Cohen et al developed rules for identifying children who did not require radiographs after acute knee injury. This can help reduce the number of unnecessary X-rays. The authors are from Children's Hospital in Columbus, Ohio.


Patient selection: The age appears to be < 18 years of age.



(1) injury > 1 week prior to ED visit

(2) superficial laceration or abrasion of knee only

(3) history of previous knee surgery

(4) return to ED to reassess knee injury


A child did not require a knee X-ray if both of the following were found:

(1) The child was able to bear his/her own weight in the Emergency Department.

(2) The child was able to flex his/her knee to 90°.


Each of these rules had a negative predictive value of 100%.


Rates of fracture:

(1) inability to bear own weight: 37%

(2) inability to flex knee to 90°: 52%



• Using these criteria reduced knee radiographs by 73% with no missed fractures.


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