Radiographic studies generally are ordered when children present with extremity injuries, including knee injuries. The Ottawa knee rule is highly sensitive in detecting clinically significant knee fractures. Application of this rule has reduced the rate of unnecessary knee radiographs in adults. Although fractures in children have complicating factors, including open growth plates and the difficulty of evaluating pain and weight bearing in a frightened child, the Ottawa knee rule may be useful in this population. Bulloch and associates evaluated the sensitivity and specificity of the Ottawa knee rule in children two to 16 years of age to determine whether use of the rule would decrease the rate of radiography.

Children with acute knee injuries who presented at five urban emergency departments were eligible for enrollment in this prospective validation study. All participating physicians were trained in the use of the Ottawa knee rule and were asked to order radiographs at their discretion. Results of the Ottawa knee rule decision tree were recorded for each child. The radiologists who read the radiographs at each institution were blinded to the results of the Ottawa knee rule assessment. A fracture of any size or type on a radiograph was a positive result. Attempts were made to contact all children with normal radiographs or their parents by telephone 14 days later. Children who underwent radiography and remained symptomatic after 14 days were asked to have repeat radiography, because fractures cannot always be identified on initial films.

Of the 750 children enrolled in the study, 70 had fractures. Two had Salter-Harris type 1 fractures (i.e., normal radiographic result but tenderness at the growth plate) that were diagnosed clinically on initial examination. The most common fracture was patellar fracture, followed by fractures of the tibial spine and proximal tibia. The Ottawa knee rule was 100 percent sensitive and 42.8 percent specific. A total of 670 radiographs were obtained in the study group. If the Ottawa knee rule had been followed, only 460 radiographs would have been required.

The authors conclude that the Ottawa knee rule performs well in children older than five years who have knee injuries. They note, however, that the study finding may be less certain in younger children because of the low number of participants who were two to five years of age.