Pediatric ankle exam predicts need for x-rays

As part of ongoing efforts to reduce emergency room delays and costs, a group of U.S. and Canadian researchers have apparently improved upon the Ottawa Ankle Rule (OAR) for determining whether children need x-rays after an ankle injury.

Researchers from Children’s Hospital in Boston and the Hospital for Sick Children in Toronto tested a modified version of the OAR in a prospective study of 607 children with acute ankle injuries. The modified rule was found to have 100% sensitivity and 100% negative predictive value: None of the 381 children deemed to have low-risk injuries based on the clinical exam were found to have high-risk fractures on subsequent radiographs.

The modified OAR would have spared 63% of the children from unnecessary ankle x-rays, the researchers found. In contrast, the Ottawa rule alone would have reduced imaging by only 12%. The findings were published in the British medical journal The Lancet (December 22, 2001; Vol. 358:9299, pp. 2118-2121).

The alternative rule varies from the OAR mainly by eliminating x-rays for the Salter-Harris type 1 fracture of the distal fibular epiphysis, the most common ankle fracture among pre-adolescents. This fracture is commonly diagnosed clinically, the authors stated, while x-rays in such cases are either normal or show widening of the fibular physis and soft-tissue edema centered around the fibular physis, adding little to the clinical diagnosis.

The study excluded children younger than 3 and older than 16. Also excluded were those with pre-existing related disease, previous ankle surgery or recent ankle injury, multisystem trauma, and those who had x-rays before reaching the study group.

Low-risk patients were defined by the clinical exam as those with isolated pain, tenderness, or both, with or without edema or ecchymosis of the distal fibula below the level of the joint line of the ankle or over the adjacent lateral ligaments. All other findings were classified as high risk. The final diagnoses were based on masked interpretations of the initial radiographs and follow-up information.

"In our study, no children with acute ankle injury and isolated clinical findings restricted to the distal fibula below the level of the joint line of the ankle or adjacent lateral ligaments had a subsequent high-risk diagnosis," the authors wrote.

In a couple of cases, clinical exams proved more accurate than the first x-ray readings in identifying high-risk patients. "Two patients who despite a high-risk examination in the emergency department had a radiograph initially interpreted by both the non-study staff radiologist and the emergency-department staff as normal, were later found to have a Tillaux fracture on orthopedic follow-up and by the study radiologists," the researchers wrote.

The misinterpretations highlight the importance of clinical findings, including a high-impact mechanism of injury, the authors wrote, adding that "we encourage follow-up of patients within a week to identify those who need repeated radiography or other imaging modalities because of persistent symptoms."

Low-risk diagnoses in the study included sprains, contusions, lateral talar avulsion fractures, and fractures of the distal fibula including non-displaced Salter-Harris I and II, metaphyseal buckle, and epiphyseal avulsion fractures. The authors describe these as "stable" injuries, as opposed to other high-risk fractures that may destabilize the ankle. The prognosis is good for low-risk injuries, the authors stated, with management geared mainly toward maximizing patient compliance and comfort.

By eliminating a number of unneeded x-rays on low-risk injuries, the modified OAR "could substantially reduce costs and improve flow of patients in the emergency department, without increasing the likelihood of missing clinically significant high-risk fractures," the authors stated.

The researchers cautioned that their results might not carry over to facilities where staff was not fully trained in the clinical assessment of children's ankles. However, they expressed confidence that their clinical exam rule could be learned and appropriately applied by others.

"We used a definition of low-risk clinical examination that is simple and easy to use in a busy emergency department," the authors wrote. "The low-risk and high-risk findings were easily distinguished by the clinicians, as assessed by a high degree of agreement between observers."

By Tracie L. Thompson contributing writer
November 1, 2002

Related Reading

Turf Wars in Radiology, Part V: Radiologists, orthopedists put best foot forward, October 1, 2002

Lateral process of the talus fracture plagues snowboarders: a case study, February 24, 2002

Ottawa Knee Rule cuts costs when institutions maintain high sensitivity, May 15, 2000

Copyright © 2002

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