Jangʼs Pearls Does This 12-Year-Old Need an X-ray?

Case A 12-year-old boy playing basketball jumped for a rebound, twisting his knee on landing. He reported feeling a pop, and subsequently developed pain. He played for several more minutes, but then had worsening pain, so he stopped, biked home, and was brought to the ED by his mother for further care. On exam, he hurts everywhere you touch him, but has a clear knee effusion without other deformity or ecchymosis. He is able to bear weight but has an antalgic gait. You give him some Vicodin, and order x-rays. On reassessment, he has no patellar or fibular head thrombocytopenic purpura (TTP), is able to slowly extend his knee to full range, and has no TTP of the tibial tuberosity. He does have some mild laxity of the medial collateral ligament compared with the other knee. Questions: What are the Ottawa knee rules? Do they apply here? What are the Pittsburgh knee rules? Do they apply here? What makes application of knee rules difficult in children? What should this patient's disposition be? Discussion: The Ottawa knee rules were derived from a prospective evaluation of about 1,000 patients (convenience sample) over 18 with knee injuries. It was then validated in another 1,000 adult patients (convenience sample), and found to be very sensitive but not specific for knee fractures. Under the Ottawa guidelines, knee films are obtained if the patient is over 55, if there is tenderness of the fibular head, if there is tenderness of the patella, if flexion is limited to less than 90 degrees, or if the patient cannot bear weight for four steps immediately after the injury and in the ED. Use of the Ottawa rules would decrease unnecessary use of knee films by about 30 percent. Strictly speaking, the Ottawa knee rules do not apply here because this patient is under 18, but two studies suggested that the rules could be applied in children. (Pediatr Emerg Care 2001;17[6]:401 and Ann Emerg Med 2003;42[1]:48.) The Pediatric Emergency Care study was done in 234 kids and had a sensitivity of 92% for knee fractures (but there were only 13 total fractures). The Annals study was done in 750 kids (with 70 fractures), and concluded that you could use the Ottawa knee rules in children and decrease the need for radiographs by about 30 percent. But the mean age of the children in the Annals study was 12, and there were only 45 children who were 2 to 5 so it's difficult to know for sure if the rules would work in young kids. You decide if the rules apply here. The Pittsburgh knee rule was derived from a retrospective evaluation of about 200 consecutive patients and then validated in another 150 consecutive patients. It was found to be more sensitive and specific than the Ottawa knee rules for knee fractures. It was further validated in 934 patients 12 to 50 (Ann Emerg Med 1998;32[1]:8.) Under the Pittsburgh guidelines, knee films are obtained if there is a history of trauma, if the patient is older than 50 or younger than 12, or if the patient cannot fully bear weight for four steps in the ED. Use of the Pittsburgh guidelines would decrease unnecessary use of knee films by about 50 percent with 100% sensitivity for knee fractures. According to the Pittsburgh folks, their rules outperform the Ottawa rules, but there is less prospective and head-to-head data on this. Strictly speaking, the Pittsburgh rules were studied in a population that included 12-year-olds, but there were only 10 fractures in 55 children so the confidence intervals were wide (just like with the Ottawa studies). We still don't know if they really work in young kids. That ought to highlight for you the problem with using clinical decision rules in the ED; even the ones supposedly derived in ED populations may not be adequately powered to definitively help us manage the patients we see. Application of knee rules in older children is easier than in small children because there are fewer physeal issues, they can actually cooperate with you, and they are able to localize and vocalize better. That's why I think both sets of rules probably can be applied to children over 12, though I'm not sure I'd use them in younger kids. If you follow the Pittsburgh guidelines, the boy in this case does not need x-rays because there was no history of direct trauma to the knee and he is able to bear weight. If you use the Ottawa rules in this kid, x-rays are not indicated either. By exam, the risk of fracture is extremely low, precluding even a Salter I fracture because he has no tenderness to any of the physeal areas. His exam is consistent with at least a grade II MCL sprain given the detection of laxity on exam with mild effusion. (Bonus question for the well informed, what other injury would you expect in someone with an MCL high grade sprain or tear?). This patient should be placed in a mobile knee brace (a hinged one that allows flexing and extending but that prevents valgus/varus deviation) and follow-up with orthopedics. The patient does not need x-rays by the Ottawa or Pittsburgh knee rules, or even by history and physical, but because the orthopedist won't know what to do without x-rays, you should either schedule an outpatient x-ray or just do them in the ED and give a copy to the patient to take to follow-up.

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