to 90°, 3) presence of bony tenderness. The radiographs were interpreted by a radiologist blinded to the study; those with findings reported as consistent with acute fracture were considered positive. A total of 146 patients were enrolled (65% male, mean age 11.6 years). Of these, 15 (10.3%) had a fracture on their radiograph, 6 of which were related to trampoline use. Seventy-seven (53%) were negative for criterion 1 (i.e., able to bear weight immediately after the accident and in the ED), none (0%) of whom had fractures. The negative predictive value of this criterion was 1.0 (95% CI 0.94–1.0). The positive predictive value was 0.22 (95% CI 0.13–0.34). The sensitivity was 1.0 (95% CI 0.82–1.0). The specificity was 0.59 (95% CI 0.50–0.67). Three patients negative for criterion 3 were found to have fractures. The proximal tibia was the most common fracture site (47%). In conclusion, assessment of the ability to bear weight would have decreased the use of radiography by 53% without missing any fractures in our study population. No additional value to the rule was found by adding assessment of the ability to flex the knee or bony tenderness.

Introduction

Acute knee injuries are common complaints in children presenting to the emergency department (ED). Despite the large number of children seeking acute medical attention for these injuries, knee fractures are relatively uncommon. In previous studies, fracture rates in adults have ranged from 5–12% and approximately 4–5% in children (1, 2, 3, 4, 5, 6, 7, 8). Although knee radiographs are routinely obtained in many acute care settings, the low incidence of fractures suggests that much of the associated cost and expense of these evaluations can be avoided (9).

Clinical decision rules have been developed for adults with knee injuries (1, 2, 3, 4, 5, 6). The most widely recognized rule is the Ottawa Knee Rule (OKR) (1, 2, 3). This decision rule was developed as a screening tool for adults with knee injuries. The OKR recommends knee radiographs in patients with one or more of the following criteria: age greater than 55 years, inability to bear weight immediately after the injury and in the ED, inability to flex the knee to 90°, and isolated bony tenderness at the head of the fibula or patella (3). Patients under 18 years of age were explicitly excluded during the development of the OKR, and its authors have not suggested that it be routinely applied to pediatric injuries (3, 10).

Cohen et al. applied an adapted version of the OKR retrospectively to children under age 18 with acute knee injuries (7). They combined the inability to bear weight and the inability to flex to 90°, resulting in a theoretical reduction in the number of knee radiographs by 73% and no missed fractures. In their study, point tenderness was not a good predictor of knee fracture in children and did not add to the sensitivity of the rule. Recently, Khine et al. prospectively sought to validate a version of the OKR in children (8). In their study, this version of the OKR did not identify all children with a knee fracture. The purpose of our study was to assess the performance of this adaptation of the OKR in our pediatric ED population.

Section snippets

Methods

Prospective cohorts were identified in three pediatric acute care settings between October 2000 and March 2002. The study was approved by the Colorado Multiple Institutional Review Board and the Institutional Review Boards at the participating facilities. Our standard of care was to obtain radiographs of an injured knee, and this study did not require any deviation from the standard of care. Written, informed consent and applicable assent was obtained from the parent and patient before

Results

A total of 146 patients met inclusion criteria and were enrolled. One patient’s caregiver was approached but declined to participate for unspecified reasons. The demographic and clinical characteristics of the study population are listed in Table 1. These characteristics mirrored those of other patients seen in our settings for extremity injuries: the majority of the patients were male, and many of the injuries were sports related.

All patients had radiographs performed and all had clinical

Discussion

Stiell et al. assessed 23 standardized clinical findings to derive a clinical decision rule for adults with acute knee injuries (2). They then prospectively validated the rule, known as the Ottawa Knee Rule, in 1047 adult patients (3). The rule was 100% sensitive for detecting clinically significant fractures by requiring radiographs in patients with one or more of the following criteria: 1) inability to bear weight either immediately after the injury or in the ED, 2) inability to flex the knee

Conclusions

Decision rules for radiography of acute knee injuries have been shown to be useful and cost-effective in adult patients. However, widespread agreement on the applicability of similar decision rules to pediatric knee injuries does not exist. Our data suggest that a simplified decision rule incorporating only the ability to bear weight has a high negative predictive value for knee fractures in children and may reduce the number of unnecessary, negative radiographs.

Acknowledgments

We thank Carol Turner, md for study development and Shayne Bland, msc for statistical analysis. We also thank Mark Roback, md, for manuscript review.

References (13)

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Original Contributions is coordinated by John Marx, md, of Carolinas Medical Center, Charlotte, North Carolina

1

Current Affiliation: Mayo Clinic, Rochester, Minnesota

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